Majorana-Raychaudhuri Seminars

Title:- Gravitational waves from primordial black hole Poisson fluctuations

Abstract:- A gas of Poisson distributed primordial black holes (PBH) can induce at second order in cosmological perturbation theory a stochastic gravitational-wave (GW) background. This GW background can act as a novel method to extract constraints on cosmological models and gravitational theories. In this talk, we will discuss the above mentioned GW portal within the context of general relativity by accounting as well for the effect of realistic extended PBH mass functions and checking its potential detectability by GW experiments. Interestingly, by requiring not to have GW overproduction we set model-independent constraints the initial PBH abundance at PBH formation time as a function their mass. Finally, we study the aforementioned GW signal within the context of modified theories of gravity showing that it can serve as a novel probe constraining the underlying gravity theory.

Title: "Affleck-Dine Leptogenesis from Higgs Inflation" & "Gravitational Leptogenesis in Bounce Cosmology"

Abstract:  In this presentation, I will discuss two recent papers regarding Leptogenesis.

Firstly, I will examine the possibility of simultaneously explaining inflation, the neutrino masses and the baryon asymmetry through extending the Standard Model by a triplet Higgs. The neutrino masses are generated by the vacuum expectation value of the triplet Higgs, while a combination of the triplet and doublet Higgs' plays the role of the inflaton. Additionally, the dynamics of the triplet, and its inherent lepton number violating interactions, lead to the generation of a lepton asymmetry during inflation. The resultant baryon asymmetry, inflationary predictions and neutrino masses are consistent with current observational and experimental results. (2106.03381)

After which, I will explain how Gravitational Leptogenesis can take place during an Ekpyrotic contraction phase. Two possible paths by which this can occur are coupling the Ekpyrotic scalar to a gravitational Chern-Simons term, or to a U(1) gauge field Chern-Simons term. These couplings lead to the production of chiral gravitational waves, which generate a lepton number asymmetry through the gravitational-lepton number anomaly. We find successful Gravitational Leptogenesis to be possible in Ekpyrotic bounce cosmologies through both of these mechanisms. (JCAP 06 (2021) 049, 2105.06624)

Speakers: 

Jeff Kost (Sussex, UK)

Title: Massless Preheating and Electroweak Vacuum Metastability

Abstract: Current measurements of Standard-Model parameters suggest that the electroweak vacuum is metastable.  This metastability has important cosmological implications because large fluctuations in the Higgs field could trigger vacuum decay in the early universe.  For the false vacuum to survive, interactions which stabilize the Higgs during inflation—e.g., inflaton-Higgs interactions or non-minimal couplings to gravity—are typically necessary.  However, the post-inflationary preheating dynamics of these same interactions could also trigger vacuum decay, thereby recreating the problem we sought to avoid.  This dynamics is often assumed catastrophic for models exhibiting scale invariance since these generically allow for unimpeded growth of fluctuations.  In this talk, we examine the dynamics of such "massless preheating" scenarios and show that the competing threats to metastability can nonetheless be balanced to ensure viability.  We find that fully accounting for both the backreaction from particle production and the effects of perturbative decays reveals a large number of disjoint "islands of (meta)stability" over the parameter space of couplings.  Ultimately, the interplay among Higgs-stabilizing interactions plays a significant role, leading to a sequence of dynamical phases that effectively extend the metastable regions to large Higgs-curvature couplings.

Yuta Hamada (Harvard, US)

Title: On Preheating in Higgs Inflation

Abstract: It is known that the unitarity violation occurs at the preheating stage of Higgs inflation. In this talk, I first clarify that the unitarity violation is viewed as a strong coupling problem for dimensionless effective couplings. Then, I argue that the existence of the problem is highly dependent on the choice of higher-dimensional operators. Finally, I show that there exist choices where the strong coupling does not arise, and the analysis of the preheating of Higgs inflation is self-consistent.

Pankaj Saha (IIT-Madras, India)

Title: Reheating After Inflation: Characteristics and Constraints 

Abstract: In this talk, we will discuss the characteristics and constraints of the reheating phase after inflation. The reheating generally consists of multiple episodes. We will discuss the general characteristics of the initial non-perturbative phase presenting the results of lattice simulation. We will culminate with the constraints of reheating from CMB observables considering the perturbative decay of the inflation.

Cem Eroncel (DESY, Germany)

Title: Fragmentation of the axion field in the early universe

Abstract: Axion-like-particle (ALP) is a well-motivated candidate for dark matter, and it has been subject to extensive theoretical and experimental research in recent years. The most popular ALP production mechanism studied in the literature is the misalignment mechanism, where the ALP field has negligible kinetic energy initially, and it starts oscillating when its mass becomes comparable to the Hubble scale. In most of these studies, the ALP field has been assumed to be a homogeneous classical field, and its quantum fluctuations have been ignored. However a non-zero initial velocity can cause exponential growth in the amplitude of fluctuations, and most of the energy density in the homogeneous mode can be converted to axion particles, known as fragmentation. In this talk, I will present a semi-analytical study of this process, and describe the necessary ingredients for an efficient fragmentation. I will also mention the consequences of fragmentation on ALP dark matter parameter space and discuss some observational prospects.

Title: Confronting dark matter with Dirac neutrinos

Abstract: In this presentation, I will discuss two of our recent papers. I will 

try to talk about some possible connections between dark matter and 

the Dirac nature of neutrinos. The nature of the neutrino, Dirac or 

Majorana, is still an open question in particle physics, and there 

have been no such observations yet which can confirm Majorana nature 

of light neutrinos.

Firstly, I will discuss a Dirac neutrino portal dark matter scenario 

by minimally extending the particle content of the Standard Model(SM) 

with three right-handed neutrinos (RHN), a Dirac fermion dark matter 

(DM) candidate, and a complex scalar. Both the right-handed neutrinos 

and the dark matter thermalize with the SM plasma due to a new Yukawa 

interaction involving RHNs, DM, and complex scalar, while the latter 

maintains thermal contact via the Higgs portal interaction. We have 

found that in the present scenario, some portion of low mass DM is 

already excluded by the Planck 2018 data for keeping RHNs in the 

thermal bath below a temperature of 600 MeV and thereby producing an 

excess contribution to effective relativistic degrees of freedom in 

the early universe. The next-generation experiments like CMB-S4, 

SPT-3G, etc., will have the required sensitivities to probe the entire 

model parameter space of this minimal scenario, especially the low 

mass range of DM where direct detection experiments are still not 

capable enough for detection. After that, I will briefly discuss the 

possibility of probing a very well-studied model known as the 

left-right symmetric model (LRSM) due to the Dirac nature of light 

neutrinos and its connection with the dark matter.

Title: Statistics of low-energy physics in the string landscape

Abstract: String theory yields a plethora of 4D solutions at low-energy which is known as the string landscape. I will derive the statistical distribution in this landscape of some quantities relevant for phenomenology like the supersymmetry breaking scale and the axion dark matter abundance. 

Title: Sound speed resonance of gravitational waves

Abstract: I will introduce a novel mechanism where the parametric

resonance occurs via the oscillatory sound speed of gravitational waves.

The primary feature of this mechanism is a sharp peak on the stochastic

gravitational waves spectrum. This phenomenon can naturally arise in a

large class of gravity theories beyond Einstein's general relativity,

including Horndeski theory, and theories beyond Horndeski. The speech

will be delivered in the pedagogical manner.

Title: CP violation in Yukawa couplings and electroweak baryogenesis

Abstract: CP violation in the third generation fermion Higgs couplings could  play  important role in the electroweak baryogenesis. In the effective field theory framework to beyond the Standard Model physics, it can originate from dimension six operators, however it is strongly bounded by the experimental limits on the electron electric dipole moment (EDM). Given those bounds it has been claimed that the only coupling relevant for baryogenesis can still be the h tau tau coupling. It is pointed out that under such assumptions like Minimal Flavour Violation or flavour symmetries, the Wilson coefficients of those operators have some flavour structure and the bound on the imaginary part of the  h tau tau  becomes two orders of magnitude stronger than previously claimed. Under such assumptions, the electroweak baryogenesis becomes highly unlikely

Title: Flavor anomalies confront asymptotic safety

Abstract: I will discuss how the framework of asymptotic safety (AS) above the Planck scale can be employed to derive specific predictions for new physics solutions to the recent anomalies in flavor and the muon g-2. The presence of interactive UV fixed points in the system of gauge and Yukawa couplings imposes a set of boundary conditions at the Planck scale, which allows one to determine low-energy values of the Yukawa matrix elements. As a consequence, the allowed new physics mass range can be significantly narrowed down. To be in agreement with the b -> s anomalies, we find that AS predicts a leptoquark mass between 4 and 10 TeV, comfortably in reach of a hadron-hadron collider with 100 TeV c.o.m. energy. In the case of the muon g-2, AS can discriminate between several models presenting the same phenomenology. 

Title: Conformal Extensions of the Standard Model

Abstract: The talk will cover reasons and obstacles for conformally symmetric extensions of the standard model. Furthermore models which realize the underlying ideas and their phenomenology will be discussed.

Title: Neutrino Portal to FIMP Dark Matter with an Early Matter Era

Abstract: In this talk, I will discuss the freeze-in production of Feebly Interacting Massive Particle (FIMP) dark matter candidates through a neutrino portal, in the case where an early matter-dominated era took place for some period between inflation and Big Bang Nucleosynthesis. In this model, we consider a hidden sector comprised of a fermion and a complex scalar, with the lightest one regarded as a FIMP candidate, and three heavy neutrinos, responsible for mediating the interactions between the Standard Model and the dark matter sectors and for generating the masses of the Standard Model neutrinos. I will present the dynamics of the dark matter candidate throughout the modified cosmic history, evaluate the relevant constraints of the model, and discuss the consequences of the duration of the early matter-dominated era for dark matter production. Finally, I will show that, under some circumstances, this scenario becomes testable through indirect detection searches.

Title: Low-energy baryon number violation as a probe for baryogenesis mechanisms

Abstract: An observation of neutron-antineutron oscillations at experiments like the Deep Underground Neutrino Experiment (DUNE) or the European Spallation Source (ESS), would imply baryon number violation by two units and will directly point towards physics beyond the Standard Model (SM). The discovery of such a signal will not only be interesting for validating several well-motivated ultraviolet completions of the SM in connection with neutrino masses but also can have far-reaching implications for baryogenesis mechanisms explaining the observed baryon asymmetry of the Universe. In this talk, I shall discuss how an observed rate for neutron-antineutron oscillations can directly be correlated with the washout of baryon asymmetry in the early Universe and therefore, can probe high- and low-scale baryogenesis scenarios in synergy with current and future collider searches, as well as other low-energy observables like dinucleon decay, meson oscillations, etc. 

Title: Slow-roll inflation in Palatini $F(R)$ gravity

Abstract: We study slow-roll single field inflation in presence of

$F(R)$ gravity in the Palatini formulation. In contrast to metric

$F(R)$, when rewritten in terms of an auxiliary field and moved to the

Einstein frame, Palatini $F(R)$ does not develop a new dynamical

degree of freedom. However, it is not possible to solve the equation

of motion of such auxiliary field for any kind of $F(R)$. We propose a

method that allows to circumvent this issue and compute the

inflationary observables. We apply this method to a couple of test

scenarios.

Title: Probing electroweak baryogenesis at the collider experiments

Abstract: The existence of the matter-antimatter asymmetry of the Universe is

strongly established over the years by various cosmological observations

such as the cosmic microwave background and  big-bang nucleosynthesis.

After the discovery of 125 GeV Higgs boson electroweak baryogenesis has

drawn significant attention as a possible mechanism to account for the

matter antimatter asymmetry primarily due to its connection to Higgs

physics. In this talk I will discuss how current and future collider

experiments can probe the parameter space required for electroweak

baryogenesis. The context is general Two Higgs Doublet Model (g2HDM),

where the presence of additional Higgs bosons and extra Yukawa couplings

may drive successful electroweak baryogenesis, leaving behind novel

signatures for the Large Hadron Collider and other ongoing  and  future

experiments.

Title: Beyond the Standard Model - scalar extensions

Abstract: In this pedagogical talk, I will motivate non-minimal Higgs frameworks as successful candidate scenarios for addressing many of the Standard Model (SM) shortcomings. I will review simple scalar extensions and justify going beyond one-singlet and one-doublet scalar extensions of the SM. I will then point out theoretical predictions and collider and cosmological signatures of these frameworks to be probed by the upcoming experiments.

Title: Probing dark matter through gravitational waves

Abstract: The LIGO-Virgo observations have already demonstrated the power of gravitational wave astronomy. In near future various experiments will probe gravitational wave signals across a broad range of frequencies providing invaluable insight into astrophysics, cosmology and fundamental physics. In this talk I will discuss how we can use these observations to test dark matter properties. I will focus on two signatures of compact dark matter objects: gravitational waves produced by their mergers, and lensing of gravitational waves. I will show that the LIGO-Virgo observations already provide constraints on compact dark matter and I will discuss the future prospects of gravitational wave probes of dark matter.

Title: Cogenesis of Dark Matter and Baryons from PBH

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Title: Flavor anomalies, and the Bc lifetime

Abstract: Discrepancies between theoretical expectations and experimental measurements of some heavy meson decays  have built up over the last decade. In particular, deviations are seen in decays of the pseudoscalar  B-meson to a K or a K* mesons accompanied by a mu+mu- pair, and as  increased rates of semileptonic decays of B-mesons into tau-leptons. We will first review the status of these so-called "flavor anomalies", including statistical analysis of new data published last month (Oct 2021). An important theoretical activity consists of constraining putative new-physics explanations of these anomalies through independent measurements. The lifetime  of the Bc meson is very well measured, and can be sensitive to the presence of new interactions that increase the rate of B decays to tau-leptons. We will present our recent effort to improve the theoretical estimate of the Bc lifetime and  describe some challenges encountered -- most notably,  the surprisingly limited success in the analogous calculation of lifetimes of B and D mesons. We take a stab at the possible underlying theoretical issues (aka, unjustifiable assumptions). 

Title: New physics behind the new muon g-2 puzzle? 

Abstract: The recent measurement of the muon g-2 at Fermilab confirms the previous Brookhaven result. The leading hadronic vacuum polarization (HVP) contribution to the muon g-2 represents a crucial ingredient to establish if the Standard Model prediction differs from the experimental value. A recent lattice QCD result by the BMW collaboration shows a tension with the low-energy e+e− → hadrons data which are currently used to determine the HVP contribution. In this talk I will consider the possibility to solve this tension, referred to as the new muon g-2 puzzle, invoking new physics in the hadronic cross-section. 

Title: The Interplay Between Primordial Black Hole Evaporation and Dark Matter Production

Abstract: Hawking evaporation of black holes is expected to copiously produce all kinds of particles, regardless of their charges. For primordial black holes of a certain mass, this effect has huge implications on dark matter phenomenology. I will discuss such implications in the context of models that contain one or more dark sector particles, as well as models which couple to the Standard Model. Specifically, we investigate when primordial black hole evaporation can have important effects on thermal freeze-in and out. We explore the production of spin-2 particles, entropy dilution and the potential for re-thermalization after black hole evaporation. This talk will be based on Phys.Rev.D 105 (2022) 1, 015022 and Phys.Rev.D 105 (2022) 1, 015023. 

Title: Breakdown of an Effective Field Theory Description of

        Early Universe Cosmology

Abstract: I will argue that no effective field theory analysis

will be adquate to describe the evolution of the very early

universe. The argument is based on quantum gravity, unitarity

and thermodynamical considerations.

Title: Q-Monopole-Ball

Abstract: A soliton state with both topological and non-topological charges is shown to exist in a certain broken gauge theory with an additional global U(1) symmetry. This new soliton state, Q-monopole-ball, is shown to be stable from decaying into an isolated Q-ball and a magnetic monopole state. There exists a minimum global charge for a Q-monopole-ball being stable from decaying into free global U(1)-charged particles and an isolated monopole. Q-monopole-balls with a large magnetic charge can also be stable if the topological charge is smaller than the cubic root of the global charge. Q-monopole-balls could be produced from a phase transition in the early universe and account for all dark matter.

Title: Cosmological Imprints of Hot Axions

Abstract: Scattering and decay processes of thermal bath particles in the early universe can dump hot axions in the primordial plasma, and they would manifest themselves in the cosmic microwave spectrum as additional neutrinos. In this talk, I will review predictions for such an effect due to different axion couplings. Finally, I will present predictions for concrete UV complete axion models and explore the discovery reach of future cosmological surveys.

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Title: Additional Baryons and Mesons

Abstract: In a particle theory model whose most readily discovered new particle is the ∼1TeV bilepton resonance in same-sign leptons, currently being sought at CERN’s LHC, there exist three quarks D, S, T which will be bound by QCD into baryons and mesons. We consider the decays of these additional baryons and mesons whose detailed experimental study will be beyond the reach of the 14 TeV CERN collider and accessible only at an O(100 TeV) collider.

Title: Connection between Dark Matter and flavor anomalies.

Abstract: I will illustrate a series of simple and minimal models aiming at providing an interpretation of observed anomalies in flavor physics, in particular g-2 and anomalies in decays of the B-mesons, and, at the same time, viable Dark Matter candidates achieving the correct relic density via the freeze-out paradigm.

Title: Phenomenology of  Lepton Number Charged Scalars

Abstract: In this talk, I'll discuss the neutrino non-standard  self interaction induced by leptonic scalars, $\phi$, which are SM gauge-singlets, and carry two units of lepton-number-charge. These leptonic scalars are forbidden from interacting with the Standard Model (SM) fermions at the renormalizable level and if one allows for higher-dimensional operators, couple predominantly to SM neutrinos. For masses at or below the electroweak scale, $\phi$ decays exclusively into neutrinos. Its unique production signature at hadron collider experiments like the LHC would be via the vector boson fusion process and lead to same-sign dileptons, two forward jets in opposite hemispheres, and missing transverse energy. I'll discuss that the sensitivity of high-energy colliders is largely complementary to that of low-energy and precision measurements of the decays of charged leptons, charged mesons, W and Z bosons, neutrino beam experiments like MINOS and searches for neutrino self-interactions at IceCube and in cosmological observations. For $\phi$ mass larger than a few GeV, our projected LHC sensitivity would surpass all existing bounds. Finally, I'll introduce a UV complete model containing a leptonic scalar and briefly discuss additional exotic signals it can give rise to at colliders.

Title: Dark Matter interpretation of the neutron decay anomaly and more

Abstract: The talk will summarize https://arxiv.org/abs/2111.14808 and https://arxiv.org/abs/2112.09111

Title: Neutrinos connecting energy, intensity and cosmic frontiers

Abstract: Neutrino oscillation and flavor mixings proved the existence of tiny neutrino masses. It strongly suggests scenarios involving the physics beyond the Standard Model (SM). To explain the origin of tiny neutrino mass a plethora of models have been proposed. The tree level neutrino mass models are simple extensions of the SM. Apart from explaining the origin of tiny neutrino mass such scenarios can explain a variety of beyond the SM aspects. In this talk, describing a simple model we will explore scenarios which could be probed at energy, intensity and cosmic frontiers in the near future.​

Title: Thermal Misalignment of Scalar Dark Matter

Abstract: The conventional misalignment mechanism for scalar dark matter depends on the initial field value, which governs the oscillation amplitude and present-day abundance. We present a mechanism by which a feeble (Planck-suppressed) coupling of dark matter to a fermion in thermal equilibrium drives the scalar towards its high-temperature potential minimum at large field values, dynamically generating misalignment before oscillations begin. Unlike conventional misalignment production, the dark matter abundance is dictated by microphysics and not by initial conditions. As an application of the generic mechanism, we discuss a realistic scenario in which dark matter couples to the muon.

Title: Inflationary reheating and particle production

Abstract: The graceful exit out of inflationary expansion is a key element of 

any model of inflation. While many physical processes can be well

approximated by assuming, instantaneous reheating, many others can not.

In this talk, I consider the process of producing a radiation bath

during the oscillations of the inflaton after inflation. The detailed

evolution of the radiation depends not only on the shape of the inflaton

potential (about which oscillations occur), but also on the mode of 

producing radiation (inflaton decay to fermions, bosons, or through scattering).

During this period, particle production may occur and may be influenced

by these process.  Gravitational portals, often thought to be weak

and subdominant because of their Planck-scale suppression,

can in fact be very important in the early stages of the reheating process. 

Title: Primordial Black Holes from Sound Speed Resonance and Induced Gravitational Waves

Abstract: Primordial black holes (PBHs) may be formed from density fluctuations in the very early Universe, which can be tested through their effects on a variety of cosmological and astronomical processes. In this regard, PBHs can serve as an inspiring tool to probe physics in the very early Universe. In this talk, we will introduce sound speed resonance mechanism for PBH formation: an oscillating sound speed squared can yield nonperturbative parametric amplification on certain perturbation modes during inflation. Accordingly, the power spectrum of primordial density perturbations can have a narrow major peak on small scales, while it remains nearly scale invariant on large scales as predicted by inflationary cosmology. On the other hand, the induced GWs associated with PBH formation have attracted great attention in recent years. The overlarge primordial curvature perturbations for PBH formation should induce sizeable GW signals after their reentry into the Hubble horizon during the radiation-dominated era. This strong correlation between PBHs and the concomitant GW signals could be a promising approach to detecting PBHs in the upcoming GW experiments.

Title: Freeze-In of radiative keV-scale neutrino dark matter from a new U(1)_B-L

Abstract: We extend the Dirac Scotogenic model with the aim of realizing  neutrino masses together with the mass of a keV-scale  dark matter (DM) candidate via the same one-loop topology.  Two of the Standard Model (SM) neutrinos become massive Dirac fermions while the third one remains massless. Our particle content is motivated by an anomaly free U(1)_B-L gauge symmetry with exotic irrational charges and we need to enforce an additional Z_5 symmetry. The dark matter candidate does not mix with the active neutrinos and does not have any decay modes to SM particles. DM is produced together with dark radiation in the form of right handed neutrinos via out of equilibrium annihilations of the SM fermions mediated by the heavy B-L gauge boson. In order to avoid DM over-production from Higgs decays and to comply with Lyman-alpha bounds  we work  in a low temperature reheating scenario with a reheating temperature between about 5 GeV and 4 MeV.   Our setup predicts a dark radiation abundance that decreases for larger DM masses  and is below the sensitivity of upcoming precision measurements such as CMB-S4. A future observation of a signal with an effective number of extra neutrinos larger than about 0.012 would exclude our scenario. We further sketch how inflation, reheating and Affleck-Dine baryogenesis can also be potentially realized in this unified framework.

Title: Primordial black holes from vacuum bubbles

Abstract: The LIGO-Virgo Collaboration has so far detected more than 100 black holes, whose mass distribution appears to have a peak at ∼ 30M☉ and two tails on the ends. By assuming that they all have a primordial origin, we analyzed the LIGO datasets by performing maximum likelihood estimation on a broken power-law mass function, which appears to behave better than the popular log-normal mass function. Surprisingly, such a simple distribution can be realized in our previously proposed mechanism of primordial black holes, where the black holes are formed by vacuum bubbles that nucleate during inflation via quantum tunneling. These black holes could also serve as seeds of supermassive black holes. 

Title: Dark Baryons Near a GeV

Abstract: New states at the GeV scale that mix with standard model baryons can have interesting implications for baryogengesis and dark matter as well as the neutron lifetime puzzle. I’ll describe simple models that involve such new particles and novel ways to look for them, for example, by looking at novel sources of radiation here on Earth, anomalous heating mechanisms of neutron stars, cosmological observations, and at particle colliders.

Title: Gravitational wave from first order phase transition during inflation

Abstract: Large excursion of the inflaton field can trigger interesting dynamics. One important example is a first order phase transition in a spectator sector which couples to the inflaton.  Gravitational waves (GWs) from a first order phase transition during inflation, which is an example of an instantaneous source, has an oscillatory feature. This feature is generic for the source to happen in a universe experiencing accelerating expansion. The shape of the GW signal contains information about the evolution of the early universe following the phase transition. In particular, the slope of the infrared part of the GW spectrum is sensitive to the evolution of the Hubble parameter when the GW modes reenter the horizon after inflation, the slope of the profile of the intermediate oscillatory part depends on both the evolutions of the Hubble parameter when the modes reenter the horizon and the Hubble parameter when the modes exit the horizon during inflation, and the slope of the ultraviolet part depends on the evolutions of the Hubble parameter when the modes reenter the horizon and the Hubble parameter when the modes exit the horizon during inflation, and the details of the of the dynamics of the phase transition. We consider several examples of non-minimal  models of evolution during and after the inflation, and we demonstrate that shape of the GW can be used to distinguishing them from the minimal scenario of quasi-de Sitter inflation and radiation domination after a fast reheating.

Title: Filtered Dark Matter, Baryogenesis, Black Holes and Phase Transitions

Abstract: We describe a new production mechanism of particle dark matter, which hinges on a first-order cosmological phase transition.  We then show that this mechanism can be slightly modified in one way to also give a new baryogenesis mechanism, and in another way to produce primordial black holes.

Title: Freeze-in, glaciation, and UV sensitivity from light mediators.

Abstract: Dark matter (DM) freeze-in through a light mediator is an appealing model with excellent detection prospects at current and future experiments. Light mediator freeze-in is UV-insensitive insofar as most DM is produced at late times, and thus the DM abundance does not depend on the unknown early evolution of our universe.  However the final DM yield retains a dependency on the initial conditions for the DM abundance, which is usually assumed to be exactly zero. We point out that in models with light mediators, the final DM yield will also depend on the initial conditions assumed for the light mediator population. We describe a class of scenarios we call “glaciation” where DM freezing in from the SM encounters a pre-existing thermal bath of mediators, and study the dependence of the final DM yield on the initial temperature of this dark radiation bath. We quantify the dependence of the DM yield on the initial dark temperature and find that it can be sizeable in regions near the traditional (zero initial abundance) freeze-in curve. We generalize the freeze-in curve to a glaciation band, which can extend as much as an order of magnitude below the traditional freeze-in direct detection target, and point out that the DM phase space distribution as well as the yield can be strongly dependent on initial conditions.

Title: Phenomenological Motivation for Gravitational Positivity Bounds: A Case Study of Dark Sector Physics 

Abstract: Positivity bounds on scattering amplitudes provide a necessary condition for a low-energy effective field theory to have a consistent ultraviolet completion. Their extension to gravity theories has been studied in the past years aiming at application to the swampland program, showing that positivity bounds hold at least approximately even in the presence of gravity. An issue in this context is how much negativity is allowed for a given scattering process. In this talk we address importance of this rather technical issue by demonstrating that it is relevant to physics within the scope of ongoing experiments, especially in the context of dark sector physics. In particular, we provide detailed analysis of dark photon scenarios as an illustrative example. This motivates further studies on gravitational positivity bounds. 

Title: Probing Poincare-Violating QED

Abstract: Time and space translation invariance are amongst the most fundamental but also generally accepted symmetry assumptions in physics, in turn giving rise to energy and momentum conservation. It is nevertheless prudent to put such assumptions to experimental and observational tests. In this talk we take a first step in this direction, specifying a simple periodic time dependence that violates time translation invariance and setting phenomenological constraints on it. We discuss similarities and differences to the case of a light bosonic dark matter field that usually also causes oscillating effects.

Title: Peering at CMB through foreground fog

Abstract: Planck has given us the near ultimate picture of the early Universe by observing high-resolution CMB temperature anisotropy. Cosmologists are now aiming to unveil the complete picture of the evolution of the Universe using CMB polarization data. Several forthcoming/proposed missions, e.g., CMB-S4, Simons Observatory, LiteBIRD, PICO, CMB-Bharat, etc., will be scanning the microwave sky with unprecedented sensitivity. Potential detection of inflationary B-mode in CMB, reconstruction of mass distribution in the late Universe, history of reionization etc., are the ultimate challenges to cosmologists in the coming decades. All these scientific goals of forthcoming CMB experiments are complicated by the fact that the CMB polarization signal is buried under orders of magnitude below the Galactic foregrounds. In this talk, I will start with an overview of the CMB foregrounds and the cleaning procedures of foreground emissions from CMB. Next, I will focus on the challenges we will face in the next-generation CMB experiments and the possibility of detecting inflation given the available technology and our understanding of the foregrounds. Finally, I will discuss the participation of the Indian CMB community in this worldwide effort.

Title: Origins of CMB Anomalies in a Cosmic Bounce

Abstract: Standard model of cosmology has been able to provide a good fit to the  temperature spectrum of Cosmic Microwave Background (CMB). However, certain anomalous signals in the CMB have been observed which are in tension with the predictions of the standard model. If we consider these signals individually, the statistical significance of these signals is perhaps not significant enough and can be thought of as a statistical fluke. However, the presence of several such independent anomalies, either imply that we live in an extremely rare configuration of the universe described by the standard model or perhaps that these signals could be collectively pointing to physics beyond the standard model. In this talk we will discuss the latter possibility. In particular, we discuss how  CMB anomalies such as lack of power at large angular scales, dipolar modulation, lensing anomaly and preference for odd parity could be tell-tale signatures of a cosmic bounce.

Title: Gravitational waves from primordial fluctuations

Abstract: Fluctuations in the primordial universe inevitably induce gravitational waves. The resulting gravitational wave spectrum not only contains information about the spectrum of such fluctuations but on the composition of the universe at the time of wave generation. In this talk, I will present recent advancements on induced gravitational waves, including, among other possibilities, gravitational waves sourced by primordial isocurvature fluctuations and by a primordial black hole dominated universe. 

Title: Asymptotic safety of gravity and matter

Abstract: In this talk, I review the current status of asymptotic safety in gravity-matter systems. Renormalization Group flows provide a link between the Planck scale and observable physics at the electroweak scale. The observed Standard-Model parameters can thereby impose significant indirect constraints on the underlying quantum-gravitational parameter space.

Vice versa, asymptotic safety, that is quantum scale symmetry at an induced Renormalization-Group fixed point, could explain seemingly random relations among couplings in the matter sector. Gravitationally-induced quantum scale symmetry generically predicts any sufficiently screened gauge coupling, leads to gauge-mediated mass differences between up-type and down-type Yukawa couplings, and can determine the shape of scalar potentials. I will explain the generic mechanisms relevant for asymptotically safe model building and explicitly discuss the CKM-sector of the Standard Model as well as models of grand unification.

Title: Searching for heavy QCD axions at B-factories

Abstract: Heavy QCD axion (mass~GeV) is poorly constrained at the experiments due to technical challenges. On the other hand, such an axion is well motivated as it ameliorates the axion quality problem. Motivated by these issues, we studied rare B-meson decays as a powerful probe of such a heavy QCD axion. I will discuss some interesting new results of our work, present limits and future projections on the axion parameter space. I will also show some limits and projections for Dark Photons/Light Z' using similar experimental constraints.

Title: Searching for New Physics in Neutrino Oscillations

Abstract: Existence of neutrino masses and mixing was the first hint for physics beyond the standard model of elementary particles. Most models that explain neutrino masses and mixing would also predict additional physics beyond the standard model. This new physics could manifest itself as sub-dominant effects in neutrino oscillations. On the other hand, neutrino oscillation experiments are reaching precision level. The next generation neutrino experiments aim to finally nail all the missing ingredients of the neutrino conundrum.  These bigger and better experiments can also be used to study sub-dominant effects coming from new physics. We will discuss the most promising forthcoming experiments on the horizon and present the reach of these experiments to physics beyond the standard model.

Title: Revisiting Q-Balls

Abstract: Classical field theories of scalars that are invariant under a U(1) symmetry can have non-perturbative soliton solutions called Q-balls: spherical bound states that are the energy minimum for a fixed U(1) charge Q. The underlying non-linear differential equations cannot be solved analytically, but I will present analytical approximations that work remarkably well and allow us to understand both ground and excited Q-ball states with ease. The global U(1) symmetry can also be promoted to a gauge symmetry, leading to gauged Q-balls and Q-shells; once again we can find exceptionally good analytic approximations to describe these objects and their stability.

Title: Majorana Neutrinos, Lepton Number Violation and Double Beta Decay

Abstract: The nature of neutrinos and the mechanism of generating their tiny masses are among the most important unknowns in fundamental physics. Being the only electrically neutral fermions in the Standard Model, neutrinos can be of Majorana nature, i.e., particle and antiparticle are indistinguishable. As such, any U(1) quantum number carried by a Majorana fermion will be violated and in the context of the Standard Model, Majorana neutrinos will break total lepton number, an otherwise accidental global symmetry. I will discuss scenarios beyond the Standard Model where Majorana neutrinos are realized, as well as scenarios that incorporate so-called quasi-Dirac Majorana states. As the most important probe of Majorana neutrinos, I will focus on neutrinoless double beta decay as the crucial signature, and I will discuss the latest theoretical and experimental developments. 

Title: An Asymmetric SIMP Dark Matter Model

Abstract: In this talk, we show for the first time an asymmetric strongly interacting massive particles (SIMP) dark matter (DM) model, where a new vector-like fermion and a new complex scalar both having nonzero chemical potentials can be asymmetric DM particles. After the spontaneous breaking of a U(1)_D dark gauge symmetry, these two particles can have accidental Z_4 charges making them stable. By adding one more complex scalar as a mediator between the SIMP DM, the relic density of DM is determined by 3 to 2 and two-loop induced 2 to 2 annihilations in this model. On the other hand, the SIMP DM can maintain kinetic equilibrium with the thermal bath until the DM freeze-out temperature via the new gauge interaction. Interestingly, this model can have a bouncing effect on DM, whereby the DM number density rises after the chemical freeze-out of DM. With this effect, the prediction of the DM self-interacting cross section in this model can be consistent with astrophysical observations, and the ratio of the DM energy density to the baryonic matter energy density can be explained by primordial asymmetries. We also predict the DM-electron elastic scattering cross section that can be used to test this model in future projected experiments.

Title: Stochastic inflation and primordial black holes

Abstract: Cosmic inflation is a hypothetical, early cosmological era where the

universe was dominated by a scalar field and underwent rapid expansion.

Quantum fluctuations of this scalar field became the seeds of all cosmic

structure. The strongest fluctuations collapsed into primordial black

holes, a candidate for dark matter. Stochastic inflation is a way to

study the evolution of these cosmological fluctuations beyond the usual

linear perturbation theory. In particular, it reveals a non-Gaussian,

exponential tail in the perturbation probability distribution, important

for black hole statistics but inaccessible by most other methods. I

review the formalism and present a numerical study of stochastic

inflation where backreaction between the perturbations and the

background is taken into account, improving the method's accuracy over

previous computations.

Title: Falsifying the standard cosmological model

Abstract: In the standard cosmological model the universe is assumed to

 be statistically isotropic & homogeneous when averaged on large scales. The dipole anisotropy of the CMB is ascribed to our peculiar motion due to local inhomogeneity. There should then be a corresponding dipole in the sky map of high redshift sources. Using catalogues of radio galaxies and quasars we find that this expectation is rejected at >5σ. This undermines the standard practice of boosting to the ‘CMB frame’ to analyse cosmological data, in particular for inferring an isotropic acceleration of the Hubble expansion rate which is interpreted as due to Λ. 

Title: WIMP and FIMP Dark Matter in Singlet-Triplet Fermionic Model

Abstract: We present an extension of the SM involving three triplet fermions, one triplet scalar and one singlet fermion, 

which can explain both neutrino masses and dark matter.  One triplet of fermions and the singlet are odd under a $Z_2$ symmetry, thus the model features two possible dark matter candidates. The two remaining $Z_2$-even triplet fermions can reproduce the neutrino masses and oscillation parameters consistent with observations.  We consider the case where the singlet has feeble couplings while the triplet is weakly interacting and investigate the different possibilities for reproducing the observed dark matter relic density.  This includes production of the triplet WIMP from freeze-out and from decay of the singlet as well as freeze-in production of the singlet from decay of particles that belong to the thermal bath or are thermally decoupled. While freeze-in production is usually dominated by decay processes, we also show cases where the annihilation of bath particles give substantial contribution to the final relic density. This occurs when the new scalars are below the TeV scale, thus in the reach of the LHC. The next-to-lightest odd particle can be long-lived and can alter the successful BBN predictions for the abundance of light elements, these constraints are relevant in both the scenarios where the singlet or the triplet are the long-lived particle. In the case where the triplet is the DM, the model is subject to constraints from ongoing direct, indirect and collider experiments. When the singlet is the DM, the triplet which is the next-to-lightest odd particle can be long-lived and can be probed at the proposed MATHUSLA detector. Finally we also address the detection prospects of triplet fermions and scalars at the LHC.

Title: Dark Radiation Constraints on Heavy QCD Axion Theories

Abstract: The explicit breaking of the PQ symmetry by higher dimensional operators can spoil the dynamical relaxation of the strong CP angle to its minimum of zero. One solution to this PQ “quality problem” is to introduce heavy QCD axions. Such axions acquire a mass from physics occurring far above the QCD scale and possess a potential more robust to corrections from higher dimensional PQ breaking operators. However, in much of the (m_a, f_a) plane, heavy QCD axions can generate large amounts of dark radiation when decaying. In this talk, I will discuss the cosmological evolution of heavy QCD axions in the early Universe, their interactions with the Standard Model thermal bath, and precise dark radiation constraints arising from their decays. In addition, I will discuss how including a mirror photon - common in heavy axion theories involving mirror QCD sectors - modifies this picture and can lead to dangerous amounts of dark radiation.

Title: Polarized solitons in higher-spin dark sector

Abstract: Beyond the Standard Model, our Universe could be host to a diverse set of degrees of freedom (dark sector). The dark sector could comprise of various bosonic fields with possible self interactions alongside gravity, containing macroscopic/astrophysical bound states known as solitons. For higher (than zero) spin fields, these solitons can even carry huge amounts of intrinsic spin polarization!, leading to interesting phenomenology. In this talk, I will discuss such solitons arising in spin-1 and higher fields including Abelian Higgs and Yang-Mills theories in the Higgs phase. If enough time, I will also talk about the small-scale structure of fuzzy dark matter, in light of its distinguishability between scalar and vector case in particular. 

Title: First-order electroweak phase transition from a naturally light singlet scalar

Abstract: We investigate a minimal singlet-scalar extension to the Standard Model that achieves a strong first-order electroweak phase transition. The singlet can be naturally light because of an approximate shift symmetry and no extra hierarchy problem beyond that of the Standard Model Higgs is introduced. We discuss the two-field dynamics of the phase transition in detail and find that the gravitational-wave signal is too weak to be detected by near-future observations. We also discuss the meta-stability of the zero-temperature scalar potential. Despite the apparent instability just above the electroweak scale, we show that the lifetime of the electroweak vacuum is much longer than the age of the universe and hence the setup does not require UV completion near the electroweak scale. The baryon asymmetry of the universe may be explained by local electroweak baryogenesis arising from a coupling between the singlet and weak gauge boson. The viable parameter space can be probed by the observations of rare Kaon decay and the cosmic microwave background. This model has the potential to be embedded into a left-right symmetric model so that the strong CP problem is solved. based on  https://arxiv.org/abs/2207.02867

Title: Quintessential inflation: A tale of emergent and broken symmetries

Abstract: In this talk, I will first review the basics of quintessential inflation and how this paradigm can be embedded in a general scalar-tensor formulation and its relation to variable gravity scenarios. Particular emphasis will be placed on the role played by symmetries.  In the second part of the talk, I will present some phenomenological aspects related to the breaking of symmetries triggered by the dynamics of the cosmon field and explore observational features of quintessential inflation.

Title: A Study of Neural Network Field Theories

Abstract: The backbones of modern-day Deep Learning, known as Neural Networks, define field theories on Euclidean background through their architectures. Variations in architecture parameters lead to variations in particle interaction strengths, controllably. The infinite width limit of NN architectures, combined with independent stochastic NN parameters, lead to generalized free field theories by the Central Limit Theorem (CLT). Small and large deviations from the CLT, due to finite architecture width and/or correlated stochastic parameters, respectively give rise to weakly coupled field theories and non-perturbative non-Lagrangian field theories in Neural Networks. I will present a systematic study of Neural Network field theories by a dual framework given in terms of architecture parameters: non-Gaussianities, symmetries, and locality by cluster decomposition are explored in the absence of an action. This dual description to NN field theories can have potential implications for physics, as some NN architectures define quantum field theories, when the NN output correlation functions satisfy Osterwalder-Schrader axioms.

Title: The Short-Baseline Neutrino Anomalies

Abstract: We discuss the intriguing anomalies reported by several

short-baseline neutrino oscillation experiments. We will show how the

long-standing reactor antineutrino anomaly - a flux deficit observed

from nuclear reactors - has been resolved, while the closely related

gallium anomaly has been reinforced. We will then discuss at length the

MiniBooNE anomaly, highlighting possible explanations both within the

Standard Model and beyond.

Title: Systematizing the Effective Theory of SIDM & the QM Swampland

Abstract: If dark matter has strong self-interactions, future astrophysical and cosmological observations, together with a clearer understanding of baryonic feedback effects, might be used to extract the velocity dependence of the dark matter scattering rate. To interpret such data, we should understand what predictions for this quantity are made by various models of the underlying particle nature of dark matter. In this talk, we systematically compute this function for fermionic dark matter with light bosonic mediators of vector, scalar, axial vector, and pseudoscalar type. We do this by matching to the nonrelativistic effective theory of self-interacting dark matter and then computing the spin-averaged viscosity cross section nonperturbatively by solving the Schrodinger equation, thus accounting for any possible Sommerfeld enhancement of the low-velocity cross section. In the pseudoscalar case, this requires a coupled-channel analysis of different angular momentum modes. We find, contrary to some earlier analyses, that nonrelativistic effects only provide a significant enhancement for the cases of light scalar and vector mediators. Scattering from light pseudoscalar and axial vector mediators is well described by tree-level quantum field theory.

This leads to a more general investigation of the non-relativistic quantum mechanical potentials generated between fermions by various classes of QFT operators. Evaluating their singularity structure, we find that the potentials are nonsingular and propose the Quantum Mechanics Swampland, in which the Landscape consists of non-relativistic quantum mechanical potentials that can be UV completed to a QFT, and the Swampland consists of pathological potentials which cannot. We identify preliminary criteria for distinguishing potentials which reside in the Landscape from those that reside in the Swampland. We also consider extensions to potentials in higher dimensions and find that Coulomb potentials are nonsingular in an arbitrary number of spacetime dimensions. 

Title: Quantum formation of topological defects

Abstract: After a quantum phase transition, the quantum vacuum can break up to form classical topological defects. In this seminar, I will discuss these phase transitions with global symmetry breaking and their dynamics, where the only interactions are with external parameters that induce the phase transition. I will evaluate the number density of the defects in 1,2 and 3-dimensions (kinks, vortices, and monopoles respectively) and show that it scales as $t^{−d/2}$ and evolve towards attractor solutions that are independent of the externally controlled time dependence. These can be relevant in a wide range of systems from condensed matter to cosmology.

Title: Grand unification and the Planck scale

Abstract: Grand unification of gauge couplings and fermionic representations remains an appealing proposal to explain the seemingly coincidental structure of the Standard Model. However, to realise the Standard Model at low energies, the unified symmetry group has to be partially broken by a suitable scalar potential in just the right way. The scalar potential contains several couplings, whose values dictate the residual symmetry at a global minimum. Some (and possibly many) of the corresponding symmetry-breaking patterns are incompatible with the Standard Model and therefore non-admissible.Here, we initiate a systematic study of radiative symmetry breaking to thereby constrain viable initial conditions for the scalar couplings, for instance, at the Planck scale. We combine these new constraints on an admissible scalar potential with well-known constraints in the gauge-Yukawa sector into a general blueprint that carves out the viable effective-field-theory parameter space of any underlying theory of quantum gravity.We exemplify the constraining power of our blueprint within a non-supersymmetric SO(10) GUT containing a 16 and a 45 dimensional scalar representation. We explicitly demonstrate that the requirement of successful radiative symmetry breaking to the correct subgroups significantly constraints the underlying microscopic dynamics. The presence of non-admissible radiative minima can even entirely exclude specific breaking chains: in the SO(10) example, Pati-Salam breaking chains cannot be realised since the respective minima are never the deepest ones.

Title: Improved Constraints on Dark Matter Annihilations Around Primordial Black Holes

Abstract: It is quite conceivable that cosmology may give rise to appreciable populations of both particle dark matter and primordial black holes (PBH) with the combined mass density providing the observationally inferred value $\Omega_{\rm DM}\approx0.26$. However, previous studies have highlighted that scenarios with both particle dark matter and PBH are strongly excluded $\gamma$-ray limits assuming particle dark matter with a velocity independent thermal cross section  $\langle\sigma v\rangle\sim3\times10^{-26}{\rm cm}^3/{\rm s}$, as is the case for classic WIMP dark matter. Here we extend these existing studies on $s$-wave annihilating particle dark matter to ascertain the limits from diffuse $\gamma$-rays on velocity dependent annihilations which are  $p$-wave with $\langle\sigma v \rangle\propto v^2$ or $d$-wave  with $\langle\sigma v \rangle\propto v^4$. Furthermore, we highlight that even if the freeze-out process is $p$-wave it is relatively common for (loop/phase-space) suppressed $s$-wave processes to actually provide the leading contributions to the experimentally constrained $\gamma$-ray flux from the PBH halo.

Title: Gravitational waves and PBH formation during an early matter era

Abstract: I will discuss the generation of Gravitational Waves (GWs) from large

density perturbations in the early universe and the possibility of

primordial black hole (PBH) formation. I will particularly focus on the

scenario of GW production from an early matter  domination era and I will

present the form of the corresponding GW spectrum.

Title: Cosmic coincidences of primordial-black-hole dark matter

Abstract: If primordial black holes (PBHs) contribute more than 10 percent of the dark matter (DM) density, their energy density today is of the same order as that of the baryons. Such a cosmic coincidence might hint at a mutual origin for the formation scenario of PBHs and the baryon asymmetry of the Universe. In this talk, I will introduce how baryogenesis can be triggered by the so-called ultra-slow-roll inflation that produces large curvature perturbations for PBH formation in single-field inflationary models. Within the inferred mass range for PBHs as important DM components, the "cosmic coincidence" requirement restricts the scaling frequencies of the stochastic gravitational wave background induced by ultra-slow-roll inflation, which can be tested by future experiments such as LISA, Einstein Telescope or DECIGO.

Title: Light thermal Dark Matter enabled by a second Higgs

Abstract: Thermal relic particles are a prime Dark Matter candidate. As searches for electroweak-scale WIMPs are well under way, lighter sub-GeV particles have become a focus of attention. I will introduce the basic requirements for light thermal relic dark matter, before presenting a minimal UV-complete model. The latter is based on the realisation that adding a second Higgs doublet to the Standard Model allows for a light scalar that can mediate between dark matter and the visible world. 

Title: Asymptotic safety - from particle physics to quantum gravity

Abstract: Fixed points of the renormalisation group play an important

role in quantum field theory (QFT). High energy fixed points can be

free such as in asymptotic freedom, or interacting, such as in

asymptotic safety, while low energy fixed points often describe

continuous phase transitions.

In this talk, I give an overview of asymptotically safe fixed points

in general 4d QFTs and gravity. In particle physics, I explain the

significance of non-Abelian gauge fields and Yukawa interactions, and

highlight implications for conformal field theories, and applications

to BSM model building. I further discuss the prospect for asymptotic

safety of gravity covering recent results and open challenges.

Title: Features in the Inflaton Potential and the Spectrum of Cosmological Perturbations

Abstract: I discuss inflationary models with particular features

in the potential that lead to the temporary violation of the slow-roll

conditions during the evolution of the inflaton. These features can enhance

the power spectrum of the curvature perturbations by several orders of

magnitude at certain scales and also produce prominent oscillatory patterns.

In single-field inflation the interesting features include inflection points

and steep steps. In two-field inflation sharp turns have a similar effect.

The slow-roll parameter eta is identified as the quantity that can trigger

the rapid growth of perturbations.

I present analytical and numerical studies of the inflationary dynamics.

The aim is to describe quantitatively the size of the enhancement, as well

as the profile of the oscillations, which are shaped by the number and

position

of the features in the potential.

The induced tensor power spectrum

inherits the distinctive oscillatory profile of the curvature spectrum

and is potentially detectable by near-future space interferometers.

Title: Non-parametric Reconstruction Of Some Cosmological Parameters.

Abstract: I shall focus on the non-parametric reconstruction of some cosmological parameters using diverse recent observational datasets. The prime endeavour is to directly ascertain the evolution of different cosmological quantities from observational data without assuming any prior functional form. The method adopted is the Gaussian Process regression. The universe is assumed to be spatially homogeneous and isotropic, thus described by the FLRW metric. I have assessed the validity of the cosmic distance-duality relation (CDDR), carried out the reconstruction of some kinematical quantities, and explored the possibility of a non-gravitational interaction in the cosmic dark sector between dark energy and dark matter. Finally, I investigated the possible effect of a non-zero spatial curvature and obtained constraints on the curvature density parameter independent of any background cosmological model.

Title: Massive amplitudes from momentum space CFTs

Abstract: There are evidences that the perturbative S-matrices in the flat space can be obtained by taking a flat limit of conformal field theory (CFT) correlators. Some progress has been made in this direction for scalar and gauge fields. Most of these works have made use of the position and mellin spaces. I shall review some of these developments and describe some progress in this direction in which I have been involved. In particular, I shall describe how to derive the CFT correlators involving non conserved tensorial operators in momentum space and use these to obtain the flat space S matrix involving massive fields. 

Title: TBA

Abstract: TBA

Title: Probing the early universe with gravitational waves

Abstract: Stochastic gravitational wave backgrounds can be generated by a variety of processes in the early universe, most notably inflation. These backgrounds are characterized by their spectral shape, polarization, (non-)Gaussianity and anisotropies. In this talk I will discuss the possibility of using these signatures to extract information about inflation and early universe physics as well as the prospects of observing such signatures with next generation CMB and interferometer experiments.

Title: Phenomenology of Partially Composite Neutrinos

Abstract: I will consider a class of models in which the neutrinos acquire their masses through mixing with singlet neutrinos that emerge as composite states of a strongly coupled hidden sector. In this framework, the light neutrinos are partially composite Majorana particles that obtain their masses through the inverse seesaw mechanism. I will focus on the scenario in which the strong dynamics is approximately conformal in the ultraviolet, and the compositeness scale lies at or below the weak scale. The small parameters in the Lagrangian necessary to realize the observed neutrino masses can naturally arise as a consequence of the scaling dimensions of operators in the conformal field theory. I will show that this class of models has interesting implications for a wide variety of experiments, including colliders and beam dumps, searches for lepton flavor violation and neutrinoless double beta decay, and cosmological observations.

Title: Axio-dilaton wormholes and their puzzling low-energy effects

Abstract: An important open question in the study of quantum gravity is whether topologically non trivial spacetime configurations (Euclidean wormholes) should be taken into account in the path integral. If present, they can generate phenomenologically relevant couplings and play an important role, e.g. in breaking axionic shift symmetries. At the same time, they pose deep conceptual problems such as the appearance of random couplings in the effective action or conflicts with holography. I will introduce in this talk some of the basic features of Euclidean wormholes and their phenomenological applications, focusing in particular on axionic wormholes and the role played by (massive) dilatons in their construction.

Title: Dark Matter Searches on a Chip

Abstract: In a large part of the viable dark matter (DM) mass range, DM consists of ultralight bosons with large occupation numbers. Axion-like particles and dark photons provide well-motivated examples of such DM candidates with simple non-thermal production mechanisms in the early universe. In these scenarios DM can interact with Standard Model photons. Such interactions enable searches for DM in which the dark particle converts into detectable light. This approach is employed by, for example, the flagship axion search, ADMX, which uses high-quality radio frequency cavities to look for conversions of micro-eV DM. At higher DM masses, this approach needs to be extended as the required cavity size becomes prohibitively small. I will review the requirements for implementing efficient DM-photon conversion in a physical system. I will then show that detectors based on integrated photonics (optical and near-infrared waveguides and resonators at the micron scale) provide a new, useful way to search for DM at these higher masses. These types of devices are practically important in, e.g., telecommunications and quantum information science, allowing us to leverage developments from those fields, including mass production of these structures; this is important since signal power scales with the total sensitive volume, so a large number of detectors can be used to implement a very sensitive DM search.

Title: Gravitational Wave Probes of Massive Gauge Bosons at the Cosmological Collider

Abstract: I will talk about extending the reach of the “cosmological collider” for massive gauge boson production during inflation from the CMB scales to the interferometer scales. Considering a Chern-Simons coupling between the gauge bosons and the pseudoscalar inflaton, one of the transverse gauge modes is efficiently produced and its inverse decay leaves imprint in primordial scalar and tensor perturbations. I will talk about the correlation functions of these perturbations and show the updated constraints on the parameter space from CMB observables. I will then extrapolate the tensor power spectrum to smaller scales consistently taking into account the impact of the gauge field on inflationary dynamics. I will show that the presence of massive gauge fields during inflation can be detected from characteristic gravitational wave signals encompassing the whole range of current and planned interferometers.

Title: From axion quality and naturalness problems to a high-quality Z_4N QCD relaxion

Abstract: We highlight general issues associated with quality and naturalness problems in theories of light QCD-axions, axion-like particles, and relaxions. We show the presence of Planck-suppressed operators generically lead to scalar coupling of axions with the SM. We present a new class of Z_4N QCD relaxion models that can address both the QCD relaxion CP problem as well as its quality problem. This new class of models also leads to interesting experimental signatures, which can be searched for at the precision frontier.

Title: Chiral asymmetry in the early Universe

Abstract: Since the SM model is a chiral theory, asymmetries in matter generically result in chiral asymmetries. Nevertheless the effect of the primordial chiral asymmetry is often neglected in the study of the early Universe because the baryon asymmetry is tiny. In this talk I will discuss some examples where a sizable chiral asymmetry plays an essential role, in particular in the context of baryogenesis.

Title: Making massive spin-2 particles from gravity during inflation

Abstract: The phenomenon of cosmological gravitational particle production (CGPP) occurs during and after inflation as light fields “feel” the cosmological expansion and their mode functions evolve non-adiabatically.  CGPP is a compelling and minimal explanation for the origin of dark matter, which might only interact gravitationally, as well as other cosmological relics.  Various studies have explored CGPP for massive particles with spin up to 3/2, and by doing so, identified interesting and unexpected features such as quantum interference effects and “catastrophic” production of high-momentum modes.  In this presentation, I will describe how CGPP arises for massive spin-2 particles in the context of bigravity.  I’ll discuss the implications for massive spin-2 particles as a dark matter candidate and related issues including the avoidance of ghost instabilities (FRW-generalized Higuchi bound).  

Title: Seesaw determination of the dark matter relic density

Abstract: We show that in the usual type-I seesaw framework, augmented solely by a neutrino portal interaction, the dark matter relic density can be created through freeze-in, in a manner fully determined by the seesaw interactions and the DM particle mass. This simple freeze-in scenario, where dark matter is not in a seesaw state, proceeds through slow, seesaw-induced decays of Higgs W and Z bosons. We identify two scenarios, one of which predicts the existence of an observable neutrino line.

Title: Non-equilibrium evolution and quantum entanglement during inflation

Abstract: In this talk, I will discuss inflation as an open quantum system and derive quantum corrections to cosmological observables, such as the power spectrum, showing explicitly why it is important to go beyond standard (Wilsonian) effective field theory. I will highlight deep insights this approach provides regarding quantum entanglement in the early universe and emphasize some features which apply to other gravitational systems.

Title: Detection of dark matter boosted by cosmic rays

Abstract: Direct detection experiments attempt to reveal dark matter particles scattering with nuclei in a detector, however, their reach is limited to dark matter with mass roughly above 100 MeV if only halo dark matter is considered. In my talk I will present a method, how to use the data from direct detection experiments to constrain lighter dark matter that interacts relatively strongly with baryons and gets, hence, boosted by galactic cosmic rays. Particular attention will be paid to interactions of these relativistic dark matter particles with nuclei within the Earth's crust that may stop the dark matter particles before reaching the underground detectors. It will be shown that inelastic scattering of dark matter with nuclei is a crucial ingredient for obtaining realistic results.

Title: Dark Matter Production in Nonstandard Cosmologies: from WIMPs to Axions

Abstract: The Universe is typically assumed to be radiation dominated in the

period preceding big bang nucleosynthesis, however we do not currently

have any observational probes to confirm this. Nonstandard cosmological

histories, where some other form of energy density dominates for a time,

commonly arise in theories of the early Universe. These histories have

important consequences for processes such as dark matter production

occurring in that time. In this talk I will briefly review nonstandard

cosmological histories and their effects on dark matter production

before presenting a recent example of axion production via misalignment

in a history with a period of increasing temperature.

Title: Title: Light mediator models and neutrino experiments

Abstract: In this talk, I will first discuss the low mass mediator models with specific examples.  These models contain new particles, e.g., light mediators, dark matter candidates, etc. I will discuss various ways of detecting these models in the ongoing/upcoming beam-based neutrino experiments with shorter baselines. The high-intensity proton beams in these experiments provide tremendous opportunities to investigate low-scale models. It is also possible to explain the excess of electron-like events at MiniBooNE in the context of some of these dark sector models.

Title: Curvature perturbations and primordial black holes from cosmological first-order phase transitions

Abstract: The randomness of quantum tunneling during cosmological first-order phase transitions (FOPTs) induces curvature perturbations both inside and outside the Hubble horizon. Since the vacuum energy density remains almost constant while other components are quickly diluted by the expansion of the Universe, the total energy density becomes larger than the averaged one in the regions where vacuum decay is slower. The current upper bounds on the curvature perturbation spectrum, both from the observations of CMB spectral distortions and ultracompact minihalos, can then be applied to give strict constraints on the PT parameters, especially for low-scale FOPTs and slow FOPTs. Considering this mechanism, we find generating PBHs is a universal consequence of FOPTs independent of specific models. For slow and strong FOPTs, these PBHs may constitute some fraction of dark matter.

Title: Neutron Star Tests of Pseudoscalar-Mediated Dark Matter

Abstract: Dark matter that interacts with visible matter primarily through a pseudoscalar mediator is generically difficult to test in direct detection due to a suppression by powers of the DM velocity. This effect does impact DM capture in neutron stars (NS) very much since the DM is accelerated to near relativistic speeds by the very dense body. In this talk I will show that measurements of neutron stars can test pseudoscalar-mediated DM beyond what is possible with direct detection as well as searches for pseudoscalar mediators themselves within a pair of UV complete theories. 

Title: Bubble wall dynamics at the electroweak phase transition

Abstract: Bubble nucleation is a key ingredient in a cosmological first order phase transition. The non-equilibrium bubble dynamics and the properties of the transition are controlled by the density perturbations in the hot plasma. We present, for the first time, the full solution of the linearized Boltzmann equation. Our approach, differently from the traditional one based on the fluid approximation, does not rely on any ansatz. We focus on the contributions arising from the top quark species coupled to the Higgs field during a first-order electroweak phase transition. Our results significantly differ from the ones obtained in the fluid approximation with sizeable differences for the friction acting on the bubble wall.

Title: Model independent explorations of the dark matter

Abstract: The absence of any visible signatures of dark matter candidates

make them elusive. In this talk, I will briefly highlight the 

theoretical and experimental advances which have taken place in the field for determination of the

dark matter properties. The field has largely moved from the model 

dependent to model independent methods which includes the classification of broad 

nature of the dark matter candidates to reduce the theoretical biases 

at the experiments. In this context, I will talk about two of my 

recent works, which highlights the importance and necessity of model 

independent probes

a) in context of determining the maximum reach of the thermal dark 

matter candidates

b) in context of the dark matter search experiments at Large Hadron Collider.

Title: Cosmological singularities in non-standard backgrounds

Abstract: The universe’s late-time acceleration has prompted a great deal of research into cosmological singularities, overseeing a proper classification of such singularities into strong and weak based on their strength. I’d be discussing a variety of new findings in this regard in various exotic cosmologies

where to begin we will consider RS-II braneworld-based scalar field dark energy models and demonstrate the presence of both weak and strong cosmological singularities in these regimes using two different approaches. The treatment would be really general, not restricted to any specific class of potentials or any constrained parameter region for the brane tension, and valid for both quintessence and phantom dark energy regimes. I then discuss about the occurence of type V singularities in non- GR based cosmological backgrounds, namely the RS-II, f(R) and Chern-Simons type and show that type V singularities occur in almost the same conditions in all these scenarios as they do in the usual GR based cosmology. However, I then also discuss that if we consider inhomogenous equations of state for matter than the occurence conditions of these singularities changes considerably. Finally, we also discuss singularities in an asymptotically safe cosmology where I show that one can have Type I - Type IV singularities in such a cosmology in a variety

of exotic setups with various equations of state. The work as a whole would explore various deep connections of cosmological singularities with quantum gravitational dark energy paradigms.

Title: Dark Matter Freeze-in: Forbidden Decay vs Scattering 

Abstract: Nonthermal dark matter can be produced from a light thermal mediator that connects the standard model with the hidden sector. At high temperatures, thermal corrections to the light mediator allows kinematically forbidden decay to heavy dark matter, which is a thermally induced process and is absent at zero temperature. In this talk, I will consider such kinematically forbidden decay for thermal scalar and fermion mediators. Special attention will be paid to the relative effects of the forbidden decay and the scattering on the dark matter relic density. I will show that the scattering is generically the dominant channel unless the thermal interaction of the mediator is strong.

Title: Polyakov's confinement mechanism for generalized Maxwell theory

Abstract: In the study of defect gauge theories and Large N QED, an effective action with fractional-derivative Maxwell term may appear, what we will call the generalized Maxwell theories. It can be thought of as a non-local theory with infinitely many higher derivative terms. In some cases, this fractional-derivative term is an exact marginal deformation of the usual QED.

In this talk, I will discuss a generalized Maxwell theory in three dimensions. When it is UV completed on a lattice, we can generalize the classic Polyakov's confinement mechanism and argue for confinement or deconfinement in different phases.

Title: Journey of PBHs: Formation to Evaporation

Abstract: Primordial Black Holes (PBHs) can be formed in the early Universe through the gravitational collapse of overdensities triggered by large fluctuations and other mechanisms such as phase transition, the collapse of topological defects, etc.

Since PBHs are not produced through Stellar collapse, their mass (theoretically) can be anything from the cut-off scale associated with the effective theory to the mass of the Universe enclosed by the Hubble horizon today.

One of the exciting reasons for PBHs existence, is effectively PBHs can explain the total Dark Matter (DM) density of the

Universe. Thus, it can be a perfect riposte to the illusive nature of DM. Even if PBHs are not DM, small-mass PBHs can have many interesting effects in the early Universe. PBHs that are going through evaporation today can impact particle DM through Lorentz boost.

In this talk, I will encapsulate the story of PBHs from their formation to evaporation and their cosmological impact.

Title: Phenomenological and cosmological implications of Alternative left-right model

Abstract: Left-Right (LR) theories are one of the successful beyond Standard Model (SM) scenarios to provide a unified explanation to the origin of small neutrino mass and low-energy parity violation. However, the conventional LR theory faces a challenge with the inevitable presence of flavor changing neutral currents (FCNCs). We have studied an alternative approach to LR theory, also known as Alternative LR model (ALRM) which can evade the constraints from this unavoidable FCNCs. Here we have shown that the different new physics signatures contributing significantly as compared to conventional LRSM scenarios in the context of decay and leptogenesis, respectively. The new type of vector-scalar diagram contributes significantly in while the minuscule Dirac CP-phase in the right handed neutrino sector can saturate current BAU bound. Moreover, we perform an analytical investigation of the scalar potential and vacuum structure to ensure its stability via bounded from below and co-positivity criteria. This yields constraints on scalar potential parameters and necessary criteria for electromagnetic charge-preserving vacua. We also obtain constraints on model parameters from collider data on exotic Higgs searches. Moreover, our model predicts several dark matter candidates stabilised by an R-parity similar to supersymmetry, where some of the new particles are odd and all SM particles are even under this symmetry.

Title: New probes of the early universe: Gravitational Waves and Primordial Black Holes

Abstract: The latest observation of the Cosmic Microwave Background (CMB) sky constrains the epoch of inflation in the early universe to have a simple slow-roll dynamics that leads to tiny, nearly scale-invariant scalar fluctuations and even tinier tensor fluctuations. However, CMB can only probe large cosmological scales, so that the smaller scales that exit the inflationary horizon closer to the end of inflation remain unexplored by direct observational techniques. Scalar and tensor fluctuations can have peaks and features at small scales when the dynamics of inflation deviates from standard slow-roll. In particular, large scalar fluctuations can result in abundant primordial black holes (PBH) after inflation and can induce large tensor fluctuations that propagate as stochastic background of induced gravitational waves (GW). With the tremendous sensitivities proposed by upcoming GW surveys and several bounds on the abundance of PBH over a huge range of masses, it is exciting to analyse relevant inflation models for their predictions for PBH and induced GW. I will elaborate on a specific example of multifield axion monodromy model of inflation, where large and sharp turns in the field-space manifold lead to enhanced scalar fluctuations. Apart from inflationary history, non-standard post-inflationary evolution can also influence the predictions for PBH and GW, which will be discussed.

Title : Cosmological singularities in non-standard backgrounds

Abstract : The universe’s late-time acceleration has prompted a great deal of research into cosmological singularities, overseeing a proper classification of such singularities into strong and weak based on their strength. I’d be discussing a variety of new findings in this regard in various exotic cosmologies

where to begin we will consider RS-II braneworld-based scalar field dark energy models and demonstrate the presence of both weak and strong cosmological singularities in these regimes using two different approaches. The treatment would be really general, not restricted to any specific class of potentials or any constrained parameter region for the brane tension, and valid for both quintessence and phantom dark energy regimes. I then discuss about the occurence of type V singularities in non- GR based cosmological backgrounds, namely the RS-II, f(R) and Chern-Simons type and show that type V singularities occur in almost the same conditions in all these scenarios as they do in the usual GR based cosmology. However, I then also discuss that if we consider inhomogenous equations of state for matter than the occurence conditions of these singularities changes considerably. Finally, we also discuss singularities in an asymptotically safe cosmology where I show that one can have Type I - Type IV singularities in such a cosmology in a variety

of exotic setups with various equations of state. The work as a whole would explore various deep connections of cosmological singularities with quantum gravitational dark energy paradigms.

Title: Gravitational waves from seeded phase transitions

Abstract: First order phase transitions in cosmology are usually assumed to proceed via bubble nucleation in homogeneous spacetime. The presence of impurities, or seeds, in the early Universe can however alter this picture by providing an additional channel for the false vacuum decay with exponentially enhanced tunneling probability. In this talk we will show how a seeded electroweak phase transition is realized already in the simplest extension of the SM including a scalar singlet with Z_2 symmetry (xSM), where the role of impurities is played by the Z_2 domain walls. We will discuss the various methods that allow us to evaluate the seeded nucleation rate, and show that this is generically faster than the homogeneous process. In this case gravitational waves are then produced by colliding walls rather than ordinary bubbles, with the duration of the phase transition set by the distance between the walls. For defects close to the scaling regime the resulting gravitational wave signal is generically amplified and shifted to lower frequencies. 

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Title:- Strong cosmic censorship conjecture for a charged BTZ black hole

Abstract:- The strong cosmic censorship conjecture, whose validation

asserts the deterministic nature of general relativity, has been studied

for charged BTZ black holes in three-dimensional general relativity, as

well as for Nth-order pure Lovelock gravity in d=2N+1 spacetime

dimensions. Through both analytical and numerical routes, we have computed

the ratio of the imaginary part of the quasi-normal mode frequencies with

the surface gravity at the Cauchy horizon. The lowest of which corresponds

to the key parameter associated with the violation of strong cosmic

censorship conjecture. Our results demonstrate that this parameter is

always less than the critical value (1/2), thereby respecting the strong

cosmic censorship conjecture. This is in complete contrast to the four or,

higher-dimensional black holes, as well as for rotating BTZ black holes,

where the violation of strong cosmic censorship conjecture exists.

Title:- Dark Matter Freeze-in: Forbidden Decay vs Scattering 

Abstract:- Nonthermal dark matter can be produced from a light thermal mediator that connects the standard model with the hidden sector. At high temperatures, thermal corrections to the light mediator allows kinematically forbidden decay to heavy dark matter, which is a thermally induced process and is absent at zero temperature. In this talk, I will consider such kinematically forbidden decay for thermal scalar and fermion mediators. Special attention will be paid to the relative effects of the forbidden decay and the scattering on the dark matter relic density. I will show that the scattering is generically the dominant channel unless the thermal interaction of the mediator is strong.

Title:- Neutrino Self-Interactions. Hubble Tension, and Inflation

Abstract:- In the Lambda-CDM model, Planck data provides a value of the Hubble constant H0 equal to 67.5 km/s/Mpc, which is around 5-sigma away from the locally measured value from Type Ia Supernovae, H0 equal to 73 km/s/Mpc. This Hubble tension is currently the biggest discrepancy in cosmology. Here we looked at the cosmological model that incorporates massive neutrino non-standard interaction mediated via a heavy scalar, which had previously shown a lot of promise in solving the Hubble tension in the strong interaction regime where the coupling strength is approximately 10^9 times the weak interaction coupling. However, with the latest Planck 2018 data, we found that the Planck high-multipole CMB polarization data disfavours such strong interactions. We also test the viability of Natural Inflation and Coleman-Weinberg Inflation in the presence of massive neutrino non-standard interactions, against CMB, BAO, and LSS data, with a particular focus on Planck and BICEP/Keck data. These inflationary models are ruled out at more than 2-sigma in the standard Lambda-CDM model with current cosmological data. But interestingly, we find that predictions from these inflationary models are allowed within 2-sigma when we include massive neutrino non-standard interactions.

Title:- Cosmic Inflation, Origin of Matter Asymmetry, and GW Background

Abstract:- Modern cosmology has been remarkably successful in describing the Universe from a second after the Big Bang until today. However, our current understanding of the cosmos before that time is less precise. Moreover, cosmology profoundly involves particle theory beyond the Standard Model to explain its long-standing puzzles: the origin of the observed matter asymmetry, particle nature of dark matter, and cosmic inflation. In this talk, I will explain that relic axion-gauge fields in fractions of a second after the Big Bang can relate and explain these seemingly unrelated puzzles in early and late cosmology. This new particle physics for inflation breaks matter-antimatter symmetry in inflation and does not require CP violation in the neutrino sector.  As a smoking gun, such relics would provide a new window into the early Universe through blue tilted primordial gravitational waves. Therefore, they are testable by future probes of GWs across 21 decades in frequency.

Title:- Primordial black holes and stochastic inflation beyond slow roll

Abstract:- Primordial Black Holes (PBHs) may form in the early universe, from the gravitational collapse of large density perturbations, generated by large quantum fluctuations during inflation. Since PBHs form from rare over-densities, their abundance is sensitive to the tail of the primordial probability distribution function (PDF) of the perturbations. It is therefore important to calculate the full PDF of the perturbations, which can be carried out non-perturbatively using the 'stochastic inflation' framework. In single field inflationary models, generating large enough perturbations to produce an interesting abundance of PBHs requires violation of slow roll. It is therefore necessary to extend the stochastic inflation formalism beyond slow roll, and consequently there has been a surge in the research interest in this direction in the recent years. A crucial ingredient for this is the stochastic noise matrix corresponding to the small wavelength fluctuations. In this talk, after providing a brief introduction to PBHs and ultra slow-roll inflation, the speaker will discuss analytical and numerical calculations of these matrix elements for an inflaton potential with a feature which violates slow roll and produces large, potentially PBH generating, perturbations. The seminar will be based on the following work carried out at the Particle Cosmology Group, University of Nottingham, in collaboration with Prof. Edmund J. Copeland and Prof. Anne M. Green : https://arxiv.org/abs/2303.17375

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Title:- Subtleties of supercooled cosmological phase transitions

Abstract:- In this talk I highlight the main results of our recent paper entitled

"Supercool subtleties of cosmological phase transitions".  As this title

suggests some of these results are fairly counter-intuitive and quite

surprising.  We may not be surprised to hear that satisfying the

traditional nucleation condition does not necessarily ensure the

finishing of the phase transition.  But the opposite statement may raise

some eyebrows: We spell out the conditions under which the finishing

condition is satisfied while the usual nucleation condition is not.  We

support these findings by analytical approximations that aid physical

intuition, and full numerical results that show that our analytical

approximations are valid.  Altogether, we find that the nucleation

temperature is not a reliable indicator of the "temperature of the phase

transition", and suggest more reliable alternatives.  All these findings

affect the gravitational wave spectrum calculated from the thermal

properties of these phase transitions, which is important since

supercooled transitions tend to yield the highest gravitational wave

amplitudes.

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Title:- Primordial Stochastic Gravitational Wave Backgrounds from a Sharp Feature in Three-field Inflation

Abstract:- The detection of a primordial stochastic gravitational wave background has the potential to reveal unprecedented insights into the early universe and possibly into the dynamics of inflation. Generically, UV-complete inflationary models predict an abundance of light scalars, so any inflationary stochastic background may well be formed in a model with several interacting degrees of freedom. The stochastic backgrounds possible from two-field inflation have been well-studied in the literature, but it is unclear how similar they are to the possibilities from many-field inflation. In this work, we study stochastic backgrounds from more-than-two-field inflation for the first time, focusing on the scalar-induced background produced by a brief turn in three-field space. We find an analytic expression for the enhancement in the power spectrum as a function of the turn rate and the torsion. We show that unique signatures of three-field dynamics are possible in the primordial power spectrum and gravitational wave spectrum. We confirm our analytic results with a suite of numerical simulations and find good agreement in the shape and amplitude of the power spectra. We also comment on the detection prospects in LISA and other future detectors. We do not expect the moderately large growth of the inflationary perturbations necessary for detection to cause a breakdown of perturbation theory. However, this must be verified case-by-case for specific microphysical models to make a definitive claim.