SEPTEMBER 29

Jens Niemeyer

Slides  📥

Title: Gravitational structure formation with nonrelativistic scalar fields

Abstract: Scenarios of structure formation with axion-like particle dark matter can have distinctive signatures on scales ranging from kiloparsecs to astronomical units. They are governed almost entirely by the particle mass and therefore very predictive. However, much of the phenomenology is highly nonlinear, requiring large simulations and, in some cases, novel computational tools. Very similar phenomena might have appeared in an early matter-dominated epoch after inflation. Here, the inflaton field itself fragments gravitationally, forming structures on microscopic scales that closely resemble cosmological large-scale structure.

Tonatiuh Matos

Slides 📥

Title: On the Physics of the Gravitational Wave Background

Abstract: It is a matter of fact that the universe lives on a Gravitational Wave Background (GWB). This GWB is extra energy that is not contained in Einstein's equations. In RMF67 (2021) 040703, a new model was developed to explain the accelerating expansion of the universe where a GWB was incorporated into Einstein's equations by extending them as $R_{\mu\nu} - \frac{1}{2} R g_{\mu\nu} + \frac{2\pi^2}{{\lambda}^2} g_{\mu\nu} = \kappa^2 T_{\mu\nu}$, where ${\lambda}$ is the Compton wavelength of the graviton. In this talk, we explain the important points of this new paradigm. Due to GWB, quantum particles cannot follow geodesics, but rather stochastic trajectories. We start by adding a stochastic term to the trajectories of quantum particles and derive the corresponding field equations for a quantum particle. We arrive at the Klein-Gordon equation in a curved spacetime and from it we obtain a generalized Schrödinger equation. This leads to the following relevant result: the Schrödinger equation can be a direct consequence of the fact that the universe lives in a GWB. At the end, we briefly talk about the cosmology derived from this paradigm.

Luis A. Ureña-López

Title: Update 2023 on Scalar Field Dark Matter

Abstract: We will present a brief update of the developments in the last year of the Scalar Field Dark Matter model, from different perspectives: gravitational, astrophysical and cosmological. Special emphasis is considered on the different observational constraints on the mass of the ultralight boson, and the possibilities to detect a quartic self-interaction which could point out to a more complex field potential in the model. 

Pierre-Henri Chavanis

Title: A heuristic wave equation parameterizing BEC dark matter halos with a quantum core and an isothermal atmosphere

Abstract: The Gross-Pitaevskii-Poisson equations that govern the evolution of self-gravitating Bose-Einstein condensates, possibly representing dark matter halos, experience a process of gravitational cooling and violent relaxation. We propose a heuristic parametrization of this complicated process in the spirit of Lynden-Bell's theory of violent relaxation for collisionless stellar systems. Starting from the coarse-grained Wigner equation and taking its hydrodynamic moments, we derive a generalized wave equation involving a logarithmic nonlinearity associated with an effective temperature $T_{\rm eff}$ and a damping term associated with a friction $\xi$ [P.H. Chavanis, Eur. Phys. J. B 95, 48 (2022)]. These terms can be obtained from a maximum entropy production principle and are linked by a form of Einstein relation expressing the fluctuation-dissipation theorem. The wave equation satisfies an $H$-theorem for the Lynden-Bell entropy and relaxes towards a stable equilibrium state which is a maximum of entropy at fixed mass and energy. This equilibrium state represents the most probable state of a Bose-Einstein condensate dark matter halo. It generically has a core-halo structure [P.H. Chavanis, Phys. Rev. D 100, 083022 (2019)]. The quantum core prevents gravitational collapse and may solve the core-cusp problem. The isothermal halo leads to flat rotation curves in agreement with the observations. These results are consistent with the phenomenology of dark matter halos. Furthermore, as shown in a previous paper [P.H. Chavanis, Phys. Rev. D 100, 123506 (2019)], the maximization of entropy with respect to the core mass at fixed total mass and total energy determines a core mass-halo mass relation which agrees with the relation obtained in certain direct numerical simulations. We stress the importance of using a microcanonical description instead of a canonical one. We also explain how our formalism can be applied to the case of fermionic dark matter halos.

Ana A. Avilez-López

Title: Studying the Dynamics of Fuzzy Dark Matter in Groups of Galaxies

Abstract: In this talk, some results and perspectives will be presented regarding the following project: By using multi-body solutions of the Schrödinger-Poisson system we study the evolution of agglomerations of galaxies whose members are made of Fuzzy Dark Matter. We consider a variety of initial configurations holding from 3 to 10 members with similar masses which are constructed from cosmological N-body simulations. This talk will be specially focused in explaining this construction. In addition, we aim to track the evolution of the total energy, virial energy and other evolution quantifiers of these groups along the cosmic history and to study the disruption effect suffered by the members produced by the interactions between subhalos and by the possible presence of a host halo.

SEPTEMBER 30

Verónica Lora

Title: The importance of baryons in cosmological simulations

Abstract: In this talk I will present some results about the importance of dwarf galaxies that challenge the standard LCDM cosmological model. First I will talk about the core-cusp problem and how it is not exactly solved in the LCDM paradigm. Then I will talk about the importance of baryons, which let us study the formation and evolution of dwarf galaxies which are formed without the need of a dark matter halo: Tidal dwarf galaxies and a new type of galaxies that we call ram-pressure-stripped dwarf galaxies. In the future to include baryons in scalar field cosmological simulations will impact out understanding of galaxy formation in the smaller scales.

Francisco S. Guzmán

Title: Small Steps: Insights into Fuzzy Dark Matter Dynamics with the CAFE Code

Abstract: In this contribution, we provide a concise description of our code CAFE, specifically tailored for the study of Fuzzy Dark Matter dynamics. Throughout our research, we have pursued various incremental steps, each contributing to a certain understanding of the subject. Our endeavors include: constructing simple stationary solutions with spherical symmetry, exclusively composed of FDM, that show core-tail structures; developing stationary solutions that encompass both FDM and an ideal gas, broadening the scope of our investigations; constructing halos based on a multimode expansion of the wave function; exploring the evolution of systems governed by the GPP system, which include binary and multi-mergers, multimode halos, as well as the evolution of merger trees; introducing the coupling with an ideal gas, thereby enabling the exploration of mergers resulting in the formation of disks; conducting a detailed study of the influence of domain topology on various dynamical processes at local scales, revealing valuable insights into their behavior; investigating the core-halo scaling relation and its dependency on boundary conditions, further enriching our comprehension of FDM dynamics. These incremental steps have advanced our understanding of Fuzzy Dark Matter dynamics and hold the potential to contribute positively to the community.

Juan Carlos Degollado

Title: Dynamical scalarization in compact objects 

Abstract: We describe the dynamics of the phenomenon of spontaneous scalarization predicted in neutron stars within the framework of scalar-tensor tensor theories of gravity, By using full nonlinear evolution of the Einstein-Klein-Gordon system we analyze the dynamical transition to a scalarized state in two types of compact objects namely boson stars and neutron stars. We also describe some possible observational consequences of the dynamical process.

Carlos Herdeiro

Title: Landscape (and surprises) of compact objects with bosonic fields in GR

Abstract: In Einstein-Maxwell's theory there are no solitons, there are uniqueness theorems for black holes, which have "no hair" and there are no balanced neutral multi-black hole solutions. We discuss, with concrete examples, how these different properties change in Einstein-Klein-Gordon and Einstein-Proca models, where the bosonic fields are candidates for ultralight bosonic matter, yielding a much richer landscape of solutions, both solitonic and with black holes, with some dynamical surprises.

Paul Shapiro

Title: Topics in SFDM Cosmology and Structure Formation 

Abstract: Scalar Field Dark Matter (SFDM) comprised of ultralight (>~10-22 eV) bosons was proposed as an alternative to standard Cold Dark Matter (CDM) because of its novel structure formation dynamics as a Bose-Einstein condensate and quantum superfluid, described by the Gross-Pitaevski and Poisson equations. In the free-field ("fuzzy'') limit of SFDM (FDM), structure is inhibited below the de Broglie wavelength, λ_deB, but resembles CDM on larger scales. Virialized haloes have solitonic cores of radius ~λ_deB, surrounded by CDM-like envelopes. When a strong enough repulsive self-interaction (SI) is also present, structure can be inhibited below a second length scale, λ_SI, with λ_SI >λ_deB - the Thomas-Fermi (TF) regime. Structure formation in the TF regime differs significantly from FDM. We will discuss the internal structure of haloes that form from gravitational instability in the TF regime, distinguishing the outcomes of static vs. infall boundary conditions. We will then place the TF regime in the context of halo and large-scale structure formation from cosmological perturbations, including observational constraints.

FDM dynamics differ from CDM on small scales because of quantum pressure, and SFDM-TF differs further by adding SI pressure. Smoothed on scales large compared with λ_deB, however, SFDM obeys the same collisionless Boltzmann equation as standard CDM. In the small-λ_deB limit, in fact, this allows us to model all three by fluid conservation equations for a compressible, γ = 5/3 ideal gas, with ideal gas pressure sourced by internal velocity dispersion and, for the TF regime, an added SI pressure, P_SI ∝ ρ^2, that results from the SI potential. We will show why this makes the CDM-like halo envelopes of all three cases explainable as the inevitable consequence of their cosmological infall boundary conditions. We further illustrate the importance of boundary conditions by fully 3D simulations of FDM that solve the coupled GP-Poisson equations, contrasting the halo mass profiles that arise from isolated vs. periodic BCs.

Finally, we will address some consequences of assuming cosmic dark matter is a complex scalar field, with a U(1) symmetry. In this case, SFDM can have an early phase in which it behaves as a relativistic fluid with a stiff equation of state (w= p/rho=1), when its oscillation period exceeds the Hubble time and the kinetic energy term dominates in the KleinGordon equation, an example of the phenomenon of kination. We will discuss the cosmological implications of this, including BBN and the stiff-amplification of the stochastic gravitational wave background “SGWB” from tensor modes during inflation and its backreaction on the expansion history of the universe, with observable consequences. 

SEPTEMBER 29

António Morais

Title: Audible Gravitational Echoes of New Physics 

Abstract: Based on the recent article [2023.02399], we discuss the LISA potential for finding evidence of New Physics from measurements of the Stochastic GW Background (SGWB). As a benchmark scenario, we study a version of the low-scale Majoron model equipped with lepton number symmetry and an inverse seesaw mechanism for neutrino mass generation. In particular, we discuss under which circumstances the model can be probed at LISA, when does the Majoron is a viable scalar dark matter candidate and which implications result for collider physics observables.

Eric Santiago Escobar Aguilar

Title: Connecting three stochastic theories that lead to quantum mechanics in curved space-time

Abstract: In this talk we explore the connection between three theories that lead to quantum mechanics in curved space-time, namely Scale relativity (SR), Stochastic Quantum Mechanics (SQM) and Stochastic Electrodynamics (SED). We explore the differences and similarities between the dynamical equations and different proposal are made in order to complement each other. The final field equations correspond to generalized Klein-Gordon equation, derived via stochastic formalism and relativistic Boltzmann Equation.

Iván Álvarez Rios

Title: Constructing BEC Dark Matter Halos through a Multimode Expansion with Genetic Algorithms

Abstract: We present a novel method for constructing BEC-DM (Bose-Einstein Condensate Dark Matter) galactic halos using a multimode expansion based on a target density. The assumptions underlying this approach are as follows: 1) Both the BEC density and gravitational potential exhibit spherical symmetry, 2) The wave function is expressed as a linear combination of modes defined by the quantum numbers $n$ and $\ell$, and 3) These modes are assumed to be orthogonal. Differing from previous similar approaches e.g. [Yavetz et al. 2022] and [S-C Lin et al 2018], we determine the expansion coefficients using a Genetic Algorithm. In this approach, we evolve organisms with DNA whose genes are the expansion coefficients, while the fitness function is defined as a decreasing function of the error between the produced radial density and the target density.

Jorge H. Mastache de los Santos

Title: Scalar Fields in Non-Relativistic Boson Stars: Structural Configurations and Implications for Dark Matter

Abstract: We investigated the structural intricacies of non-relativistic bosons forming a gravitational bound Bose-Einstein condensate, identified as a non-relativistic boson star. Under specific conditions, the Newtonian gravitational potential can be represented as a harmonic oscillator potential due to the scalar field's influence. Using four distinct ansätze, we computed the statistical properties of these stars from the single-particle properties, revealing consistent structural and gravitational equilibria across varied parameter sets. Notably, for a system resembling a dark matter halo surrounding a galaxy in the Gaussian ansätze, the required scattering length (a) is a = 9 x 10^{-75} m, with a boson particle mass (m) of m = 1.3 x 10^{-22} eV. Conversely, for a Sun-like system, the particle mass is m = 1.3 x 10^{-12} eV with a scattering length of a = 9.6 x 10^{-69} m. These results highlight the potential link between scalar fields, boson stars, and dark matter, suggesting that the scalar field's mass and properties could offer insights into dark matter's nature.

José Salvador Negrete Serrato

Title: Strong gravitational lensing with a subhalo mass function

Abstract: We study the properties of strong lenses generated by dark matter galaxy halos in the Universe and the statistical inference process to understand the density profile of the lens. For that, we used mock data of strong gravitational lenses using the publicly available software paltas, which is a pipeline based on the well-known package lenstronomy and written in Python. Lenses are modeled according to simple lens profiles such as the Singular Isothermal Sphere (SIS) and the Singular Isothermal Ellipsoid (SIE), and the background cosmology is assumed to be that of the standard cosmological model ΛCDM. The generated lensing observations include the contribution of dark matter substructure in the form of subhalos modeled after a truncated Navarro-Frenk-White (NFW) profile. Performing a statistical inference process on these mock observations, assuming these can be described by a simple lens profile, our final aim is to identify the influence of the substructure in terms of the inferred parameters that describe the lens profile.

Leonardo Sánchez Hernández

Title: Proca Stars with Dark Photons from Spontaneous Symmetry Breaking of the Scalar Field Dark Matter

Abstract: Recently, the Scalar Field Dark Matter (SFDM) model (also known as Fuzzy, Wave, Bose-Einstein, Ultra-light Dark Matter) has gained a lot of attention because it has provided simpler and more natural explanations for various phenomena observed in galaxies, as a natural explanation for the center of galaxies, the number of satellite galaxies around their host and, more recently, a natural explanation for anomalous trajectories of satellite galaxies called Vast Polar Orbits (VPO) observed in various galaxies. In the present work we study the assumption that the SFDM is a type of charged dark boson whose gauge charge is associated with the Dark Photon (DP). Inspired by these results, we study the formation of compact bosonic objects, such as Boson Stars (BS) and focus on the possibility that, due to spontaneous $U(1)$ SFDM symmetry breaking, the DP may acquire mass and form compact objects like Proca Stars (PS). If this is true, we can expect measurable effects on the electromagnetic field of the Standard Model (SM) of particles due to their interaction with the DP on the formation of compact objects.

Tula Bernal

Title: Scalar field dark matter in galaxies and the anisotropy of the satellite galaxies

Abstract: In this talk, I introduce an analytical model of multistate scalar field dark matter as an alternative to cold dark matter (CDM). Despite behaving similarly to CDM at the cosmological level, this model exhibits significant differences at galactic scales. These discrepancies could provide an explanation for the non-uniform distribution of satellite galaxies around the Milky Way, Andromeda, and other galaxies. The results of fitting this model to the rotation curves of various galaxies, along with the potential distribution of their associated satellites, are presented.

Yadir Garnica

Title: PBH's abundance in a superradiant scenario

Abstract: "Superradiant phenomena enable the study of scalar field properties arising from the development of particle clouds around black holes in an approximation similar to hydrogen atom solutions. Consequently, it is feasible to impose constraints on the presence of these systems within the framework of scalar-photon coupling. Given the significance of axions and ALPs as potential candidates for dark matter, in conjunction with the envisaged coupling, it becomes possible to compute limitations on the existence of specific black holes as contributors to the overall dark matter content (both locally and within the extragalactic background). These restrictions prove to be more compelling compared to those commonly encountered in the literature (such as microlensing or evaporation), owing to the stabilizing mechanisms of the superradiant phenomenon and the stimulated production of the scalar field."