2022

11:45 am, Friday, Dec 16th

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11:45 am, Friday, Dec 9th

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Title: Applying Noble Liquid Particle Detection in Nuclear Imaging: Positron Emission Tomography

Abstract: In the field of astroparticle physics, noble liquids such as Argon and Xenon are widely used in underground particle detectors searching for candidate dark matter particles. They offer a variety of advantages over solid, room temperature scintillators and therefore these liquid scintillators can be utilized in other fields of research such as medical imaging.

Positron Emission Tomography (PET) is used to observe metabolic processes within patients. It works by reconstructing the annihilation origin of incident gamma rays produced by a positron emitting tracer. However, inefficiencies of current PET technology, such photomultiplier tubes, can result in poor imaging. We propose 3Dπ: a full body, Time of Flight (TOF) PET scanner using Silicon Photomultipliers (SiPM) coupled with a xenon-doped Liquid Argon (Lar+Xe) scintillator. We simulated this design using Geant4 while following the National Electrical Manufacturers Association's evaluation tests for performance assessment. We will present results that highlight a 200-fold increase in sensitivity, spatial resolutions comparable to commercial PET scanners and produce PET images from 15-30 second scans faster than traditional 30-35-minute scans. Further studies will involve optimizing the layer thickness of Lar+Xe. With this scintillator and SiPMs, we can use the precise TOF info of gamma rays to improve the localization of individual positron annihilations and provide low-dose PET scans for patients who may be at high risk for exposure to radiation.

11:45 am, Friday, Dec 2nd

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11:45 am, Friday, Nov 18th

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Guest: Pawan Dhakal

Title: New Constraints on Macroscopic Dark Matter Using Radar Meteor Detectors

Abstract: We show that dark-matter candidates with large masses and large nuclear interaction cross sections are detectable with terrestrial radar systems. We develop our results in close comparison to successful radar searches for tiny meteoroids, aggregates of ordinary matter. The path of a meteoroid (or suitable dark-matter particle) through the atmosphere produces ionization deposits that reflect incident radio waves. We calculate the equivalent radar echoing area or `radar cross section' for dark matter. By comparing the expected number of dark-matter-induced echoes with observations, we set new limits in the plane of dark-matter mass and cross section, complementary to pre-existing cosmological limits. Our results are valuable because (A) they open a new detection technique for which the reach can be greatly improved and (B) in case of a detection, the radar technique provides differential sensitivity to the mass and cross section, unlike cosmological probes.

11:45 am, Friday, Nov 4th

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Guest: Joaquim Iguaz (LAPTh, CNRS)

Title: Are PBHs everything everywhere all at once? Astrophysical and cosmological signatures of PBHs

Abstract: In recent years, Primordial Black Holes (PBHs) have been presented as extremely versatile objects providing a unique probe of the early Universe, gravitational phenomena, high energy physics and quantum gravity. Of particular interest is the role of PBHs as a non-particle candidate for the dark matter (DM). Although most of the PBH DM parameter space is tightly constrained, the asteroid mass range is still potentially viable. The lower end is accessible via high-energy astrophysical probes, sensitive to their Hawking evaporation spectrum. In the first part of the talk, I will revisit the constraints on evaporating PBHs from both the isotropic X-ray and soft γ-ray background, and the diffuse soft γ-ray emission towards the inner Galaxy as measured by INTEGRAL, setting the strongest limit on PBH DM for masses up to 4×10^17 g. The interest for PBHs has also been revamped in the light of recent LIGO/Virgo measurements of coalescing black hole binaries with typical masses of tens of M⊙. The best-motivated scenario for a sizable PBH contribution to such events invokes the QCD phase transition, which naturally enhances the probability to form PBH with masses of stellar scale. In the second part of the talk, I will reconsider the expected mass function associated not only to the QCD phase transition proper, but also the following particle antiparticle annihilation processes, and analyse the constraints on this scenario from a number of observations. We find that the scenario is not viable, unless ad hoc features in the power-spectrum are introduced by hand. Despite these negative results, we note that a future detection of coalescing binaries involving sub-solar PBHs has the potential to check the cosmological origin of SMBHs at the e± annihilation epoch, if indeed the PBH mass function is shaped by the changes to the equation of state driven by the thermal history of the universe.

Guest: Christopher Cappiello (Queen's U)

[https://arxiv.org/abs/2210.09448]

Title: Dark Matter from Monogem

Abstract: As a supernova shock expands into space, it may collide with dark matter particles, scattering them up to velocities more than an order of magnitude larger than typical dark matter velocities in the Milky Way. If a supernova remnant is close enough to Earth, and the appropriate age, this flux of high-velocity dark matter could be detectable in direct detection experiments, particularly if the dark matter interacts via a velocity-dependent operator. This could make it easier to detect light dark matter that would otherwise have too little energy to be detected. We show that the Monogem Ring supernova remnant is both close enough and the correct age to produce such a flux, and thus we produce novel direct detection constraints and sensitivities for future experiments.

PAST EVENTS

11:45 am, Friday, Oct 28th

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11:45 am, Friday, Oct 21st

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11:45 am, Friday, Oct 6th

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Guest: Gonzalo Herrera (TUM)

Title: Neutrino and gamma-ray attenuation by dark matter spikes

[https://arxiv.org/abs/2209.06339]

Abstract:

In this talk, I will discuss the attenuation of high energy neutrinos and photons produced in a blazar when they propagate through the dark matter spike around the central black hole and the halo of the host galaxy. In particular, I will discuss new constraints on the dark matter-neutrino and dark matter-photon scattering cross sections obtained from the observation by IceCube of a few high-energy neutrino events from TXS 0506+056, and their coincident gamma-ray events. I will emphasize the dependence of the constraints with the location where the neutrinos and gamma-rays are produced, and the dependence with the dark matter self-annihilation cross section. The constraints are orders of magnitude more stringent than those derived from considering the attenuation through the intergalactic medium and the Milky Way dark matter halo. When the cross-section increases with energy, the constraints are also stronger than those derived from the CMB and large-scale structure.

Guest: Rostom Mbarek (U Chicago)

Title: High-Energy Neutrino Emission from Espresso-Accelerated Ions in Jets of Active Galactic Nuclei

[https://arxiv.org/abs/2207.07130]

Abstract:

We present a bottom-up calculation of the flux of ultra-high energy cosmic rays (UHECRs) and high-energy neutrinos produced by powerful jets of active galactic nuclei (AGNs). By propagating test particles in 3D relativistic magnetohydrodynamic jet simulations, including a Monte Carlo treatment of sub-grid pitch-angle scattering and attenuation losses due to realistic photon fields, we study the spectrum and composition of the accelerated UHECRs and estimate the amount of neutrinos produced in such sources. We find that UHECRs may not be significantly affected by photodisintegration in AGN jets where the espresso mechanism efficiently accelerates particles, consistent with Auger's results that favor a heavy composition at the highest energies. Moreover, we present estimates and upper bounds for the flux of high-energy neutrinos expected from AGN jets. In particular, we find that: i) source neutrinos may account for a sizable fraction, or even dominate, the expected flux of cosmogenic neutrinos; ii) neutrinos from the \beta-decay of secondary neutrons produced in nucleus photodisintegration could in principle contribute to the PeV neutrino flux observed by IceCube, but can hardly account for all of it; iii) UHECRs accelerated via the espresso mechanism lead to nearly isotropic neutrino emission, which suggests that nearby radio galaxies may be more promising as potential sources. We discuss our results in the light of multimessenger astronomy and current/future neutrino experiments.

11:45 am, Friday, Sept 23rd

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11:45 am, Friday, Sept 16th

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11:45 am, Friday, Sept 9nd

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11:45 am, Friday, Sept 2nd

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11:45 am, Friday, Aug 19th

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11:45 am, Friday, Aug 5th

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11:45 am, Friday, July 29th

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11:45 am, Friday, July 22nd

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11:45 am, Friday, July 15th (Pure virtual)

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11:45 am, Friday, July 8th (Pure virtual)

Guest: Marc Oncins (ICC-UB)

Title: Primordial black holes capture by stars and induced collapse to low-mass stellar black holes

[https://arxiv.org/abs/2205.13003]

Abstract:

Primordial black holes in the asteroid-mass window (∼10^(−16) to 10^(−11) M⊙), which might constitute all the dark matter, can be captured by stars when they traverse them at low enough velocity. After being placed on a bound orbit during star formation, they can repeatedly cross the star if the orbit happens to be highly eccentric, slow down by dynamical friction and end up in the stellar core. The rate of these captures is highest in halos of high dark matter density and low velocity dispersion, when the first stars form at redshift z∼20. We compute this capture rate for low-metallicity stars of 0.3 to 1M⊙, and find that a high fraction of these stars formed in the first dwarf galaxies would capture a primordial black hole, which would then grow by accretion up to a mass that may be close to the total star mass. We show the capture rate of primordial black holes does not depend on their mass over this asteroid-mass window, and should not be much affected by external tidal perturbations. These low-mass stellar black holes could be discovered today in low-metallicity, old binary systems in the Milky Way containing a surviving low-mass main-sequence star or a white dwarf, or via gravitational waves emitted in a merger with another compact object. No mechanisms in standard stellar evolution theory are known to form black holes of less than a Chandrasekhar mass, so detecting a low-mass black hole would fundamentally impact our understanding of stellar evolution, dark matter and the early Universe.

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11:45 am, Friday, June 24th

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11:45 am, Friday, June 17th

Guest: Yu-Dai Tsai (UC, Irvine)

Title: Planetary Defense and Space Quantum Technologies for Fundamental Physics: Dark Matter, Gravity, and Cosmic Neutrinos

[https://arxiv.org/abs/2112.07674 & https://arxiv.org/abs/2107.04038]

Abstract:

I will talk about using planetary/asteroidal data and space quantum technologies to study fundamental physics.

I will first show a proposal using space quantum clocks to study solar-halo ultralight dark matter, motivated by the NASA deep space atomic clock (DSAC) and Parker Solar Probe (PSP).

We then discuss new constraints on fifth forces using asteroidal data. We will show preliminary results of the robust constraints by using the NASA JPL program and asteroid tracking data that are used for planetary defense purposes.

We then discuss model-independent constraints on any dark matter models through pure gravity.

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11:45 am, Friday, June 10th

Guest: Taylor Murphy (Ohio State)

Title: The many distinctive signals of frustrated dark matter

Abstract:

We study a renormalizable model of Dirac fermion dark matter (DM) that communicates with the Standard Model (SM) through a pair of mediators -- one scalar, one fermion -- in the representation (6,1,43) of the SM gauge group SU(3)c×SU(2)L×U(1)Y. While such assignments preclude direct coupling of the dark matter to the Standard Model at tree level, we examine the many effective operators generated at one-loop order when the mediators are heavy, and find that they are often phenomenologically relevant. We reinterpret dijet and pair-produced resonance and jets+EmissT searches at the Large Hadron Collider (LHC) in order to constrain the mediator sector, and we examine an array of DM constraints ranging from the observed relic density Ωχh2Planck to indirect and direct searches for dark matter. Tree-level annihilation, available for DM masses starting at the TeV scale, is required in order to produce Ωχh2Planck through freeze-out, but loops -- led by the dimension-five DM magnetic dipole moment -- are nonetheless able to produce signals large enough to be constrained, particularly by the XENON1T experiment. We find that the parameter space left open by experiment and compatible with freeze-out is quite small, indicating a potential need for further model-building and/or non-standard cosmologies.

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11:45 am, Friday, June 3rd

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11:45 am, Friday, May 27th

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11:45 am, Friday, May 13th

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Guest: Jan Heisig (RWTH Aachen)

Title: Lyman-alpha constraints on freeze-in and superWIMPs

Abstract:

Dark matter (DM) from freeze-in or superWIMP production is well known to imprint non-cold DM signatures on cosmological observables. We derive constraints from Lyman-alpha forest observations for both cases, basing ourselves on a reinterpretation of the existing Lyman-alpha limits on thermal warm DM. We exclude DM masses below 15 keV for freeze-in, in good agreement with previous literature, and provide a generic lower mass bound for superWIMPs that depends on the mother particle decay width. Special emphasis is placed on the mixed scenario, where contributions from both freeze-in and superWIMP are similarly important. In this case, the imprint on cosmological observables can deviate significantly from thermal warm DM. Furthermore, we provide a modified version of the Boltzmann code class, analytic expressions for the DM distributions, and fits to the DM transfer functions that account for both mechanisms of production. For illustration, we apply the above generic limits to a coloured t-channel mediator DM model, in which case contributions from both freeze-in through scatterings and decays, as well as superWIMP production can be important. We map out the entire cosmologically viable parameter space, cornered by bounds from Lyman-alpha observations, the LHC, and Big Bang Nucleosynthesis.

11:45 am, Friday, May 6th

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Guest: Jakob van Santen (DESY)

Title: toise: a framework to describe the performance of high-energy neutrino detectors

Abstract:

Neutrinos offer a unique window to the distant, high-energy universe. Several next-generation instruments are being designed and proposed to characterize the flux of TeV--EeV neutrinos. The projected physics reach of the detectors is often quantified with simulation studies. However, a complete Monte Carlo estimate of detector performance is costly from a computational perspective, restricting the number of detector configurations considered when designing the instruments. In this paper, we present a new Python-based software framework, toise, which forecasts the performance of a high-energy neutrino detector using parameterizations of the detector performance, such as the effective areas, angular and energy resolutions, etc. The framework can be used to forecast performance of a variety of physics analyses, including sensitivities to diffuse fluxes of neutrinos and sensitivity to both transient and steady state point sources. This parameterized approach reduces the need for extensive simulation studies in order to estimate detector performance, and allows the user to study the influence of single performance metrics, like the angular resolution, in isolation. The framework is designed to allow for multiple detector components, each with different responses and exposure times, and supports paramterization of both optical- and radio-Cherenkov (Askaryan) neutrino telescopes. In the paper, we describe the mathematical concepts behind toise and provide detailed instructive examples to introduce the reader to use of the framework.

11:45 am, Friday, April 29th

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11:45 am, Friday, April 22th

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11:45 am, Friday, April 15th

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11:45 am, Friday, April 1st

Guest: Pedro De la Torre Luque (Stockholm University)

Title: The FLUKA cross sections for cosmic-ray propagation

Abstract:

While the accuracy of current cosmic-ray (CR) data allows us to carry out precise tests of our models of propagation of charged particles in the Galaxy, the precision of cross sections data for the production of secondary particles (secondary CRs, neutrinos, gamma rays) is very poor, considerably limiting these tests. Given that most of the calculations of these cross sections from fundamental models of particle interactions are in disagreement with data, we rely on parameterizations fitted to the very scarce and uncertain experimental data.

In the last years, the FLUKA Monte Carlo nuclear toolkit has been optimized to be used in different kinds of CR studies and has been extensively tested against data. In this talk, we present new sets of spallation cross sections of CR interactions in the Galaxy, both inelastic and inclusive, computed with FLUKA. Furthermore, these cross sections have been implemented in the DRAGON2 code to characterize the spectra of CR nuclei up to Z=26 (Iron) and study the main propagation parameters predicted from the spectra of secondary CRs such as B, Be and Li. These results and their implications will be discussed in the talk.

Guest: Akaxia Cruz (Washington U., Seattle)

Title: Astrophysical Plasma Instabilities induced by Long-Range Interacting Dark Matter

Abstract:

If dark matter (DM) is millicharged or darkly charged, collective plasma processes may dominate momentum exchange over direct particle collisions. In particular, plasma streaming instabilities can couple the momentum of DM to counter-streaming baryons or other DM and result in the counter-streaming fluids coming to rest with each other, just as happens for baryonic collisionless shocks in astrophysical systems. While electrostatic plasma instabilities (such as the two stream) are highly suppressed by Landau damping in the cosmological situations of interest, electromagnetic instabilities such as the Weibel can couple the momenta. Their growth rates are slower than the prior assumption that they would grow at the plasma frequency of DM. We find that the streaming of DM in the pre-Recombination universe is affected more strongly by direct collisions than collective processes, validating previous constraints. However, when considering unmagnetized instabilities the properties of the Bullet Cluster merger would be substantially altered if [qχ/mχ]≳10−4[q_\chi/m_\chi] \gtrsim 10^{-4}[qχ/mχ]≳10−4, where [qχ/mχ][qχ/mχ]][qχ/mχ] is the charge-to-mass ratio of DM relative to that of the proton. When a magnetic field is added consistent with cluster observations, Weibel and Firehose instabilities result in the constraint [qχ/mχ]≳10−12−10−11[qχ/mχ]] \gtrsim 10^{-12}-10^{-11}[qχ/mχ]≳10−12−10−11. The constraints are even stronger in the case of a dark U(1)U(1)U(1) charge, ruling out [qχ/mχ]≳10−14[qχ/mχ]] \gtrsim 10^{-14}[qχ/mχ]≳10−14 in the Bullet Cluster system. The strongest previous limits on millicharged DM arise from considering the spin down of galactic disks. We show that plasma instabilities or tangled background magnetic fields could lead to diffusive propagation of DM, weakening these spin down limits. Thus, our constraints from considering plasma instabilities are the most stringent over much of the millicharged and especially dark-charged parameter space.

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11:45 am, Friday, March 25th

Guest: Kayla Leonard (UW–Madison)

Title: Low Energy Event Reconstruction in IceCube DeepCore

Abstract:

The reconstruction of event-level information, such as the direction or energy of a neutrino interacting in IceCube DeepCore, is a crucial ingredient to many physics analyses. Algorithms to extract this high level information from the detector’s raw data have been successfully developed and used for high energy events. In this work, we address unique challenges associated with the reconstruction of lower energy events in the range of a few to hundreds of GeV and present two separate, state-of-the-art algorithms. One algorithm focuses on the fast directional reconstruction of events based on unscattered light. The second algorithm is a likelihood-based multipurpose reconstruction offering superior resolutions, at the expense of larger computational cost.

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11:45 am, Friday, March 11th

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11:45 am, Friday, March 4th

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11:45 am, Friday, Feb 25th

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11:45 am, Friday, Feb 18th

Guest: Andrea Caputo (Weizmann Institute of Science)

Title: Low-Energy Supernovae Severely Constrain Radiative Particle Decays

Abstract:

The hot and dense core formed in the collapse of a massive star is a powerful source of hypothetical feebly-interacting particles such as sterile neutrinos, dark photons, axion-like particles (ALPs), and others. Radiative decays such as a→2γ deposit this energy in the surrounding material if the mean free path is less than the radius of the progenitor star. For the first time, we use a supernova (SN) population with particularly low explosion energies as the most sensitive calorimeters to constrain this possibility. These SNe are observationally identified as low-luminosity events with low ejecta velocities and low masses of ejected 56Ni. Their low energies limit the energy deposition from particle decays to less than about 0.1 B, where 1 B (bethe)=1051 erg. For 1-500 MeV-mass ALPs, this generic argument excludes ALP-photon couplings Gaγγ in the 10−10-10−8 GeV−1 range.

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11:45 am, Friday, Feb 11th

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11:45 am, Friday, Feb 4th

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11:30 am, Friday, Jan 28th

Guest: Kanji Mori (Research Institute of Stellar Explosive Phenomena, Fukuoka University)

Title: Shock Revival in Core-collapse Supernovae Assisted by Heavy Axion-like Particles

Abstract:

Axion-like particles (ALPs) are a class of hypothetical pseudoscalar particles which feebly interact with ordinary matter. The hot plasma of stars and core-collapse supernovae is a possible laboratory to explore physics beyond the standard model including ALPs. Once produced in a supernova, some of the ALPs can be absorbed by the supernova matter and affect energy transfer. We recently calculated the ALP emission in core-collapse supernovae and the backreaction on supernova dynamics consistently. It is found that the stalled bounce shock can be revived if the coupling between ALPs and photons is as high as $g_{a\gamma}\sim 10^{-9}$ GeV$^{-1}$ and the ALP mass is 40-400 MeV.

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11:45 am, Friday, Jan 21st

Guest: Anna Suliga (Bohr Inst., UC, Berkeley, Wisconsin U., Madison, and DARK Cosmology Ctr.)

Title: Towards Probing the Diffuse Supernova Neutrino Background in All Flavors

Abstract:

Fully understanding the average core-collapse supernova requires detecting the diffuse supernova neutrino background (DSNB) in all flavors. While the DSNB \bar{νe} flux is near detection, and the DSNB νe flux has a good upper limit and promising prospects for improved sensitivity, the DSNB νx (each of νμ, ντ, \bar{νμ}, \bar{ντ}) flux has a poor limit and heretofore had no clear path for improved sensitivity. We show that a succession of xenon-based dark matter detectors -- XENON1T (completed), XENONnT (under construction), and DARWIN (proposed) -- can dramatically improve sensitivity to DSNB νx the neutrino-nucleus coherent scattering channel. XENON1T could match the present sensitivity of ∼ 10^3 cm^(−2) s^(−1) per νx flavor, XENONnT would have linear improvement of sensitivity with exposure, and a long run of DARWIN could reach a flux sensitivity of ∼ 10 cm^(−2) s^(−1). Together, these would also contribute to greatly improve bounds on non-standard scenarios. Ultimately, to reach the standard flux range of ∼ 1 cm^(−2) s^(−1), even larger exposures will be needed, which we show may be possible with the series of proposed lead-based RES-NOVA detectors.

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11:45 am, Friday, Jan 14th

Guest: Yu-Dai Tsai (UC, Irvine and Fermilab and Chicago U. ,KICP)

Title: SpaceQ -- Direct Detection of Ultralight Dark Matter with Space Quantum Sensors

Abstract:

Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock (DSAC), we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If an atomic clock were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter which couples to electron, photon, and gluon fields, based on current and future atomic, molecular, and nuclear clocks.

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11:45 am, Friday, Jan 7th

Guest: Federica Bradascio (IRFU, Saclay)

Title: A search for neutrino emission from cores of Active Galactic Nuclei

Abstract:

The sources of the majority of the high-energy astrophysical neutrinos observed with the IceCube neutrino telescope at the South Pole are unknown. So far, only a gamma-ray blazar was compellingly associated with the emission of high-energy neutrinos. In addition, several studies suggest that the neutrino emission from the gamma-ray blazar population only accounts for a small fraction of the total astrophysical neutrino flux. In this work we probe the production of high-energy neutrinos in the cores of Active Galactic Nuclei (AGN), induced by accelerated cosmic rays in the accretion disk region. We present a likelihood analysis based on eight years of IceCube data, searching for a cumulative neutrino signal from three AGN samples created for this work. The neutrino emission is assumed to be proportional to the accretion disk luminosity estimated from the soft X-ray flux. Next to the observed soft X-ray flux, the objects for the three samples have been selected based on their radio emission and infrared color properties. For the largest sample in this search, an excess of high-energy neutrino events with respect to an isotropic background of atmospheric andastrophysical neutrinos is found, corresponding to a post-trial significance of 2.60 sigma. . Assuming a power-law spectrum, the best-fit spectral index is 2.03^{+0.14}_{-0.11}, consistent with expectations from particle acceleration in astrophysical sources. If interpreted as a genuine signal with the assumptions of a proportionality of X-ray and neutrino fluxes and a model for the sub-threshold flux distribution, this observation implies that at 100 TeV, 27% - 100% of the observed neutrinos arise from particle acceleration in the core of AGN.

Guest: Simeon Reusch (DESY)

Title: Neutrinos from tidal disruption and accretion events

Abstract:

The origins of the high-energy cosmic neutrino flux remain largely unknown. Last year, a high-energy neutrino was associated with the tidal disruption event (TDE) AT2019dsg by our group. I will present AT2019fdr, an exceptionally luminous TDE candidate, coincident with another high-energy neutrino detected by IceCube. I will present observations that further support a TDE origin of this flare. These include a bright dust echo and soft late-time X-ray emission. The probability of finding two such bright events in neutrino follow-up by chance is just 0.034%. Furthermore, we have evaluated several models for neutrino production and can show that AT2019fdr is capable of producing the observed high-energy neutrino. I will also present further evidence on accretion events accompanied by luminous dust echoes being connected to high-energy neutrinos, as we have found another event with such a signature coincident with a high-energy neutrino (AT2019aalc). This reinforces the case for TDEs as neutrino sources.

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