Registration and Coffee Room: 02.430

Probing Dark Sectors with Evaporating Black Holes

• Michael Baker (University of Melbourne)

Room: 02.430 Photons radiated from an evaporating black hole in principle provide complete information on the particle spectrum of nature up to the Planck scale. If an evaporating black hole were to be observed, it would open a unique window onto models beyond the Standard Model of particle physics. To demonstrate this, we compute the limits that could be placed on the size of a dark sector. We find that observation of an evaporating black hole at a distance of 0.01 parsecs could probe dark sector models containing one or more copies of the Standard Model particles, with any mass scale up to 100 TeV.

Spectral Distortions from Dark Turbulence

• Wolfram Ratzinger (JGU Mainz)

Room: 02.430 Deviations of the CMB from a black body spectrum, so called spectral distortions, provide a powerful probe of the early universe. For example they can be sourced by gravitational waves (GWs) with frequencies too large to be probed by CMB polarization and too low for pulsar timing arrays. But what if your favorite source of GWs, e.g. a phase transition or cosmic defects, only sources the GWs as these modes enter the horizon? We show that in this case a much larger spectral distortion is caused through gravitationally induced acoustic waves in the baryon-photon fluid. We give an analytic estimate of this effect and compare to the numerical result of a toy model. Finally we show that spectral distortions can test and constraint a large class of purely gravitationally coupled sectors, complementing GW searches.

Discussions and Coffee Room: 02.430

Sterile neutrino dark matter and neutrino self-interactions

• Walter Tangarife

Room: 02.430 Neutrino self-interactions can play an essential role in the origin of dark matter. The existence of these new neutrino interactions may manifest itself in next-generation experiments, including DUNE. I will present an anatomy of production mechanisms for sterile neutrino dark matter in the presence of secret interactions among active neutrinos. I will also present the effects of a scalar-mediated neutrino self-interaction on the supernova cooling luminosity, which allows to constrain the self-interaction parameter space in a complementary way to terrestrial experiments or cosmological probes.

Alternative ways of QCD axion dark matter search with spectroscopy, interferometry, and accelerometry

• Hyungjin Kim

Room: 02.430 In this talk, I will discuss some of the alternative ways to search for QCD axion dark matter with atomic spectroscopy, interferometry, and accelerometry.

Discussions and Coffee Room: 02.430

Deciphering the behaviour of scattering amplitudes of theories of compactified extra dimensions

• Dipan Sengupta

Room: 02.430 Theories of compactified extra dimensions are well motivated as a BSM candidate. I will talk about the behaviour of scattering amplitudes of Kaluza-Klein gravitons in both flat and warped extra dimensions. These scattering amplitudes are characterized by intricate cancellations between different contributions: although individual contributions may grow anomalously fast, the full results are well behaved. We demonstrate that the cancellations persist for all incoming and outgoing particle helicities and examine how truncating the computation to only include a finite number of intermediate states impacts the accuracy of the results. We also carefully assess the range of validity of the low-energy effective Kaluza-Klein theory. In particular, for the warped case we demonstrate directly how an emergent low-energy scale controls the size of the scattering amplitude, as conjectured by the AdS/CFT correspondence.

Rollercoaster Cosmology

• Nemanja Kaloper

Room: 02.430 Does inflation have to happen all in one go? The answer is a resounding no! All cosmological problems can be solved by a sequence of short bursts of cosmic acceleration, interrupted by short epochs of decelerated expansion. I will explain this simple and yet ignored possibility, show you the proof, outline some simple realizations and discuss the consequences and implications.

Discussions and Coffee Room: 02.430

Boson stars and dark matter substructure

• Marco Gorghetto

Room: 02.430 I will argue that many theories in which the dark matter is a light boson (with a mass < eV) lead to theoretically and observationally interesting dark matter substructure. As a particular, directly calculable, example I will show that this is the case for any new vector boson with non-zero mass (a ‘dark photon’ or ‘Proca boson’) that is present during inflation, at which time a relic abundance is automatically produced purely from vacuum fluctuations. Due to a remarkable parametric coincidence between the size of the primordial density perturbations and the scale at which quantum pressure is relevant, a substantial fraction of the dark matter inevitably collapses into gravitationally bound solitons. The central densities of these ‘dark photon star’, or ‘Proca star’, solitons are typically a factor 10^6 larger than the local background dark matter density today. I will also mention some possible observational consequences and directions for future work.

Reheating with Non-minimally Coupled Scalars

• Toby Opferkuch

Room: 02.430

Discussions and Coffee Room: 02.430

Hunting for axions in the solar basin

• William DeRocco

Room: 02.430 A large flux of axion-like particles can be produced in the solar core. While the majority of these particles will have high velocities and escape the Sun’s gravitational pull, a small fraction of low-velocity particles will become trapped on bound orbits. Over time, an appreciable density of slow-moving axions can accumulate in this “solar basin.” Their subsequent decay to two photons provides a distinct observational signature. I will present a recent analysis using data taken by the NuSTAR X-ray telescope to search for the decay products of keV-scale axions trapped in the solar basin. Our results ultimately set limits on the axion-photon and axion-electron couplings well over an order of magnitude beyond current constraints and motivate the further exploration of stellar basins in other astrophysical systems.

Crunching Naturalness

• Michael Geller

Room: 02.430

Discussion: Light axions shrink white dwarfs

• Konstantin Springmann

Room: 02.430

Registration and Coffee Room: 02.430

Axion couplings in grand unified theories

• Mario Reig

Room: 02.430

Condensation and Evaporation of Boson Stars

• Wei Xue

Room: 02.430 Axion-like particles, including the QCD axion, are well-motivated dark matter candidates. Numerical simulations have revealed coherent soliton configurations, also known as boson stars, in the centers of axion halos. We study evolution of axion solitons immersed into a gas of axion waves with Maxwellian velocity distribution. Combining analytical approach with controlled numerical simulations we find that heavy solitons grow by condensation of axions from the gas, while light solitons evaporate. We deduce the parametric dependence of the soliton growth/evaporation rate and show that it is proportional to the rate of the kinetic relaxation in the gas. The proportionality coefficient is controlled by the product of the soliton radius and the typical gas momentum or, equivalently, the ratio of the gas and soliton virial temperatures. We discuss the asymptotics of the rate when this parameter is large or small.

Discussions and Coffee Room: 02.430

Heavy axions as dark matter and baryogenesis candidates

• Soubhik Kumar

Room: 02.430 Heavy axions can arise in the context of Grand Unified theories where a dark gauge group unifies with the SM gauge group. In this talk, I will describe how keV-MeV mass axions can account for DM relic density in the presence of an early matter dominated era due to the glueballs of the same dark sector. The resulting parameter space motivates searches for decaying dark matter with the next generation X-ray and gamma-ray telescopes. I will also describe how a second, heavier axion can explain the observed baryon asymmetry with the lighter axion still serving as the DM candidate.

Cosmological Constraints on Light (but Massive) Relics

• Weishuang Linda Xu

Room: 02.430 An intriguing possibility for the particle makeup of the dark sector is that a small fraction of the observed abundance is made up of light, feebly-interacting particle species. Neutrinos, with their yet-unresolved masses, are a concrete example in this category, but more exotic candidates readily arise from new physics scenarios. Due to their weakness of interaction but comparatively large number abundance, cosmological datasets are particularly powerful tools to leverage here. In this talk I describe the impact of these new particle species on observables, present a comprehensive set of state-of-the-art constraints, and discuss the added power that near future experiments might lend us.

Discussions and Coffee Room: 02.430

Parity symmetry breaking scale and Standard Model parameters

• Keisuke Harigaya

Room: 02.430 The strong CP problem can be solved by parity symmetry. We argue that the parity symmetry breaking scale is predicted to be the energy scale at which the standard model Higgs quartic coupling vanishes. Surprisingly, after fixing the parity symmetry breaking scale in this way, the gauge coupling constants unify at a high energy scale. We also discuss a model with a dark matter candidate and show that the dark matter direct detection rate is predicted as a function of the standard model parameters.

False vacuum decay in the thin wall approximation

• Lorenzo Ubaldi

Room: 02.430 The decay rate of the false vacuum in scalar field theory has the form A Exp(-B). In a famous paper from 1977 Coleman laid down the theory to compute the coefficient B. In a subsequent paper with Callan, they set up the recipe to compute the pre-factor A, but did not manage to compute it explicitly. In their own words: "we are not able to obtain a closed-form expression for A; we are stymied by an obdurate functional determinant". My collaborators and I recently found such a closed-form expression for A in the thin-wall approximation. In this talk I will start from our final result, then I will outline the main ingredients of our calculation.

Discussions and Coffee Room: 02.430

a-Anomalous Interactions of the Holographic Dilaton

• Gabriele Rigo

Room: 02.430 We explore higher-derivative terms in the low-energy effective action for the dilaton, the Goldstone boson of spontaneously broken scale invariance. Focusing on the simplest holographic realization of spontaneously broken scale invariance, the Randall–Sundrum (RS) scenario, we identify the nonlinear action for the RS dilaton by integrating out Kaluza–Klein graviton modes. The coefficient of a particular four-derivative dilaton self-interaction can be identified with the Weyl a-anomaly of the dual conformal field theory, which we use to verify anomaly matching arguments. We also find novel, a-dependent couplings of the dilaton to light matter fields. These anomalous interactions can have a significant effect on the collider phenomenology and the cosmology, potentially allowing us to probe the structure of the underlying conformal sector via low-energy physics. The dilaton effective theory also serves as an interesting scalar analog of gravity, and we study solutions to the equation of motion that parallel black holes and cosmologies.

Gravitational Waves from Cosmic Strings

• Ed Hardy

Room: 02.430 If the Peccei-Quinn symmetry associated to an axion has ever been restored after inflation, axion strings inevitably produce a contribution to the stochastic gravitational wave background. Combining effective field theory analysis with numerical simulations, I will show that the resulting gravitational wave spectrum has logarithmic deviations from a scale invariant form with an amplitude that is significantly enhanced at low frequencies.

Axion Fragmentation

• Enrico Morgante (JGU Mainz)

Room: 02.430

Discussions and Coffee Room: 02.430

Composite Dark Matter and Neutrino Masses from a Light Hidden Sector

• Saereh Najjari

Room: 02.430