Towards the Next Fundamental Scale of Nature: New Approaches in Particle Physics and Cosmology

11 Jul 2022, 09:00 → 22 Jul 2022, 16:00 Europe/Berlin

02.430 (Mainz Institute for Theoretical Physics, Johannes Gutenberg University)

Many of the most well motivated theories of beyond the Standard Model (BSM) physics from the pre- LHC era postulated new states at the TeV scale. However, results from the recently completed Run-II of the LHC have indicated that the next fundamental scale of nature is likely higher. With upcoming runs of the LHC not expected to dramatically increase the reach of the machine, it is appropriate to re-evaluate theoretical approaches to seeking the next scale of fundamental physics in an era which may be lacking data from colliders.

Cosmology can provide a window into energy scales far beyond those which are accessible with terrestrial particle colliders. Contrary to the situation in high-energy particle physics, there are already many terrestrial and space-based cosmological experiments planned over the next few decades. Indeed, the next major insights in fundamental physics may come from cosmological data rather than colliders. Consequently, strengthening connections between particle physics and cosmology will be essential so that these experiments can be used to guide the approach of BSM particle physicists until the next frontier collider can be constructed. Such a scenario is mutually beneficial, since theoretical input from particle physics could also help to guide the planning of next generation cosmological experiments.

The goal of this Scientific Program is to bring together experts in order to explore new directions and unconventional approaches in fundamental particle physics, cosmology, and quantum field theory. The Scientific Program will include discussion on what the modern approaches to BSM physics should be, and how e.g. we can use links between particle physics and cosmology to guide this philosophy. The desired outcome of the event is to identify, taking into account the experiments that will have data in the next decade, what the most well-motivated approaches to BSM physics in the modern era are and to begin new projects/collaborations working in these directions.

Participant List.pdf

Monday 11 July

1 Registration and Coffee

2 Probing Dark Sectors with Evaporating Black Holes

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.

Speaker: Michael Baker (University of Melbourne)

3 Spectral Distortions from Dark Turbulence

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.

Speaker: Wolfram Ratzinger (JGU Mainz)

Tuesday 12 July

4 Discussions and Coffee

5 Sterile neutrino dark matter and neutrino self-interactions

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.

Speaker: Walter Tangarife

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

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

Speaker: Hyungjin Kim

Wednesday 13 July

7 Discussions and Coffee

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

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.

Speaker: Dipan Sengupta

9 Rollercoaster Cosmology

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.

Speaker: Nemanja Kaloper

Thursday 14 July

10 Discussions and Coffee

11 Boson stars and dark matter substructure

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.

Speaker: Marco Gorghetto

12 Reheating with Non-minimally Coupled Scalars

Speaker: Toby Opferkuch

Friday 15 July

13 Discussions and Coffee

14 Hunting for axions in the solar basin

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.

Speaker: William DeRocco

15 Crunching Naturalness

Speaker: Michael Geller

16 Discussion: Light axions shrink white dwarfs

Speaker: Konstantin Springmann

Monday 18 July

17 Registration and Coffee

18 Axion couplings in grand unified theories

Speaker: Mario Reig

19 Condensation and Evaporation of Boson Stars

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.

Speaker: Wei Xue

Tuesday 19 July

20 Discussions and Coffee

21 Heavy axions as dark matter and baryogenesis candidates

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.

Speaker: Soubhik Kumar

22 Cosmological Constraints on Light (but Massive) Relics

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.

Speaker: Weishuang Linda Xu

Wednesday 20 July

23 Discussions and Coffee

24 Parity symmetry breaking scale and Standard Model parameters

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.

Speaker: Keisuke Harigaya

25 False vacuum decay in the thin wall approximation

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.

Speaker: Lorenzo Ubaldi

Thursday 21 July

26 Discussions and Coffee

27 a-Anomalous Interactions of the Holographic Dilaton

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.

Speaker: Gabriele Rigo

28 Gravitational Waves from Cosmic Strings

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.

Speaker: Ed Hardy

29 Axion Fragmentation

Speaker: Enrico Morgante (JGU Mainz)

Friday 22 July

30 Discussions and Coffee

31 Composite Dark Matter and Neutrino Masses from a Light Hidden Sector

Speaker: Saereh Najjari