Particle Physics

Direct detection experiments search for dark matter through its potential interactions with the SM particles. However, light dark matter models with particle masses below the GeV scale are still largely unconstrained. As we will see in this talk, sensitivity to such small momentum transfer can benefit from quantum sensors, which employ fundamental quantum mechanical phenomena to notice energy depositions otherwise unreachable. Quantum sensors can considerably extend the range in dark matter mass of traditional WIMP experiments and be complementary to other direct detection methods. In the first part of the talk, I will examine a proposal to use atom interferometers to detect a light dark matter subcomponent at sub-GeV masses. DM scattering off of one “arm” of the atom interferometer can cause trackable decoherence and phase shifts. Two key factors render atom interferometers highly competitive experiments for very low masses: they are sensitive to extremely low momentum deposition and their coherent atoms give them a boost in sensitivity. On the second part of the talk, I will present a new proposal to search for axions with optomechanical cavities.  As we will see, the Bose-enhancement of a final state coherent population of photons or phonons can help overcoming the strong suppression from the axion to photon coupling. A unique advantage of this novel search, axioptomechanics, is that the cavity size need no longer be matched to the axion mass, which allows to probe a wide window of axion masses.

Zoom Link:  https://pitp.zoom.us/j/92645586400?pwd=bm1VUEVqUzNOOXV2VnhEUkJtdWZrZz09

Searches for dark matter decaying into photons constrain its lifetime to be many orders of magnitude larger than the age of the Universe. A corollary statement is that the abundance of any particle that can decay into photons over cosmological timescales is constrained to be much smaller than the cold dark-matter density. We show that an irreducible freeze-in contribution to the relic density of axions is in violation of that statement in a large portion of the parameter space. This allows us to set stringent constraints on axions in the mass range 100 eV - 100 MeV. 

Zoom Link:  https://pitp.zoom.us/j/99147137560?pwd=MC81d3h0OE9BZzZQcGpJakVvOFVOQT09

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons and pions benefit from their small total decay widths and the availability of very large datasets. In this talk, we first give an overview of new opportunities to search for axion-like particles (ALPs) in light meson decays. Second, we revisit the theory and constraints on ALPs interacting with leptons, pointing out the relevance of charged current meson and W decays to ALPs. This is particularly prominent in models where the ALP couples in an isospin-violating way. Finally, we highlight the role of the future PIONEER experiment in probing these new charged current pion decays to ALPs.

Zoom Link:  https://pitp.zoom.us/j/98376159809?pwd=eDNHd1NhTUlVTmV4Y1RONjllNTNPdz09

In the early 1980s, axions and WIMPs were identified as promising dark matter candidates. The last forty years have seen a spectacularly successful experimental program attempting to discover the WIMPs, with sensitivity that has by now improved by many orders of magnitude compared to the earliest results. The parallel program to search for axions has made less progress and has reached the necessary sensitivity only over a very limited mass range. However, progress has recently accelerated, with the invention of many new axion detection techniques that may eventually provide a definitive answer to the question of whether the dark matter is made of axions. I will review some of these new developments with emphasis on Fermilab’s program, including ADMX- Extended Frequency Range and Broadband Reflector Experiment for Axion Detection (BREAD).

Zoom link:  https://pitp.zoom.us/j/97234421735?pwd=UGNJRWxYMkErRmdWSnJiWTdoOFNaZz09

Sphaleron heating has been recently proposed as a mechanism to realize warm inflation when inflaton is an axion coupled to pure Yang-Mills. As a result of heating, there is a friction coefficient γ\propto T^3 in the equation of motion for the inflaton, and a thermal contribution to cosmological fluctuations. Without the knowledge of the inflaton potential, non-Gaussianity is the most promising way of searching for the signatures of this model. Building on an earlier work by Bastero-Gil, Berera, Moss and Ramos, we compute the scalar three-point correlation function and point out some distinct features in the squeezed and folded limits. As a detection strategy, we show that the combination of the equilateral template and one new template has a large overlap with the shape of non-Gaussianity over the range 0.01 <= γ/Η <= 1000 and in this range 0.7<|f_NL|<50.

Zoom link:  https://pitp.zoom.us/j/95921707772?pwd=NUNhU1QrRm5HaDJNMEYyaTJXQmZnQT09

The polarization measurements of particles produced in heavy-ion collisions allow us to study amazing phenomena such as, the collective rotation of the nuclear medium, quark spin-alignment with the global angular momenta, local vs global polarization effects and their evolution when there are drastic changes in the properties of the hot, dense and whirly medium. Recently, measurements by the STAR collaboration at RHIC and the HADES collaboration at GSI, show the rising of Lambda and anti-Lambda global polarization with decreasing collision energy and what seems to be a differentiated peak with a sharp decrease at a lower bound in collision energy. In this talk I will report on our recent work where we predict this differentiated peak behavior using a core-corona model, so that measuring the polarization of hyperons becomes a tool to learn about strangeness availability in the medium created in heavy-ion collisions for different initial conditions. I will also present a few new developments we have made to probe the strong magnetic field produced early after the collision with primordial photons and mention other relevant signals that we are working on in order to learn about the critical end-point in the QCD phase diagram.

Zoom link:  https://pitp.zoom.us/j/95896792626?pwd=QlovbE5EWEJBSDdOZjUyK2MxYktmQT09

This course uses quantum electrodynamics (QED) as a vehicle for covering several more advanced topics within quantum field theory, and so is aimed at graduate students that already have had an introductory course on quantum field theory. Among the topics hoped to be covered are: gauge invariance for massless spin-1 particles from special relativity and quantum mechanics; Ward identities; photon scattering and loops; UV and IR divergences and why they are handled differently; effective theories and the renormalization group; anomalies.

Bang Nucleosynthesis (BBN) is one of the greatest outcome of the Standard Model of Particle Physics when put next to ΛCDM cosmology. In this talk, I will first review the key aspects of standard BBN and illustrate a new code -- PRyMordial -- to make state-of-the-art predictions of primordial light-element abundances within and beyond the Standard Model. I will then highlight the latest measurements regarding the primordial abundance of helium-4 and deuterium, and present evidence at the 2 sigma level for a nonzero lepton asymmetry from BBN data jointly with the Cosmic Microwave Background. I will leave some final comments on how a large total lepton asymmetry can be consistently realized in the Early Universe.

Zoom Link: https://pitp.zoom.us/j/95011247645?pwd=S0EwZG9nSHQvTjV0QjBxeHNUWWtmUT09

Models of dark sectors with a mass threshold can have important cosmological signatures. If, in the era prior to recombination, a relativistic species becomes non-relativistic and is then depopulated in equilibrium, there can be measurable impacts on the CMB as the entropy is transferred to lighter relativistic particles. In particular, if this "step'" occurs near z = 20,000, the model can naturally accommodate larger values of $H_0$. If this stepped radiation is additionally coupled to dark matter, there can be a meaningful impact on the matter power spectrum as dark matter can be coupled via a species that becomes non-relativistic and depleted. This can naturally lead to suppressed power at scales inside the sound horizon before the step, while leaving conventional CDM signatures for power outside the sound horizon. We study these effects and show such models can naturally provide lower values of $S_8$ than scenarios without a step. This suggests these models may provide an interesting framework to address the $S_8$ tension, both in concert with the $H_0$ tension and without.

Zoom Link:  https://pitp.zoom.us/j/96399847158?pwd=RkNHMkJHeEo5Q1Q2MkhHSHZ6c1BoQT09

With no hints of dark matter in the "classical WIMP" region of parameter space, experimentalists have begun searching in earnest for low mass (MeV-GeV scale) dark matter. However, efforts to probe this region of parameter space have been hindered by an unexpected and mysterious source of background events, dubbed the "low energy excess." Recently, mechanical stress has been shown to create a "low energy excess"-like source of events, and a microphysical picture of how stress creates this background is emerging. In addition to providing a path forward for low mass dark matter searches, these results may address several outstanding problems limiting the performance of superconducting quantum computers.

Zoom Link:  https://pitp.zoom.us/j/92147233613?pwd=RW5PaUNUZlE3SUNnTlZHaVFrdnV3dz09

Observations indicate the existence of natural particle accelerators in the Milky Way, capable of producing PeV cosmic rays (“PeVatrons”). Observations also indicate the existence of extreme sources in the Milky Way, capable of producing gamma-ray radiations above 100 TeV. If these gamma-ray sources are hadronic cosmic-ray accelerators, then they must also be neutrino sources. However, no neutrino sources have been detected. How can we consistently understand the observations of cosmic rays, gamma rays, and neutrinos? We point out two extreme scenarios are allowed: (1) the hadronic cosmic-ray accelerators and the gamma-ray sources are the same objects, so that neutrino sources exist and improved telescopes can detect them, versus (2) the hadronic cosmic-ray accelerators and the gamma-ray sources are distinct, so that there are no detectable neutrino sources. We discuss the nature of Milky Way’s highest energy gamma-ray sources and outline future prospects toward understanding the origin of hadronic cosmic rays. 

Zoom link:  https://pitp.zoom.us/j/91390039665?pwd=dGJ2b3VCbVFhUVpSelpjYzJHdk1Gdz09

Based on arXiv:2208.04334. We consider oscillons - localized, quasiperiodic, and extremely long-living classical solutions in models with real scalar fields. We develop their effective description in the limit of large size at finite field strength. Namely, we note that nonlinear long-range field configurations can be described by an effective complex field ψ(t, x) which is related to the original fields by a canonical transformation. The action for ψ has the form of a systematic gradient expansion. At every order of the expansion, such an effective theory has a global U(1) symmetry and hence a family of stationary nontopological solitons - oscillons. The decay of the latter objects is a nonperturbative process from the viewpoint of the effective theory. Our approach gives an intuitive understanding of oscillons in full nonlinearity and explains their longevity. Importantly, it also provides reliable selection criteria for models with long-lived oscillons. This technique is more precise in the nonrelativistic limit, in the notable cases of nonlinear, extremely long-lived, and large objects, and also in lower spatial dimensions. We test the effective theory by performing explicit numerical simulations of a (d+1)-dimensional scalar field with a plateau potential. 

Zoom link: https://pitp.zoom.us/j/98801138609?pwd=VUJsZm41bnpBQzFoUEFwcUV6SG5Xdz09