Particle Physics

The cosmic microwave background is a sensitive probe of early-Universe physics, and yet fundamental constants at recombination can differ from their present-day values due to degeneracies in the standard cosmological model. Such scenarios have been invoked to reconcile discrepant measurements of the present-day expansion rate, but even absent such motivation they raise the intriguing possibility of yet-undiscovered physics coupled directly to Standard Model particles. I will discuss theories in which a new scalar field shifts the electron's mass at early times; viable models are already stringently constrained by measurements of quasar absorption lines, the abundances of light elements, and the universality of free fall. I will show that the remaining parameter space is exactly that which allows not only the primary cosmic microwave background but also low-redshift distances to be consistent with observations. After presenting the results of parameter inference I will discuss additional cosmological and laboratory signatures of the model.

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Zoom link https://pitp.zoom.us/j/99705853481?pwd=MTZRWC9hREkvOXpiZkxCM3UvdnRNQT09

Significant effort has been devoted to searching for new fundamental forces of nature. At short length scales (below approximately 10 nm), many of the strongest experimental constraints come from neutron scattering from individual nuclei in gases. The leading experiments at longer length scales instead measure forces between macroscopic test masses. I will present a proposal that combines these two approaches: scattering neutrons off of a target that has spatial structure at nanoscopic length scales. Such structures will give a coherent enhancement to small-angle scattering, where the new force is most significant. This can considerably improve the sensitivity of neutron scattering experiments for new forces in the 0.1 - 100 nm range. I will discuss the backgrounds due to Standard Model interactions and a variety of potential target structures that could be used, estimating the resulting sensitivities. I will show that, using only one day of beam time at a modern neutron scattering facility, our proposal has the potential to detect new forces as much as four orders of magnitude beyond current laboratory constraints at the appropriate length scales.

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Zoom link https://pitp.zoom.us/j/98201041537?pwd=MS9weFpNcHVFTVIwMTVoYmpxeTd6Zz09

The recent data releases by multiple pulsar timing array (PTA) experiments show evidence for Hellings-Downs angular correlations indicating that the observed stochastic common spectrum can be interpreted as a stochastic gravitational wave background. We study whether the signal may originate from gravitational waves induced by high-amplitude primordial curvature perturbations. Such large perturbations may be accompanied by the generation of a sizable primordial black hole (PBH) abundance. We discuss in which scenarios the inclusion of non-Gaussianities in the computation of the abundance can lead to a signal compatible with the PTA experiments without overproducing PBHs.

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Zoom link https://pitp.zoom.us/j/95261778825?pwd=QndRd0xQVFpNVzk0VXpRUkNqR1JXZz09

Quantum vortices are two-dimensional solitons which carry a topological charge - the first Chern number n. They play a crucial role in many physical concepts from cosmic strings to mirror symmetry and dualities of supersymmetric models. When n grows the vortices become giant. The giant vortices are observed experimentally in a variety of quantum systems. Thus, it is quite appealing to identify their characteristic features and universal properties, which is quite a challenging mathematical problem. Though the nonlinear vortex equations may look deceptively simple, their analytic solution is not available. In this talk I demonstrate how by borrowing the asymptotic methods of fluid dynamics such a solution can be found in the large-n limit. I then construct a systematic expansion in inverse powers of the topological charge about this asymptotic solution which works amazingly well all the way down to the elementary vortex with n=1. I use this result to study the Majorana zero modes bound to giant vortices. The resulting local density of states has a number of features which give remarkable signatures for an experimental observation of the "Majorana fermions" in two dimensions.

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Zoom link https://pitp.zoom.us/j/98994856372?pwd=ZFBOemRZQS9WbHAzMTN6R2lKZEdXQT09

Axions and axion-like particles are well motivated candidates for dark matter (DM) and have a signature two photon vertex. The most sensitive axion DM search is at the gigahertz (GHz) regime. It relies on microwave cavities with high quality factors resonantly converting axion DM to cavity photons in the background of a static magnetic field. However, axion DM mass could span a vast range above or below GHz. We describe a new proposal using integrated/on-chip photonic systems to search for axion DM at the optical frequency. This enables the use of waveguides to collect signal photons, which improves the detection efficiency, as well as the use of single photon, micron-sized detector, such as a skipper charge-coupled device, which has a dark count rate as low as 1e-9 per second per pixel. Furthermore, by coupling a series of resonators of different frequencies to a single receiver bus, the detection can be broadband in terms of the axion masses and has sensitivities to the axion-photon couplings expected for the QCD axion at the axion masses of around 0.2 eV.

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Zoom link https://pitp.zoom.us/j/94515300239?pwd=VVBkaGM5K24yN2F4SFV0MGZ5Vk9LZz09

If dark energy evolves in time its dynamical component could be dominated by a bath of dark radiation. Since dark energy was subdominant in the early universe, the dark energy radiation evades the usual stringent constraints on extra relativistic species from the cosmic microwave background, allowing for an O(1) fraction of the energy density today to be dark radiation. In this talk, I will discuss how dark energy radiation can emerge from a fundamental theory, its predictions for cosmological observables, as well as discovery potential and constraints with existing and future precision cosmological datasets including measurements of the cosmic microwave background, baryon acoustic oscillations, and supernova data. I’ll conclude with the prospects of measuring the particle content of the dark energy radiation in direct-detection experiments in the presence of interactions between the Standard Model and the dark radiation sector, focusing on neutrinos, axions and dark photons.

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Zoom link https://pitp.zoom.us/j/97180285756?pwd=aEtlYmFSRzFSZVBvY3lnMmtPYWc3Zz09

Higgs coupling deviations from Standard Model predictions contain information about two scales of Nature: that of new physics responsible for the deviation, and the scale where new bosons must appear. The two can coincide, but they do not have to. The scale of new bosons can be calculated by going beyond an effective field theory description of the coupling deviation. I will discuss model-independent upper bounds on the scale of new bosons for deviations in Higgs to WW and ZZ couplings, and explain how any measured deviation at present or future colliders requires the existence of new bosons within experimental reach. This has potentially interesting implications for naturalness.

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Zoom link https://pitp.zoom.us/j/97203814123?pwd=U3F3N2xxTmJSQmxIQ0Rib3ZwN3Fldz09

The QUEST-DMC experiment, aimed at detecting sub-GeV dark matter, utilizes a unique approach by employing superfluid Helium-3 (He-3) in conjunction with quantum sensors. Superfluid He-3 stands out as an ideal target medium for sub-GeV dark matter searches, especially in the context of spin-dependent interactions. This choice aligns seamlessly with a wide array of theoretically motivated dark matter models. The experiment's projected sensitivity to various dark matter models, as well as its potential to set upper limits on dark matter interactions, will be presented.

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Zoom link https://pitp.zoom.us/j/99386484623?pwd=dGVQdFJKbEpPMUcrRUNLbHdIR2p3Zz09

The rich EM phenomenology in the seconds, minutes, and hours just before, during, and after a compact object merger encodes the magnetization of the binary components, the nature of the post-merger remnant, the neutron star equation of state, the free neutron abundance, and a wide array of other compelling physics. Unfortunately, the requirement to search, find, and classify an electromagnetic counterpart within the large GW localization regions before targeted follow-up with sensitive instruments can begin, excludes access to these earliest times, even for the most well localized GW sources. The ability to promptly localize a GW source to within the field-of-view of a narrow-field sensitive facility, would enable extraordinary science. I will discuss the science cases that require extremely early time observations, and the coordination, instruments, and analyses necessary to achieve it. These include gamma-ray imaging, novel data analysis techniques, pre-merger GW detection, faster space telescopes, and new experiments.

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Zoom link https://pitp.zoom.us/j/96186614241?pwd=R0xpT0dDZVZzek5RT0x4Q1c3Z1RuUT09

The Callan Rubakov Effect describes the interaction between (massless) fermions and a smooth monopole in 4d gauge theory. In this scenario, the fermions can probe the UV physics inside the monopole core which leads to interesting effects such as proton decay in GUT models. However, the monopole-fermion scattering appears to lead to out-states that are not in the perturbative Hilbert space. In this talk, we will review this issue and propose a new physical mechanism that resolves this long-standing confusion.

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Zoom link: https://pitp.zoom.us/j/93551249905?pwd=REJvOUtTMlh6RU0vRjZnRVdZckgyZz09

SNOLAB is a laboratory two kilometers underground in Sudbury, Ontario, Canada. This laboratory boasts the lowest muon flux on Earth. This low muon flux is utilized for a variety of research on Quantum computing and the nature of dark matter, which are some of the highest priority research topics in fundamental and applied physics. New sensors are required for light dark matter searches that extend current capabilities by three orders of magnitude in energy. The required energy scales overlap with the energy scale of environmental disturbances that limit the coherence time of many candidate qubit systems, like superconducting circuits. I will give a short overview of SNOLAB. I will then focus on the requirements and alignment of light dark matter searches and cutting-edge qubit performance. Finally, I will say a few words on how future experiments can leverage these maturing quantum computing technologies for fundamental physics searches.

Zoom Link:  https://pitp.zoom.us/j/95345167872?pwd=eDhYREd2Q04yV21DUC84NnVEcHRmUT09

Despite first observing cosmic rays with energies above an EeV (10^18 eV) in the 1960s, the source of these particles remains an open question. Modern observatories, in particular the Pierre Auger Observatory and Telescope Array, have firmly established that the cosmic ray spectrum continues up to ~10^20.3 eV and have significantly advanced our understanding of these particles. However, limited statistics, uncertainties in particle physics, and significant deflections in the Galactic magnetic field have made progress towards discovering their astrophysical source extremely challenging. One key astrophysical input needed to understand ultrahigh energy cosmic ray data is the distribution of their sources, or the source evolution. In this talk, I will focus on multimessenger observations which have the potential to pin down the source evolution for the very first time.

Zoom Link:  https://pitp.zoom.us/j/94054513261?pwd=aHRNWE04VDI2cDA2RmRYQmtNRnd3dz09