High Energy Physics Journal Club

Abstract: Generalized global symmetries are present in theories of particle physics, and understanding their structure can give insight into these theories and UV completions thereof.  We will identify noninvertible chiral symmetries in certain flavorful Z' extensions of the Standard Model, and our understanding of generalized symmetry breaking will lead us to short-distance theories of gauged non-Abelian flavor where nonperturbative effects can resolve important naturalness questions. For the leptons we will find naturally exponentially small Dirac neutrino masses, and in the quark sector we will construct a massless down-type quarks solution to strong CP in color-flavor unification. Intriguingly, the fact that we have three generations of fermions plays a crucial role in the existence of these noninvertible symmetries.

Abstract: A B-mode polarization signal in the cosmic microwave background (CMB) is widely regarded as smoking gun evidence for gravitational waves produced during inflation. In this talk, I demonstrate that tensor perturbations from a cosmological phase transition can produce a B-mode signal whose strength rivals that from inflationary predictions across a range of observable scales. Although phase transitions arise from sub-horizon physics, they nevertheless exhibit a white noise power spectrum on super-horizon scales. Power is suppressed on the large scales relevant for CMB B-mode polarization, but it is not necessarily negligible. For appropriately chosen phase transition parameters, the maximal B-mode amplitude can compete with inflationary predictions that can be tested with current and future experiments. These scenarios can be differentiated by performing measurements on multiple angular scales, since the phase transition signal predicts peak power on smaller scales.

Abstract: Cosmological correlators, observed through the structures of the universe, contain rich information on the physics of the early universe. However, in general, the calculation of the cosmological correlators is quite involved due to the loss of the time translation invariance.

In this talk, I derive a cutting rule for equal-time in-in correlators, including cosmological correlators, which decomposes diagrams into fully retarded functions and cut-propagators consisting of Wightman functions. Our derivation relies only on basic assumptions such as unitarity and, therefore, holds for theories with arbitrary particle contents and local interactions at any loop order. As an application, we show that non-local cosmological collider signals, particle production signals in the correlators, arise solely from cut-propagators under the assumption of microcausality. The cut factorizes the conformal time integrals, simplifying practical calculations.

Abstract: In this talk I will describe the Axion Kination mechanism and elaborate its associated phenomenology including baryogenesis, amplification of gravitational waves, imapct on CMB, matter power spectrum and Hubble tension and a novel way to produce axions through "acoustic misalignment mechanism".

Abstract: In this talk, I will focus on the QCD axion misalignment mechanism. The first part will explore the light QCD axion, which addresses the strong CP problem while having a mass smaller than that of the conventional QCD axion. We introduce a mirror sector where the QCD theta angle is shifted by π compared to the Standard Model (SM) sector. This allows for the tuning of the mirror axion potential against the usual QCD axion potential. The explicit cosmological evolution of the axion field will also be discussed. In the second part, we turn to the conventional QCD axion, but with the addition of entropy injection that reheats the SM thermal bath to temperatures on the order of GeV. The axion then behaves like kination, potentially producing the correct dark matter relic abundance for a wide range of PQ scale. Furthermore, if the entropy injection occurs through a first-order phase transition, the stochastic nature of bubble nucleation could induce spatial fluctuations, leading to the formation of domain walls in the later stage.

Abstract: The direct detection of dark matter (DM) is critical for understanding its identity and properties—mass, spin, and couplings—and would also solve many fundamental questions in particle physics and cosmology, but its weak energy deposition is difficult to detect. Axions are a particularly well-motivated DM candidate, entering as a solution to the standard model’s strong charge-parity problem. Many experiments and proposals search various axion masses using the Primakoff effect (axion-photon conversion in a magnetic field), yet the meV (THz) regime remains poorly constrained. Dielectric and plasma haloscopes operating at low frequencies require smaller and more precise structures for the THz range, and material resonance detectors for higher frequencies suffer from a lack of well-studied low-loss THz materials, while mechanical tuning limits practicality in both. We propose the THz-Radiometer for AXions (T-RAX) using recent advancements in quantum structures and metamaterials with electromagnetically tunable plasma frequencies for meV DM detection. We simulate multiple quantum wells (MQWs) using experimentally-obtained electronic properties and show that resonant enhancements of the axion-induced electromagnetic signal may probe the QCD axion parameter space. 

Abstract: Dark matter (DM) environments around black holes (BHs) can influence their mergers through dynamical friction, causing gravitational wave (GW) dephasing during the inspiral phase. While this effect is well studied for collisionless dark matter (CDM), it remains unexplored for self-interacting dark matter (SIDM) due to the typically low DM density in SIDM halo cores. In this work, we show that SIDM models with a massive force mediator can support dense enough DM spikes, significantly affecting BH mergers and producing a distinct GW dephasing. Using N-body simulations, we analyze GW dephasing in binary BH inspirals within CDM and SIDM spikes. By tracking the binary's motion in different SIDM environments, we show that the Laser Interferometer Space Antenna (LISA) can distinguish DM profiles shaped by varying DM interaction strengths, revealing detailed properties of SIDM.

Abstract: TBD