Abstract: The QCD axion or axion-like particles are candidates of dark matter of the universe. On the other hand, axion-like excitations exist in certain condensed matter systems, which implies that there can be interactions of dark matter particles with condensed matter axions. We discuss the relationship between the condensed matter axion and a collective spin-wave excitation in an anti-ferromagnetic insulator … Read More
First-order phase transitions in the early universe could produce stochastic gravitational wave signals observable at future space-based observatories such as LISA; however, existing methods for predicting these signals are limited to weakly-coupled theories. In this talk, I present a new, nonperturbative formalism for false vacuum decay that integrates over local fluctuations in field space using the functional renormalization group. As … Read More
Abstract: I begin with a bird’s eye view of the recent progress on the EFT for black hole inspirals, with an emphasis on the key role played by gravity loop amplitudes. I then present some work in progress on an alternative approach to the problem. In this alternative approach, the classical scattering angle emerges from the phase shifts of a QM scattering … Read More
Massive field excitations during the inflationary era, imprinted on cosmological correlation functions, can provide us with a unique opportunity to probe heavy degrees of freedom far beyond the reach of terrestrial colliders. In the simplest inflationary models, any such cosmological collider signal is exponentially suppressed for particles much heavier than the inflationary Hubble scale, limiting the potential reach of such … Read More
Lawrence Berkeley National Laboratory Physics Division 4D Seminar Monday, June 07, 2020ZOOM TALK https://lbnl.zoom.us/j/215429094 12:30 PM Anirudh Prabu (Stanford) “Axion Production in Pulsar Magnetosphere Gaps”Abstract: Pulsar magnetospheres admit non-stationary vacuum gaps that are characterized by non-vanishing E⋅B. The vacuum gaps play an important role in plasma production and electromagnetic wave emission. We show that these gaps generate axions whose energy … Read More
Title: Direct detection of dark matter far from the weak scale The WIMP may not be dead, but its decline has opened a number of new frontiers in the search for dark matter. Numerous candidates now line a vast range of scales, and the weak scale is no longer such a clear guidepost. This is especially problematic for traditional direct … Read More
The symmetry breaking of grand unified gauge groups in the early universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains, hybrid defects can form where cosmic strings attach to domain walls or monopoles attach to strings. In general, such hybrid defects are unstable and can leave behind unique gravitational … Read More
Abstract: 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 … Read More
Abstract: Can the spin of light dark matter reveal itself on macroscopic/astrophysical scales? I will first show that the non-relativistic limit, bosonic spin-s dark fields are described by a 2s+1 component Schrodinger-Poisson (SP) system. This can be very useful in numerically simulating structure formation in higher-spin dark matter. I will then show that in this multi-component SP system, there exist solitons with … Read More
Title: Hunting for axions in the solar basin Abstract: Stars can produce large fluxes of new BSM particles. While most of this energy is radiated away to infinity, some fraction can become gravitationally trapped by the star, forming a “stellar basin.” After a brief review of stellar basins, I will present ongoing work using the NuSTAR telescope to hunt for … Read More