Event Category: 4D Seminar

4D Seminar series:
Monday at 2:30 on campus

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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

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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

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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

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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

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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

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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

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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

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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

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Abstract: A generic low-energy prediction of string theory is the existence of a large collection of axions, commonly known as a string axiverse. In a realistic axiverse, string axions can be distributed densely over many orders of magnitude in mass, and are expected to interact with one another through their joint potential. In this talk, I will show how non-linearities … Read More

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In this talk, I will discuss the vector-portal dark matter model, with a dark photon that is slightly heavier than the dark matter. In this regime, a sub-GeV dark matter particle leads naturally to the correct relic abundance, with freezeout controlled by forbidden and 3-to-2 processes. The thermal freezeout behavior of dark matter can be classified into several different phases … Read More