Particle Physics

Finite density systems can be described by effective field theories with non-linearly realized space-time symmetries, whose construction resembles that of the QCD chiral lagrangian. Based on that similarity, one would expect the construction to work equally well classically and quantum mechanically. While that is true for superfluids and solids, one instead finds that for genuine fluids things are made more complicated by the unusual dynamics of their transverse modes, which are not described by a Fock space. Focussing on the incompressible limit for a fluid in 2+1 dimensions, I illustrate its analogy with the ordinary rigid body. Indeed both systems describe motion on a group manifold. Proceeding from this analogy I develop  a consistent quantum mechanical description of a perfect fluid using the known equivalence between the area preserving diffeomorfism group in 2D and SU(N) for N->\infty

In this talk I will discuss the rich interplay of light particles with density. In particular, I will show that the couplings of the QCD axion get modified in high density conditions. I will discuss the implications on astrophysical constraints, such as supernova and neutron star bounds. I will then look at the impact that axion-like particles can have on the structure of neutron stars

An intense beam of Standard Model (SM) particles colliding with a fixed target is one of oldest types of accelerator-based experiments. With recent interest in production and detection of relatively light, weakly-coupled (``dark sector'') states, these set-ups are again playing a central role in the search for beyond-SM (BSM) physics. Signal rate prediction is often challenging in fixed-target experiments, requiring the simulation of many SM and BSM processes as the beam particle propagates through the target. Both play a key role in determining the flux of dark sector particles through a detector. An accurate description of these fluxes is needed, since small errors in angular and energy distribution predictions can lead to significant over or under estimates of signal rate in the detector. Focusing for simplicity on BSM particle production from electromagnetic cascades, I will describe how we can model production of BSM particles, highlighting some frequently-used approximations used in the past. I will then show that improvements in both SM and BSM modelling are desirable. We implemented several of these improvements in a code, PETITE. Using this tool we can show how mismodelling of SM or BSM processes can lead to orders of magnitude difference in signal rates at realistic experimental setups.

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Fuzzy dark matter can form cored density distributions, named solitons, at the center of galaxies. Such cores can be viewed as approximate mass sheets and can affect the time delay cosmography Hubble constant (H_0) measurement via the mass sheet degeneracy. We show that a subdominant component of fuzzy dark matter can yield a 10 percent shift in the inferred H_0, if the particle mass is of order 10^-25 eV. The sensitivity of time delays on such cores (difficult to spot otherwise) may give a further probe in constraining the fuzzy dark matter scenario, if an H_0 prior is assumed.

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“Saturons" are macroscopic objects that saturate the field theoretic upper bound on microstate degeneracy. Due to their maximal microstate entropy, from a quantum information perspective, saturons and black holes belong to the same universality class with common key properties.  However, as opposed to black holes,  saturons do not require gravity and can emerge via ordinary renormalizable interactions, such as QCD, in the form  of soliton-like states. Due to this feature, saturons serve as laboratories for understanding certain properties of black holes. After reviewing the general properties of saturons, we discuss their implications for fundamental physics and cosmology. In particular, we explain how saturons can lead to a new form of phase transition. 

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