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Nuclear seminar

Probing nonlinear gluon dynamics at RHIC and the EIC

The gluon distribution function grows with lower and lower momentum fraction very fast. As the total scattering cross section is bound by quantum mechanics, the raise of the gluon density has to be tamed, which is explained by gluon recombination under the color glass condensate (CGC) framework. A definitive discovery of nonlinear effects in QCD and as such the saturation regime would significantly improve our understanding of the nucleon structure and of nuclear interactions at high energy. Two particle azimuthal correlation is one of the most direct and sensitive channels to access the underlying nonlinear gluon dynamics. In this talk, we will present the recent results of forward di-hadron correlations measured at RHIC, together with the signatures of gluon saturation predicted by CGC. New opportunities for measurements with the STAR forward upgrade and future EIC to study the nonlinear effects in QCD will also be discussed.

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Resonant Shattering Flares: Multimessenger Probes of Nuclear Physics

The era of multi-messenger astronomy has unlocked new probes of physics, allowing natural experiments to be carried out on matter at extremes unattainable using terrestrial experiments. Neutron stars, and their mergers, are natural sites to seek probes of nuclear physics, as these compact objects contain the densest matter in the universe. I will discuss multi-messenger astrophysical observables from the point of view of nuclear physics constraints. In particular I will highlight resonant shattering flares (RSFs), which can provide strong constraints on the nuclear symmetry energy parameters of nuclear matter, comparable to those obtained by terrestrial nuclear experiments, such as those found in dipole polarizability and neutron skin thickness measurements.

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Searching for Ultralight Dark Matter with Pulsar Timing Arrays

Pulsar Timing Arrays (PTAs) are exceptionally sensitive detectors in the nHz to uHz frequency window. While their primary purpose is to detect the stochastic gravitational wave background, they can also be used to search for new physics. Ultralight dark matter (ULDM), with mass between 10^{-23} eV and 10^{-20} eV, can generate a variety of different signals within the sensitivity window of PTAs. I will give an overview of the effects which have been studied previously, and then discuss new signals generated by variations in the fundamental constants. There are two main avenues to induce a PTA signal via variations in fundamental constants: changing the pulsar spin rate, e.g., by fluctutating particle masses, or shifting the reference clock. Using the standard analysis pipeline of the PTA collaborations, PTAs are shown to be competitive with atomic clock and torsion balance constraints for many ULDM models, especially those varying the electron and muon mass. Lastly, I will discuss how future PTAs may improve the sensitivity, and unique correlations in the signals which may further distinguish them from background.

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First results from the LUX-ZEPLIN (LZ) dark matter experiment

LUX-ZEPLIN (LZ) is a direct detection dark matter experiment currently being operated at the Sanford Underground Research Facility (SURF) in Lead, South Dakota. The experiment utilizes 7 tonnes of liquid xenon in a dual phase time projection chamber to look for dark matter in the form of Weakly Interacting Massive Particles (WIMPs), as well as a broad range of other novel physics signals. LZ has recently released its first WIMP search results with an exposure of 60 live days using a fiducial mass of 5.5 tonnes. These results set new limits on spin-independent WIMP-nucleon cross-sections for WIMP masses above 9 GeV/c^2. This talk will give an overview of the LZ detector, a description of the first results, and a brief look at the science program that is now accessible with the LZ experiment.

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QCD in the cores of neutron stars

Abstract: Rapid advancement in neutron-star observations allows unprecedented empirical access to cold, ultra-dense QCD matter, complementing collider experiments. The combination of these observations with theoretical calculations reveals previously inaccessible features of the equation of state and the phase diagram of QCD. In this talk, I demonstrate how perturbative-QCD calculations at asymptotically high densities robustly constrain the equation of state at neutron-star densities using a new method solely based on causality and stability. I confront these calculations with neutron-star observations in a Gaussian-process-based Bayesian framework and demonstrate that the perturbative-QCD calculations offer significant and nontrivial information, going beyond that which is obtainable from current observations. The main effect of the QCD input is to soften the equation of state at high densities, supporting the hypothesis that most massive neutron stars have quark matter cores.

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