Dark Matter (DM) provides strong evidence for physics beyond the Standard Model (SM). Arguably, rather than suggesting a specific mass scale for New Physics, it may point to a dark sector, weakly-coupled to the SM, as hinted at by the comparable abundances of dark matter and visible baryons. In the past few years, a program of new experiments has expanded DM searches far beyond the WIMP paradigm to include new hidden forces and matter. While this program has made impressive progress, there are considerable challenges that must be overcome to fully explore the viable dark sector scenarios over a wide range of mass scales. In this seminar, I will discuss new search strategies to test dark sectors at low-energy high-intensity experiments, with a special emphasis on existing and planned experiments at Fermilab. I will highlight the complementarity of these experiments with LHC searches and with DM direct and indirect detection experiments in probing the parameter space of well motivated models as, for example, models of Strongly Interacting Dark Matter or Inelastic Dark Matter.

There exists a class of ultralight Dark Matter (DM) models which could form a Bose-Einstein condensate (BEC) in the early universe and behave as a single coherent wave instead of individual particles in galaxies. We show that a generic BEC DM halo intervening along the line of sight of a gravitational wave (GW) signal could induce an observable change in the speed of GW, with the effective refractive index depending only on the mass and self-interaction of the constituent DM particles and the GW frequency. Hence, we propose to use the deviation in the speed of GW as a new probe of the BEC DM parameter space. With a multi-messenger approach to GW astronomy and/or with extended sensitivity to lower GW frequencies, the entire BEC DM parameter space can be effectively probed by our new method in the near future.

We will discuss a simple model of low-energy baryon number violation in order to simultaneously explain the observed matter-antimatter asymmetry and dark matter relic density in the universe. The stability of dark matter is related to the stability of the proton. The model predicts a sizeable rate for the neutron-antineutron oscillation at low energy and a new type of monojet signal at the LHC. There exists an interesting complementarity between the observed baryon asymmetry, ratio of dark matter and baryon abundances, neutron-antineutron oscillation lifetime and the LHC monojet signal. 

Nab, an experiment that allows studying unpolarized neutron beta decay at the Spallation Neutron Source at Oak Ridge National Lab, aims to determine a, the neutrino-electron correlation coefficient, and b, the Fierz interference term, with high precision. Such measurements provide opportunities to search for evidence of extensions to the Standard Model. Nab is presently being constructed. The spectrometer magnet is supposed to arrive in the week I am giving this seminar. Beam readiness planned for end of summer 2018. I will discuss the experiment’s motivation and design, the planned modes of operation, and the performance of its components.

Title: Constraining dense matter properties from thermal and spin evolution of neutron stars

Abstract:  Neutron star interiors are the only laboratory to harbor cold (temperatures less than tens of MeV) and dense (densities higher than normal nuclear density but lower than those where perturbative QCD is applicable) matter in the universe. In this talk, I will report on our recent endeavors to answer the intriguing question: are exotic degrees of freedom realized in the densest cores of the most compact stars?

We analyze the thermal states of accreting neutron stars in quiescence, confining the studies within nucleons-only framework, and find the stringent limitation imposed by observation of the hottest and coldest sources disfavors the assumption without exotic matter. In addition, combining temperature and spin frequency data I will describe an interesting feature of hybrid stars with a sharp interface between nuclear matter mantle and quark matter core: capability of damping density oscillations e.g. r-modes in neutron stars that otherwise cannot be explained in the standard scenario of purely hadronic matter. These results we obtained could therefore provide theoretical predictions of the presence of exotic matter for future observations to confirm or rule out.

Over the past several years, “hidden sectors” have attracted a surge of interest in the particle physics community. I’ll summarize the underlying physics motivation and give an update on various search strategies. Most of the talk will focus on new bounds on dark sector models, emphasizing where Standard Model uncertainties still play a big part. In particular, we’ll examine bounds on "dark photons" from Supernova 1987A, where we have incorporated finite-temperature effects on the production and trapping for the first time, utilized a realistic model of the high-mixing parameter space, and shown the effect of systematic uncertainties from stellar progenitor models. Other hidden sector scenarios will be addressed as time permits.

The existence of dark matter is one of the few solid hints for physics beyond the standard model. If dark matter has indeed particle nature, then direct detection via scattering on atomic nuclei is one of the most promising discovery channels. In order to connect this nonrelativistic process with astrophysical and collider searches, as well as UV model building, a consistent setup of effective field theories for the different energy scales is necessary.

After an introduction to the physics of dark matter, I will present our work on the explicit connection between these energy scales, from the UV down to the nuclear scale, including a systematic error estimate. I will, in particular, discuss the effects of higher-order chiral and electroweak corrections.

I will discuss our ongoing efforts aimed at constraining the systematic errors in long-baseline neutrino experiments through ab initio computations of neutrino-nucleus quasielastic scattering cross sections using a powerful quantum many-body method---the coupled-cluster theory---with nuclear forces and electroweak currents derived in chiral effective field theory ($\chi$EFT). After showing  precision results for the electroweak properties of the deuteron, which we use to benchmark our harmonic oscillator-basis representation of the $\chi$EFT electroweak currents, I will present recent results for some electron-scattering observables of $^4$He and $^{40}$Ca.