Detection of early-universe gravitational-wave signatures and fundamental physics.

Detection of a gravitational-wave signal of non-astrophysical origin would be a landmark discovery, potentially providing a significant clue to some of our most basic, big-picture scientific questions about the Universe. In this white paper, we survey the leading early-Universe mechanisms that may produce a detectable signal-including inflation, phase transitions, topological defects, as well as primordial black holes-and highlight the connections to fundamental physics. We review the complementarity with collider searches for new physics, and multimessenger probes of the large-scale structure of the Universe.

New physics searches at kaon and hyperon factories.

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements.

Boosted Dark Matter Interpretation of the XENON1T Excess.

We propose boosted dark matter (BDM) as a possible explanation for the excess of keV electron recoil events observed by XENON1T. BDM particles have velocities much larger than those typical of virialized dark matter, and, as such, BDM-electron scattering can naturally produce keV electron recoils. We show that the required BDM-electron scattering cross sections can be easily realized in a simple model with a heavy vector mediator.

Erratum: Dark Matter Interpretation of the Neutron Decay Anomaly [Phys. Rev. Lett. 120, 191801 (2018)].

This corrects the article DOI: 10.1103/PhysRevLett.120.

Dark Matter Interpretation of the Neutron Decay Anomaly.

There is a long-standing discrepancy between the neutron lifetime measured in beam and bottle experiments. We propose to explain this anomaly by a dark decay channel for the neutron, involving one or more dark sector particles in the final state. If any of these particles are stable, they can be the dark matter.

SU(5) Unification without Proton Decay.

We construct a four-dimensional SU(5) grand unified theory in which the proton is stable. The standard model leptons reside in the 5 and 10 irreps of SU(5), whereas the quarks live in the 40 and 50 irreps. The SU(5) gauge symmetry is broken by the vacuum expectation values of the scalar 24 and 75 irreps.

Protophobic Fifth-Force Interpretation of the Observed Anomaly in ^{8}Be Nuclear Transitions.

Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e^{+}e^{-} pairs produced in ^{8}Be nuclear transitions. The data are explained by a 17 MeV vector gauge boson X that is produced in the decay of an excited state to the ground state, ^{8}Be^{*}→^{8}Be X, and then decays through X→e^{+}e^{-}.