Dark Matter Annihilation inside Large-Volume Neutrino Detectors.

New particles in theories beyond the standard model can manifest as stable relics that interact strongly with visible matter and make up a small fraction of the total dark matter abundance. Such particles represent an interesting physics target since they can evade existing bounds from direct detection due to their rapid thermalization in high-density environments. In this work we point out that their annihilation to visible matter inside large-volume neutrino telescopes can provide a new way to constrain or discover such particles. The signal is the most pronounced for relic masses in the GeV range, and can be efficiently constrained by existing Super-Kamiokande searches for dinucleon annihilation. We also provide an explicit realization of this scenario in the form of secluded dark matter coupled to a dark photon, and we show that the present method implies novel and stringent bounds on the model that are complementary to direct constraints from beam dumps, colliders, and direct detection experiments.

Neutron Star Internal Heating Constraints on Mirror Matter.

Mirror sectors have been proposed to address the problems of dark matter, baryogenesis, and the neutron lifetime anomaly. In this work we study a new, powerful probe of mirror neutrons: neutron star temperatures. When neutrons in the neutron star core convert to mirror neutrons during collisions, the vacancies left behind in the nucleon Fermi seas are refilled by more energetic nucleons, releasing immense amounts of heat in the process. We derive a new constraint on the allowed strength of neutron-mirror-neutron mixing from observations of the coldest (sub-40 000 Kelvin) neutron star, PSR 2144-3933. Our limits compete with laboratory searches for neutron-mirror-neutron transitions but apply to a range of mass splittings between the neutron and mirror neutron that is 19 orders of magnitude larger. This heating mechanism, also pertinent to other neutron disappearance channels such as exotic neutron decay, provides a compelling physics target for upcoming ultraviolet, optical, and infrared telescopes to study thermal emissions of cold neutron stars.

Breaking up the Proton: An Affair with Dark Forces.

Deep inelastic scattering of e^{±} off protons is sensitive to contributions from "dark photon" exchange. Using HERA data fit to HERA's parton distribution functions (PDFs), we obtain the model-independent bound ε≲0.02 on the kinetic mixing between hypercharge and the dark photon for dark photon masses ≲10 GeV. This slightly improves on the bound obtained from electroweak precision observables. For higher masses, the limit weakens monotonically; ε≲1 for a dark photon mass of 5 TeV. Utilizing PDF sum rules, we demonstrate that the effects of the dark photon cannot be (trivially) absorbed into refit PDFs and, in fact, lead to non-Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (Bjorken x_{B}-independent) scaling violations that could provide a smoking gun in data. The proposed e^{±}p collider operating at sqrt[s]=1.3 TeV (Large Hadron Electron Collider) is anticipated to accumulate 10^{3} times the luminosity of HERA, providing substantial improvements in probing the effects of a dark photon: sensitivity to ε well below that probed by electroweak precision data is possible throughout virtually the entire dark photon mass range, as well as being able to probe to much higher dark photon masses, up to 100 TeV.

Hydrogen Portal to Exotic Radioactivity.

We show that in a special class of dark sector models, the hydrogen atom can serve as a portal to new physics, through its decay occurring in abundant populations in the Sun and on Earth. The large fluxes of hydrogen decay daughter states can be detected via their decay or scattering. By constructing two models for either detection channel, we show that the recently reported excess in electron recoils at xenon1t could be explained by such signals in large regions of parameter space unconstrained by proton and hydrogen decay limits.

Neutron Stars Exclude Light Dark Baryons.

Exotic particles carrying baryon number and with a mass of the order of the nucleon mass have been proposed for various reasons including baryogenesis, dark matter, mirror worlds, and the neutron lifetime puzzle. We show that the existence of neutron stars with a mass greater than 0.7 M_{⊙} places severe constraints on such particles, requiring them to be heavier than 1.2 GeV or to have strongly repulsive self-interactions.

A facility to search for hidden particles at the CERN SPS: the SHiP physics case.

This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, [Formula: see text] and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals-scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.

Electrophobic Scalar Boson and Muonic Puzzles.

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both problems limit the mass of the scalar to between about 100 keV and 100 MeV. We identify two unexplored regions in the coupling constant-mass plane. Potential future experiments and their implications for theories with mass-weighted lepton couplings are discussed.

Testing parity with atomic radiative capture of µ(-).

The next generation of "intensity frontier" facilities will bring a significant increase in the intensity of subrelativistic beams of µ(-). We show that the use of these beams in combination with thin targets of Z~30 elements opens up the possibility of testing parity-violating interactions of muons with nuclei via direct radiative capture of muons into atomic 2S orbitals. Since atomic capture preserves longitudinal muon polarization, the measurements of the gamma ray angular asymmetry in the single photon 2S(1/2)-1S(1/2) transition will offer a direct test of parity. We calculate the probability of atomic radiative capture taking into account the finite size of the nucleus to show that this process can dominate over the usual muonic atom cascade and that the as-yet unobserved single photon 2S(1/2)-1S(1/2) transition in muonic atoms can be detected in this way using current muon facilities.

New parity-violating muonic forces and the proton charge radius.

The recent discrepancy between proton charge radius measurements extracted from electron-proton versus muon-proton systems is suggestive of a new force that differentiates between lepton species. We identify a class of models with gauged right-handed muon number, which contains new vector and scalar force carriers at the ∼100 MeV scale or lighter, that is consistent with observations. Such forces would lead to an enhancement by several orders-of-magnitude of the parity-violating asymmetries in the scattering of low-energy muons on nuclei. The relatively large size of such asymmetries, O(10(-4)), opens up the possibility for new tests of parity violation in neutral currents with existing low-energy muon beams.