Search for Heavy Neutral Leptons in Decays of W Bosons Using a Dilepton Displaced Vertex in sqrt[s]=13 TeV pp Collisions with the ATLAS Detector.

A search for a long-lived, heavy neutral lepton (N) in 139  fb^{-1} of sqrt[s]=13  TeV pp collision data collected by the ATLAS detector at the Large Hadron Collider is reported. The N is produced via W→Nμ or W→Ne and decays into two charged leptons and a neutrino, forming a displaced vertex. The N mass is used to discriminate between signal and background.

Observation of Collider Muon Neutrinos with the SND@LHC Experiment.

We report the direct observation of muon neutrino interactions with the SND@LHC detector at the Large Hadron Collider. A dataset of proton-proton collisions at sqrt[s]=13.6  TeV collected by SND@LHC in 2022 is used, corresponding to an integrated luminosity of 36.

Evolution of the Primordial Axial Charge across Cosmic Times.

We investigate collisional decay of the axial charge in an electron-photon plasma at temperatures 10 MeV-100 GeV. We demonstrate that the decay rate of the axial charge is first order in the fine-structure constant Γ_{flip}∝αm_{e}^{2}/T and thus orders of magnitude greater than the naive estimate which has been in use for decades. This counterintuitive result arises through infrared divergences regularized at high temperature by environmental effects.

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.

Checking the Dark Matter Origin of a 3.53 keV Line with the Milky Way Center.

We detect a line at 3.539±0.011  keV in the deep exposure data set of the Galactic center region, observed with the x-ray multi-mirror mission Newton.

Unidentified line in x-ray spectra of the Andromeda galaxy and Perseus galaxy cluster.

We report a weak line at 3.52±0.02  keV in x-ray spectra of the Andromeda galaxy and the Perseus galaxy cluster observed by the metal-oxide-silicon (MOS) and p-n (PN) CCD cameras of the XMM-Newton telescope.

Long-range magnetic fields in the ground state of the Standard Model plasma.

In thermal equilibrium the ground state of the plasma of Standard Model particles is determined by temperature and exactly conserved combinations of baryon and lepton numbers. We show that at nonzero values of the global charges a translation invariant and homogeneous state of the plasma becomes unstable and the system transits into a new equilibrium state, containing a large-scale magnetic field. The origin of this effect is the parity-breaking character of weak interactions and chiral anomaly.

Self-consistent evolution of magnetic fields and chiral asymmetry in the early universe.

We show that the evolution of magnetic fields in a primordial plasma, filled with standard model particles at temperatures T≳10 MeV, is strongly affected by the chiral anomaly-an effect previously neglected. Although reactions, equilibrating left and right electrons, are in thermal equilibrium for T≲80 TeV, a left-right asymmetry develops in the presence of strong magnetic fields. This results in magnetic helicity transfer from shorter to longer scales and lepton asymmetry present in the plasma until T~10 MeV, which may strongly affect many processes in the early Universe.

Universal properties of dark matter halos.

We discuss the universal relation between density and size of observed dark matter halos that was recently shown to hold on a wide range of scales, from dwarf galaxies to galaxy clusters. Predictions of cold dark matter (ΛCDM) N-body simulations are consistent with this relation. We demonstrate that this property of ΛCDM can be understood analytically in the secondary infall model.

Realistic sterile neutrino dark matter with keV mass does not contradict cosmological bounds.

Previous fits of sterile neutrino dark matter (DM) models to cosmological data ruled out masses smaller than approximately 8 keV, assuming a production mechanism that is not the best motivated from a particle physics point of view. Here we focus on a realistic extension of the standard model with three sterile neutrinos, consistent with neutrino oscillation data and baryogenesis, with the lightest sterile neutrino being the DM particle. We show that for each mass >or= 2 keV there exists at least one model accounting for 100% of DM and consistent with Lyman-alpha and other cosmological, astrophysical, and particle physics data.

Strategy for searching for a dark matter sterile neutrino.

We propose a strategy for how to look for dark matter particles possessing a radiative decay channel and derive constraints on their parameters from observations of x rays from our own Galaxy and its dwarf satellites. When applied to sterile neutrinos in the keV mass range this approach gives a significant improvement to restrictions on neutrino parameters compared with previous works.