Particle theory

Abstract:

The IceCube South Pole Neutrino Observatory has discovered the presence of a diffuse astrophysical neutrino flux at energies of TeV and beyond using neutrino induced muon tracks and cascade events from neutrino interactions. We present two analyses sensitive to neutrino events in the energy range 1 TeV to 10 PeV, using more than 10 years of IceCube data. Both analyses consistently reject a neutrino spectrum following a single power-law with a significance of >4σ in favor of a broken power law. We describe the methods implemented in the two analyses, the spectral constraints obtained, and the validation of the robustness of the results. Additionally, we report the detection of a muon neutrino in the medium energy starting events sample, or MESE, with an energy of 11.4-2.53+2.46 PeV, the highest energy neutrino observed by IceCube to date. The results presented here show insights into the spectral shape of astrophysical neutrinos, which has important implications for inferring their production processes in a multimessenger picture.

Abstract:

Axion models generically suffer from a severe quality problem when coupled to gravity. In this article we provide a very simple model with a high quality axion. The axion is a pseudo-Nambu-Goldstone boson of the baryon number symmetry, U(1)B, of a new composite sector that breaks U(1)B spontaneously when it confines. A controlled example is a supersymmetric QCD (SQCD) with Nc = Nf. The axion shift symmetry is automatically protected due to the high dimension of the gauge-invariant baryon operator, with the Peccei-Quinn breaking operators arising at dimension Nc + 2. The standard model gauge group is embedded as a subgroup of the flavor symmetry group of SQCD that has an anomaly with U(1)B, generating the standard coupling with gluons.

Abstract:

We revisit cooling bounds on light Kaluza-Klein (KK) gravitons, as arise in the dark dimension scenario, considering globular clusters, neutron stars, and supernovae. In addition to bremsstrahlung, we account for two novel production channels: resonant mixing with the in-medium photon and a pion-induced process in supernovae. The strongest limits arise from SN 1987A, with the emissivity from the pion process exceeding that from bremsstrahlung by a factor of a few albeit with substantial uncertainties, while resonant production is heavily suppressed. We obtain a bound on the KK mass scale of mKK ≳ 0.6 eV (≳ 500 eV) for 2 (3) extra dimensions, which, having accounted for these previously neglected processes, is broadly compatible with existing analyses. Improved understanding of the properties of pions in supernovae could strengthen these limits to roughly eV (keV). For 1 extra dimension, the bounds are weaker than those from laboratory searches. We also show that constraints from KK graviton decays to Standard Model particles are less stringent than the cooling bounds if there is KK number violation at the level typically assumed in the dark dimension scenario, although these bounds could be strengthened by future observations.

Abstract:

Here we present results from an experiment performed at the GSI Helmholtz Center for Heavy Ion Research. A mono-energetic beam of chromium ions with initial energies of  ~ 450 MeV was fired through a magnetized interaction region formed by the collision of two counter-propagating laser-ablated plasma jets. While laser interferometry revealed the absence of strong fluid-scale turbulence, acceleration and diffusion of the beam ions was driven by wave-particle interactions. A possible mechanism is particle acceleration by electrostatic, short scale length kinetic turbulence, such as the lower-hybrid drift instability.