Letters in High Energy Physics

Hot versus Cold Hidden Sectors and Their Effects on Thermal Relics

Pran Nath — 2024-02-04

A variety of possibilities exist for dark matter aside from WIMPS, such as hidden sector dark matter. We
discuss the synchronous thermal evolution of visible and hidden sectors and show that the density of
thermal relics can change O(100%) and ∆Neff by a factor of up to 105 depending on whether the hidden
sector was hot or cold at the reheat temperature. It is also shown that the approximation of using separate
entropy conservation for the visible and hidden sectors is invalid even for a very feeble coupling between
the two.

Dark Matter and Muon (g − 2) from a Discrete Z4 Symmetric Model

Simran Arora — 2024-02-04

The nonzero neutrino mass and nature of Dark Matter (DM) is still unknown within the Standard Model
(SM). In 2021, there was a 4.2σ discrepancy with SM results in the measurement of muon magnetic moment
reported by Fermilab. Recently, Fermilab released its precise results for muon’s magnetic moment, and it
shows a 5.1σ discrepancy. In this work, we study the corelation between neutrino masses, muon (g − 2)
anomaly, and Dark Matter within a framework based on the Z4 extension of the scotogenic model, in which
the neutrino masses are generated at one loop level. We extend the model with a vector-like lepton (VLL)
triplet in order to explain muon (g − 2). Here, the coupling of VLL triplet ψT to inert doublet η provides a
positive contribution to muon anomalous magnetic moment. We also studied the DM phenomenology of
ψT by considering the neutral component of ψT as the lightest DM candidate. We show that, for the mass of
the VLL triplet Mψ in TeV scale, the model can well explain muon (g − 2) anomaly and also gives required
relic density.

New Results on 0νββ Decay from the CUORE Experiment

Alice Campani — 2024-03-19

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment
searching for neutrinoless double beta decay (0νββ) that has successfully reached the tonne mass scale.
The detector, located at the LNGS in Italy, consists of an array of 988 TeO2 crystals arranged in a compact
cylindrical structure of 19 towers. CUORE began its first physics data run in 2017 at a base temperature of
about 10 mK and has been collecting data continuously since 2019, reaching a TeO2 exposure of 2 tonne-
year in spring 2023. This is the largest amount of data ever acquired with a solid-state cryogenic detector,
which allows for a significant improvement in the sensitivity to 0νββ decay in 130Te. In this article, we
present the analysis of new CUORE data, corresponding to ∼1 tonne · yr TeO2 exposure. This analysis
relies on significant enhancements to the data processing chain and high-level analysis. Combining the new
data with the former data release, we find no evidence for 0νββ decay and set a preliminary 90% credibility
interval Bayesian lower limit of 3.3 · 1025 yr on the 130Te half-life for this process. In the hypothesis that 0νββ
decay is mediated by light Majorana neutrinos, this results in an upper limit on the effective Majorana mass
of 75–255 meV, depending on the nuclear matrix element used.

Search for Leptonic CP Violation with the ESSnuSBplus Project

Tamer Tolba — 2024-03-25

ESSνSB is a design study for a next-generation long-baseline neutrino experiment that aims at the precise
measurement of the CP-violating phase, δCP, in the leptonic sector at the second oscillation maximum. The
conceptual design report published from the first phase of the project showed that after 10 years of data
taking, more than 70% of the possible δCP range will be covered with 5σ C.L. to reject the no-CP-violation
hypothesis. The expected value of δCP precision is smaller than 8◦ for all δCP values. The next phase of the
project, the ESSνSB+, aims at using the intense muon flux produced together with neutrinos to measure
the neutrino-nucleus cross-section, the dominant term of the systematic uncertainty, in the energy range
of 0.2–0.6 GeV, using a Low Energy neutrinos from STORed Muons (LEnuSTORM) and a Low Energy
Monitored Neutrino Beam (LEMNB) facilities.