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Nuclear Theory·nucl-th

Wednesday·February 14, 2024

8 papers—5 primary·3 cross-listed

All8Primary5Cross-lists3
  1. 06

    Neutrinoless double beta decay rates in the presence of light sterile neutrinos

    W. Dekens🇺🇸 · J. de Vries🇳🇱 · D. Castillo🇪🇸 · J. Menéndez🇪🇸 · E. Mereghetti🇺🇸 · V. Plakkot🇳🇱 · P. Soriano🇪🇸 · G. Zhou🇨🇳

    We investigate neutrinoless double-beta decay () in minimal extensions of the Standard Model of particle physics where gauge-singlet right-handed neutrinos give rise to Dirac and Majorana neutrino mass terms. We argue that the standard treatment of these scenarios, based on mass-dependent nuclear matrix elements, is missing important contributions to the amplitude. First, new effects arise from the exchange of neutrinos with very small (ultrasoft) momenta, for which we compute the associated nuclear matrix elements for the decays of Ge and Xe. These contributions can dominate the rate in cases with light sterile neutrinos. The ultrasoft terms are also relevant in the more standard scenario of just three light Majorana neutrinos where they lead to a reduction of the total amplitude. Secondly, we highlight the importance of short-range terms associated with medium-heavy sterile neutrinos and provide explicit formulae that can be used in phenomenological analyses. As examples we discuss impact of these new effects in several explicit scenarios, including a realistic model with two right-handed gauge-singlet neutrinos.

    ↳ hep-phnucl-thJHEP(2024)·32 citations
  2. 07

    Effect of electron-phonon coupling on thermal transport in metals: a Monte Carlo approach for solving the coupled electron-phonon Boltzmann transport equations

    Jie Peng · W. Ryan Deskins · Maria Helena Braga · Anter El-Azab

    In this work, the effect of electron-phonon (e-ph) coupling on both electron and phonon transport of metals is investigated via first principles calculations. A Monte-Carlo (MC) approach for solving the coupled electron-phonon Boltzmann transport equations is developed to investigate thermal conductivity of metals. In this approach, the anisotropic electron band structure, phonon dispersion in the full Brillouin zone, and mode-dependent thermal relaxation time of electrons and phonons are calculated from first principles. Using this approach, MC simulations of coupled e-ph thermal transport at different temperatures in {\alpha}-U and Ag are performed. These two materials were selected as a way to demonstrate the applicability of the method in different fields. The results indicate that the electron relaxation time due to phonon scattering is orders of magnitude smaller than the phonon relaxation time due to electron scattering. The results also show that, in phonon thermal transport, the impact of ph-e scattering is almost negligible and the ph-ph scattering dominates phonon transport. At high temperature, the electrons dominate thermal transport in both {\alpha}-U and Ag. However, at low temperature, the phonon contribution to the total thermal conductivity of {\alpha}-U is significant. Moreover, the Lorenz ratio deviates from the Sommerfeld value at low to intermediate temperatures, where the Wiedemann-Franz law is not applicable. Finally, we show that the Ag electronic thermal conductivity shows a stronger size effect than its phonon thermal conductivity.

    ↳ cond-mat.mtrl-scinucl-thAIP Adv.(2025)·0 citations
  3. 08

    Constraints on Variation of the Weak Scale from Big Bang Nucleosynthesis

    Anne-Katherine Burns🇺🇸 · Venus Keus🇮🇪 · Marc Sher🇺🇸 · Tim M.P. Tait🇺🇸

    Recently, the EMPRESS collaboration has included new data in the extraction of the primordial He abundance from Big Bang Nucleosynthesis (BBN), resulting in a determination that differs from the previous value and from theoretical expectations. There have been several studies attempting to explain this anomaly which involve variation of fundamental constants between the time of BBN and the present. Since the Higgs vacuum expectation value (vev) is the only dimensionful parameter in the Standard Model and it is already known to vary during the electroweak phase transition, we consider the possibility that the vev is slightly different during BBN compared to its present value. A modification of the vev changes not only particle masses but also affects, through mass thresholds, the QCD confinement scale. We use the recently developed PRyMordial program to study this variation and its impact on the He and deuterium abundances. We find that bounds on are approximately , and that the EMPRESS result can be explained within if , but at the cost of worsening the current discrepancy in the deuterium abundance to over .

    ↳ hep-phastro-ph.HEnucl-thPRD(2024)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE