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Nuclear Theory·nucl-th

Thursday·November 11, 2021

7 papers—3 primary·4 cross-listed

All7Primary3Cross-lists4
  1. 04

    Testing Lepton Flavor Universality with Pion, Kaon, Tau, and Beta Decays

    Douglas Bryman🇨🇦 · Vincenzo Cirigliano🇺🇸 · Andreas Crivellin🇨🇭 · Gianluca Inguglia🇦🇹

    We present an overview of searches fo violation of lepton flavor universality with focus on low energy precision probes using pions, kaons, tau leptons, and nuclear beta decays. The current experimental results are reviewed, the theoretical status within the context of the Standard Model is summarized, and future prospects (both experimental and theoretical) are discussed. We review the implications of these measurements for physics beyond the Standard Model by performing a global model-independent fit to modified couplings to leptons and four-fermion operators. We also discuss new physics in the context of simplified models and review Standard Model extensions with focus on those which can explain a possible deviation from unitarity of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.

    ↳ hep-phhep-exhep-latnucl-ex+1Ann.Rev.Nucl.Part.Sci.(2022)·71 citations
  2. 05

    Infinite volume, three-body scattering formalisms in the presence of bound states

    Sebastian M. Dawid🇺🇸

    Strong interactions produce a rich spectrum of resonances that decay into three or more hadrons. Understanding their phenomenology requires a theoretical framework to extract parameters fromexperimental data and Lattice QCD simulations of hadron scattering. Two classes of relativistic three-body approaches are currently being pursued: the EFT-based and unitarity-based one. We consider a model of relativistic three-body scattering with an S-wave bound state in the two-body sub-channel using both formalisms. We present and discuss numerical solutions for the multi-hadron scattering amplitudes in different kinematical regions, obtained from integral equationsof the EFT-based approach. The connection of our work to the ongoing program of computingthe three-body spectrum from the lattice is highlighted. Finally, we show how to generalizethe unitarity-based framework to include all relevant open channels, discuss the nonphysicalsingularities near the physical region, and show how to eliminate them in a simple case.

    ↳ hep-latnucl-thPoS(2022)·5 citations
  3. 06

    Modeling general-relativistic plasmas with collisionless moments and dissipative two-fluid magnetohydrodynamics

    Elias R. Most · Jorge Noronha · Alexander A. Philippov

    Relativistic plasmas are central to the study of black hole accretion, jet physics, neutron star mergers, and compact object magnetospheres. Despite the need to accurately capture the dynamics of these plasmas and the implications for relativistic transients, their fluid modeling is typically done using a number of (overly) simplifying assumptions, which do not hold in general. This is especially true when the mean free path in the plasma is large compared to the system size, and kinetic effects start to become important. Going beyond common approaches used in the literature, we describe a fully relativistic covariant 14-moment based two-fluid system appropriate for the study of electron-ion or electron-positron plasmas. This generalized Israel-Stewart-like system of equations of motion is obtained directly from the relativistic Boltzmann-Vlasov equation. Crucially, this new formulation can account for non-ideal effects, such as anisotropic pressures and heat fluxes. We show that a relativistic two-fluid plasma can be recast as a single fluid coupled to electromagnetic fields with (potentially large) out-of-equilibrium corrections. In particular, we keep all electron degrees of freedom, which provide self-consistent evolution equations for electron temperature and momentum. The equations outlined in this paper are able to capture the full two-fluid character of collisionless plasmas found in black hole accretion and flaring processes around compact objects, as well Braginskii-like two-fluid magnetohydrodynamics applicable to weakly collisional plasmas inside accretion disks. This new formulation will be instrumental in the construction of a large class of next-generation simulations of relativistic transient phenomena produced around black holes and neutron stars.

    ↳ astro-ph.HEgr-qcnucl-thMNRAS(2022)·42 citations
  4. 07

    Light scalars in neutron star mergers

    P. S. Bhupal Dev🇺🇸 · Jean-François Fortin🇨🇦 · Steven P. Harris🇺🇸 · Kuver Sinha🇺🇸 · Yongchao Zhang🇨🇳

    Due to their unique set of multimessenger signals, neutron star mergers have emerged as a novel environment for studies of new physics beyond the Standard Model (SM). As a case study, we consider the simplest extension of the SM scalar sector involving a light CP-even scalar singlet mixing with the SM Higgs boson. These particles can be produced abundantly in neutron star mergers via the nucleon bremsstrahlung process. We show that the particles may either be trapped in or stream freely out of the merger remnant, depending on the mass, its mixing with the SM Higgs boson, and the temperature and baryon density in the merger. In the free-streaming region, the scalar will provide an extra channel to cool down the merger remnant, with cooling timescales as small as (ms). On the other hand, in the trapped region, the Bose gas of particles could contribute a larger thermal conductivity than the trapped neutrinos in some parts of the parameter space, thus leading to faster thermal equilibration than expected. Therefore, future observations of the early postmerger phase of a neutron star merger could effectively probe a unique range of the parameter space, largely complementary to the existing and future laboratory and supernova limits. In view of these results, we hope the merger simulation community will be motivated to implement the effects of light CP-even scalars into their simulations in both the free-streaming and trapped regimes.

    ↳ hep-phastro-ph.HEnucl-thJCAP(2022)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE