Nuclear Theory·nucl-th

Wednesday·February 19, 2020

15 papers—6 primary·9 cross-listed

07
Sterile neutrinos and neutrinoless double beta decay in effective field theory
Wouter Dekens🇺🇸 · Jordy de Vries🇺🇸 · Kaori Fuyuto🇺🇸 · Emanuele Mereghetti🇺🇸 · Guanghui Zhou🇺🇸
We investigate neutrinoless double beta decay ( $0 ν β β$ ) in the presence of sterile neutrinos with Majorana mass terms. These gauge-singlet fields are allowed to interact with Standard-Model (SM) fields via renormalizable Yukawa couplings as well as higher-dimensional gauge-invariant operators up to dimension seven in the Standard Model Effective Field Theory extended with sterile neutrinos. At the GeV scale, we use Chiral effective field theory involving sterile neutrinos to connect the operators at the level of quarks and gluons to hadronic interactions involving pions and nucleons. This allows us to derive an expression for $0 ν β β$ rates for various isotopes in terms of phase-space factors, hadronic low-energy constants, nuclear matrix elements, the neutrino masses, and the Wilson coefficients of higher-dimensional operators. The needed hadronic low-energy constants and nuclear matrix elements depend on the neutrino masses, for which we obtain interpolation formulae grounded in QCD and chiral perturbation theory that improve existing formulae that are only valid in a small regime of neutrino masses. The resulting framework can be used directly to assess the impact of $0 ν β β$ experiments on scenarios with light sterile neutrinos and should prove useful in global analyses of sterile-neutrino searches. We perform several phenomenological studies of $0 ν β β$ in the presence of sterile neutrinos with and without higher-dimensional operators. We find that non-standard interactions involving sterile neutrinos have a dramatic impact on $0 ν β β$ phenomenology, and next-generation experiments can probe such interactions up to scales of $O (100)$ TeV.
↳ hep-phnucl-exnucl-thJHEP(2020)·116 citations
08
Beta decays as sensitive probes of lepton flavor universality
Andreas Crivellin🇨🇭 · Martin Hoferichter🇨🇭
Nuclear $β$ decays as well as the decay of the neutron are well-established low-energy probes of physics beyond the Standard Model (SM). In particular, with the axial-vector coupling of the nucleon $g_{A}$ determined from lattice QCD, the comparison between experiment and SM prediction is commonly used to derive constraints on right-handed currents. Further, in addition to the CKM element $V_{u s}$ from kaon decays, $V_{u d}$ from $β$ decays is a critical input for the test of CKM unitarity. Here, we point out that the available information on $β$ decays can be re-interpreted as a stringent test of lepton flavor universality (LFU). In fact, we find that the ratio of $V_{u s}$ from kaon decays over $V_{u s}$ from $β$ decays (assuming CKM unitarity) is extremely sensitive to LFU violation (LFUV) in $W$ - $μ$ - $ν$ couplings thanks to a CKM enhancement by $(V_{u d} / V_{u s})^{2} \sim 20$ . From this perspective, recent hints for the violation of CKM unitarity can be viewed as further evidence for LFUV, fitting into the existing picture exhibited by semi-leptonic $B$ decays and the anomalous magnetic moments of muon and electron. Finally, we comment on the future sensitivity that can be reached with this LFU violating observable and discuss complementary probes of LFU that may reach a similar level of precision, such as $Γ (π \to μν) /Γ (π \to e ν)$ at the PEN and PiENu experiments or even direct measurements of $W \to μν$ at an FCC-ee.
↳ hep-phhep-exhep-latnucl-ex+1PRL(2020)·120 citations
09
Strings of diquark-quark (QQ)Q baryon before phase transition
A.S. Bakry🇨🇳 · M.A. Deliyergiyev🇨🇭 · A.A. Galal🇪🇬 · M.N. Khalil🇩🇪
We explore the limit at which the effective baryonic Y-string model of the junction approaches the mesonic stringlike behavior. We calculate and compare the numerical values of the static potential and energy-density correlators of diquark-quark and quark-antiquark configurations. The gauge model is pure Yang-Mills $S U (3)$ lattice gauge theory at coupling $β = 6.0$ and finite temperature. The diquark setup is approximated as two quarks confined within a sphere of radius $0.1$ fm. The lattice data of the potential and energy show that the string binding the diquark-quark configuration displays an identical behavior to the quark-antiquark confining string. However, with the temperature increase to a small enough neighborhood of the critical point $T_{c}$ , the gluonic similarities between the two systems do not manifest neither at short nor intermediate distance scales $R < 1.0$ fm. The comparison between the potential and the second moment of the action-density correlators for both systems shows significant splitting. This suggests that subsisted baryonic decoupled states overlap with the mesonic spectrum. The baryonic junction's model for the potential and the profile returns a good fit to the numerical lattice data of the diquark-quark arrangement. However, near the critical point, the mesonic string displays large deviations compared to fits of the corresponding quark-antiquark data.
↳ hep-lathep-phnucl-thPRD(2023)·3 citations
10
A covariant model for the decuplet to octet Dalitz decays
G. Ramalho🇧🇷
In the last years it became possible to measure in HADES the dilepton decays of several baryons. The baryon dilepton decays provide information about the electromagnetic structure of the baryons in the timelike region. In the present work, we study the $B^{'} \to e^{+} e^{-} B$ decays, where $B^{'}$ is a baryon decuplet member and $B$ is a baryon octet member. Our calculations are based on the covariant spectator quark model, where the contribution of the quark core is complemented with an $S U (3)$ contribution from the pion cloud. The pion cloud contribution prove to be relevant in the range of study. We present predictions for the $Σ^{0} (1385) \to e^{+} e^{-} Λ (1116)$ and $Σ^{+} (1385) \to e^{+} e^{-} Σ^{+} (1193)$ decays, which may be tested at HADES in a near future. Predictions for the remaining decuplet baryon Dalitz decays are also presented. We conclude that different orders of magnitudes are expected for the baryon decuplet Dalitz decay widths, according to the quark content of the baryons. We also conclude that the dependence of the transition form factors on the square momentum transfer ( $q^{2}$ ) is important for some transitions.
↳ hep-phhep-exnucl-exnucl-thPRD(2020)·18 citations
11
Universality of semisuper-Efimov effect
Yusuke Horinouchi
We study the semisuper-Efimov effect, which is found for four identical bosons with a resonant three-body interaction in 2D, in various systems. Based on solutions of bound-state and renormalization-group equations, we first demonstrate an emergence of the semisuper-Efimov effect in mass-imbalanced bosons in 2D. Compared with the Efimov and the super-Efimov effects, the mass ratio-dependent scaling parameter is unexpectedly found to take on a finite value even for extremely mass-imbalanced situations, where the mass ratio is 0 or $\infty$ . By a renormalization-group analysis, we also show that a weak two-body interaction sustains the semisuper-Efimov effect. Finally, we liberate the universality of the semisuper-Efimov effect from 2D by showing that bosons with linear-dispersion relation support the semisuper-Efimov effect in 1D.
↳ cond-mat.quant-gasnucl-th2 citations
12
Measurement of global spin alignment of $K^{* 0}$ and $ϕ$ vector mesons using the STAR detector at RHIC
Subhash Singha (for the STAR Collaboration)🇨🇳
We report the transverse momentum ( $p_{T}$ ) and centrality dependence of global spin alignment ( $ρ_{00}$ ) of $K^{* 0}$ vector meson at midrapidity ( $∣ y ∣ < 0.5$ ) in Au + Au collisions at $s_{N N}$ = 54.4 and 200~GeV with the STAR experiment at RHIC. The $K^{* 0}$ results are compared to that of $ϕ$ meson. At low- $p_{T}$ region and midcentral collisions, the $K^{* 0}$ $ρ_{00}$ is found to be smaller than 1/3 with about 4 $σ$ significance, while that of $ϕ$ meson is observed to be larger than 1/3 with about 3 $σ$ significance. The $ρ_{00}$ results are compared between RHIC and LHC energies. The physics implication of our results is also discussed.
↳ nucl-exhep-exnucl-thNPA(2021)·33 citations
13
QCD phase structure from functional methods
Fei Gao🇩🇪 · Jan M. Pawlowski🇩🇪
We discuss the QCD phase structure at finite temperature and chemical potential for $2$ -flavour and $2 + 1$ -flavour QCD. The results are achieved by computing QCD correlation functions within a generalised functional approach that combines Dyson-Schwinger equations (DSE) and the functional renormalisation group (fRG). In this setup fRG precision data from arXiv:1706.06326 for the vacuum quark-gluon vertex and gluon propagator of $2$ -flavour QCD are used as input, and the respective DSEs are expanded about this input. While the vacuum results for other correlation functions serve as a self-consistency check for functional approaches, the results at finite temperature and density are computed, for the first time, without the need of phenomenological infrared parameters.
↳ hep-phhep-exhep-latnucl-thPRD(2020)·187 citations
14
Green's functions for non-classical transport with general anisotropic scattering
Eugene d'Eon
In non-classical linear transport the chord length distribution between collisions is non-exponential and attenuation does not respect Beer's law. Generalized radiative transfer (GRT) extends the classical theory to account for such two-point correlation between collisions and neglects all higher order correlations. For this form of transport, we derive the exact time-independent Green's functions for the isotropic point source in infinite 3D homogeneous media with general anisotropic scattering. Green's functions for both collision rate density, which characterizes absorption and reaction rates in the system, and radiance/flux, which characterizes displacement of radiation/particles, are solved in Fourier space. We validate the derivations using gamma random flights to produce the first anisotropic scattering benchmark solutions for the generalized linear Boltzmann equation. For gamma-4 flights with linearly anisotropic scattering and gamma-6 flights with Rayleigh scattering the collision rate density is found explicitly in real space as a sum of diffusion modes.
↳ cond-mat.stat-mechnucl-th0 citations
15
Manifestation of kaonium in the $e^{+} e^{-} \to K^{+} K^{-}$ process
P. Lichard🇨🇿
We analyze the precise data obtained by the CMD-3 experiment on the $e^{+} e^{-}$ annihilation into two charged kaons in the vicinity of the $ϕ$ peak. A perfect fit is obtained only if a pole on the real axis below the reaction threshold is assumed. This can be interpreted as proof of the existence of the 2p state of kaonium, a compound of $K^{+}$ and $K^{-}$ . The BaBar Collaboration data on the same process supports this conclusion and, in addition, points to the strong interaction as a dominant source of the binding energy. The possibility of discovering 2p kaonium in the $e^{+} e^{-} \to π^{+} π^{-}$ process is discussed. The 2p state of $K^{0}$ -onium is indicated on the basis of the CMD-3 $e^{+} e^{-} \to K_{S}^{0} K_{L}^{0}$ data.
↳ hep-phhep-exnucl-thPRD(2020)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE