Thu·Mar 4, 2021Thursday·March 4, 2021

1. 01*

   Non-unitary neutrino mixing in short and long-baseline experiments

   D.V. Forero🇨🇴 · C. Giunti🇮🇹 · C.A. Ternes🇮🇹 · M. Tortola🇪🇸

   Non-unitary neutrino mixing in the light neutrino sector is a direct consequence of type-I seesaw neutrino mass models. In these models, light neutrino mixing is described by a sub-matrix of the full lepton mixing matrix and, then, it is not unitary in general. In consequence, neutrino oscillations are characterized by additional parameters, including new sources of CP violation. Here we perform a combined analysis of short and long-baseline neutrino oscillation data in this extended mixing scenario. We did not find a significant deviation from unitary mixing, and the complementary data sets have been used to constrain the non-unitarity parameters. We have also found that the T2K and NOvA tension in the determination of the Dirac CP-phase is not alleviated in the context of non-unitary neutrino mixing.

   hep-phPRD(2021)·61 citations
2. 02*

   The CP violation and scalar dark matter in a 331 model

   M. J. Neves🇧🇷

   The 331 model with right-handed neutrinos is re-assessed to investigate the CP violation in the quark sector. After the spontaneous symmetry breaking, the masses and physical fields of the particle content are obtained. The fermions content of the 331 model is enlarged to include exotic quarks with known electric charge and with masses defined at the TeV scale. The existence of these exotic quarks induces extra CP violations via couplings with quarks of the Standard Model mediated by charged gauge boson with mass fixed at the TeV scale. An extra discrete ${\mathbb{Z}}_2$ symmetry is introduced in the 331 model to get a stable scalar field that can be a candidate to the dark matter content. The new scalar field interacts at tree level with the $Z^{\prime }$ gauge boson that works as a dark matter portal. The relic density associated with the scalar field is calculated to yield the solution mass that satisfies the observed dark matter. The region allowed on the parameter space of the dark matter mass versus $Z^{\prime }$ mass is obtained to include the bounds of PANDAX2017, XENON1T(2t.y) and LUX experiments.

   hep-phhep-thMod.Phys.Lett.A(2021)·4 citations
3. 03*

   Nucleon axial-vector and pseudoscalar form factors, and PCAC relations

   Chen Chen🇩🇪 · Christian S. Fischer🇩🇪 · Craig D. Roberts🇨🇳 · Jorge Segovia🇪🇸

   We use a continuum quark+diquark approach to the nucleon bound-state problem in relativistic quantum field theory to deliver parameter-free predictions for the nucleon axial and induced pseudoscalar form factors, $G_A$ and $G_P$, and unify them with the pseudoscalar form factor $G_5$ or, equivalently, the pion-nucleon form factor $G_{\pi NN}$. We explain how partial conservation of the axial-vector current and the associated Goldberger-Treiman relation are satisfied once all necessary couplings of the external current to the building blocks of the nucleon are constructed consistently; in particular, we fully resolve the seagull couplings to the diquark-quark vertices associated with the axial-vector and pseudoscalar currents. Among the results we describe, the following are worth highlighting. A dipole form factor defined by an axial charge $g_A=G_A(0)=1.25(3)$ and a mass-scale $M_A=1.23(3)m_N$, where $m_N$ is the nucleon mass, can accurately describe the pointwise behaviour of $G_A$. Concerning $G_P$, we obtain the pseudoscalar charge $g_p^{\ast }=8.80(23)$, and find that the pion pole dominance approach delivers a reliable estimate of the directly computed result. Our computed value of the pion-nucleon coupling constant, $g_{\pi NN}/m_N=14.02(33)/\mathrm{GeV}$ is consistent with recent precision determinations.

   hep-phPRD(2022)·47 citations
4. 04*

   The Heavy Quark Expansion for the Charm Quark

   Th. Mannel🇩🇪 · D. Moreno🇩🇪 · A. A. Pivovarov🇷🇺

   We show that one can re-arrange the Heavy Quark Expansion for inclusive weak decays of charmed hadrons in such a way that the resulting expansion is an expansion in ${\Lambda }_{\mathrm{QCD}}/m_c$ and ${\alpha }_s(m_c)$ with order-one coefficients. Unlike in the case of the bottom quark, the leading term includes not only the contribution of the free-quark decay, but also a tower of terms related to matrix elements of four quark operators.

   hep-ph9 citations
5. 05*

   Naturally Light Dirac Neutrinos from SU(6)

   Ernest Ma (UC Riverside)🇺🇸

   A known mechanism for obtaining naturally light Dirac neutrinos is implemented in the context of $SU(6)\to SU(5)\times U(1{)}_N$.

   hep-phJHEP(2021)·4 citations
6. 06*

   Towards the three-dimensional parton structure of the pion: Integrating transverse momentum data into global QCD analysis

   N. Y. Cao🇺🇸 · P. C. Barry🇺🇸 · N. Sato🇺🇸 · W. Melnitchouk🇺🇸

   We perform a new Monte Carlo QCD analysis of pion parton distribution functions, including, for the first time, transverse momentum dependent pion-nucleus Drell-Yan cross sections together with $p_{\mathrm{T}}$-integrated Drell-Yan and leading neutron electroproduction data from HERA. We assess the sensitivity of the Monte Carlo fits to kinematic cuts, factorization scale, and parametrization choice, and we discuss the impact of the various datasets on the pion's quark and gluon distributions. This study provides the necessary step towards the simultaneous analysis of collinear and transverse momentum dependent pion distributions and the determination of the pion's three-dimensional structure.

   hep-phhep-exhep-latnucl-thPRD(2021)·42 citations
7. 07*

   Constraints on running vacuum models with the baryon-to-photon ratio

   Hao Yu🇨🇳 · Ke Yang🇨🇳 · Jin Li🇨🇳

   We study the influence of running vacuum on the baryon-to-photon ratio in running vacuum models (RVMs). When there exists a non-minimal coupling between photons and other matter in the expanding universe, the energy-momentum tensor of photons is no longer conserved, but the energy of photons could remain conserved. We discuss the conditions for the energy conservation of photons in RVMs. The photon number density and baryon number density, from the epoch of photon decoupling to the present day, are obtained in the context of RVMs by assuming that photons and baryons can be coupled to running vacuum, respectively. Both cases lead to a time-evolving baryon-to-photon ratio. However the evolution of the baryon-to-photon ratio is strictly constrained by observations. It is found that if the dynamic term of running vacuum is indeed coupled to photons or baryons, the coefficient of the dynamic term must be extremely small, which is unnatural. Therefore, our study basically rules out the possibility that running vacuum is coupled to photons or baryons in RVMs.

   hep-phastro-ph.COgr-qchep-thEPJC(2022)·7 citations
8. 08*

   Effect of relativistic kinematics on the stability of multiquarks

   Jean-Marc Richard🇫🇷 · Alfredo Valcarce🇪🇸 · Javier Vijande🇪🇸

   We discuss whether the bound nature of multiquark states in quark models could benefit from relativistic effects on the kinetic energy operator. For mesons and baryons, relativistic corrections to the kinetic energy lead to lower energies, and thus call for a retuning of the parameters of the model. For multiquark states, as well as their respective thresholds, a comparison is made of the results obtained with non-relativistic and relativistic kinetic energy. It is found that the binding energy is lower in the relativistic case. In particular, $QQ\bar{q}\bar{q}$ tetraquarks with double heavy flavor become stable for a larger ratio of the heavy to light quark masses; and the all-heavy tetraquarks $QQ\bar{Q}\bar{Q}$ that are not stable in standard non-relativistic quark models remain unstable when a relativistic form of kinetic energy is adopted

   hep-phPRD(2021)·6 citations
9. 09*

   Strong-field Breit-Wheeler pair production in ${\mathrm{QED}}_{2+1}$

   Alina Golub🇩🇪 · Selym Villalba-Chávez🇩🇪 · Carsten Müller🇩🇪

   The Breit-Wheeler pair production process in $2+1$ dimensional spacetime is investigated. In the perturbative regime, non-vanishing rates at the energy threshold are found when odd numbers of photons take part on the reaction. This behaviour is understood as a direct consequence of the reduced dimensionality and resembles a corresponding prediction made in gapped graphene monolayers. In the non-perturbative strong field regime the effect of the dimensionality manifests itself in a different rate dependence on the quantum non-linearity parameter. The consequence of this deviation is discussed briefly in line with the applicability of perturbation theory. We argue that, in addition to large values of the quantum non-linearity parameter, the superrenormalisable character of quantum electrodynamics in $2+1$ dimensional spacetime might give rise to a breakdown of perturbation theory within certain energy scales.

   hep-phPRD(2021)·12 citations
10. 10*

    One Formula To Match Them All: The Bispinor Universal One-Loop Effective Action

    Benjamin Summ🇩🇪

    Extensions of the Standard Model (SM) often contain new particles with masses far above the electroweak scale. Due to the presence of a mass hierarchy, effective field theory (EFT) is a suitable tool for the study of such extensions. In this thesis, we provide a solution to the matching problem at the one-loop level in the form of the Bispinor Universal One-Loop Effective Action (BSUOLEA), which is a pre-computed expression for the effective action, parameterised in terms of derivatives of the Lagrangian of the ultraviolet (UV) model. The BSUOLEA is derived using functional methods and is sufficiently general to match any renormalisable, Lorentz invariant UV model to an EFT, containing operators of mass dimension up to and including six at the one-loop level. This includes supersymmetric models regularised in dimensional reduction. Since the pre-computed expression contains many operators, it is implemented into a currently private Mathematica package, which automatically performs the matching based on the BSUOLEA. We illustrate the use of this package, which will be made publicly available in the near future, by applying it to the matching of the Singlet Extended SM to the SM EFT. We then expand the framework in order to apply it to a non-renormalisable extension of the SM containing a vector resonance, which is assumed to arise from the confinement of a gauge group at high energies. This model raises some interesting theoretical questions since such a vector resonance comprises a system with second-class constraints. We perform the constraint analysis of the model and derive the generating functional in order to apply functional methods to the matching. We finally match the model to the SM EFT and present the full one-loop result including operators up to mass dimension six.

    hep-ph8 citations
11. 11*

    Measuring chiral imbalance with collisional energy loss

    Stefano Carignano🇪🇸 · Cristina Manuel🇪🇸

    We compute the collisional energy loss of an {energetic} massive fermion crossing a chiral plasma at finite temperature characterized by an imbalance between the populations of left-handed and right-handed fermions. We find a new contribution to the energy loss which is proportional to the helicity of the test fermion and depends on the amount of chiral imbalance in the plasma. We then compute the difference between the energy loss of a fermion with the two opposite helicities, to assess whether this could be used to quantify the chiral imbalance in the plasma. We find that the leading contribution to these helicity-dependent energy loss contributions comes from the exchange of hard photons (or gluons for QCD) with the medium constituents, and in some scenarios can become comparable to the leading-order result for a plasma without any chiral imbalance. We also evaluate the contribution arising from soft photon exchange, which is a subleading effect, and requires regularization. We illustrate how dimensional regularization is a well suited prescription to be applied to these energy loss computations.

    hep-phPRD(2021)·18 citations
12. 12*

    Higgs-like spectator field as the origin of structure

    Alexandros Karam🇪🇪 · Tommi Markkanen🇪🇪 · Luca Marzola🇪🇪 · Sami Nurmi🇫🇮 · Martti Raidal🇪🇪 · Arttu Rajantie🇬🇧

    We show that the observed primordial perturbations can be entirely sourced by a light spectator scalar field with a quartic potential, akin to the Higgs boson, provided that the field is sufficiently displaced from vacuum during inflation. The framework relies on the indirect modulation of reheating, which is implemented without any direct coupling between the spectator field and the inflaton and does not require non-renormalisable interactions. The scenario gives rise to local non-Gaussianity with $f_{\mathrm{NL}}\simeq 5$ as the typical signal. As an example model where the indirect modulation mechanism is realised for the Higgs boson, we study the Standard Model extended with right-handed neutrinos. For the Standard Model running we find, however, that the scenario analysed does not seem to produce the observed perturbation.

    hep-phastro-ph.COEPJC(2021)·6 citations
13. 13*

    Metastable Conformal Dark Matter

    Philippe Brax🇫🇷 · Kunio Kaneta🇰🇷 · Yann Mambrini🇫🇷 · Mathias Pierre🇪🇸

    We show that a metastable dark matter candidate arises naturally from the conformal transformation between the Einstein metric, where gravitons are normalised states, and the Jordan metric dictating the coupling between gravity and matter. Despite being secluded from the Standard Model by a large scale above which the Jordan metric shows modifications to the Einstein frame metric, dark matter couples to the energy momentum tensor of the Higgs field in the primordial plasma primarily. This allows for the production of dark matter in a sufficient amount which complies with observations. The seclusion of dark matter makes it long-lived for masses $\lesssim 1$ MeV, with a lifetime much above the age of the Universe and the present experimental limits. Such a dark matter scenario has clear monochromatic signatures generated by the decay of the dark matter candidate into neutrino and/or $\gamma -$rays.

    hep-phastro-ph.COPRD(2021)·8 citations
14. 14*

    Information in AdS/QCD: mass spectroscopy of isovector mesons

    R. da Rocha🇧🇷

    The mass spectra of isovector ${\rm Y}$, $\psi$, $\varphi$, and $\omega$ meson resonances are investigated, in the AdS/QCD and information entropy setups. The differential configurational entropy is employed to obtain the mass spectra of radial $S$-wave resonances, with higher excitation levels, in each one of these meson families, whose respective first undisclosed states are discussed and matched up to candidates in the Particle Data Group.

    hep-phhep-thPRD(2021)·24 citations
15. 15*

    Optimisation based algorithm for finding the action of cosmological phase transitions

    Michael Bardsley🇦🇺

    We present the OptiBounce algorithm, a new and fast method for finding the bounce action for cosmological phase transitions. This is done by direct solution of the "reduced" minimisation problem proposed by Coleman, Glaser, and Martin. By using a new formula for the action, our method avoids the rescaling step used in other algorithms based on this formulation. The bounce path is represented using a pseudo-spectral Gauss-Legendre collocation scheme leading to a non-linear optimisation problem over the collocation coefficients. Efficient solution of this problem is enabled by recent advances in automatic differentiation, sparse matrix representation and large scale non-linear programming. The algorithm is optimised for finding nucleation temperatures by sharing model initialisation work between instances of the calculation when operating at different temperatures. We present numerical results on a range of potentials with up to 20 scalar fields, demonstrating O(1%) agreement with existing codes and highly favourable performance characteristics.

    ↳ astro-ph.COhep-phComput.Phys.Commun.(2022)·15 citations
16. 16*

    Non-perturbative methods for NN singular interactions

    D.R. Entem🇪🇸 · J.A. Oller🇪🇸

    Chiral Effective Field Theory ($\chi$EFT) has been extensively used to study the $NN$ interaction during the last three decades. In Effective Field Theories (EFTs) the renormalization is performed order by order including the necessary counter terms. Due to the strong character of the $NN$ interaction a non-perturbative resummation is needed. In this work we will review some of the methods proposed to completely remove cutoff dependencies. The methods covered are renormalization with boundary conditions, renormalization with one counter term in momentum space (or equivalently substractive renormalization) and the exact $N/D$ method. The equivalence between the methods up to one renormalization condition will be checked showing results in the $NN$ system. The exact $N/D$ method allows to go beyond the others, and using a toy model it is shown how it can renormalize singular repulsive interactions.

    ↳ nucl-thhep-phEur.Phys.J.ST(2021)·8 citations
17. 17*

    Building a testable shear viscosity across the QCD phase diagram

    Emma McLaughlin🇺🇸 · Jacob Rose🇩🇪 · Travis Dore🇺🇸 · Paolo Parotto🇩🇪 · Claudia Ratti🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸

    Current experiments at the Relativistic Heavy Ion Collider (RHIC) are probing finite baryon densities where the shear viscosity to enthalpy ratio $\eta T/w$ of the Quark Gluon Plasma remains unknown. We use the Hadron Resonance Gas (HRG) model with the most up-to-date hadron list to calculate $\eta T/w$ at low temperatures and at finite baryon densities ${\rho }_B$. We then match $\eta T/w$ to a QCD-based shear viscosity calculation within the deconfined phase to create a table across $\left\{T,{\mu }_B\right\}$ for different cross-over and critical point scenarios at a specified location. We find that these new $\eta T/w(T,{\mu }_B)$ values would require initial conditions at significantly larger ${\rho }_B$, compared to ideal hydrodynamic trajectories, in order to reach the same freeze-out point.

    ↳ nucl-thhep-phPRC(2022)·39 citations
18. 18*

    Real-time lattice gauge theory actions: unitarity, convergence, and path integral contour deformations

    Gurtej Kanwar🇺🇸 · Michael L. Wagman🇺🇸

    The Wilson action for Euclidean lattice gauge theory defines a positive-definite transfer matrix that corresponds to a unitary lattice gauge theory time-evolution operator if analytically continued to real time. Hoshina, Fujii, and Kikukawa (HFK) recently pointed out that applying the Wilson action discretization to continuum real-time gauge theory does not lead to this, or any other, unitary theory and proposed an alternate real-time lattice gauge theory action that does result in a unitary real-time transfer matrix. The character expansion defining the HFK action is divergent, and in this work we apply a path integral contour deformation to obtain a convergent representation for U(1) HFK path integrals suitable for numerical Monte Carlo calculations. We also introduce a class of real-time lattice gauge theory actions based on analytic continuation of the Euclidean heat-kernel action. Similar divergent sums are involved in defining these actions, but for one action in this class this divergence takes a particularly simple form, allowing construction of a path integral contour deformation that provides absolutely convergent representations for U(1) and SU(N) real-time lattice gauge theory path integrals. We perform proof-of-principle Monte Carlo calculations of real-time U(1) and SU(3) lattice gauge theory and verify that exact results for unitary time evolution of static quark-antiquark pairs in (1 + 1)D are reproduced.

    ↳ hep-lathep-phhep-thnucl-th+1PRD(2021)·26 citations
19. 19*

    Neutrino Fast Flavor Conversions in Neutron-star Post-Merger Accretion Disks

    Xinyu Li🇨🇦 · Daniel M. Siegel🇨🇦

    A compact accretion disk may be formed in the merger of two neutron stars or of a neutron star and a stellar-mass black hole. Outflows from such accretion disks have been identified as a major site of rapid neutron-capture (r-process) nucleosynthesis and as the source of 'red' kilonova emission following the first observed neutron-star merger GW170817. We present long-term general-relativistic radiation magnetohydrodynamic simulations of a typical post-merger accretion disk at initial accretion rates of $\dot{M}\sim 1M_{\odot }{\text{s}}^{-1}$ over 400ms post-merger. We include neutrino radiation transport that accounts for effects of neutrino fast flavor conversions dynamically. We find ubiquitous flavor oscillations that result in a significantly more neutron-rich outflow, providing lanthanide and 3rd-peak r-process abundances similar to solar abundances. This provides strong evidence that post-merger accretion disks are a major production site of heavy r-process elements. A similar flavor effect may allow for increased lanthanide production in collapsars. The formalism presented here may also be used in simulations of core-collapse supernovae to explore whether fast conversions strengthen or weaken the explosion.

    ↳ astro-ph.HEastro-ph.SRgr-qchep-ph+1PRL(2021)·132 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.