Mon·Apr 30, 2018Monday·April 30, 2018

1. 01*

   Complete electroweak two-loop corrections to Z boson production and decay

   Ievgen Dubovyk🇩🇪 · Ayres Freitas🇺🇸 · Janusz Gluza🇵🇱 · Tord Riemann🇵🇱 · Johann Usovitsch🇮🇪

   This article presents results for the last unknown two-loop contributions to the $Z$-boson partial widths and $Z$-peak cross-section. These are the so-called bosonic electroweak two-loop corrections, where "bosonic" refers to diagrams without closed fermion loops. Together with the corresponding results for the $Z$-pole asymmetries $A_l,A_b$, which have been presented earlier, this completes the theoretical description of $Z$-boson precision observables at full two-loop precision within the Standard Model. The calculation has been achieved through a combination of different methods: (a) numerical integration of Mellin-Barnes representations with contour rotations and contour shifts to improve convergence; (b) sector decomposition with numerical integration over Feynman parameters; (c) dispersion relations for sub-loop insertions. Numerical results are presented in the form of simple parameterization formulae for the total width, ${\Gamma }_{\mathrm{Z}}$, partial decay widths ${\Gamma }_{e,\mu },{\Gamma }_{\tau },{\Gamma }_{\nu },{\Gamma }_u,{\Gamma }_c,{\Gamma }_{d,s},{\Gamma }_b$, branching ratios $R_l,R_c,R_b$ and the hadronic peak cross-section, ${\sigma }_{\mathrm{had}}^0$. Theoretical intrinsic uncertainties from missing higher orders are also discussed.

   hep-phPLB(2018)·103 citations
2. 02*

   Chiral magnetic effect in the presence of an external axial-vector field

   Maxim Dvornikov (IZMIRAN, Tomsk State University)🇷🇺

   We study the excitation of the electric current of chiral fermions along the external magnetic field, known as the chiral magnetic effect, in the presence of the background axial-vector field. The calculation of the current is based on the exact solution of the Dirac equation for these fermions accounting for the external fields. First, this solution was obtained for massive particles and, then, we consider the chiral limit, which is used in the anomalous current computation. We obtain that, in this situation, the anomalous current does not contain the direct contribution of the axial-vector field. This result is compared with findings of other authors.

   hep-phhep-thPRD(2018)·11 citations
3. 03*

   Six Flavor Quark Matter

   Yang Bai🇺🇸 · Andrew J. Long🇺🇸

   Macroscopic nuggets of quark matter were proposed several decades ago as a candidate for dark matter. The formation of these objects in the early universe requires the QCD phase transition to be first order - a requirement that is not satisfied in the Standard Model where lattice simulations reveal a continuous crossover instead. In this article we point out that new physics may supercool the electroweak phase transition to below the QCD scale, and the QCD phase transition with six massless quarks becomes first-order. As a result, the quark nuggets composed of six-flavor quark matter (6FQM) may survive as a viable dark matter candidate. The size of a 6FQM nugget is estimated to be around $10^{10}$ grams in mass and $10^{-2}$ cm in radius. The calculated relic abundance of 6FQM nuggets is comparable to the observed dark matter energy density; therefore, this scenario provides a compelling explanation for the coincident energy densities of dark and baryonic matter. We have explored various potential signatures - including a gravitational wave background, gravitational lensing, and transient photon emission from collisions with compact stars and other nuggets - and demonstrated that the favored region of parameter space is still allowed by current constraints while discovery of 6FQM nugget dark matter may require new experimental probes.

   hep-phastro-ph.COJHEP(2018)·57 citations
4. 04*

   Vector-fermion dark matter

   Michal Iglicki🇵🇱

   In this thesis a simple extension of the Standard Model has been investigated. The Standard Model gauge group has been extended by an additional $U(1{)}_X$ group. The model introduces a new Higgs particle as well as three particles (a gauge boson and two Majorana fermions) that can be candidates for dark matter. The thesis also contains a discussion of derivation of the Boltzmann equation, involving detailed analysis of the assumptions. The equation has been used to investigate behaviour of the dark matter density in time, with respect to values of the parameters of the model.

   hep-ph4 citations
5. 05*

   Flavor structure from flavored Higgs mixing

   Masaki J. S. Yang🇯🇵

   In this paper, we suggest a simple model which induces realistic flavor structure from mixing of flavored Higgs doublets. The idea is based on the decoupling limit. In a model with many Higgs doublets, the mass eigenstates of scalars are linear combinations of Higgs doublets. If the mass matrix of Higgs fields has only one massless mode, and if the linear combination has flavor dependence, the induced Yukawa coupling will have nontrivial flavor structure. We suggest a mass matrix of flavored Higgs fields in a $U(2{)}_L\times U(2{)}_R$ toy model. An advantage of this model is that all of the elements in Yukawa matrix can be determined from renormalizable Higgs potential.

   hep-ph0 citations
6. 06*

   Fall to the Centre in Atom Traps and Point-Particle EFT for Absorptive Systems

   Ryan Plestid🇨🇦 · C.P. Burgess🇨🇦 · D H J O'Dell🇨🇦

   Polarizable atoms interacting with a charged wire do so through an inverse-square potential, $V=-g/r^2$. This system is known to realize scale invariance in a nontrivial way and to be subject to ambiguities associated with the choice of boundary condition at the origin, often termed the problem of `fall to the center'. Point-particle effective field theory (PPEFT) provides a systematic framework for determining the boundary condition in terms of the properties of the source residing at the origin. We apply this formalism to the charged-wire/polarizable-atom problem, finding a result that is not a self-adjoint extension because of absorption of atoms by the wire. We explore the RG flow of the complex coupling constant for the dominant low-energy effective interactions, finding flows whose character is qualitatively different when $g$ is above or below a critical value, $g_c$. Unlike the self-adjoint case, (complex) fixed points exist when $g>g_c$, which we show correspond to perfect absorber (or perfect emitter) boundary conditions. We describe experimental consequences for wire-atom interactions and the possibility of observing the anomalous breaking of scale invariance.

   hep-phcond-mat.quant-gasphysics.atom-phquant-phJHEP(2020)·14 citations
7. 07*

   Models of Total, Elastic and Diffractive Cross Sections

   Christine O. Rasmussen🇸🇪 · Torbjörn Sjöstrand🇸🇪

   The LHC has brought much new information on total, elastic and diffractive cross sections, which is not always in agreement with extrapolations from lower energies. The default framework in the Pythia event generator is one case in point. In this article we study and implement two recent models, as more realistic alternatives. Both describe total and elastic cross sections, whereas one also includes single diffraction. Noting some issues at high energies, a variant of the latter is proposed, and extended also to double and central diffraction. Further, the experimental definition of diffraction is based on the presence of rapidity gaps, which however also could be caused by colour reconnection in nondiffractive events, a phenomenon that is studied in the context of a specific model. Throughout comparisons with LHC and other data are presented.

   hep-phEPJC(2018)·31 citations
8. 08*

   Axion-Photon Conversion and Effects on 21cm Observation

   Takeo Moroi🇯🇵 · Kazunori Nakayama🇯🇵 · Yong Tang🇯🇵

   Recently the EDGES experiment reported an enhanced 21cm absorption signal in the radio wave observation, which may be interpreted as either anomalous cooling of baryons or heating of cosmic microwave background photons. In this paper, we pursue the latter possibility. We point out that dark radiation consisting of axion-like particles can resonantly convert into photons under the intergalactic magnetic field, which can effectively heat up the radiation in the frequency range relevant for the EDGES experiment. This may explain the EDGES anomaly.

   hep-phastro-ph.COPLB(2018)·75 citations
9. 09*

   Self-interacting dark matter with a stable vector mediator

   Michael Duerr🇩🇪 · Kai Schmidt-Hoberg🇩🇪 · Sebastian Wild🇩🇪

   Light vector mediators can naturally induce velocity-dependent dark matter self-interactions while at the same time allowing for the correct dark matter relic abundance via thermal freeze-out. If these mediators subsequently decay into Standard Model states such as electrons or photons however, this is robustly excluded by constraints from the Cosmic Microwave Background. We study to what extent this conclusion can be circumvented if the vector mediator is stable and hence contributes to the dark matter density while annihilating into lighter degrees of freedom. We find viable parts of parameter space which lead to the desired self-interaction cross section of dark matter to address the small-scale problems of the collisionless cold dark matter paradigm while being compatible with bounds from the Cosmic Microwave Background and Big Bang Nucleosynthesis observations.

   hep-phastro-ph.COJCAP(2018)·39 citations
10. 10*

    Quantum interference among heavy NMSSM Higgs bosons

    Biswaranjan Das🇮🇳 · Stefano Moretti🇬🇧 · Shoaib Munir🇰🇷 · Poulose Poulose🇮🇳

    In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), it is possible to have strong mass degeneracies between the new singlet-like scalar and the heavy doublet-like scalar, as well as between the singlet-like and doublet-like pseudoscalar Higgs states. When the difference in the masses of such states is comparable with the sum of their widths, the quantum mechanical interference between their propagators can become significant. We study these effects by taking into account the full Higgs boson propagator matrix in the calculation of the production process of ${\tau }^{+}{\tau }^{-}$ pairs in gluon fusion at the Large Hadron Collider (LHC). We find that, while these interference effects are sizeable, they are not resolvable in terms of the distributions of differential cross sections, owing to the poor detector resolution of the ${\tau }^{+}{\tau }^{-}$ invariant mass. They are, however, identifiable via the inclusive cross sections, which are subject to significant variations with respect to the standard approaches, wherein the propagating Higgs bosons are treated independently from one another. We quantify these effects for several representative benchmark points, extracted from a large set of points, obtained by numerical scanning of the NMSSM parameter space, that satisfy the most important experimental constraints currently available.

    hep-phPRD(2018)·3 citations
11. 11*

    Revisiting $A_4$ model for leptons in light of NuFIT 3.2

    Sin Kyu Kang🇰🇷 · Yusuke Shimizu🇯🇵 · Kenta Takagi🇯🇵 · Shunya Takahashi🇯🇵 · Morimitsu Tanimoto🇯🇵

    We revisit the $A_4$ model for leptons in light of new result of NuFIT 3.2. We introduce a new flavon $\eta$ transforming as $A_4$ singlet $1^{\prime }$ or $1"$ which couples to both charged leptons and neutrinos in next-leading order operators. The model consists of the five parameters: the lightest neutrino mass $m_1$, the vacuum expectation value of $\eta$ and three CP violating phases after inputting the experimental values of $\Delta m_{\mathrm{atm}}^2$ and $\Delta m_{\mathrm{sol}}^2$. The model with the $1"$ singlet flavon gives the prediction of ${\sin }^2{\theta }_{12}$ around the best fit of NuFIT 3.2 while keeping near the maximal mixing of ${\theta }_{23}$. Inputting the experimental mixing angles with the $1\sigma$ error-bar, the Dirac CP violating phase is clearly predicted to be $|{\delta }_{\text{CP}}|=50^{\circ }-120^{\circ }$, which will be tested by the precise observed value in the future. In order to get the best fit value ${\sin }^2{\theta }_{23}=0.538$, the sum of three neutrino masses is predicted to be larger than $90$meV. The cosmological observation for the sum of neutrino masses will also provide a crucial test of our predictions. It is remarked that the model is consistent with the experimental data only for the normal hierarchy of neutrino masses.

    hep-phhep-exPTEP(2018)·28 citations
12. 12*

    $\Delta L\ge 4$ processes

    Renato M. Fonseca🇪🇸 · Martin Hirsch🇪🇸

    We discuss the experimental prospects for observing processes which violate lepton number ($\Delta L$) in four units (or more). First, we reconsider neutrinoless quadruple beta decay, deriving a model independent and very conservative lower limit on its half-life of the order of $10^{41}$ ys for ${}^{150}$Nd. This renders quadruple beta decay unobservable for any feasible experiment. We then turn to a more general discussion of different possible low-energy processes with values of $\Delta L\ge 4$. A simple operator analysis leads to rather pessimistic conclusions about the observability at low-energy experiments in all cases we study. However, the situation looks much brighter for accelerator experiments. For two example models with $\Delta L=4$ and another one with $\Delta L=5$, we show how the LHC or a hypothetical future pp-collider, such as the FCC, could probe multi-lepton number violating operators at the TeV scale.

    hep-phPRD(2018)·11 citations
13. 13*

    Coordinate space calculation of two- and three-loop sunrise-type diagrams, elliptic functions and truncated Bessel integral identities

    S. Groote🇪🇪 · J.G. Körner🇩🇪

    We integrate three-loop sunrise-type vacuum diagrams in $D_0=4$ dimensions with four different masses using configuration space techniques. The finite parts of our results are in numerical agreement with corresponding three-loop calculations in momentum space. Using some of the closed form results of the momentum space calculation we arrive at new integral identities involving truncated integrals of products of Bessel functions. For the non-degenerate finite two-loop sunrise-type vacuum diagram in $D_0=2$ dimensions we make use of the known closed form $p$-space result to express the moment of a product of three Bessel functions in terms of a sum of Claussen polylogarithms. Using results for the nondegenerate two-loop sunrise diagram from the literature in $D_0=2$ dimensions we obtain a Bessel function integral identity in terms of elliptic functions.

    hep-phhep-thNPB(2019)·20 citations
14. 14*

    Neutrino mixing and General Covariance in the inverse beta decay

    M. Blasone🇮🇹 · G. Lambiase🇮🇹 · G. G. Luciano🇮🇹 · L. Petruzziello🇮🇹

    We review recent developments on the role of neutrino mixing in the inverse beta decay of accelerated protons. We show that calculations in the inertial and comoving frames agree (thus preserving General Covariance) only when taking neutrino asymptotic states to be flavor (rather than mass) eigenstates. Our conclusions are valid in the approximation in which Pontecorvo states are correctly representing neutrino flavor states. We speculate about the general case involving exact flavor states and finally comment on other approaches recently appeared in literature.

    hep-phhep-thPoS(2018)·12 citations
15. 15*

    ${\alpha }_s$ from the Lattice Hadronic Vacuum Polarisation

    Renwick J. Hudspith🇨🇦 · Randy Lewis🇨🇦 · Kim Maltman🇨🇦 · Eigo Shintani🇯🇵

    We present a determination of the QCD coupling constant, ${\alpha }_s$, obtained by fitting lattice results for the flavour $ud$ hadronic vacuum polarisation function to continuum perturbation theory. We use $n_f=2+1$ flavours of Domain Wall fermions generated by the RBC/UKQCD collaboration and three lattice spacings $a^{-1}=1.79,2.38$ and $3.15\text{GeV}$. Several sources of potential systematic error are identified and dealt with. After fitting and removing expected leading cut-off effects, we find for the five-flavour $\overline{\text{MS}}$ coupling the value ${\alpha }_s(M_Z)=0.1181(27{)}_{-22}^{+8}$, where the first error is statistical and the second systematic.

    ↳ hep-lathep-ph20 citations
16. 16*

    Backreaction of axion coherent oscillations

    Mor Rozner🇮🇱 · Vincent Desjacques🇮🇱

    We investigate how coherent oscillations backreact on the evolution of the condensate wave function of ultra-light axions in the non-relativistic regime appropriate to cosmic structure formation. The coherent oscillations induce higher harmonics beyond the fundamental mode considered so far when a self-interaction is present, and imprint oscillations in the gravitational potential. We emphasize that the effective self-interaction felt by the slowly-varying envelop of the wave function always differs from the bare Lagrangian interaction potential. We also point out that, in the hydrodynamical formulation of the Gross-Pitaevskii equation, oscillations in the gravitational potential result in an attractive force that counteracts the effect of the quantum pressure arising from the strong delocalization of the particles. Since these effects become significant on physical scales less than the (large) Compton wavelength of the particle, they are presumably not very relevant on the mildly nonlinear scales traced by intergalactic neutral hydrogen for axion masses consistent with the bounds from the Lyman-$\alpha$ forest. However, they might affect the formation of virialized cosmological structures and their stability.

    ↳ astro-ph.COhep-phPRD(2018)·4 citations
17. 17*

    Attractor Behaviour in Multifield Inflation

    Pedro Carrilho🇬🇧 · David Mulryne🇬🇧 · John Ronayne🇬🇧 · Tommi Tenkanen🇬🇧

    We study multifield inflation in scenarios where the fields are coupled non-minimally to gravity via ${\xi }_I({\varphi }^I{)}^n{g}^{\mu \nu }{R}_{\mu \nu }$, where ${\xi }_I$ are coupling constants, ${\varphi }^I$ the fields driving inflation, $g_{\mu \nu }$ the space-time metric, $R_{\mu \nu }$ the Ricci tensor, and $n>0$. We consider the so-called $\alpha$-attractor models in two formulations of gravity: in the usual metric case where $R_{\mu \nu }=R_{\mu \nu }(g_{\mu \nu })$, and in the Palatini formulation where $R_{\mu \nu }$ is an independent variable. As the main result, we show that, regardless of the underlying theory of gravity, the field-space curvature in the Einstein frame has no influence on the inflationary dynamics at the limit of large ${\xi }_I$, and one effectively retains the single-field case. However, the gravity formulation does play an important role: in the metric case the result means that multifield models approach the single-field $\alpha$-attractor limit, whereas in the Palatini case the attractor behaviour is lost also in the case of multifield inflation. We discuss what this means for distinguishing between different models of inflation.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2018)·79 citations
18. 18*

    Critical phenomena of charged Einstein-Gauss-Bonnet black holes with charged scalar hair

    Yves Brihaye🇧🇪 · Betti Hartmann🇧🇷

    Einstein-Gauss-Bonnet-gravity (EGB) coupled minimally to a $U(1)$ gauged, massive scalar field possesses -- for appropriate choices of the $U(1)$ charge -- black hole solutions that carry charged scalar hair if the frequency of the harmonic time-dependence of the scalar field is equal to the upper bound on the superradiant frequency. The existence of these solutions has first been discussed in \cite{Grandi:2017zgz}. In this paper, we demonstrate that the critical value of the scalar charge results from the requirement of non-extremality of the charged black hole solutions and the fact that the scalar field should not escape to infinity. Moreover, we investigate the hairy black holes in more detail and demonstrate that the branch of these solutions joins the branch of the corresponding charged EGB black hole for vanishing scalar field, but is {\it not} connected to the branch of boson stars in the limit of vanishing horizon radius. This indicates that it is unlikely that these black holes appear from the collapse of the corresponding boson stars. Finally, we prove a No-hair theorem for charged scalar fields with harmonic time-dependence for static, spherically symmetric, asymptotically flat electro-vacuum black holes in $d$ space-time dimensions and hence demonstrate that the GB term is crucial for the existence of the hairy black holes discussed in this paper.

    ↳ gr-qchep-phhep-thClass.Quant.Grav.(2018)·11 citations
19. 19*

    Net baryon diffusion in fluid dynamic simulations of relativistic heavy-ion collisions

    Gabriel S. Denicol🇧🇷 · Charles Gale🇨🇦 · Sangyong Jeon🇨🇦 · Akihiko Monnai🇫🇷 · Björn Schenke🇺🇸 · Chun Shen🇺🇸

    A hybrid (hydrodynamics + hadronic transport) theoretical framework is assembled to model the bulk dynamics of relativistic heavy-ion collisions at energies accessible in the Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) and the NA61/SHINE experiment at CERN. The system's energy-momentum tensor and net baryon current are evolved according to relativistic hydrodynamics with finite shear viscosity and non-zero net baryon diffusion. Our hydrodynamic description is matched to a hadronic transport model in the dilute region. With this fully integrated theoretical framework, we present a pilot study of the hadronic chemistry, particle spectra, and anisotropic flow. Phenomenological effects of a non-zero net-baryon current and its diffusion on hadronic observables are presented for the first time. The importance of the hadronic transport phase is also investigated.

    ↳ nucl-thhep-phnucl-exPRC(2018)·217 citations
20. 20*

    Color screening in (2+1)-flavor QCD

    TUMQCD collaboration: Alexei Bazavov (1)🇺🇸 · Nora Brambilla (2,3)🇩🇪 · Peter Petreczky (4)🇺🇸 · Antonio Vairo (2)🇩🇪 · Johannes Heinrich Weber (1,2,5) ((1) Department of Computational Mathematics, Science and Engineering and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA (2) Physik Department, Technische Universit ät München, D-85748 Garching, Germany (3) Institute of Advanced Studies, Technische Universität München, D-85748 Garching, Germany (4) Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA (5) Exzellenzcluster Universe, Technische Universität M ünchen, D-85748 Garching, Germany)🇩🇪

    We study correlation functions of spatially separated static quark-antiquark pairs in (2+1)-flavor QCD in order to investigate onset and nature of color screening at high temperatures. We perform lattice calculations in a wide temperature range, $140\le T\le 5814\mathrm{MeV}$, using the highly improved staggered quark action and several lattice spacings to control discretization effects. By comparing at high temperatures our lattice results to weak-coupling calculations as well as to the zero temperature result for the energy of a static quark-antiquark pair, we observe that color screening sets in at $rT\approx 0.3$. Furthermore, we also observe that in the range $0.3\lesssim rT\lesssim 0.6$ weak-coupling calculations in the framework of suitable effective field theories provide an adequate picture of color screening.

    ↳ hep-lathep-phhep-thnucl-thPRD(2018)·104 citations
21. 21*

    Positivity Bounds for Massive Spin-1 and Spin-2 Fields

    Claudia de Rham🇬🇧 · Scott Melville🇬🇧 · Andrew J. Tolley🇺🇸 · Shuang-Yong Zhou🇬🇧

    We apply the recently developed positivity bounds for particles with spin, applied away from the forward limit, to the low energy effective theories of massive spin-1 and spin-2 theories. For spin-1 theories, we consider the generic Proca EFT which arises at low energies from a heavy Higgs mechanism, and the special case of a charged Galileon for which the EFT is reorganized by the Galileon symmetry. For spin-2, we consider generic ${\Lambda }_5$ massive gravity theories and the special `ghost-free' ${\Lambda }_3$ theories. Remarkably we find that at the level of 2-2 scattering, the positivity bounds applied to ${\Lambda }_5$ massive gravity theories impose the special tunings which generate the ${\Lambda }_3$ structure. For ${\Lambda }_3$ massive gravity theories, the island of positivity derived in the forward limit appears relatively stable against further bounds.

    ↳ hep-thastro-ph.COgr-qchep-phJHEP(2019)·152 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.