Mon·Feb 27, 2017Monday·February 27, 2017

1. 01*

   A light sneutrino rescues the light stop

   Mikael Chala🇪🇸 · Antonio Delgado🇺🇸 · Germano Nardini🇨🇭 · Mariano Quiros🇪🇸

   Stop searches in supersymmetric frameworks with $R$-parity conservation usually assume the lightest neutralino to be the lightest supersymmetric particle. In this paper we consider an alternative scenario in which the left-handed tau sneutrino is lighter than neutralinos and stable at collider scales, but possibly unstable at cosmological scales. Moreover the (mostly right-handed) stop $\tilde{t}$ is lighter than all electroweakinos, and heavier than the scalars of the third generation doublet, whose charged component, $\tilde{\tau }$, is heavier than the neutral one, $\tilde{\nu }$. The remaining supersymmetric particles are decoupled from the stop phenomenology. In most of the parameter space, the relevant stop decays are only into $t\tilde{\tau }\tau$, $t\tilde{\nu }\nu$ and $b\tilde{\nu }\tau$ via off-shell electroweakinos. We constrain the branching ratios of these decays by recasting the most sensitive stop searches. Due to the "double invisible" kinematics of the $\tilde{t}\to t\tilde{\nu }\nu$ process, and the low efficiency in tagging the $t\tilde{\tau }\tau$ decay products, light stops are generically allowed. In the minimal supersymmetric standard model with $\sim$ 100 GeV sneutrinos, stops with masses as small as $\sim$ 350 GeV turn out to be allowed at 95% CL.

   hep-phJHEP(2017)·13 citations
2. 02*

   Event-by-event mean $p_{\mathrm{T}}$ fluctuations and transverse size of color flux tube generated in $p$-$p$ collisions at $\sqrt{s}$=0.90TeV

   Takeshi Osada🇯🇵 · Masamichi Ishihara🇯🇵

   We propose a novel phenomenological model of mean transverse momentum fluctuations based on the Geometrical Scaling hypothesis. Bose-Einstein correlations between two gluons generated from an identical color flux tube are taken into account as a source of the fluctuation. We calculate an event-by-event fluctuation measure $\sqrt{C_m}/⟨p_{\mathrm{T}}⟩$ and show that ALICE data observed at $\sqrt{s}=$0.90 TeV for $p$+$p$ collisions are reproduced. By fitting our model to the experimental data, we evaluate the transverse size of the color flux tube as a function of the multiplicity.

   hep-phnucl-thJ.Phys.G(2018)·13 citations
3. 03*

   Thermal phase transition with full 2-loop effective potential

   M. Laine🇨🇭 · M. Meyer🇩🇪 · G. Nardini🇨🇭

   Theories with extended Higgs sectors constructed in view of cosmological ramifications (gravitational wave signal, baryogenesis, dark matter) are often faced with conflicting requirements for their couplings; in particular those influencing the strength of a phase transition may be large. Large couplings compromise perturbative studies, as well as the high-temperature expansion that is invoked in dimensionally reduced lattice investigations. With the example of the inert doublet extension of the Standard Model (IDM), we show how a resummed 2-loop effective potential can be computed without a high-T expansion, and use the result to scrutinize its accuracy. With the exception of Tc, which is sensitive to contributions from heavy modes, the high-T expansion is found to perform well. 2-loop corrections weaken the transition in IDM, but they are moderate, whereby a strong transition remains an option.

   hep-phNPB(2017)·77 citations
4. 04*

   Local-duality QCD sum rules for strong isospin breaking in the decay constants of heavy-light mesons

   Wolfgang Lucha🇦🇹 · Dmitri Melikhov🇦🇹 · Silvano Simula🇮🇹

   We discuss the leptonic decay constants of heavy--light mesons by means of Borel QCD sum~rules in the local-duality (LD) limit of infinitely large Borel mass parameter. In this limit, for an appropriate choice of the invariant structures in the QCD correlation functions, all vacuum-condensate contributions vanish and all nonperturbative effects are contained in only one quantity, the effective threshold. We study properties of the LD effective thresholds in the limits of large heavy-quark mass $m_Q$ and small light-quark mass $m_q$. In the heavy-quark limit, we clarify the role played by the radiative corrections in the effective threshold for reproducing the pQCD expansion of the decay constants of pseudoscalar and vector mesons. We show that the dependence of the meson decay constants on $m_q$ arises predominantly (at the level of 70--80%) from the calculable $m_q$-dependence of the perturbative spectral densities. Making use of the lattice QCD results for the decay constants of nonstrange and strange pseudoscalar and vector heavy mesons, we obtain solid predictions for the decay constants of heavy--light mesons as functions of $m_q$ in the range from a few to 100 MeV and evaluate the corresponding strong isospin-breaking effects: $f_{D^{+}}-f_{D^0}=(0.96\pm 0.09)\mathrm{MeV}$, $f_{D^{\ast +}}-f_{D^{\ast 0}}=(1.18\pm 0.35)\mathrm{MeV}$, $f_{B^0}-f_{B^{+}}=(1.01\pm 0.10)\mathrm{MeV}$, $f_{B^{\ast 0}}-f_{B^{\ast +}}=(0.89\pm 0.30)\mathrm{MeV}$.

   hep-phEPJC(2018)·12 citations
5. 05*

   CP-symmetry of order 4 and its consequences

   I. P. Ivanov🇵🇹

   Extended Higgs sectors offer rich opportunities for various forms of CP-violation. Here, we describe a new form of CP-conservation and discuss its consequences. We give a concrete example of a three-Higgs-doublet model dubbed CP4-3HDM with a CP-symmetry of order 4 and no other other accidental symmetries. If the vacuum conserves this symmetry, the model is CP-conserving with pairwise mass-degenerate extra neutral Higgs bosons. These fields cannot be classified as CP-even or CP-odd but they can be combined into complex physical fields which are CP-half-odd, that is, they pick up the $i$ factor upon CP transformation. These CP-half-odd scalars can be Yukawa-coupled to the fermion bilinears in a CP-conserving way. We discuss fundamental and phenomenological features of the model, and stress a peculiar clash between the CP-symmetry and any convention for the particle-antiparticle assignment.

   hep-phJ.Phys.Conf.Ser.(2017)·3 citations
6. 06*

   Triple Regge exchange mechanisms of four-pion continuum production in the $pp\to pp{\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ reaction

   Radosław Kycia🇵🇱 · Piotr Lebiedowicz🇵🇱 · Antoni Szczurek🇵🇱 · Jacek Turnau🇵🇱

   We consider exclusive multi-peripheral production of four charged pions in proton-proton collisions at high energies with simultaneous exchange of three pomerons/reggeons. The amplitude(s) for the genuine $2\to 6$ process are written in the Regge approach. The calculation is performed with the help of the GenEx Monte Carlo code. Some corrections at low invariant masses in the two-body subsystems are necessary for application of the Regge formalism. We estimate the corresponding cross section and present differential distributions in rapidity, transverse momenta and two- and four-pion invariant masses. The cross section and the distributions depend on the value of the cut-off parameter of a form factor correcting amplitudes for off-shellness of $t$-channel pions. Rather large cross section is found for the whole phase space ($\sigma \sim$ 1-5 $\mu$b, including absorption corrections). Relatively large four-pion invariant masses are populated in the considered diffractive mechanism compared to other mechanisms discussed so far in the context of four-pion production. We investigate whether the triple Regge exchange processes could be identified with the existing LHC detectors. We consider the case of ATLAS and ALICE cuts. The ATLAS (or CMS) has better chances to identify the process in the region of large invariant masses $M_{4\pi }>10$ GeV. In the case of the ALICE experiment the considered mechanism competes with other mechanisms (production of $\sigma \sigma$, $\rho \rho$ pairs or single resonances) and cannot be unambiguously identified.

   hep-phPRD(2017)·11 citations
7. 07*

   Universal dual amplitudes and asymptotic expansions for $gg\to H$ and $H\to \gamma \gamma$ in four dimensions

   Felix Driencourt-Mangin🇪🇸 · German Rodrigo🇪🇸 · German F. R. Sborlini🇮🇹

   Though the one-loop amplitudes of the Higgs boson to massless gauge bosons are finite because there is no direct interaction at tree-level in the Standard Model, a well-defined regularization scheme is still required for their correct evaluation. We reanalyze these amplitudes in the framework of the four-dimensional unsubtraction and the loop-tree duality (FDU/LTD), and show how a local renormalization solves potential regularization ambiguities. The Higgs boson interactions are also used to illustrate new additional advantages of this formalism. We show that LTD naturally leads to very compact integrand expressions in four space-time dimensions of the one-loop amplitude with virtual electroweak gauge bosons. They exhibit the same functional form as the amplitudes with top quarks and charged scalars, thus opening further possibilities for simplifications in higher-order computations. Another outstanding application is the straightforward implementation of asymptotic expansions by using dual amplitudes. One of the main benefits of the LTD representation is that it is supported in a Euclidean space. This characteristic feature naturally leads to simpler asymptotic expansions.

   hep-phhep-thEPJC(2018)·61 citations
8. 08*

   Effect of sea quarks on the single-spin asymmetries $A_L^{W^{\pm }}$ in polarized pp collisions at RHIC

   Fang Tian🇨🇳 · Chang Gong🇨🇳 · Bo-Qiang Ma🇨🇳

   We calculate the single-spin asymmetries $A_L^{W^{\pm }}$ of $W^{\pm }$ bosons produced in polarized pp collisions with the valence part of the up and down quark helicity distributions modeled by the light-cone quark-spectator-diquark model while the sea part helicity distributions of the up and down quarks treated as parametrization. Comparing our results with those from experimental data at RHIC, we find that the helicity distributions of sea quarks play an important role in the determination of the shapes of $A_L^{W^{\pm }}$. It is shown that $A_L^{W^{-}}$ is sensitive to $\Delta \bar{u}$, while $A_L^{W^{+}}$ to $\Delta \bar{d}$ intuitively. The experimental data of the polarized structure functions and the sum of helicities are also important to constrain the sizes of quark helicity distributions both for the sea part and the valence part of the nucleon.

   hep-phNPA(2017)·4 citations
9. 09*

   Tensor-polarized structure function $b_1$ by convolution picture for deuteron

   W. Cosyn🇧🇪 · Yu-Bing Dong🇨🇳 · S. Kumano🇯🇵 · M. Sargsian🇺🇸

   There are polarized structure functions $b_{1-4}$ for the spin-1 deuteron. We calculated the leading-twist tensor structure function $b_1$ by using convolution description for the deuteron. We found large differences between our theoretical functions and HERMES experimental data on $b_1$. Although higher-twist effects should be considered in obtaining experimental $b_1$, it suggests a possible existence of new hadron physics mechanism for spin-1 hadrons. Furthermore, we found that there are significant distributions at large Bjorken $x$. In future, an experimental measurement is planned at JLab for $b_1$ and there is a possibility of a proton-deuteron Drell-Yan experiment at Fermilab with the tensor-polarized deuteron, so that further theoretical studies are needed for clarifying the physics origin of tensor structure in terms of quark and gluon degrees of freedom.

   hep-phhep-exhep-latnucl-ex+11 citation
10. 10*

    Revisiting $B\to K^{\ast }(\to K\pi )\nu \bar{\nu }$ decays

    Diganta Das🇮🇳 · Gudrun Hiller🇩🇪 · Ivan Nisandzic🇩🇪

    The rare decay $B\to K^{\ast }(\to K\pi )\nu \bar{\nu }$ is expected to play an important role in searches for physics beyond the Standard Model at the near future $B$-physics experiments. We investigate resonant and non-resonant backgrounds that arise beyond the narrow-width approximation for the $K^{\ast }$. Non-resonant $B\to K\pi \nu \bar{\nu }$ decays are analyzed in the region of low hadronic recoil, where $B\to K\pi$ form factors from Heavy-Hadron-Chiral-Perturbation Theory are available. In a Breit-Wigner-type model interference-induced effects in the $K^{\ast }$ signal region are found to be sizable, as large as $20\%$ in the branching ratio. Corresponding effects in the longitudinal polarization fraction $F_L$ are smaller, at most around few \%. Effects of the broad scalar states $K_0^{\ast }$ and $\kappa$ are at the level of percent in the branching fraction in the $K^{\ast }$ signal region and negligible in $F_L$. Since the backgrounds to $F_L$ are small this observable constitutes a useful probe of form factors calculations, or alternatively, of right-handed currents in the entire $q^2$-region. The forward-backward asymmetry in the $K\pi$-system, $A_{\mathrm{FB}\mathrm{L}}^K$, with normalization to the longitudinal decay rate probes predominantly S,P-wave interference free of short-distance coefficients and can therefore be used to control the resonant and non-resonant backgrounds.

    hep-phPRD(2017)·17 citations
11. 11*

    Electroweak stability and non-minimal coupling

    Marieke Postma🇳🇱 · Jorinde van de Vis🇳🇱

    The measured values of the Higgs and top quark mass indicate that the electroweak vacuum is metastable if there is no new physics below the Planck scale. This is at odds with a period of high scale inflation. A non-minimal coupling between the Higgs field and the Ricci scalar can stabilize the vacuum as it generates a large effective Higgs mass during inflation. We consider the effect of this coupling during preheating, when Higgs modes can be produced very efficiently due to the oscillating Ricci scalar. We compute their effect on the effective potential and the energy density. The Higgs excitations are defined with respect to the adiabatic vacuum. We study the adiabaticity conditions and find that the dependence of our results on the choice of the order of the adiabatic vacuum increases with time. For large enough coupling particle production is so efficient that the Higgs decays to the true vacuum before this is an issue. However, for smaller values of the Higgs-curvature coupling no definite statements can be made as the vacuum dependence is large.

    hep-phastro-ph.COJCAP(2017)·35 citations
12. 12*

    NNLO QCD counterterm contributions to $B$ \to $X_s\gamma$ for the physical value of $m_c$

    Mikolaj Misiak🇨🇭 · Abdur Rehman🇵🇰 · Matthias Steinhauser🇩🇪

    One of the most important O(${\alpha }_s^2$) corrections to the $B\to X_s\gamma$ branching ratio originates from interference of contributions from the current-current and photonic dipole operators. Its value has been estimated using an interpolation in the charm quark mass between the known results at $m_c=0$ and for $m_c\ll m_b/2$. An explicit calculation for the physical value of $m_c$ is necessary to remove the associated uncertainty. In the present work, we evaluate all the ultraviolet counterterm contributions that are relevant for this purpose.

    hep-phPLB(2017)·29 citations
13. 13*

    Electroweak oblique parameters as a probe of the trilinear Higgs boson self-interaction

    Graham D. Kribs🇺🇸 · Andreas Maier🇬🇧 · Heidi Rzehak🇩🇰 · Michael Spannowsky🇬🇧 · Philip Waite🇬🇧

    We calculate the two-loop contributions from a modified trilinear Higgs self-interaction, ${\kappa }_{\lambda }{\lambda }_{\mathrm{SM}}v{h}^3$, to the electroweak oblique parameters $S$ and $T$. Using the current bounds on $S$ and $T$ from electroweak measurements, we find the 95% C.L. constraint on the modified trilinear coupling to be $-14.0\le {\kappa }_{\lambda }\le 17.4$. The largest effects on $S$ and $T$ arise from two insertions of the modified trilinear coupling that result in $T/S\simeq -3/2$; remarkably, this is nearly parallel to the axis of the tightest experimental constraint in the $S$-$T$ plane. No contributions to $S$ and $T$ arise from a modified Higgs quartic coupling at two-loop order. These calculations utilized a gauge-invariant parameterization of the trilinear Higgs coupling in terms of higher dimensional operators $(H^{†}H{)}^n$ with $n\ge 3$. Interestingly, the bounds on ${\kappa }_{\lambda }$ that we obtain are comparable to constraints from di-Higgs production at the LHC as well as recent bounds from single Higgs production at the LHC.

    hep-phPRD(2017)·77 citations
14. 14*

    Application of the Covariant Spectator Theory to the study of heavy and heavy-light mesons

    Sofia Leitão🇵🇹 · Alfred Stadler🇵🇹 · M. T. Peña🇵🇹 · E. P. Biernat🇵🇹

    As an application of the Covariant Spectator Theory (CST) we calculate the spectrum of heavy-light and heavy-heavy mesons using covariant versions of a linear confining potential, a one- gluon exchange, and a constant interaction. The CST equations possess the correct one-body limit and are therefore well-suited to describe mesons in which one quark is much heavier than the other. We find a good fit to the mass spectrum of heavy-light and heavy-heavy mesons with just three parameters (apart from the quark masses). Remarkably, the fit parameters are nearly unchanged when we fit to experimental pseudoscalar states only or to the whole spectrum. Because pseudoscalar states are insensitive to spin-orbit interactions and do not determine spin-spin interactions separately from central interactions, this result suggests that it is the covariance of the kernel that correctly predicts the spin-dependent quark-antiquark interactions

    hep-phFew Body Syst.(2017)·4 citations
15. 15*

    Relativistic phenomenology of meson spectra with a covariant quark model in Minkowski space

    Sofia Leitão🇵🇹 · Alfred Stadler🇵🇹 · M. T. Peña🇵🇹 · E. P. Biernat🇵🇹

    In this work, we perform a covariant treatment of quark-antiquark systems. We calculate the spectra and wave functions using a formalism based on the Covariant Spectator Theory (CST). Our results not only reproduce very well the experimental data with a very small set of global parameters, but they also allow a direct test of the predictive power of covariant kernels.

    hep-phEPJ Web Conf.(2017)·1 citation
16. 16*

    Nuclear effects in leading neutron production

    B. Z. Kopeliovich🇨🇱 · I. K. Potashnikova🇨🇱 · Ivan Schmidt🇨🇱

    Absorptive corrections, known to suppress proton-neutron transitions with large fractional momentum $z\to 1$ in pp collisions, become dramatically strong on a nuclear target, and push the partial cross sections of leading neutron production to the very periphery of the nucleus. The mechanism of $\pi$-$a_1$ interference, which successfully explains the observed single-spin asymmetry in polarized $pp\to nX$, is extended to collisions of polarized protons with nuclei. Corrected for nuclear effects, it explains the observed single-spin azimuthal asymmetry of neutrons, produced in inelastic events, where the nucleus violently breaks up. The single-spin asymmetry is found to be negative and nearly $A$-independent.

    hep-phhep-exnucl-ex5 citations
17. 17*

    Enabling Forbidden Dark Matter

    James M. Cline🇨🇦 · Hongwan Liu🇺🇸 · Tracy R. Slatyer🇺🇸 · Wei Xue🇺🇸

    The thermal relic density of dark matter is conventionally set by two-body annihilations. We point out that in many simple models, $3\to 2$ annihilations can play an important role in determining the relic density over a broad range of model parameters. This occurs when the two-body annihilation is kinematically forbidden, but the $3\to 2$ process is allowed; we call this scenario "Not-Forbidden Dark Matter". We illustrate this mechanism for a vector portal dark matter model, showing that for a dark matter mass of $m_{\chi }\sim \text{MeV - 10 GeV}$, $3\to 2$ processes not only lead to the observed relic density, but also imply a self-interaction cross section that can solve the cusp/core problem. This can be accomplished while remaining consistent with stringent CMB constraints on light dark matter, and can potentially be discovered at future direct detection experiments.

    hep-phPRD(2017)·89 citations
18. 18*

    Effective Model of QCD Magnetic Monopoles From Numerical Study of One- and Two-Component Coulomb Quantum Bose Gases

    Adith Ramamurti🇺🇸 · Edward Shuryak🇺🇸

    Magnetic monopoles are suggested to play an important role in strongly coupled quark-gluon plasma (sQGP) near the deconfinement temperature. So far, their many-body treatment has only been done classically, with just binary scattering solved in quantum mechanics. In this paper we start quantum many-body studies of the monopole ensembles. Specifically, we carry out numerical simulations of the path integral for one- and two-component Coulomb Bose systems. We determine the relation between the critical temperature for the Bose-Einstein condensation phase transition $T_{\text{c}}$ and the Coulomb coupling strength using two methods, the classic finite-size scaling of the condensate and a lattice-tested method based on permutation cycles. For a one-component Coulomb Bose gas, we observe the same behavior of the critical temperature -- initially rising slightly then falling as interaction strength is increased -- as seen in the case of hard spheres; we also observe the same behavior for a two-component Coulomb Bose gas. We then calculate sets of radial correlation functions between the like and unlike charged particles. By matching those with the correlation functions previously calculated on the lattice, we derive an effective quantum model of color magnetic monopoles in QCD. From this matched model, we are able to extract the monopole contribution to QCD equation of state near $T_{\text{c}}$.

    hep-phhep-latnucl-thPRD(2017)·10 citations
19. 19*

    The Relation Between Fundamental Constants and Particle Physics Parameters

    Rodger I. Thompson🇺🇸

    The observed constraints on the variability of the proton to electron mass ratio $\mu$ and the fine structure constant $\alpha$ are used to establish constraints on the variability of the Quantum Chromodynamic Scale and a combination of the Higgs Vacuum Expectation Value and the Yukawa couplings. Further model dependent assumptions provide constraints on the Higgs VEV and the Yukawa couplings separately. A primary conclusion is that limits on the variability of dimensionless fundamental constants such as $\mu$ and $\alpha$ provide important constraints on the parameter space of new physics and cosmologies.

    ↳ astro-ph.COgr-qchep-phUniverse(2017)·3 citations
20. 20*

    New approach to initializing hydrodynamic fields and mini-jet propagation in quark-gluon fluids

    Michito Okai🇯🇵 · Koji Kawaguchi🇯🇵 · Yasuki Tachibana🇨🇳 · Tetsufumi Hirano🇯🇵

    We propose a new approach to initialize the hydrodynamic fields such as energy density distributions and four flow velocity fields in hydrodynamic modeling of high-energy nuclear collisions at the collider energies. Instead of matching the energy-momentum tensor or putting the initial conditions of quark-gluon fluids at a fixed initial time, we utilize a framework of relativistic hydrodynamic equations with source terms to describe the initial stage. Putting the energy and momentum loss rate of the initial partons into the source terms, we obtain hydrodynamic initial conditions dynamically. The resultant initial profile of the quark-gluon fluid looks highly bumpy as seen in the conventional event-by-event initial conditions. In addition, initial random flow velocity fields also are generated as a consequence of momentum deposition from the initial partons. We regard the partons that survive after the dynamical initialization process as the mini-jets and find sizable effects of both mini-jet propagation in the quark-gluon fluids and initial random transverse flow on the final momentum spectra and anisotropic flow observables. We perform event-by-event $(3+1)$-dimensional ideal hydrodynamic simulations with this new framework that enables us to describe the hydrodynamic bulk collectivity, parton energy loss, and interplay among them in a unified manner.

    ↳ nucl-thhep-phnucl-exPRC(2017)·60 citations
21. 21*

    Bound cyclic systems with the envelope theory

    C. Semay🇧🇪 · F. Buisseret🇧🇪

    Approximate but reliable solutions of a quantum system with $N$ identical particles can be easily computed with the envelope theory, also known as the auxiliary field method. This technique has been developed for Hamiltonians with arbitrary kinematics and one- or two-body potentials. It is adapted here for cyclic systems with $N$ identical particles, that is to say systems in which a particle $i$ has only an interaction with particles $i-1$ and $i+1$ (with $N+1\equiv 1$).

    ↳ quant-phhep-phFew Body Syst.(2017)·6 citations
22. 22*

    Probing QCD critical fluctuations from light nuclei production in relativistic heavy-ion collisions

    Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳 · Che Ming Ko🇺🇸 · Zhangbu Xu🇺🇸

    Based on the coalescence model for light nuclei production, we show that the yield ratio ${\mathcal{O}}_{\text{p-d-t}}=N_{{}^3\text{H}}{N}_p/N_{\text{d}}^2$ of $p$, d, and ${}^3$H in heavy-ion collisions is sensitive to the neutron relative density fluctuation $\Delta n=⟨(\delta n{)}^2⟩/⟨n{⟩}^2$ at kinetic freeze-out. From recent experimental data in central Pb+Pb collisions at $\sqrt{s_{NN}}=6.3$~GeV, $7.6$~GeV, $8.8$~GeV, $12.3$~GeV and $17.3$~GeV measured by the NA49 Collaboration at the CERN Super Proton Synchrotron (SPS), we find a possible non-monotonic behavior of $\Delta n$ as a function of the collision energy with a peak at $\sqrt{s_{NN}}=8.8$~GeV, indicating that the density fluctuations become the largest in collisions at this energy. With the known chemical freeze-out conditions determined from the statistical model fit to experimental data, we obtain a chemical freeze-out temperature of $\sim 144$MeV and baryon chemical potential of $\sim 385$MeV at this collision energy, which are close to the critical endpoint in the QCD phase diagram predicted by various theoretical studies. Our results thus suggest the potential usefulness of the yield ratio of light nuclei in relativistic heavy-ion collisions as a direct probe of the large density fluctuations associated with the QCD critical phenomena.

    ↳ nucl-thhep-phnucl-exPLB(2017)·136 citations
23. 23*

    Parity doubling in two-flavor SU(2) at high temperature

    Jong-Wan Lee🇬🇧 · Biagio Lucini🇬🇧 · Maurizio Piai🇬🇧

    We study the mass spectrum of mesons at high temperature in $SU(2)$ gauge theory with two flavors of Dirac fundamental fermions. Numerical simulations are carried out on anisotropic lattices using Wilson fermions, with lattice parameters tuned so that Euclidean symmetry is restored at low energy. We determine the pseudo-critical temperature $T_c$ using renormalized Polyakov loops. We calculate temporal and spatial meson correlation functions across $T_c$, and observe a clear sign of parity doublings above $T_c$ in both vector and scalar channels. The degeneracy between parity partners in the spectrum indicates that the enhanced $SU(4)\times U(1{)}_A$ global symmetry of the model is restored at high temperature.

    ↳ hep-lathep-phhep-thPoS(2016)·0 citations
24. 24*

    Gauss-Bonnet Chern-Simons gravitational wave leptogenesis

    Shinsuke Kawai🇰🇷 · Jinsu Kim🇰🇷

    The gravitational Chern-Simons term coupled to an evolving axion is known to generate lepton number through the gravitational anomaly. We examine this leptogenesis scenario in the presence of the Gauss-Bonnet term over and above the gravitational Chern-Simons term. We find that the lepton production can be exponentially enhanced. The Gauss-Bonnet term creates CP-violating instability of gravitational waves that may appear transiently after inflation, and during the period of instability elliptically polarized gravitational waves are exponentially amplified at sub-horizon scales. This instability does not affect the spectrum of the cosmic microwave background as it occurs at much shorter length scales. In a typical scenario based on natural inflation, the observed baryon asymmetry of the Universe corresponds to the UV cutoff scale at $10^{14-16}$ GeV.

    ↳ hep-thastro-ph.COgr-qchep-phPLB(2019)·69 citations
25. 25*

    General Relativity from Causality

    Mark P. Hertzberg🇺🇸 · McCullen Sandora🇺🇸

    We study large families of theories of interacting spin 2 particles from the point of view of causality. Although it is often stated that there is a unique Lorentz invariant effective theory of massless spin 2, namely general relativity, other theories that utilize higher derivative interactions do in fact exist. These theories are distinct from general relativity, as they permit any number of species of spin 2 particles, are described by a much larger set of parameters, and are not constrained to satisfy the equivalence principle. We consider the leading spin 2 couplings to scalars, fermions, and vectors, and systematically study signal propagation in all these other families of theories. We find that most interactions directly lead to superluminal propagation of either a spin 2 particle or a matter particle, and interactions that are subluminal generate other interactions that are superluminal. Hence, such theories of interacting multiple spin 2 species have superluminality, and by extension, acausality. This is radically different to the special case of general relativity with a single species of minimally coupled spin 2, which leads to subluminal propagation from sources satisfying the null energy condition. This pathology persists even if the spin 2 field is massive. We compare these findings to the analogous case of spin 1 theories, where higher derivative interactions can be causal. This makes the spin 2 case very special, and suggests that multiple species of spin 2 is forbidden, leading us to general relativity as essentially the unique internally consistent effective theory of spin 2.

    ↳ hep-thastro-ph.COgr-qchep-phJHEP(2017)·26 citations
26. 26*

    An asymptotically safe solution to the U(1) triviality problem

    Nicolai Christiansen🇩🇪 · Astrid Eichhorn🇩🇪

    We explore whether quantum gravity effects within the asymptotic safety paradigm can provide a predictive ultraviolet completion for Abelian gauge theories. We evaluate the effect of quantum gravity fluctuations on the running couplings in the gauge sector and discover an asymptotically safe fixed point of the Renormalization Group. In particular, if the strength of gravitational interactions remains below a critical strength, the minimal gauge coupling becomes asymptotically free. Further, we point out that a completely asymptotically free dynamics for the gauge field is impossible to achieve, as asymptotically safe quantum gravity necessarily induces nonvanishing higher-order interactions for the gauge field in the ultraviolet.

    ↳ hep-thgr-qchep-phPLB(2017)·142 citations
27. 27*

    Testing Lorentz invariance of dark matter with satellite galaxies

    Dario Bettoni🇩🇪 · Adi Nusser🇮🇱 · Diego Blas🇨🇭 · Sergey Sibiryakov🇨🇭

    We develop the framework for testing Lorentz invariance in the dark matter sector using galactic dynamics. We consider a Lorentz violating (LV) vector field acting on the dark matter component of a satellite galaxy orbiting in a host halo. We introduce a numerical model for the dynamics of satellites in a galactic halo and for a galaxy in a rich cluster to explore observational consequences of such an LV field. The orbital motion of a satellite excites a time dependent LV force which greatly affects its internal dynamics. Our analysis points out key observational signatures which serve as probes of LV forces. These include modifications to the line of sight velocity dispersion, mass profiles and shapes of satellites. With future data and a more detailed modeling these signatures can be exploited to constrain a new region of the parameter space describing the LV in the dark matter sector.

    ↳ astro-ph.COastro-ph.GAhep-phJCAP(2017)·14 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.