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High Energy Physics - Phenomenology (hep-ph) updates on the e-print archive
  • The Weak Scale from Weak Gravity. (arXiv:1904.08426v1 [hep-ph])

    Authors: Nathaniel Craig, Isabel Garcia Garcia, Seth Koren

    We explore the prospects for bounding the weak scale using the weak gravity conjecture (WGC), addressing the hierarchy problem by violating the expectations of effective field theory. Building on earlier work by Cheung and Remmen, we construct models in which a super-extremal particle satisfying the electric WGC for a new Abelian gauge group obtains some of its mass from the Higgs, setting an upper bound on the weak scale as other UV-insensitive parameters are held fixed. Avoiding undue sensitivity of the weak scale to the parameters entering the bound implies that the super-extremal particle must lie at or below the weak scale. While the magnetic version of the conjecture implies additional physics entering around the same scale, we demonstrate that this need not correspond to a cutoff for the Higgs potential or otherwise trivialize the bound. We stress that linking the WGC to the weak scale necessarily involves new light particles coupled to the Higgs, implying a variety of experimentally accessible signatures including invisible Higgs decays and radiative corrections in the electroweak sector. These models also give rise to natural dark matter candidates, providing additional paths to discovery. In particular, collective effects in the dark matter plasma may provide a telltale sign of the Abelian gauge group responsible for bounding the weak scale.

  • Dark Matter Strikes Back at the Galactic Center. (arXiv:1904.08430v1 [astro-ph.HE])

    Authors: Rebecca K. Leane, Tracy R. Slatyer

    Statistical evidence has previously suggested that the Galactic Center GeV Excess (GCE) originates largely from point sources, and not from annihilating dark matter. We examine the impact of unmodeled source populations on identifying the true origin of the GCE using non-Poissonian template fitting (NPTF) methods. In a proof-of-principle example with simulated data, we discover that unmodeled sources in the Fermi Bubbles can lead to a dark matter signal being misattributed to point sources by the NPTF. We discover striking behavior consistent with a mismodeling effect in the real Fermi data, finding that large artificial injected dark matter signals are completely misattributed to point sources. Consequently, we conclude that dark matter may provide a dominant contribution to the GCE after all.

  • No strong $CP$ violation up to the one-loop level in a two-Higgs-doublet model. (arXiv:1904.08438v1 [hep-ph])

    Authors: P.M. Ferreira, L. Lavoura

    We put forward a two-Higgs-doublet model, furnished with a $Z_3$ symmetry, wherein $CP$ is conserved in the dimension-four terms of the Lagrangian and is softly broken in the scalar potential.

    The new particles of our model are one neutral scalar $H$, one neutral pseudoscalar $A$, and two charged scalars $H^\pm$.

    In our model the only locus of $CP$ violation is the CKM matrix.

    Strong $CP$ violation is absent both at the tree and one-loop levels. We work out the phenomenological constraints on our model, which features flavour-changing neutral Yukawa interactions, showing that the new scalar particles may in some cases be lighter than 500\,GeV.

  • Discovering True Muonium at LHCb. (arXiv:1904.08458v1 [hep-ph])

    Authors: Xabier Cid Vidal, Philip Ilten, Jonathan Plews, Brian Shuve, Yotam Soreq

    We study the potential of the LHCb experiment to discover, for the first time, the $\mu^+\mu^-$ true muonium bound state. We propose a search for the vector $1^3S_1$ state, $\mathcal{T\!M}$, which kinetically mixes with the photon and dominantly decays to $e^+e^-$. We demonstrate that a search for $\eta \to \gamma \mathcal{T\!M}$, $\mathcal{T\!M}\to e^+e^-$ in a displaced vertex can exceed a significance of 5 standard deviations assuming statistical uncertainties. We present two possible searches: an inclusive search for the $e^+e^-$ vertex, and an exclusive search which requires an additional photon and a reconstruction of the $\eta$ mass.

  • Portraying Double Higgs at the Large Hadron Collider. (arXiv:1904.08549v1 [hep-ph])

    Authors: Jeong Han Kim, Minho Kim, Kyoungchul Kong, Konstantin T. Matchev, Myeonghun Park

    We examine the discovery potential for double Higgs production at the high luminosity LHC in the final state with two $b$-tagged jets, two leptons and missing transverse momentum. Although this dilepton final state has been considered a difficult channel due to the large backgrounds, we argue that it is possible to obtain sizable signal significance, by adopting a deep learning framework making full use of the relevant kinematics along with the jet images from the Higgs decay. For the relevant number of signal events we obtain a substantial increase in signal sensitivity over existing analyses. We discuss relative improvements at each stage and the correlations among the different input variables for the neutral network. The proposed method can be easily generalized to the semi-leptonic channel of double Higgs production, as well as to other processes with similar final states.

  • Vacuum Decay in Real Time and Imaginary Time Formalisms. (arXiv:1904.08565v1 [hep-th])

    Authors: Mark P. Hertzberg, Masaki Yamada

    We analyze vacuum tunneling in quantum field theory in a general formalism by using the Wigner representation. In the standard instanton formalism, one usually approximates the initial false vacuum state by an eigenstate of the field operator, imposes Dirichlet boundary conditions on the initial field value, and evolves in imaginary time. This approach does not have an obvious physical interpretation. However, an alternative approach does have a physical interpretation: in quantum field theory, tunneling can happen via classical dynamics, seeded by initial quantum fluctuations in both the field and its momentum conjugate, which was recently implemented in Ref. [1]. We show that the Wigner representation is a useful framework to calculate and understand the relationship between these two approaches. We find there are two, related, saddle point approximations for the path integral of the tunneling process: one corresponds to the instanton solution in imaginary time and the other one corresponds to classical dynamics from initial quantum fluctuations in real time. The classical approximation for the dynamics of the latter process is justified only in a system with many degrees of freedom, as can appear in field theory due to high occupancy of nucleated bubbles, while it is not justified in single particle quantum mechanics, as we explain. We mention possible applications of the real time formalism, including tunneling when the instanton vanishes, or when the imaginary time contour deformation is not possible, which may occur in cosmological settings.

  • The $\phi(2170)$ production in the process $\gamma p\to \eta \phi p$. (arXiv:1904.08569v1 [hep-ph])

    Authors: Chen-Guang Zhao, Guan-Ying Wang, Guan-Nan Li, En Wang, De-Min Li

    We have studied the $\gamma p\to \eta \phi p$ reaction within the effective Lagrangian approach, by considering the contribution of the intermediate state $\phi(2170)$ production, and the background contributions of $t$-channel $\pi^0$ and $\eta$ mesons exchanges with the intermediate states $N$ and $N(1535)$. Our calculations show that there may be a peak, at least a bump structure around 2180 MeV associated to the resonance $\phi(2170)$ in the $\eta\phi$ mass distribution. We suggest to search for the resonance $\phi(2170)$ in this reaction, which would be helpful to shed light on its nature.

  • Effective gauge theories of superfluidity with topological order. (arXiv:1904.08570v1 [hep-th])

    Authors: Yuji Hirono, Yuya Tanizaki

    We discuss the low-energy dynamics of superfluidity with topological order in $(3+1)$ spacetime dimensions. We generalize a topological $BF$ theory by introducing a non-square $K$ matrix, and this generalized $BF$ theory can describe massless Nambu-Goldstone bosons and anyonic statistics between vortices and quasiparticles. We discuss the general structure of discrete and continuous higher-form symmetries in this theory, which can be used to classify quantum phases. We describe how to identify the appearance of topological order in such systems and discuss its relation to a mixed 't Hooft anomaly between discrete higher-form symmetries. We apply this framework to the color-flavor locked phase of dense QCD, which shows anyonic particle-vortex statistics while no topological order appears. An explicit example of superfluidity with topological order is discussed.

  • Gravitino condensate in $N=1$ supergravity coupled to the $N=1$ supersymmetric Born-Infeld theory. (arXiv:1904.08586v1 [hep-th])

    Authors: Ryotaro Ishikawa, Sergei V. Ketov

    The $N=1$ supersymmetric Born-Infeld theory coupled to $N=1$ supergravity in four spacetime dimensions is studied in the presence of a cosmological term with spontaneous supersymmetry breaking. The consistency is achieved by compensating a negative contribution to the cosmological term from the Born-Infeld theory by a positive contribution originating from the gravitino condensate. This leads to an identification of the Born-Infeld scale with the supersymmetry breaking scale. The dynamical formation of the gravitino condensate in supergravity is reconsidered and the induced one-loop effective potential is derived. Slow roll cosmological inflation with the gravitino condensate as the inflaton (near the maximum of the effective potential) is viable against the Planck 2018 data and can lead to the inflationary (Hubble) scale as high as $10^{12}$ GeV. Uplifting the Minkowski vacuum (after inflation) to a de Sitter vacuum (dark energy) is possible by the use of the alternative Fayet-Iliopoulos term. Some major physical consequences of our scenario to reheating are briefly discussed also.

  • Phase ambiguity of the measure for continuum Majorana fermions. (arXiv:1904.08600v1 [hep-lat])

    Authors: Maarten Golterman, Yigal Shamir

    Integrating over a continuum Majorana fermion formally yields a functional pfaffian. We show that the phase of this pfaffian is ambiguous, as it depends on the choice of basis. This ambiguity is naturally resolved within a non-perturbative lattice definition, allowing us to discuss the relation between the phase of the lattice pfaffian and the effective $\theta$ angle of the theory. We also resolve an apparent paradox regarding the induced $\theta$ angle when a theory of $N$ Dirac fermions in a real representation of the gauge group is re-expressed in terms of $2N$ Majorana fermions. We discuss how all this is reflected in chiral perturbation theory.

  • Mean-field potential effects in the cumulants of baryons from central Au+Au collision at $E_{lab}$= 1.23 GeV$/$nucleon. (arXiv:1904.08602v1 [nucl-th])

    Authors: Yongjia Wang, Yunxiao Ye, QIngfeng Li

    The cumulants of baryon multiplicity distribution in relativistic heavy-ion collisions (HICs) have attracted considerable attention recently. It has been conjectured that they may serve as a promising observable to detect the critical end point in the QCD phase diagram, while the cumulants in HICs at intermediate energies have not been widely studied to date. How to interpret the cumulants data at intermediate energies and compare with the data at relativistic energies is now being actively discussed. Both meam-field potential and clustering are highly important to HICs at intermediate energies. In this talk, we discuss these effects on the cumulant ratios of baryon number distributions in Au+Au collisions at beam energies of 1.23 GeV$/$nucleon which have been currently performed by the HADES Collaboration at GSI. Within the newest version of the ultrarelativistic quantum molecular dynamics (UrQMD) model, calculations with different mean field potentials as well as without mean field potential are performed. It is found that the mean field potential enhances fluctuations in the momentum space during the expanding stage, especially in a small rapidity acceptance window. The enhancement of cumulant ratios for free protons is suppressed compared with that for all baryons.

  • Two-particle angular correlations in heavy ion collisions from a multiphase transport model. (arXiv:1904.08603v1 [nucl-th])

    Authors: Liu-Yao Zhang, Jin-Hui Chen, Zi-Wei Lin, Yu-Gang Ma, Song Zhang

    We extend our earlier study on two-particle angular correlations in $pp$ collisions at low transverse momentum ($p_T$) to $p$-Pb, Pb-Pb and Au-Au collisions at RHIC and LHC energies. We mainly use the string melting version of a multiphase transport model with improved quark coalescence for this study. We start from the analysis of $\pi^{\pm}$, $K^{\pm}$ and $p$($\bar{p}$) $p_T$ and rapidity distributions at different centralities. We then focus on two-particle angular correlations in $p$-Pb collisions at $\mathrm{\sqrt{s_{NN}} = 5.02}$ TeV and Pb-Pb collisions at $\mathrm{\sqrt{s_{NN}}= 2.76}$ TeV. For $p$-Pb collisions, a near side depression in the angular correlation is observed for low $p_T$ proton pairs and $\Lambda$ pairs but not for pion pairs or kaon pairs, similar to our earlier finding for $pp$ collisions at $\mathrm{\sqrt{s}= 7}$ TeV. This is also the case for very low multiplicity Pb-Pb and Au-Au collisions. We also find that parton interactions and the improved quark coalescence are mainly responsible for the depression feature in baryon pair angular correlations. However, no such baryon-baryon anti-correlations are observed in Pb-Pb and Au-Au collisions at higher multiplicities. Therefore our results suggest that low $p_T$ baryon-baryon angular anti-correlations have a strong multiplicity dependence.

  • Emergence of hydrodynamical behavior in expanding quark-gluon plasmas. (arXiv:1904.08677v1 [nucl-th])

    Authors: Jean-Paul Blaizot, Li Yan

    We use a set of simple angular moments to solve the Boltzmann equation in the relaxation time approximation for a boost invariant longitudinally expanding gluonic plasma. The transition from the free streaming regime at early time to the hydrodynamic regime at late time is well captured by the first two-moments, corresponding to the monopole and quadrupole components of the momentum distribution, or equivalently to the energy density and the difference between the longitudinal and the transverse pressures. We relate this property to the existence of fixed points in the infinite hierarchy of equations satisfied by the moments. These fixed points are already present in the two-moment truncations and are only moderately affected by the coupling to higher moments. Collisions contribute to a damping of all the non trivial moments. At late time, when the hydrodynamic regime is entered, only the monopole and quadrupole moments are significant and remain strongly coupled, the decay of the quadrupole moment being delayed by the expansion, causing in turn a delay in the full isotropization of the system. The two-moment truncation contains second order viscous hydrodynamics, in its various variants, and third order hydrodynamics, together with explicit values of the relevant transport coefficients, can be easily obtained from the three-moment truncation.

  • $B$-hadron fragmentation functions at next-to-next-to-leading order from global analysis of $e^+e^-$ annihilation data. (arXiv:1904.08718v1 [hep-ph])

    Authors: Maral Salajegheh, S. Mohammad Moosavi Nejad, Hamzeh Khanpour, Bernd A. Kniehl, Maryam Soleymaninia

    We present nonperturbative fragmentation functions (FFs) for bottom-flavored ($B$) hadrons both at next-to-leading (NLO) and, for the first time, at next-to-next-to-leading order (NNLO) in the $\overline{\mathrm{MS}}$ factorization scheme with five massless quark flavors. They are determined by fitting all available experimental data of inclusive single $B$-hadron production in $e^+e^-$ annihilation, from the ALEPH, DELPHI, and OPAL Collaborations at CERN LEP1 and the SLD Collaboration at SLAC SLC.

    The uncertainties in these FFs as well as in the corresponding observables are estimated using the Hessian approach.

    We perform comparisons with available NLO sets of $B$-hadron FFs.

    We apply our new FFs to generate theoretical predictions for the energy distribution of $B$ hadrons produced through the decay of unpolarized or polarized top quarks, to be measured at the CERN LHC.

  • Light-meson leptonic decay rates in lattice QCD+QED. (arXiv:1904.08731v1 [hep-lat])

    Authors: M. Di Carlo, D. Giusti, V. Lubicz, G. Martinelli, C.T. Sachrajda, F. Sanfilippo, S. Simula, N. Tantalo

    The leading electromagnetic (e.m.) and strong isospin-breaking corrections to the $\pi^+ \to \mu^+ \nu[\gamma]$ and $K^+ \to \mu^+ \nu[\gamma]$ leptonic decay rates are evaluated for the first time on the lattice. The results are obtained using gauge ensembles produced by the European Twisted Mass Collaboration with $N_f = 2 + 1 + 1$ dynamical quarks. The relative leading-order e.m. and strong isospin-breaking corrections to the decay rates are 1.53(19) % for $\pi_{\mu 2}$ decays and 0.24(10) % for $K_{\mu 2}$ decays. Using the experimental values of the $\pi_{\mu 2}$ and $K_{\mu 2}$ decay rates and updated lattice QCD results for the pion and kaon decay constants in isosymmetric QCD, we find that the Cabibbo-Kobayashi-Maskawa matrix element $\vert V_{us}\vert = 0.22538(38)$, reducing by a factor of about $1.8$ the corresponding uncertainty in the PDG review. Our calculation of $|V_{us}|$ allows also an accurate determination of the first-row CKM unitarity relation $\vert V_{ud}\vert^2 + \vert V_{us}\vert^2 + \vert V_{ub}\vert^2 = 0.99988(44)$. Theoretical developments in this paper include a detailed discussion of how QCD can be defined in the full QCD+QED theory and an improved renormalisation procedure in which the bare lattice operators are renormalised non-perturbatively into the RI$^\prime$-MOM scheme and subsequently matched pertubatively at $O(\alpha_{em}\alpha_s(M_W))$ into the W-regularisation scheme appropriate for these calculations.

  • Resummation of soft and Coulomb corrections for $t\bar{t}h$ production at the LHC. (arXiv:1904.08744v1 [hep-ph])

    Authors: Wan-Li Ju, Li Lin Yang

    In this paper, a combined resummation of soft and Coulomb corrections is performed for the associated production of the Higgs boson with a top quark pair at the LHC. We illustrate the similarities and critical differences between this process and the $t\bar{t}$ production process. We show that up to the next-to-leading power, the total cross section for $t\bar{t}h$ production admits a similar factorization formula in the threshold limit as that for $t\bar{t}$ production. This fact, however, is not expected to hold at higher powers. Based on the factorization formula, we perform the resummation at the improved next-to-leading logarithmic accuracy, and match to the next-to-leading order result. This allows us to give NLL$'$+NLO predictions for the total cross sections at the LHC. We find that the resummation effects enhance the NLO cross sections by about 6\%, and significantly reduce the scale dependence of the theoretical predictions.

  • Proton decay in flux compactifications. (arXiv:1904.08810v1 [hep-ph])

    Authors: Wilfried Buchmuller, Ketan M. Patel

    We study proton decay in a six-dimensional orbifold GUT model with gauge group $SO(10)\times U(1)_A$. Magnetic $U(1)_A$ flux in the compact dimensions determines the multiplicity of quark-lepton generations, and it also breaks supersymmetry by giving universal GUT scale masses to scalar quarks and leptons. The model can successfully account for quark and lepton masses and mixings. Our analysis of proton decay leads to the conclusion that the proton lifetime must be close to the current experimental lower bound. Moreover, we find that the branching ratios for the decay channels $p \rightarrow e^+\pi^0$ and $p\rightarrow \mu^+\pi^0$ are of similar size, in fact the latter one can even be dominant. This is due to flavour non-diagonal couplings of heavy vector bosons together with large off-diagonal Higgs couplings, which appears to be a generic feature of flux compactifications.

  • Nonlinear flavor development of a two-dimensional neutrino gas. (arXiv:1904.08877v1 [hep-ph])

    Authors: Joshua D. Martin, Sajad Abbar, Huaiyu Duan

    We present a numerical survey of the nonlinear flavor development of dense neutrino gases. This study is based on the stationary, two-dimensional ($x$ and $z$), two-beam, monochromatic neutrino line model with a periodic boundary condition along the $x$ direction. Similar to a previous work, we find that small-scale flavor structures can develop in a neutrino gas even if the physical conditions are nearly homogeneous along the $x$ axis initially. The power diffusion from the large-scale to small-scale structures increases with the neutrino density and helps to establish a semi-exponential dependence of the magnitudes of the Fourier moments on the corresponding wave numbers. The overall flavor conversion probabilities in the neutrino gases with small initial sinusoidal perturbations reach certain equilibrium values at large distances which are mainly determined by the neutrino-antineutrino asymmetry. Similar phenomena also exist in a neutrino gas with a localized initial perturbation, albeit only inside an expanding flavor conversion region. Our work suggests that a statistical treatment may be possible for the collective flavor oscillations of a dense neutrino gas in a multi-dimensional environment.

  • Strong dynamics with matter in multiple representations: SU(4) gauge theory with fundamental and sextet fermions. (arXiv:1904.08885v1 [hep-lat])

    Authors: Guido Cossu, Luigi Del Debbio, Marco Panero, David Preti

    We present a non-perturbative lattice study of SU(4) gauge theory with two flavors of fermions in the fundamental representation and two in the two-index antisymmetric representation: a theory closely related to a minimal partial-compositeness model for physics beyond the Standard Model, that was proposed by G. Ferretti. We discuss the phase structure of the lattice theory and report results for various observables of interest, including the masses of states obtained from different combinations of valence fermions and the spectrum of the Dirac operator. Finally, we comment on the extension of this type of studies to other partial-compositeness models (including, in particular, one that was recently suggested by H. Gertov et al.), which could admit lighter top-quark partners, highlighting some key features of our lattice simulation algorithm, that make it suitable for such generalizations.

  • Identifying Higgsino-like neutralino with a keV-scale dark matter. (arXiv:1904.08906v1 [hep-ph])

    Authors: Juhi Dutta, Biswarup Mukhopadhyaya, Santosh Kumar Rai

    The presence of a Higgsino-like neutralino NLSP and a keV scale gravitino ($\widetilde{G}$) LSP opens up new decay modes of the NLSP, mainly to a Higgs/$Z$ boson and the LSP. Besides, a keV-scale gravitino as a warm dark matter candidate salvages a relatively-light Higgsino-like NLSP from dark matter constraints. We focus on the prospects of observing $\geq 1 b$ $+$ $ \ell^+\ell^-+\slashed{E}_T$ signal at the LHC. A distinguishing feature of this scenario is the production of longitudinal $Z$ bosons in neutralino decays, unlike in the case of gaugino-like neutralinos, where the $Z$ is mostly transverse. The polarisation information of the parent $Z$ boson gets reflected in the angular distributions of the decay leptons and in some other variables derived therefrom.

  • The Polarized Two-Loop Massive Pure Singlet Wilson Coefficient for Deep-Inelastic Scattering. (arXiv:1904.08911v1 [hep-ph])

    Authors: J. Blümlein, C.G. Raab, K. Schönwald

    We calculate the polarized massive two--loop pure singlet Wilson coefficient contributing to the structure functions $g_1(x,Q^2)$ analytically in the whole kinematic region. The Wilson coefficient contains Kummer--elliptic integrals. We derive the representation in the asymptotic region $Q^2 \gg m^2$, retaining power corrections, and in the threshold region. The massless Wilson coefficient is recalculated. The corresponding twist--2 corrections to the structure function $g_2(x,Q^2)$ are obtained by the Wandzura--Wilczek relation. Numerical results are presented.

  • Axion-Dilaton Destabilization and the Hubble Tension. (arXiv:1904.08912v1 [astro-ph.CO])

    Authors: Stephon Alexander, Evan McDonough

    The discrepancy in measurements of the Hubble constant indicates new physics in dark energy, dark matter, or both. Drawing inspiration from string theory, where axions interact with the other moduli fields, including the dilaton, here we demonstrate that the dynamics of an interacting dilaton and axion naturally realizes the proposal of Early Dark Energy. In this setup, stabilization of the the dilaton is in part due to the axion, and in the early universe the dilaton contributes to dark energy. The combined axion-dilaton system is destabilized when the Hubble constant falls below the mass of the axion, triggering a phase of fast-roll evolution of the dilaton wherein its equation of state is $w=1$, and the early dark energy redshifts away as $a^{-6}$.

  • Cosmic-ray transport from AMS-02 B/C data: benchmark models and interpretation. (arXiv:1904.08917v1 [astro-ph.HE])

    Authors: Yoann Genolini, Mathieu Boudaud, Pedro Ivo Batista, Sami Caroff, Laurent Derome, Julien Lavalle, Alexandre Marcowith, David Maurin, Vincent Poireau, Vivian Poulin, Sylvie Rosier, Pierre Salati, Pasquale Dario Serpico, Manuela Vecchi

    This article aims at establishing new benchmark scenarios for Galactic cosmic-ray propagation in the GV-TV rigidity range, based on fits to the AMS-02 B/C data with the USINE v3.5 propagation code. We employ a new fitting procedure, cautiously taking into account data systematic error correlations in different rigidity bins and considering Solar modulation potential and leading nuclear cross-section as nuisance parameters. We delineate specific low, intermediate, and high-rigidity ranges that can be related to both features in the data and peculiar microphysics mechanisms resulting in spectral breaks. We single out a scenario which yields excellent fits to the data and includes all the presumably relevant complexity, the BIG model. This model has two limiting regimes: (i) the SLIM model, a minimal diffusion-only setup, and (ii) the QUAINT model, a convection-reacceleration model where transport is tuned by non-relativistic effects. All models lead to robust predictions in the high-energy regime ($\gtrsim10$GV), i.e. independent of the propagation scenario: at $1\sigma$, the diffusion slope $\delta$ is $[0.43-0.53]$, whereas $K_{10}$, the diffusion coefficient at 10GV, is $[0.26-0.36]$kpc$^2$Myr$^{-1}$; we confirm the robustness of the high-energy break, with a typical value $\Delta_h\sim 0.2$. We also find a hint for a similar (reversed) feature at low rigidity around the B/C peak ($\sim 4$GV) which might be related to some effective damping scale in the magnetic turbulence.

  • Observational constraints on the tilted flat-XCDM and the untilted nonflat XCDM dynamical dark energy inflation parameterizations. (arXiv:1803.05522v4 [astro-ph.CO] UPDATED)

    Authors: Chan-Gyung Park, Bharat Ratra

    We constrain tilted spatially-flat and untilted nonflat XCDM dynamical dark energy inflation parameterizations using Planck 2015 cosmic microwave background (CMB) anisotropy data and recent baryonic acoustic oscillations distance measurements, Type Ia supernovae data, Hubble parameter observations, and growth rate measurements. Inclusion of the four non-CMB data sets results in a significant strengthening of the evidence for nonflatness in the nonflat XCDM model from 1.1$\sigma$ for the CMB data alone to 3.4$\sigma$ for the full data combination. In this untilted nonflat XCDM case the data favor a spatially-closed model in which spatial curvature contributes a little less than a percent of the current cosmological energy budget; they also mildly favor dynamical dark energy over a cosmological constant at 1.2$\sigma$. These data are also better fit by the flat-XCDM parameterization than by the standard $\Lambda$CDM model, but only at 0.3$\sigma$ significance. Current data is unable to rule out dark energy dynamics. The nonflat XCDM parameterization is compatible with the Dark Energy Survey limits on the present value of the rms mass fluctuations amplitude ($\sigma_8$) as a function of the present value of the nonrelativistic matter density parameter ($\Omega_m$), however it does not provide as good a fit to the higher multipole CMB temperature anisotropy data as does the standard tilted flat-$\Lambda$CDM model. A number of measured cosmological parameter values differ significantly when determined using the tilted flat-XCDM and the nonflat XCDM parameterizations, including the baryonic matter density parameter and the reionization optical depth.

  • Further study on the textures of neutrino mass matrix for maximal atmospherical mixing angle and Dirac CP phase. (arXiv:1808.06837v2 [hep-ph] UPDATED)

    Authors: Zhi-Cheng Liu, Chong-Xing Yue, Zhen-hua Zhao

    In this paper, we derive in a novel approach the possible textures of neutrino mass matrix that can lead to maximal atmospherical mixing angle ($\theta^{}_{23} = \pi/4$) and Dirac CP phase ($\delta = - \pi/2$) in two phenomenologically appealing scenarios: (1) one neutrino mass matrix element being vanishing (2) one neutrino mass being vanishing. For the obtained textures, some neutrino mass sum rules which relate the neutrino masses and mixing parameters will emerge. With the help of these sum rules, the unknown absolute neutrino mass scale and Majorana CP phases can be determined. Some discussions about the possible textures of neutrino mass matrix that can lead to $\theta^{}_{23} = \pi/4$, $\delta = - \pi/2$ and maximal Majorana CP phases ($\rho, \sigma = \pi/4$ or $3\pi/4$) as well as the model realization and breakings of the obtained textures are also given.

  • Ballistic Dark Matter oscillates above $\Lambda$CDM. (arXiv:1811.00028v2 [astro-ph.CO] UPDATED)

    Authors: Anirban Das (Tata Inst.), Basudeb Dasgupta (Tata Inst.), Rishi Khatri (Tata Inst.)

    Dark matter may have been relativistic and collisional until relatively late times and become cold and collisionless after a phase transition before the matter-radiation equality of the standard $\Lambda$CDM cosmology. We show that such a dark matter has large peculiar velocities due to acoustic oscillations before the phase transition, and evolves ballistically after the phase transition in the collisionless phase until the initial acoustic velocities are redshifted away. We show that this Ballistic Dark Matter (BDM) results in new non-trivial interesting features in the cosmological observables. In particular, the linear matter power spectrum exhibits acoustic oscillations on scales smaller than the Hubble scale at the time of phase transition, and for fast transitions the power at the acoustic peaks in the matter power spectrum exceeds that in a $\Lambda$CDM cosmology. If BDM only forms a part of the total dark matter, an odd vs. even acoustic peak asymmetry becomes prominent. We give an approximate analytical treatment of the linear perturbations in BDM, explaining these features. We also discuss the possibility to constrain BDM using cosmic microwave background and large scale structure data.

  • Models of vacuum energy interacting with cold dark matter: Constraints and comparison. (arXiv:1812.00319v2 [astro-ph.CO] UPDATED)

    Authors: Hai-Li Li, Lu Feng, Jing-Fei Zhang, Xin Zhang

    In this paper, we investigate the observational constraints on the models of vacuum energy interacting with cold dark matter. We consider eight typical interaction forms, i.e., $Q=\beta H_{0}\rho_{\rm{vac}}$, $Q=\beta H_{0}\rho_{\rm{c}}$, $Q=\beta H_{0}(\rho_{\rm{vac}}+\rho_{\rm c})$, $Q=\beta H_{0}\frac{\rho_{\rm{vac}}\rho_{c}}{\rho_{\rm{vac}}+\rho_{\rm c}}$, $Q=\beta H\rho_{\rm{vac}}$, $Q=\beta H\rho_{\rm{c}}$, $Q=\beta H(\rho_{\rm{vac}}+\rho_{\rm c})$, and $Q=\beta H\frac{\rho_{\rm{vac}}\rho_{c}}{\rho_{\rm{vac}}+\rho_{\rm c}}$. The observational data used in this work to constrain these models include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors data of cosmic microwave background anisotropies observation, the baryon acoustic oscillations data, and the Hubble constant direct measurement. We find that the current observational data almost equally favor these interacting vacuum energy models. We also find that for all these I$\Lambda$CDM models the case of $\beta=0$ is actually well consistent with the current observational data within 1$\sigma$ range.

  • De Sitter Swampland Bound in Dirac-Born-Infeld Inflation Model. (arXiv:1812.07670v2 [hep-th] UPDATED)

    Authors: Min-Seok Seo

    We study the de Sitter (dS) swampland conjecture in Dirac-Born-Infeld (DBI) inflation model. We obtain the dS swampland bound for the relativistic regime using Bousso's entropy bound argument and proper distance. It restricts $m_{\rm Pl}\nabla V/V$ by some positive constant depending on warping and the field range. In the specific case of the DBI model driven by the quadratic potential, the model dependent backreaction argument is interpreted as a natural bound for slow-roll parameter. This shows that quasi-dS spacetime in the DBI model is a result of tuning.

  • Foraging for dark matter in large volume liquid scintillator neutrino detectors with multiscatter events. (arXiv:1812.09325v2 [hep-ph] UPDATED)

    Authors: Joseph Bramante, Benjamin Broerman, Jason Kumar, Rafael F. Lang, Maxim Pospelov, Nirmal Raj

    We show that dark matter with a per-nucleon scattering cross section $\gtrsim 10^{-28}~{\rm cm^2}$ could be discovered by liquid scintillator neutrino detectors like BOREXINO, SNO+, and JUNO. Due to the large dark matter fluxes admitted, these detectors could find dark matter with masses up to $10^{21}$ GeV, surpassing the mass sensitivity of current direct detection experiments (such as XENON1T and PICO) by over two orders of magnitude. We derive the spin-independent and spin-dependent cross section sensitivity of these detectors using existing selection triggers, and propose an improved trigger program that enhances this sensitivity by two orders of magnitude. We interpret these sensitivities in terms of three dark matter scenarios: (1) effective contact operators for scattering, (2) QCD-charged dark matter, and (3) a recently proposed model of Planck-mass baryon-charged dark matter. We calculate the flux attenuation of dark matter at these detectors due to the earth overburden, taking into account the earth's density profile and elemental composition, and nuclear spins.

  • Hydrodynamics of Fermi arcs: Bulk flow and surface collective modes. (arXiv:1901.00006v2 [cond-mat.str-el] UPDATED)

    Authors: E. V. Gorbar, V. A. Miransky, I. A. Shovkovy, P. O. Sukhachov

    The hydrodynamic description of the Fermi arc surface states is proposed. In view of the strong suppression of scattering on impurities, the hydrodynamic regime for Fermi arc states should be, in principle, plausible. By using the kinetic theory, the Fermi arc hydrodynamics is derived and the corresponding effects on the bulk flow and surface collective modes are studied. For the bulk flow, the key effect of the proposed Fermi arc hydrodynamics is the modification of the corresponding boundary conditions. In a slab geometry, it is shown that, depending on the transfer rates between the surface and bulk, the hydrodynamic flow of the electron fluid inside the slab could be significantly altered and even enhanced near the surfaces. As to the spectrum of the surface collective modes, in agreement with earlier studies, it is found that the Fermi arcs allow for an additional gapless spectrum branch and a strong anisotropy of the surface plasmon dispersion relations in momentum space. The gapped modes are characterized by closed elliptic contours of constant frequency in momentum space.

  • Effective long distance $q\bar{q} $ potential in holographic RG flows. (arXiv:1902.04279v2 [hep-th] UPDATED)

    Authors: Jorge Casalderrey-Solana, Diego Gutiez, Carlos Hoyos

    We study the $q\bar{q}$ potential in strongly coupled non-conformal field theories with a non-trivial renormalization group flow via holography. We focus on the properties of this potential at an inter-quark separation $L$ large compared to the characteristic scale of the field theory. These are determined by the leading order IR physics plus a series of corrections, sensitive to the properties of the RG-flow. To determine those corrections, we propose a general method applying holographic Wilsonian renormalization to a dual string. We apply this method to examine in detail two sets of examples, $3+1$-dimensional theories with an RG flow ending in an IR fixed point; and theories that are confining in the IR, in particular, the Witten QCD and Klebanov-Strassler models. In both cases, we find corrections with a universal dependence on the inter-quark separation. When there is an IR fixed point, that correction decays as a power $\sim 1/L^4$. We explain that dependence in terms of a double-trace deformation in a one-dimensional defect theory. For a confining theory, the decay is exponential $\sim e^{-ML}$, with $M$ a scale of the order of the glueball mass. We interpret this correction using an effective flux tube description as produced by a background internal mode excitation induced by sources localized at the endpoints of the flux tube. We discuss how these results could be confronted with lattice QCD data to test whether the description of confinement via the gauge/gravity is qualitatively correct.

  • Constraints on Disconnected Contributions in $\pi\pi$ Scattering. (arXiv:1902.10290v2 [hep-lat] UPDATED)

    Authors: N. Ripunjay Acharya, Feng-Kun Guo, Ulf-G. Meißner, Chien-Yeah Seng

    The accuracy of the lattice QCD computation of hadron-hadron scattering at low isospin depends critically on the ability to compute correlation functions with fermionic disconnected Wick contractions. This happens, for instance, in isospin $I=0$ $\pi\pi$ scattering, which receives contributions from rectangular and vacuum types of contractions among other easier calculable ones. Combining L\"{u}scher's formula and partially-quenched chiral perturbation theory, we provide precise theory predictions of the discrete energy levels extracted from specific linear combinations of lattice correlation functions corresponding to various types of contractions. Expressions are provided for extracting the unphysical low-energy constants in the partially-quenched chiral perturbation theory from the energy levels for these contractions. The predictions for the rectangular and vacuum contractions may serve as solid tests of the accuracy for existing and future lattice studies of $\pi\pi$ scattering.

  • Nature of the $Y(4260)$: A light-quark perspective. (arXiv:1902.10957v2 [hep-ph] UPDATED)

    Authors: Yun-Hua Chen, Ling-Yun Dai, Feng-Kun Guo, Bastian Kubis

    The $Y(4260)$ has been one of the most puzzling pieces among the so-called $XYZ$ states. In this paper, we try to gain insights into the structure of the $Y(4260)$ from the light-quark perspective. We study the dipion invariant mass spectrum of the $e^+ e^- \to Y(4260) \to J/\psi \pi^+\pi^-$ process and the ratio of the cross sections ${\sigma(e^+e^- \to J/\psi K^+ K^-)}/{\sigma(e^+e^- \to J/\psi \pi^+\pi^-)}$. In particular, we consider the effects of different light-quark SU(3) eigenstates inside the $Y(4260)$. The strong pion-pion final-state interactions as well as the $K\bar{K}$ coupled channel in the $S$-wave are taken into account in a model-independent way using dispersion theory. We find that the SU(3) octet state plays a significant role in these transitions, implying that the $Y(4260)$ contains a large light-quark component. Our findings suggest that the $Y(4260)$ is neither a hybrid nor a conventional charmonium state, and they are consistent with the $Y(4260)$ having a sizeable $\bar D D_1$ component which, however, is not completely dominant.

  • Spinorial Structure of $O(3)$ and Application to Dark Sector. (arXiv:1903.04439v3 [hep-ph] UPDATED)

    Authors: Masaki Yasuè

    An $O(3)$ spinor, $\Phi$, as a doublet denoted by ${\bf 2}_D$ consists of an $SO(3)$ spinor, $\phi$, and its complex conjugate, $\phi^\ast$, which form $\Phi=\left(\phi,\phi^\ast\right)^T$ to be identified with a Majorana type spinor of $O(4)$. The four gamma matrices $\Gamma_\mu$ ($\mu=1\sim 4$) are given by $\Gamma_i=\text{diag.}\left(\tau_i,\tau^\ast_i\right)$ and $\Gamma_4=-\tau_2\otimes\tau_2$, where $\tau_i$ ($i=1,2,3$) denote the Pauli matrices. While $\Phi$ is regarded as a scalar, a fermionic $O(3)$ spinor is constructed out of an $SO(3)$ doublet Dirac spinor and its charge conjugate. These $O(3)$ spinors serve as candidates of dark matter because they are restricted to be neutral and cannot carry the standard model quantum numbers. It is possible to introduce a gauge symmetry based on $SO(3)\times\boldsymbol{Z}_2$ equivalent to $O(3)$, where the $\boldsymbol{Z}_2$ parity is described by a $U(1)$ charge giving 1 for a particle as the $SO(3)$ spinor and $-1$ for an antiparticle as its conjugate. The triplet gauge bosons transform as the axial vector of $O(3)$ and the singlet one as the pseudoscalar of $O(3)$.

  • Semileptonic decays $B_c \to (\eta_c,J/\psi) l \bar{\nu}_l $ in the "PQCD + Lattice" approach. (arXiv:1904.07530v2 [hep-ph] UPDATED)

    Authors: Xue-Qing Hu, Su-Ping Jin, Zhen-Jun Xiao

    In this paper, we studied the semileptonic decays $B_c^- \to (\eta_c, J/\psi) l ^- \bar{\nu}_l$ by employing the PQCD factorization approach, using the newly defined distribution amplitudes of the $B_c$ meson and also taking into account the Lattice NRQCD results about the relevant form factors. We found the following main results: (a) the PQCD predictions for the branching ratios will become smaller by about $(10-50)\%$ when the Lattice NRQCD results about the form factors are taken into account in the extrapolation of the relevant form factors; (b) the PQCD predictions for the ratio $R_{\eta_c, J/\psi}$ and the longitudinal polarization $P_{\tau}$ are $R_{\eta_c}=0.373^{+0.003}_{-0.012} , R_{J/\psi}=0.300^{+0.005}_{-0.004}$, $P_{\tau}^{ \eta_c} = 0.356^{+0.003}_{-0.005}$ and $P_{\tau}^{J/\psi } = -0.557 \pm 0.002$ ; and (c) after the inclusion of the Lattice NRQCD results the predictions are changed moderately: $R_{\rm \eta_c}=0.300^{+0.033}_{-0.031} $, $ R_{\rm J/\psi}=0.230^{+0.041}_{-0.035}$, $P_{\tau}^{ \eta_c} = 0.345\pm 0.010$ and $P_{\tau}^{ J/\psi} = -0.427 ^{+0.127}_{-0.093}$ The theoretical predictions for $R_{ J/\psi}$ agree with the measured one within errors, and other predictions could be tested in the future LHCb experiments.

  • Geometry of ultraperipheral nuclear collisions. (arXiv:1903.12377v3 [nucl-th] CROSS LISTED)

    Authors: I.M. Dremin

    It is advocated that geometry of the interaction region of two heavy nuclei colliding at large impact parameters is important for the relative role of light-by-light scattering and QCD-initiated processes. Exclusive production of resonances is possible by dense electromagnetic fields in the interior space between the nuclei. The cross section of these processes is evaluated and some examples are considered. It is speculated that the exclusive production of $\rho ^0$-mesons by two-photon processes forbidden by the Landau-Yang rule may become allowed within strong magnetic fields.

  • Complementarity of Stacking and Multiplet Constraints on the Blazar Contribution to the Cumulative High-Energy Neutrino Intensity. (arXiv:1904.06371v2 [astro-ph.HE] CROSS LISTED)

    Authors: Chengchao Yuan, Kohta Murase, Peter Mészáros

    We investigate the blazar contribution to the cumulative neutrino intensity assuming a generic relationship between neutrino and gamma-ray luminosities, $\log (L_{\nu})\propto \log(L_{\rm ph})$. Using the gamma-ray luminosity functions for blazars including flat spectrum radio quasars (FSRQs) and BL Lac objects, as well as the Fermi-LAT detection efficiency, we estimate contributions from resolved blazars and all blazars. Combining the existing upper limits from stacking analyses, the cumulative neutrino flux from all blazars are constrained. We also evaluate effects of the redshift evolution and the effective local number densities for each class of FSRQs, BL Lacs, and all blazars, by which we place another type of constraints on the blazar contribution using the non-detection of high-energy neutrino multiplets. We demonstrate that these two upper limits are complementary, and the joint consideration of stacking and multiplet analyses support arguments that blazars are disfavored as the dominant sources in the 100 TeV neutrino sky.

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