Mon·Mar 7, 2016Monday·March 7, 2016

1. 01*

   A Critical Analysis of One-Loop Neutrino Mass Models with Minimal Dark Matter

   Amine Ahriche (Constantine U. & ICTP, Trieste)🇩🇿 · Kristian L. McDonald (Sydney U.)🇦🇺 · Salah Nasri (United Arab Emirates U.)🇦🇪 · Ivica Picek (Zagreb U.)🇭🇷

   A recent paper investigated minimal R$\nu$MDM models with the type T1-iii and T3 one-loop topologies. However, the candidate most-minimal model does not possess an accidental symmetry - the scalar potential contains an explicit symmetry breaking term, rendering the dark matter unstable. We present two models that cure this problem. However, we further show that all of the proposed minimal one-loop R$\nu$MDM models suffer from a second problem - an additional source of explicit $Z_2$ symmetry breaking in the Yukawa sector. We perform a more-general analysis to show that neutrino mass models using either the type T3 or type T1-iii one-loop topologies do not give viable minimal dark matter candidates. Consequently, one-loop models of neutrino mass with minimal dark matter do not appear possible. Thus, presently there remains a single known (three-loop) model of neutrino mass that gives stable dark matter without invoking any new symmetries.

   hep-phPLB(2016)·39 citations
2. 02*

   Diphoton Excess through Dark Mediators

   Chien-Yi Chen🇨🇦 · Michel Lefebvre🇨🇦 · Maxim Pospelov🇨🇦 · Yi-Ming Zhong🇺🇸

   Preliminary ATLAS and CMS results from the first 13 TeV LHC run have encountered an intriguing excess of events in the diphoton channel around the invariant mass of 750 GeV. We investigate a possibility that the current excess is due to a heavy resonance decaying to light metastable states, which in turn give displaced decays to very highly collimated $e^{+}{e}^{-}$ pairs. Such decays may pass the photon selection criteria, and successfully mimic the diphoton events, especially at low counts. We investigate two classes of such models, characterized by the following underlying production and decay chains: $gg\to S\to A^{\prime }{A}^{\prime }\to (e^{+}{e}^{-})(e^{+}{e}^{-})$ and $q\bar{q}\to Z^{\prime }\to sa\to (e^{+}{e}^{-})(e^{+}{e}^{-})$, where at the first step a heavy scalar, $S$, or vector, $Z^{\prime }$, resonances are produced that decay to light metastable vectors, $A^{\prime }$, or (pseudo-)scalars, $s$ and $a$. Setting the parameters of the models to explain the existing excess, and taking the ATLAS detector geometry into account, we marginalize over the properties of heavy resonances in order to derive the expected lifetimes and couplings of metastable light resonances. We observe that in the case of $A^{\prime }$, the suggested range of masses and mixing angles $ϵ$ is within reach of several new-generation intensity frontier experiments.

   hep-phhep-exJHEP(2016)·15 citations
3. 03*

   On Mono-W Signatures in Spin-1 Simplified Models

   Ulrich Haisch🇬🇧 · Felix Kahlhoefer🇩🇪 · Tim M.P. Tait🇺🇸

   The potential sensitivity to isospin-breaking effects makes LHC searches for mono-W signatures promising probes of the coupling structure between the Standard Model and dark matter. It has been shown, however, that the strong sensitivity of the mono-W channel to the relative magnitude and sign of the up-type and down-type quark couplings to dark matter is an artefact of unitarity violation. We provide three different solutions to this mono-W problem in the context of spin-1 simplified models and briefly discuss the impact that our findings have on the prospects of mono-W searches at future LHC runs.

   hep-phhep-exPLB(2016)·40 citations
4. 04*

   Diagonalizing the Hamiltonian of $\lambda {\varphi }^4$ Theory in 2 Space-Time Dimensions

   Neil Christensen🇺🇸

   We propose a new non-perturbative technique for calculating the field-theory S-matrix directly from the eigenstates of the Hamiltonian. Our method involves a discretized momentum space and a momentum cutoff, thereby truncating the Hilbert space and making numerical diagonalization of the Hamiltonian achievable. We show how to do this in the context of a simplified $\lambda {\varphi }^4$ theory in two space-time dimensions. We present the results of our diagonalization, its dependence on time, its dependence on the parameters of the theory and its renormalization.

   hep-phhep-latComput.Phys.Commun.(2018)·6 citations
5. 05*

   Hidden Photons in Aharonov-Bohm-Type Experiments

   Paola Arias🇨🇱 · Christian Diaz🇨🇱 · Marco Aurelio Diaz🇨🇱 · Joerg Jaeckel🇩🇪 · Benjamin Koch🇨🇱 · Javier Redondo🇪🇸

   We discuss the Aharonov-Bohm effect in the presence of hidden photons kinetically mixed with the ordinary electromagnetic photons. The hidden photon field causes a slight phase shift in the observable interference pattern. It is then shown how the limited sensitivity of this experiment can be largely improved. The key observation is that the hidden photon field causes a leakage of the ordinary magnetic field into the supposedly field-free region. The direct measurement of this magnetic field can provide a sensitive experiment with a good discovery potential, particularly below the $\sim$ meV mass range for hidden photons.

   hep-phhep-exPRD(2016)·6 citations
6. 06*

   Charge-multiplicity and collision-energy dependence of $p_t$ spectra from $p$-$p$ collisions at the relativistic heavy-ion collider and large hadron collider

   Thomas A. Trainor🇺🇸

   A two-component (soft + hard) model (TCM) of hadron production in yields and spectra derived from the charge-multiplicity dependence of 200 GeV p-p collisions at the relativistic heavy ion collider (RHIC) is extended to describe p-p spectrum data from the large hadron collider (LHC) up to 13 TeV. The LHC data include spectrum ratios that provide only partial information on the TCM. The LHC ratio method is applied to well-understood 200 GeV spectrum data to derive an algebraic link between spectrum ratios and the full TCM. Some aspects of the form of the hard component on transverse momentum are found to be $n_{ch}$ dependent. LHC spectrum ratios are then analyzed to obtain $n_{ch}$ and collision-energy (over three orders of magnitude) dependence of isolated soft and hard TCM spectrum components. The energy dependence of the spectrum soft component is a new result suggesting a relation to Gribov diffusion. The spectrum hard component varies simply and smoothly with $n_{ch}$ suggesting bias of the underlying jet spectrum and linearly with QCD parameter $\log (s/s_0)$, its properties consistent with minimum-bias reconstructed-jet spectrum measurements.

   hep-phJ.Phys.G(2017)·28 citations
7. 07*

   Collide and Conquer: Constraints on Simplified Dark Matter Models using Mono-X Collider Searches

   A. J. Brennan🇦🇺 · M. F. McDonald🇦🇺 · J. Gramling🇨🇭 · T. D. Jacques🇮🇹

   The use of simplified models as a tool for interpreting dark matter collider searches has become increasingly prevalent, and while early Run II results are beginning to appear, we look to see what further information can be extracted from the Run I dataset. We consider three `standard' simplified models that couple quarks to fermionic singlet dark matter: an $s$-channel vector mediator with vector or axial-vector couplings, and a $t$-channel scalar mediator. Upper limits on the couplings are calculated and compared across three alternate channels, namely mono-jet, mono-$Z$ (leptonic) and mono-$W/Z$ (hadronic). The strongest limits are observed in the mono-jet channel, however the computational simplicity and absence of significant $t$-channel model width effects in the mono-boson channels make these a straightforward and competitive alternative. We also include a comparison with relic density and direct detection constraints.

   hep-phhep-exJHEP(2016)·44 citations
8. 08*

   Dark-Photon searches via Higgs-boson production at the LHC

   Sanjoy Biswas🇰🇷 · Emidio Gabrielli🇮🇹 · Matti Heikinheimo🇫🇮 · Barbara Mele🇮🇹

   Dark photons $\bar{\gamma }$ mediating long-range forces in a dark sector are predicted by various new physics scenarios, and are being intensively searched for in experiments. We extend a previous study of a new discovery process for dark photons proceedings via Higgs-boson production at the LHC. Thanks to the non-decoupling properties of the Higgs boson, BR($H\to \gamma \bar{\gamma }$) values up to a few percent are possible for a massless dark photon, even for heavy dark-sector scenarios. The corresponding signature consists (for a Higgs boson at rest) of a striking monochromatic photon with energy $E_{\gamma }=m_H/2$, and similar amount of missing energy. We perform a model independent analysis at the LHC of both the gluon-fusion and VBF Higgs production mechanisms at 14 TeV, including parton-shower effects, and updating our previous parton-level analysis at 8 TeV in the gluon-fusion channel by a more realistic background modeling. We find that a $5\sigma$ sensitivity can be reached in the gluon-fusion channel for BR($H\to \gamma \bar{\gamma })\simeq$0.1% with an integrated luminosity of $L\simeq 300{\mathrm{fb}}^{-1}$. The corresponding VBF reach is instead restricted to 1%. Such decay rates can be naturally obtained in dark-photon scenarios arising from unbroken $U(1{)}_F$ models explaining the origin and hierarchy of the Yukawa couplings, strongly motivating the search for this exotic Higgs decay at the LHC.

   hep-phhep-exPRD(2016)·50 citations
9. 09*

   Non-standard interactions spoiling the CP violation sensitivity at DUNE and other long baseline experiments

   Mehedi Masud🇮🇳 · Poonam Mehta🇮🇳

   It is by now established that neutrino oscillations occur due to non-zero masses and parameters in the leptonic mixing matrix. The extraction of oscillation parameters may be complicated due to subleading effects such as non-standard neutrino interactions (NSI) and one needs to have a fresh look how a particular parameter value is inferred from experimental data. In the present work, we focus on an important parameter entering the oscillation framework - the leptonic CP violating phase $\delta$, about which we know very little. We demonstrate that the sensitivity to CP violation gets significantly impacted due to NSI effects for the upcoming long baseline experiment, Deep Underground Neutrino Experiment (DUNE). We also draw a comparison with the sensitivities of other ongoing neutrino beam experiments such as NOvA, and T2K, as well as a future generation experiment, T2HK.

   hep-phhep-exPRD(2016)·95 citations
10. 10*

    Self-consistent Calculation of the Sommerfeld Enhancement

    Kfir Blum🇮🇱 · Ryosuke Sato🇮🇱 · Tracy R. Slatyer🇺🇸

    A calculation of the Sommerfeld enhancement is presented and applied to the problem of s-wave non-relativistic dark matter annihilation. The difference from previous computations in the literature is that the effect of the underlying short-range scattering process is consistently included together with the long-range force in the effective QM Schrödinger problem. Our procedure satisfies partial-wave unitarity where previous calculations fail. We provide analytic results for some potentials of phenomenological relevance.

    hep-phJCAP(2016)·96 citations
11. 11*

    CP-Violation in the $ZZZ$ and $ZWW$ vertices at $e^{+}{e}^{-}$ colliders in Two-Higgs-Doublet Models

    B. Grzadkowski🇵🇱 · O. M. Ogreid🇳🇴 · P. Osland🇳🇴

    We discuss possibilities of measuring CP violation in the Two-Higgs-Doublet Model by studying effects of one-loop generated $ZZZ$ and $ZWW$ vertices. We discuss a set of CP-sensitive asymmetries for $ZZ$ and $W^{+}{W}^{-}$ production at linear $e^{+}{e}^{-}$-colliders, that directly depends on the weak-basis invariant Im $J_2$ that parametrises the strength of CP violation. Given the restrictions on this model that follow from the LHC measurements, the predicted effects are small. Pursuing such measurements is however very important, as an observed signal might point to a richer scalar sector.

    hep-phJHEP(2016)·32 citations
12. 12*

    Regge spectra of excited mesons, harmonic confinement and QCD vacuum structure

    Sergei N. Nedelko🇷🇺 · Vladimir E. Voronin🇷🇺

    An approach to QCD vacuum as a medium describable in terms of statistical ensemble of almost everywhere homogeneous Abelian (anti-)self-dual gluon fields is briefly reviewed. These fields play the role of the confining medium for color charged fields as well as underline the mechanism of realization of chiral $S{U}_{\mathrm{L}}(N_f)\times S{U}_{\mathrm{R}}(N_f)$ and $U_A(1)$ symmetries. Hadronization formalism based on this ensemble leads to manifestly defined quantum effective meson action. Strong, electromagnetic and weak interactions of mesons are represented in the action in terms of nonlocal $n$-point interaction vertices given by the quark-gluon loops averaged over the background ensemble. New systematic results for the mass spectrum and decay constants of radially excited light, heavy-light mesons and heavy quarkonia are presented. Interrelation between the present approach, models based on ideas of soft wall AdS/QCD, light front holographic QCD, and the picture of harmonic confinement is outlined.

    hep-phPRD(2016)·21 citations
13. 13*

    Charmed partner of the exotic $X(5568)$ state and its properties

    S. S. Agaev🇦🇿 · K. Azizi🇹🇷 · H. Sundu🇹🇷

    The mass, decay constant and width of a hypothetical charmed partner $X_c$ of the newly observed exotic $X_b(5568)$ state are calculated using a technique of QCD sum rule method. The $X_c=[su][\overline{c}\overline{d}]$ state with $J^P=0^{+}$ is described employing two types of the diquark-antidiquark interpolating currents. The evaluation of the mass $m_{X_c}$ and decay constant $f_{X_c}$ is carried out utilizing the two-point sum rule method by including vacuum condensates up to eight dimensions. The widths of the decay channels $X_c\to D_s^{-}{\pi }^{+}$ and $X_c\to D^0{K}^0$ are also found. To this end, the strong couplings $g_{X_c{D}_s\pi }$ and $g_{X_{c}DK}$ are computed by means of QCD sum rules on the light-cone and soft-meson approximation.

    hep-phhep-exhep-latnucl-thPRD(2016)·49 citations
14. 14*

    Improved analyses for ${\mu }^{-}{e}^{-}\to e^{-}{e}^{-}$ in muonic atoms by contact interactions

    Yuichi Uesaka🇯🇵 · Yoshitaka Kuno🇯🇵 · Joe Sato🇯🇵 · Toru Sato🇯🇵 · Masato Yamanaka🇯🇵

    The charged lepton flavor violating (CLFV) processes of ${\mu }^{-}{e}^{-}\to e^{-}{e}^{-}$ decay by four Fermi contact interactions in a muonic atom for various atoms are investigated. The wave functions of bound and scattering state leptons are properly treated by solving Dirac equations with Coulomb interaction of the finite nuclear charge distributions. This new effect contributes significantly in particular for heavier atoms, where the obtained decay rate is about one order of magnitude larger than the previous estimation for ${}^{208}$Pb. We find that, as the atomic number $Z$ increases, the ${\mu }^{-}{e}^{-}\to e^{-}{e}^{-}$ decay rates increase more rapidly than the result of the previous work of $Z^3$, suggesting this decay as one of the promising processes to search for CLFV interaction.

    hep-phPRD(2016)·22 citations
15. 15*

    Improved separation of soft and hard components in multiple Coulomb scattering

    M.V. Bondarenco🇺🇦

    Evaluation of the angular distribution function of particles scattered in an amorphous medium is improved by deforming the integration path in the Fourier integral representation into the complex plane. That allows us to present the distribution function as a sum of two positive components, soft and hard, the soft component being close to a Gaussian, and the hard component vanishing in the forward direction, while including the Rutherford asymptotics and all the power corrections to it at large scattering angles. Detailed properties of those components, and their interplay at intermediate deflection angles are discussed. Comparison with the Molière theory is given.

    hep-phPRD(2016)·2 citations
16. 16*

    Propose economical and stable lepton mass matrices with texture zeros

    Shu-jun Rong🇨🇳

    There are many viable combinations of texture zeros in lepton mass matrices. We propose an economical and stable mass texture. Analytical and numerical results on mixing parameters and the effective mass of neutrinos are obtained. These results satisfy new constraints from neutrinos oscillation experiments and cosmological observations. Our proposition reveals that in the complex forest of neutrinos mixing models, a simple and robust one is still possible.

    hep-phAdv.High Energy Phys.(2017)·0 citations
17. 17*

    Thermodynamics, transport and relaxation in non-conformal theories

    Maximilian Attems🇪🇸 · Jorge Casalderrey-Solana🇬🇧 · David Mateos🇪🇸 · Ioannis Papadimitriou🇮🇹 · Daniel Santos-Oliván🇪🇸 · Carlos F. Sopuerta🇪🇸 · Miquel Triana🇪🇸 · Miguel Zilhão🇪🇸

    We study the equilibrium and near-equilibrium properties of a holographic five-dimensional model consisting of Einstein gravity coupled to a scalar field with a non-trivial potential. The dual four-dimensional gauge theory is not conformal and, at zero temperature, exhibits a renormalisation group flow between two different fixed points. We quantify the deviations from conformality both in terms of thermodynamic observables and in terms of the bulk viscosity of the theory. The ratio of bulk over shear viscosity violates Buchel's bound. We study relaxation of small-amplitude, homogeneous perturbations by computing the quasi-normal modes of the system at zero spatial momentum. In this approximation we identify two different relaxation channels. At high temperatures, the different pressures first become approximately equal to one another, and subsequently this average pressure evolves towards the equilibrium value dictated by the equation of state. At low temperatures, the average pressure first evolves towards the equilibrium pressure, and only later the different pressures become approximately equal to one another.

    ↳ hep-thhep-phnucl-thJHEP(2016)·95 citations
18. 18*

    Cosmological perturbations on the Phantom brane

    Satadru Bag🇮🇳 · Alexander Viznyuk🇺🇦 · Yuri Shtanov🇺🇦 · Varun Sahni🇮🇳

    We obtain a closed system of equations for scalar perturbations in a multi-component braneworld. Our braneworld possesses a phantom-like equation of state at late times, $w_{\mathrm{eff}}<-1$, but no big-rip future singularity. In addition to matter and radiation, the braneworld possesses a new effective degree of freedom - the 'Weyl fluid' or 'dark radiation'. Setting initial conditions on super-Hubble spatial scales at the epoch of radiation domination, we evolve perturbations of radiation, pressureless matter and the Weyl fluid until the present epoch. We observe a gradual decrease in the amplitude of the Weyl-fluid perturbations after Hubble-radius crossing, which results in a negligible effect of the Weyl fluid on the evolution of matter perturbations on spatial scales relevant for structure formation. Consequently, the quasi-static approximation of Koyama and Maartens provides a good fit to the exact results during the matter-dominated epoch. We find that the late-time growth of density perturbations on the brane proceeds at a faster rate than in $\Lambda$CDM. Additionally, the gravitational potentials $\Phi$ and $\Psi$ evolve differently on the brane than in $\Lambda$CDM, for which $\Phi =\Psi$. On the brane, by contrast, the ratio $\Phi /\Psi$ exceeds unity during the late matter-dominated epoch ($z\lesssim 50$). These features emerge as "smoking gun" tests of phantom brane cosmology and allow predictions of this scenario to be tested against observations of galaxy clustering and large-scale structure.

    ↳ gr-qcastro-ph.COhep-phhep-thJCAP(2016)·13 citations
19. 19*

    Primordial gravitational waves for universality classes of pseudoscalar inflation

    Valerie Domcke🇫🇷 · Mauro Pieroni🇫🇷 · Pierre Binétruy🇫🇷

    Current bounds from the polarization of the CMB predict the scale-invariant gravitational wave (GW) background of inflation to be out of reach for upcoming GW interferometers. This prospect dramatically changes if the inflaton is a pseudoscalar, in which case its generic coupling to any abelian gauge field provides a new source of GWs, directly related to the dynamics of inflation. This opens up new ways of probing the scalar potential responsible for cosmic inflation. Dividing inflation models into universality classes, we analyze the possible observational signatures. One of the most promising scenarios is Starobinsky inflation, which may lead to observational signatures both in direct GW detection as well as in upcoming CMB detectors. In this case, the complementarity between the CMB and direct GW detection, as well as the possibility of a multi-frequency analysis with upcoming ground and space based GW interferometers, may provide a first clue to the microphysics of inflation.

    ↳ astro-ph.COhep-phJCAP(2016)·155 citations
20. 20*

    Convexity at finite temperature and non-extensive thermodynamics

    Jean Alexandre🇬🇧

    Assuming that tunnel effect between two degenerate bare minima occurs, in a scalar field theory at finite volume, this article studies the consequences for the effective potential, to all loop orders. Convexity is achieved only if the two bare minima are taken into account in the path integral, and a new derivation of the effective potential is given, in the large volume limit. The effective potential has then has a universal form, it is suppressed by the space time volume, and does not feature spontaneous symmetry breaking as long as the volume is finite. The finite temperature analysis leads to surprising thermal properties, following from the non-extensive expression for the free energy. Although the physical relevance of these results is not clear, the potential application to ultra-light scalar particles is discussed.

    ↳ hep-thcond-mat.stat-mechhep-phNPB(2016)·5 citations
21. 21*

    Lifshitz-scaling to Lorentz-violating high derivative operator and gamma-ray busts

    E. Passos🇧🇷 · E. M. C. Abreu🇧🇷 · M. A. Anacleto🇧🇷 · F. A. Brito🇧🇷 · C. Wotzasek🇧🇷 · C. A. D. Zarro🇧🇷

    In this work we have used a Hořava-Lifshitz scaling to rewrite a Lorentz-violating higher-order derivative electrodynamics controlled by a background four-vector $n_{\mu }$. The photon propagator was obtained and we have analyzed the dispersion relation and the observational results of gamma-ray burst (GRB) experiments were used. The limits of the critical exponent were discussed in the light of the GRB data and the physical implications were compared with the current GRB-Lorentz-invariance-violation literature. We show that the bound for the Lorentz-violating coupling for dimension-six operators, obtained from a Hořava-Lifshitz scaling, is eight orders of magnitude better than the result found without considering a Hořava-Lifshitz scaling, also this bound is nearby one, which is expected to be relevant phenomenologically.

    ↳ hep-thhep-phPRD(2016)·10 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.