Mon·Oct 12, 2015Monday·October 12, 2015

1. 01*

   Comparison of Horace and Photos Algorithms for Multi-Photon Emission in the Context of the W Boson Mass Measurement

   A. V. Kotwal🇺🇸 · B. Jayatilaka🇺🇸

   The W boson mass measurement is sensitive to QED radiative corrections due to virtual photon loops and real photon emission. The largest shift in the measured mass, which depends on the transverse momentum spectrum of the charged lepton from the boson decay, is caused by the emission of real photons from the final-state lepton. There are a number of calculations and codes available to model the final-state photon emission. We perform a detailed study, comparing the results from the Horace and Photos implementations of the final-state multi-photon emission in the context of a direct measurement of the W boson mass at the Tevatron. Mass fits are performed using a simulation of the CDF II detector.

   hep-phAdv.High Energy Phys.(2016)·7 citations
2. 02*

   Semi-Inclusive Wino and Higgsino Annihilation to LL'

   Matthew Baumgart🇺🇸 · Varun Vaidya🇺🇸

   We systematically compute the annihilation rate for winos and higgsinos into the final state relevant for indirect detection experiments, gamma + X. The radiative corrections to this process receive enhancement from the large Bloch-Nordsieck-Violating Sudakov logarithm, log(2 M_chi/M_W). We resum the double logs and include single logs to fixed order using a formalism that combines nonrelativistic and soft-collinear effective field theories. For the wino case, we update an earlier exclusion adapting results of the HESS experiment. At the thermal relic mass of 3 TeV, LL' corrections result in a ~30% reduction in rate relative to LL. Nonetheless, single logs do not save the wino, and it is still excluded by an order of magnitude. Experimental cuts produce an endpoint region which, our results show, significantly effects the higgsino rate at its thermal-relic mass near 1 TeV and is deserving of further study.

   hep-phJHEP(2016)·46 citations
3. 03*

   Leading QCD Corrections for Indirect Dark Matter Searches: a Fresh Look

   Torsten Bringmann🇳🇴 · Ahmad J. Galea🇳🇴 · Parampreet Walia🇳🇴

   The annihilation of non-relativistic dark matter particles at tree level can be strongly enhanced by the radiation of an additional gauge boson. This is particularly true for the helicity-suppressed annihilation of Majorana particles, like neutralinos, into fermion pairs. Surprisingly, and despite the potentially large effect due to the strong coupling, this has so far been studied in much less detail for the internal bremsstrahlung of gluons than for photons or electroweak gauge bosons. Here, we aim at bridging that gap by presenting a general analysis of neutralino annihilation into quark anti-quark pairs and a gluon, allowing e.g. for arbitrary neutralino compositions and keeping the leading quark mass dependence at all stages in the calculation. We find in some cases largely enhanced annihilation rates, especially for scenarios with squarks being close to degenerate in mass with the lightest neutralino, but also notable distortions in the associated antiproton and gamma-ray spectra. Both effects significantly impact limits from indirect searches for dark matter and are thus important to be taken into account in, e.g., global scans. For extensive scans, on the other hand, full calculations of QCD corrections are numerically typically too expensive to perform for each point in parameter space. We present here for the first time an efficient, numerically fast implementation of QCD corrections, extendable in a straight-forward way to non-supersymmetric models, which avoids computationally demanding full one-loop calculations or event generator runs and yet fully captures the leading effects relevant for indirect dark matter searches. In this context, we also present updated constraints on dark matter annihilation from cosmic-ray antiproton data. Finally, we comment on the impact of our results on relic density calculations.

   hep-phastro-ph.COPRD(2016)·32 citations
4. 04*

   A Case Study of the Sensitivity to LFV Operators with Precision Measurements and the LHC

   Yi Cai🇦🇺 · Michael A. Schmidt🇦🇺

   We compare the sensitivity of precision measurements of lepton flavour observables to the reach of the LHC in a case study of lepton-flavour violating operators of dimension six with two leptons and two quarks. For light quarks precision measurements always yield the more stringent constraints. The LHC complements precision measurements for operators with heavier quarks. Competitive limits can already be set on the cutoff scale $\Lambda$ > 600 - 800 GeV for operators with right-handed $\tau$ leptons using the LHC run 1 data.

   hep-phhep-exJHEP(2016)·18 citations
5. 05*

   Charm in Deep-Inelastic Scattering

   Richard D. Ball🇬🇧 · Marco Bonvini🇬🇧 · Luca Rottoli🇬🇧

   We show how to extend systematically the FONLL scheme for inclusion of heavy quark mass effects in DIS to account for the possible effects of an intrinsic charm component in the nucleon. We show that when there is no intrinsic charm, FONLL is equivalent to S-ACOT to any order in perturbation theory, while when an intrinsic charm component is included FONLL is identical to ACOT, again to all orders in perturbation theory. We discuss in detail the inclusion of top and bottom quarks to construct a variable flavour number scheme, and give explicit expressions for the construction of the structure functions $F_2^c$, $F_L^c$ and $F_3^c$ to NNLO.

   hep-phJHEP(2015)·56 citations
6. 06*

   Neutralino dark matter and naturalness of the electroweak scale

   Geneviève Bélanger🇫🇷 · Cédric Delaunay🇫🇷 · Andreas Goudelis🇦🇹

   If weak scale supersymmetry (SUSY) is to somehow explain the radiative stability of the Higgs boson mass, it is likely that non-minimal variants of SUSY models should be considered. Under the assumption that the dark matter of the universe is comprised of neutralinos, recent limits from direct detection experiments as well as dark matter abundance measurements place stringent bounds on the naturalness of minimal supersymmetric models. We show that even non-minimal models introducing moderately decoupled new physics in order to address the Higgs boson mass problem face similar issues, with one interesting exception.

   hep-phPoS(2015)·2 citations
7. 07*

   Neutrino Mixing: $A_4$ Variations

   Ernest Ma🇺🇸

   In the context of the non-Abelian discrete symmetry $A_4$, the neutrino mass matrix has been studied extensively. A brief update is presented to focus on the conceptual shift from tribimaximal mixing (${\theta }_{13}=0$, ${\theta }_{23}=\pi /4$, ${\tan }^2{\theta }_{12}=1/2$) to $\underline{\mathrm{cobimaximal}}$ mixing (${\theta }_{13}\ne 0$, ${\theta }_{23}=\pi /4$, ${\delta }_{CP}=\pm \pi /2$) which agrees well with present data. Three specific realistic examples are proposed, two with three and the third with just two parameters.

   hep-phPLB(2016)·70 citations
8. 08*

   Virtuality and Transverse Momentum Dependence of Pion Distribution Amplitude

   A. V. Radyushkin🇺🇸

   We describe basics of a new approach to transverse momentum dependence in hard exclusive processes. We develop it in application to the transition process \gamma^* \gamma -> \pi^0 at the handbag level. Our starting point is coordinate representation for matrix elements of operators (in the simplest case, bilocal O (0,z) ) describing a hadron with momentum p. Treated as functions of (pz) and z^2, they are parametrized through virtuality distribution amplitudes (VDA) \Phi (x, \sigma), with x being Fourier-conjugate to (pz) and \sigma Laplace-conjugate to z^2. For intervals with z^+=0, we introduce the transverse momentum distribution amplitude (TMDA) \Psi (x, k_\perp), and write it in terms of VDA \Phi (x, \sigma). The results of covariant calculations, written in terms of \Phi (x, \sigma) are converted into expressions involving \Psi (x, k_\perp). Starting with scalar toy models, we extend the analysis onto the case of spin-1/2 quarks and QCD. We propose simple models for soft VDAs/TMDAs, and use them for comparison of handbag results with experimental (BaBar and BELLE) data on the pion transition form factor. We also discuss how one can generate high-k_\perp tails from primordial soft distributions.

   hep-phPRD(2016)·13 citations
9. 09*

   Modelling the nucleon structure

   M. Burkardt (New Mexico State U.)🇺🇸 · B. Pasquini (Pavia U. and INFN-Pavia)🇮🇹

   We review the status of our understanding of nucleon structure based on the modelling of different kinds of parton distributions. We use the concept of generalized transverse momentum dependent parton distributions and Wigner distributions, which combine the features of transverse-momentum dependent parton distributions and generalized parton distributions. We revisit various quark models which account for different aspects of these parton distributions. We then identify applications of these distributions to gain a simple interpretation of key properties of the quark and gluon dynamics in the nucleon.

   hep-phhep-exnucl-thEPJA(2016)·53 citations
10. 10*

    Indirect searches for sterile neutrinos at a high-luminosity Z-factory

    Valentina De Romeri🇫🇷 · Asmaa Abada🇫🇷 · Stéphane Monteil🇫🇷 · Jean Orloff🇫🇷 · Ana M. Teixeira🇫🇷

    A future high-luminosity $Z$-factory has the potential to investigate lepton flavour violation. Rare decays such as $Z\to {\ell }_1^{\mp }{\ell }_2^{\pm }$ can be complementary to low-energy (high-intensity) observables of lepton flavour violation. Here we consider two extensions of the Standard Model which add to its particle content one or more sterile neutrinos. We address the impact of the sterile fermions on lepton flavour violating $Z$ decays, focusing on potential searches at FCC-ee (TLEP), and taking into account experimental and observational constraints. We show that sterile neutrinos can give rise to contributions to BR($Z\to {\ell }_1^{\mp }{\ell }_2^{\pm }$) within reach of the FCC-ee. We discuss the complementarity between a high-luminosity $Z$-factory and low-energy charged lepton flavour violation facilities.

    hep-phPoS(2015)·2 citations
11. 11*

    Flavour symmetries in a renormalizable SO(10) model

    P.M. Ferreira🇵🇹 · W. Grimus🇦🇹 · D. Jurčiukonis🇱🇹 · L. Lavoura🇵🇹

    In the context of a renormalizable supersymmetric SO(10) Grand Unified Theory, we consider the fermion mass matrices generated by the Yukawa couplings to a $10\oplus 120\oplus \overline{126}$ representation of scalars. We perform a complete investigation of the possibilities of imposing flavour symmetries in this scenario; the purpose is to reduce the number of Yukawa coupling constants in order to identify potentially predictive models. We have found that there are only 14 inequivalent cases of Yukawa coupling matrices, out of which 13 cases are generated by $Z_n$ symmetries, with suitable $n$, and one case is generated by a $Z_2\times Z_2$ symmetry. A numerical analysis of the 14 cases reveals that only two of them---dubbed A and B in the present paper---allow good fits to the experimentally known fermion masses and mixings.

    hep-phNPB(2016)·17 citations
12. 12*

    R-parity violating supersymmetry and neutrino physics: experimental signatures

    Vasiliki A. Mitsou🇪🇸

    $R$-parity violating supersymmetric models (RPV SUSY) are becoming increasingly more appealing than its $R$-parity conserving counterpart in view of the hitherto non-observation of SUSY signals at the LHC. In this paper, we discuss RPV scenarios where neutrino masses are naturally generated, namely RPV through bilinear terms (bRPV) and the $\mu$-from-$\nu$ supersymmetric standard model ($\mu \nu$SSM). The latter is characterised by a rich Higgs sector that easily accommodates a 125-GeV Higgs boson. The phenomenology of such models at the LHC is reviewed, giving emphasis on final states with displaced objects, and relevant results obtained by LHC experiments are presented. The implications for dark matter for these theoretical proposals is also addressed.

    hep-phPoS(2015)·17 citations
13. 13*

    LHC phenomenology of light pseudoscalars in the NMSSM

    N.-E. Bomark🇳🇴 · S. Moretti🇬🇧 · S. Munir🇰🇷 · L. Roszkowski🇵🇱

    After the discovery of the 125 GeV Higgs boson, the Next-to-Minimal Supersymmetric Standard Model (NMSSM) has become more interesting as a model for new physics since new tree-level contributions to the Higgs mass makes it easier to accommodate the relatively high measured value, as compared to the MSSM. One very distinctive feature of the NMSSM is the possible existence of a light singlet-like pseudoscalar. As this pseudoscalar may be lighter than the discovered Higgs boson without conflict with data, it may lead to LHC signatures rather different to what is usually searched for in terms of new physics. In these proceedings we will discuss studies concerning the discoverability of such light pseudoscalars. It is demonstrated that heavier scalars decaying to pairs of pseudoscalars or pseudoscalars and Z bosons may lead to discovery in a large part of the parameter space. This is especially important for the non-SM like of the two lightest scalars, as it may have an almost 100% branching ratio for decay into pairs of pseudoscalars. In such a case the discussed channels might be our only means of discovery, also for the scalar.

    hep-phPoS(2015)·1 citation
14. 14*

    NP models with extended gauge groups and extra dimensions: Impact on flavour observables in RS${}_c$

    Fulvia De Fazio🇮🇹

    Deviations with respect to Standard Model predictions have recently shown up in angular distributions of the FCNC induced mode $B^0\to K^{\ast 0}{\mu }^{+}{\mu }^{-}$. Within New Physics models, such tensions might be explained by new contributions to the Wilson coefficients of the effective Hamiltonian governing this decay. I discuss the issue in the framework of the Randall-Sundrum model with custodial protection (RS${}_c$), giving also predictions for other rare $B$ decays.

    hep-phhep-exPoS(2015)·0 citations
15. 15*

    Spinor-vector duality and light Z' in heterotic string vacua

    Alon E. Faraggi🇬🇧 · John Rizos🇬🇷

    We discuss the construction of heterotic--string models that allow for the existence of an extra $Z^{\prime }$ at low scales. One of the main difficulties encountered is that the desired symmetries tend to be anomalous in the prevailing three generation constructions. The reason is that these models utilise the symmetry breaking pattern $E_6\to SO(10)\times U(1{)}_{\zeta }$ by GGSO projections. Consequently, $U(1{)}_{\zeta }$ becomes anomalous. The spinor--vector duality that was observed in the fermionic $Z_2\times Z_2$ orbifold compactifications is used to construct a phenomenological three generation Pati--Salam heterotic--string model in which $U(1{)}_{\zeta }$ is anomaly free and therefore can be a component of a low scale $Z^{\prime }$. The model implies existence of matter states at the $Z^{\prime }$ breaking scale, which are required for anomaly cancelation. Moreover, the string model gives rise to exotic states, which are $SO(10)$ singlets but carry exotic $U(1{)}_{\zeta }$ charges. These states arise due to the breaking of $E_6$ by discrete Wilson lines and provide natural dark matter candidates. Initial indications suggest that the existence of additional gauge symmetries at the TeV scale may be confirmed in run II of the LHC experiment.

    hep-phhep-thPoS(2016)·2 citations
16. 16*

    Automated NLO QCD Corrections with WHIZARD

    C. Weiss🇩🇪 · B. Chokoufe Nejad🇩🇪 · W. Kilian🇩🇪 · J. Reuter🇩🇪

    We briefly discuss the current status of NLO QCD automation in the Monte Carlo event generator WHIZARD. The functionality is presented for the explicit study of off-shell top quark production with associated backgrounds at a lepton collider.

    hep-phPoS(2015)·25 citations
17. 17*

    Gravitational waves from the first order phase transition of the Higgs field at high energy scales

    Ryusuke Jinno🇯🇵 · Kazunori Nakayama🇯🇵 · Masahiro Takimoto🇯🇵

    In a wide class of new physics models, there exist scalar fields that obtain vacuum expectation values of high energy scales. We study the possibility that the standard model Higgs field has experienced first order phase transition at the high energy scale due to the couplings with these scalar fields. We estimate the amount of gravitational waves produced by the phase transition, and discuss observational consequences.

    hep-phastro-ph.COPRD(2016)·42 citations
18. 18*

    Matching NLO QCD Corrections in WHIZARD with the POWHEG scheme

    B. Chokoufe Nejad🇩🇪 · W. Kilian🇩🇪 · J. Reuter🇩🇪 · C. Weiss🇩🇪

    Building on the new automatic subtraction of NLO amplitudes in WHIZARD, we present our implementation of the POWHEG scheme to match radiative corrections consistently with the parton shower. We apply this general framework to two linear collider processes, $e^{+}{e}^{-}\to t\bar{t}$ and $e^{+}{e}^{-}\to t\bar{t}H$.

    hep-phPoS(2015)·26 citations
19. 19*

    BEC-BCS crossover in a cold and magnetized two color NJL model

    Dyana C. Duarte🇧🇷 · P. G. Allen🇦🇷 · R. L. S. Farias🇧🇷 · Patrícia H. A. Manso🇧🇷 · Rudnei O. Ramos🇧🇷 · N. N. Scoccola🇦🇷

    The BEC-BCS crossover for a NJL model with diquark interactions is studied in the presence of an external magnetic field. Particular attention is paid to different regularization schemes used in the literature. A thorough comparison of results is performed for the case of a cold and magnetized two-color NJL model. According to our results, the critical chemical potential for the BEC transition exhibits a clear inverse magnetic catalysis effect for magnetic fields in the range $1\lesssim eB/m_{\pi }^2\lesssim 20$. As for the BEC-BCS crossover, the corresponding critical chemical potential is very weakly sensitive to magnetic fields up to $eB\sim 9m_{\pi }^2$, showing a much smaller inverse magnetic catalysis as compared to the BEC transition, and displays a strong magnetic catalysis from this point on.

    hep-phcond-mat.supr-conhep-thnucl-thPRD(2016)·44 citations
20. 20*

    Neutrino spin and dispersion in magnetized medium

    P.A.Eminov (Moscow State University of Information Technologies, Radioengineering and Electronics)🇷🇺

    The neutrino dispersion in the magnetized medium was analyzed as a function of the neutrino spin and mass. It was shown that in a super-strong magnetic field plasma contribution to the neutrino energy greatly exceeds the analogous correction in the field-free case.

    hep-phAdv.High Energy Phys.(2016)·6 citations
21. 21*

    Composite Vector Particles in External Electromagnetic Fields

    Zohreh Davoudi🇺🇸 · William Detmold🇺🇸

    Lattice quantum chromodynamics (QCD) studies of electromagnetic properties of hadrons and light nuclei, such as magnetic moments and polarizabilities, have proven successful with the use of background field methods. With an implementation of nonuniform background electromagnetic fields, properties such as charge radii and higher electromagnetic multipole moments (for states of higher spin) can be additionally obtained. This can be achieved by matching lattice QCD calculations to a corresponding low-energy effective theory that describes the static and quasi-static response of hadrons and nuclei to weak external fields. With particular interest in the case of vector mesons and spin-1 nuclei such as the deuteron, we present an effective field theory of spin-1 particles coupled to external electromagnetic fields. To constrain the charge radius and the electric quadrupole moment of the composite spin-1 field, the single-particle Green's functions in a linearly varying electric field in space are obtained within the effective theory, providing explicit expressions that can be used to match directly onto lattice QCD correlation functions. The viability of an extraction of the charge radius and the electric quadrupole moment of the deuteron from the upcoming lattice QCD calculations of this nucleus is discussed.

    ↳ hep-lathep-phnucl-thPRD(2016)·7 citations
22. 22*

    Novel Scenarios for Majorana Neutrino Mass Generation and Leptogenesis from Kalb-Ramond Torsion

    Nick E. Mavromatos🇬🇧

    The Kalb-Ramond (KR) antisymmetric tensor field arises naturally in the gravitational multiplet of string theory. Nevertheless, the respective low-energy field theory action, in which, for reasons of gauge invariance, the only dependence on the KR field is through its field strength, constitutes an interesting model \emph{per se}. In this context, the KR field strength also acts as a totally antisymmetric torsion field, while in four space-time dimensions is \emph{dual} to an (KR) axion-like pseudoscalar field. In this context, we review here first the rôle of quantum fluctuations of the KR axion on the generation of Majorana mass for neutrinos, via a mixing with ordinary axions that may exist in the theory as providers of dark matter candidates. Then we proceed to discuss the rôle of constant in time (thus Lorentz violating) KR torsion backgrounds, that may exist in the early Universe but are completely negligible today, on inducing Leptogenesis by means of \emph{tree-level} CP violating decays of Right Handed Massive Majorana neutrinos in the presence of such H-torsion backgrounds. Some speculations regarding microscopic D-brane world models, where such scenarios may be realised, are also given.

    ↳ hep-thhep-phPoS(2015)·0 citations
23. 23*

    Explaining TeV Cosmic-Ray Anisotropies with Non-Diffusive Cosmic-Ray Propagation

    J. Patrick Harding🇺🇸 · Chris L. Fryer🇺🇸 · Susan Mendel🇺🇸

    Constraining the behavior of cosmic ray data observed at Earth requires a precise understanding of how the cosmic rays propagate in the interstellar medium. The interstellar medium is not homogeneous; although turbulent magnetic fields dominate over large scales, small coherent regions of magnetic field exist on scales relevant to particle propagation in the nearby Galaxy. Guided propagation through a coherent field is significantly different from random particle diffusion and could be the explanation of spatial anisotropies in the observed cosmic rays. We present a Monte Carlo code to propagate cosmic particle through realistic magnetic field structures. We discuss the details of the model as well as some preliminary studies which indicate that coherent magnetic structures are important effects in local cosmic-ray propagation, increasing the flux of cosmic rays by over two orders of magnitude at anisotropic locations on the sky. The features induced by coherent magnetic structure could be the cause of the observed TeV cosmic-ray anisotropy.

    ↳ astro-ph.HEastro-ph.GAhep-phApJ(2016)·16 citations
24. 24*

    A Study of Fluctuations of Voids in Relativistic Ion-Ion Collisions

    Shakeel Ahmad🇮🇳 · M.M. Khan🇮🇳 · Shaista Khan🇮🇳 · A. Khatun🇮🇳 · M. Irfan🇮🇳

    Event-by-event fluctuations (ebe) of hadronic patterns are investigated in terms of voids by analyzing the experimental data on 4.5, 14.5 and 60A GeV/c 16O-AgBr collisions. The findings are compared with the predictions of a multi-phase transport AMPT model. Dependence of voids on phase space bin width is examined in terms of two lowest moments of event-by-event fluctuations of voids, <Gq> and Sq. The findings reveal that scaling exponent estimated from the observed power-law behavior of the voids may be used to characterize the various properties of hadronic phase transition. The results also rule out occurrence of 2nd order quark-hadron phase transition at the projectile energies considered.

    ↳ nucl-exhep-phnucl-thIJMPE(2015)·3 citations
25. 25*

    Comparison of semiclassical and Wigner function methods in pair production in rotating fields

    Alexander Blinne🇩🇪 · Eckhard Strobel🇮🇹

    We present a comparison of two methods to compute the momentum spectrum and the Schwinger pair creation rate for pulsed rotating electric fields: one based upon the real-time Dirac--Heisenberg--Wigner (DHW) formalism and a semiclassical approximation based on a scattering ansatz. For the semiclassical method we propose to either perform numerical calculations or an additional approximation based on an analytical solution for the constant rotating field. We find that both numerical methods are complementary with respect to computation time as well as accuracy. The approximate method shows the same qualitative features while being computationally much faster. We additionally find that the unequal production of pairs in different spin states reported for constant rotating fields with the scattering method is in agreement with the Wigner function method.

    ↳ hep-thhep-phPRD(2016)·54 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.