Thu·May 12, 2016Thursday·May 12, 2016

1. 01*

   Assessing lepton-flavour non-universality from $B\to K^{\ast }\ell \ell$ angular analyses

   Bernat Capdevila🇪🇸 · Sebastien Descotes-Genon🇫🇷 · Joaquim Matias🇪🇸 · Javier Virto🇩🇪

   The $B\to K^{\ast }\mu \mu$ decay exhibits deviations with respect to Standard Model expectations and the measurement of the ratio $R_K$ hints at a violation of lepton-flavour universality in $B\to K\ell \ell$ transitions. Both effects can be understood in model-independent fits as a short-distance contribution to the Wilson coefficient $C_{9\mu }$, with some room for similar contributions in other Wilson coefficients for $b\to s\mu \mu$ transitions. We discuss how a full angular analysis of $B\to K^{\ast }ee$ and its comparison with $B\to K^{\ast }\mu \mu$ could improve our understanding of these anomalies and help confirming their interpretation in terms of short-distance New Physics. We discuss several observables of interest in this context and provide predictions for them within the Standard Model as well as within several New Physics benchmark scenarios. We pay special attention to the sensitivity of these observables to hadronic uncertainties from SM contributions with charm loops.

   hep-phhep-exJHEP(2016)·146 citations
2. 02*

   Adaptive Integrand Decomposition in parallel and orthogonal space

   Pierpaolo Mastrolia🇮🇹 · Tiziano Peraro🇬🇧 · Amedeo Primo🇮🇹

   We present the integrand decomposition of multiloop scattering amplitudes in parallel and orthogonal space-time dimensions, $d=d_{\parallel }+d_{\perp }$, being $d_{\parallel }$ the dimension of the parallel space spanned by the legs of the diagrams. When the number $n$ of external legs is $n\le 4$, the corresponding representation of the multiloop integrals exposes a subset of integration variables which can be easily integrated away by means of Gegenbauer polynomials orthogonality condition. By decomposing the integration momenta along parallel and orthogonal directions, the polynomial division algorithm is drastically simplified. Moreover, the orthogonality conditions of Gegenbauer polynomials can be suitably applied to integrate the decomposed integrand, yielding the systematic annihilation of spurious terms. Consequently, multiloop amplitudes are expressed in terms of integrals corresponding to irreducible scalar products of loop momenta and external momenta. We revisit the one-loop decomposition, which turns out to be controlled by the maximum-cut theorem in different dimensions, and we discuss the integrand reduction of two-loop planar and non-planar integrals up to $n=8$ legs, for arbitrary external and internal kinematics. The proposed algorithm extends to all orders in perturbation theory.

   hep-phhep-thJHEP(2016)·91 citations
3. 03*

   The masses of the neutrinos

   Peter S. Cooper🇺🇸

   If the cosmological limits on the sum of the neutrino masses are taken seriously we have first measurements of the masses of the neutrinos. Using the Planck experiment's limit ${\sum }_{i=1}^3{m}_i<230meV$ and some simple assumptions on measurement uncertainties the mass of the heaviest neutrino is $63\pm 11meV$ and the lightest $40\pm 18meV$ for either hierarchy.

   hep-ph1 citation
4. 04*

   Solving the Wrong Hierarchy Problem

   Nikita Blinov🇺🇸 · Anson Hook🇺🇸

   Many theories require augmenting the Standard Model with additional scalar fields with large order one couplings. We present a new solution to the hierarchy problem for these scalar fields. We explore parity- and ${\mathbb{Z}}_2$-symmetric theories where the Standard Model Higgs potential has two vacua. The parity or ${\mathbb{Z}}_2$ copy of the Higgs lives in the minimum far from the origin while our Higgs occupies the minimum near the origin of the potential. This approach results in a theory with multiple light scalar fields but with only a single hierarchy problem, since the bare mass is tied to the Higgs mass by a discrete symmetry. The new scalar does not have a new hierarchy problem associated with it because its expectation value and mass are generated by dimensional transmutation of the scalar quartic coupling. The location of the second Higgs minimum is not a free parameter, but is rather a function of the matter content of the theory. As a result, these theories are extremely predictive. We develop this idea in the context of a solution to the strong CP problem. We show this mechanism postdicts the top Yukawa to be within $1\sigma$ of the currently measured value and predicts scalar color octets with masses in the range 9-200 TeV.

   hep-phJHEP(2016)·17 citations
5. 05*

   QCDLoop: a comprehensive framework for one-loop scalar integrals

   Stefano Carrazza🇨🇭 · R. Keith Ellis🇬🇧 · Giulia Zanderighi🇨🇭

   We present a new release of the QCDLoop library based on a modern object-oriented framework. We discuss the available new features such as the extension to the complex masses, the possibility to perform computations in double and quadruple precision simultaneously, and useful caching mechanisms to improve the computational speed. We benchmark the performance of the new library, and provide practical examples of phenomenological implementations by interfacing this new library to Monte Carlo programs.

   hep-phhep-exhep-thComput.Phys.Commun.(2016)·80 citations
6. 06*

   SusHi Bento: Beyond NNLO and the heavy-top limit

   Robert V. Harlander🇩🇪 · Stefan Liebler🇩🇪 · Hendrik Mantler🇩🇪

   Version 1.6.0 of the code SusHi is presented. Concerning inclusive CP-even Higgs production in gluon fusion, the following new features with respect to previous versions have been implemented: expansion of the partonic cross section in the soft limit, i.e. around $x=M_H^2/\hat{s}\to 1$; N${}^3$LO QCD corrections in terms of the soft expansion; top-quark mass suppressed terms through NNLO; matching to the cross section at $x\to 0$ through N${}^3$LO. For CP-even and -odd scalars, an efficient evaluation of the renormalization-scale dependence is included, and effects of dimension-5 operators can be studied, which we demonstrate for the SM Higgs boson and for a CP-even scalar with a mass of $750$ GeV. In addition, as a generalization of the previously available $b\bar{b}\to H$ cross section, SusHi 1.6.0 provides the cross section for charged and neutral Higgs production in the annihilation of arbitrary heavy quarks. At fixed order in perturbation theory, SusHi thus allows to obtain Higgs cross-section predictions in different models to the highest precision known today. For the SM Higgs boson of $M_H=125$ GeV, SusHi yields $48.28$ pb for the gluon-fusion cross section at the LHC at $13$ TeV. Simultaneously, SusHi provides the renormalization-scale uncertainty of $\pm 1.97$ pb.

   hep-phComput.Phys.Commun.(2017)·219 citations
7. 07*

   Charged Particles Multiplicity and Scaling Violation of Fragmentation Functions in Electron-Positron Annihilation

   Tooraj Ghaffary🇮🇷

   In electron positron annihilation, changing quarks into the final hadron states is being described by fragmentation function. Based on the scaling hypothesis, this function will be independent from the center of mass energy. Gluon radiation violates the scaling feature. Transverse momentum distribution plays an important role in scaling violation of fragmentation functions. In this article, by the use of data resulted from the annihilation process of electron positron in AMY detector at 60 GeV center of mass energy, first, charged particles multiplicity distribution will be obtained and it will be fitted with the KNO scaling. Furthermore, momentum spectra of charged particles and momentum distribution respect to the jet axis will be obtained. Then, the results will be compared regarding the different models of QCD; as well, the distribution of fragmentation functions and scaling violations will be studied. It is being expected that the scaling violations of the fragmentation functions of gluon jet are stronger to the quark one. One of the reasons for such case is that splitting function of jet is larger than splitting function of gluon.

   hep-phAdv.High Energy Phys.(2016)·1 citation
8. 08*

   Gamma-ray Signals from Dark Matter Annihilation Via Charged Mediators

   Jason Kumar🇺🇸 · Pearl Sandick🇺🇸 · Fei Teng🇺🇸 · Takahiro Yamamoto🇺🇸

   We consider a simplified model in which Majorana fermion dark matter annihilates to charged fermions through exchange of charged mediators. We consider the gamma-ray signals arising from the processes $XX\to \bar{f}f\gamma$, $\gamma \gamma$, and $\gamma Z$ in the most general case, including non-trivial fermion mass and non-trivial left-right mixing and $CP$-violating phase for the charged mediators. In particular, we find the most general spectrum for internal bremsstrahlung, which interpolates between the regimes dominated by virtual internal bremsstrahlung and by final state radiation. We also examine the variation in the ratio $\sigma (\gamma \gamma )/\sigma (\gamma Z)$ and the helicity asymmetry in the $XX\to \gamma \gamma$ process, each as a function of mixing angle and $CP$-violating phase. As an application, we apply these results to searches for a class of MSSM models.

   hep-phastro-ph.COastro-ph.HEPRD(2016)·29 citations
9. 09*

   Partially Natural Two Higgs Doublet Models

   Patrick Draper🇺🇸 · Howard E. Haber🇺🇸 · Joshua T. Ruderman🇺🇸

   It is possible that the electroweak scale is low due to the fine-tuning of microscopic parameters, which can result from selection effects. The experimental discovery of new light fundamental scalars other than the Standard Model Higgs boson would seem to disfavor this possibility, since generically such states imply parametrically worse fine-tuning with no compelling connection to selection effects. We discuss counterexamples where the Higgs boson is light because of fine-tuning, and a second scalar doublet is light because a discrete symmetry relates its mass to the mass of the Standard Model Higgs boson. Our examples require new vectorlike fermions at the electroweak scale, and the models possess a rich electroweak vacuum structure. The mechanism that we discuss does not protect a small CP-odd Higgs mass in split or high-scale supersymmetry-breaking scenarios of the MSSM due to an incompatibility between the discrete symmetries and holomorphy.

   hep-phJHEP(2016)·14 citations
10. 10*

    QCD unitarity constraints on Reggeon Field Theory

    Alex Kovner🇺🇸 · Eugene Levin🇮🇱 · Michael Lublinsky🇮🇱

    We point out that the $s$-channel unitarity of QCD imposes meaningful constraints on a possible form of the QCD Reggeon Field Theory. We show that neither the BFKL nor JIMWLK nor Braun's Hamiltonian satisfy the said constraints. In a toy, zero transverse dimensional case we construct a model that satisfies the analogous constraint and show that at infinite energy it indeed tends to a "black disk limit" as opposed to the model with triple Pomeron vertex only, routinely used as a toy model in the literature.

    hep-phhep-thJHEP(2016)·20 citations
11. 11*

    Opportunities with (semi)leptonic rare charm decays

    Stefan de Boer🇩🇪

    We study (semi)leptonic rare charm decays and its opportunities in searches for physics beyond the Standard Model (BSM). In particular, we analyse the impact of potential BSM physics in $c\to ul{l}^{\prime }$ transitions, notably branching ratios, angular observables, asymmetries and Lepton Flavour Violating (LFV) decays. Testable effects are worked out model-independently and within Leptoquark models supplemented with flavour patterns to link $K$/$B$ decays.

    hep-ph1 citation
12. 12*

    Next-to-leading-order electroweak corrections to $pp\to W^{+}{W}^{-}\to$ 4 leptons at the LHC

    Benedikt Biedermann🇩🇪 · Marina Billoni🇩🇪 · Ansgar Denner🇩🇪 · Stefan Dittmaier🇩🇪 · Lars Hofer🇪🇸 · Barbara Jager🇩🇪 · Lukas Salfelder🇩🇪

    We present results of the first calculation of next-to-leading-order electroweak corrections to W-boson pair production at the LHC that fully takes into account leptonic W-boson decays and off-shell effects. Employing realistic event selections, we discuss the corrections in situations that are typical for the study of W-boson pairs as a signal process or of Higgs-boson decays $H\to W{W}^{\ast }$, to which W-boson pair production represents an irreducible background. In particular, we compare the full off-shell results, obtained treating the W-boson resonances in the complex-mass scheme, to previous results in the so-called double-pole approximation, which is based on an expansion of the loop amplitudes about the W resonance poles. At small and intermediate scales, i.e. in particular in angular and rapidity distributions, the two approaches show the expected agreement at the level of fractions of a percent, but larger differences appear in the TeV range. For transverse-momentum distributions, the differences can even exceed the 10% level in the TeV range where "background diagrams" with one instead of two resonant W bosons gain in importance because of recoil effects.

    hep-phhep-exJHEP(2016)·104 citations
13. 13*

    Modeling two-boson mass distributions, E(38 MeV) and Z(57.5 GeV)

    Eef van Beveren🇵🇹 · George Rupp🇵🇹 · Susana Coito🇨🇳

    Besides general features of two-boson mass distributions, experimental results are are discussed. Furthermore, E(38 MeV) and Z(57.5 GeV) are highlighted.

    hep-phhep-exActa Phys.Polon.Supp.(2016)·2 citations
14. 14*

    Quasi-exotic open-flavor mesons

    T. Hilger🇦🇹 · A. Krassnigg🇦🇹

    Meson states with exotic quantum numbers arise naturally in a covariant bound-state framework in QCD. We investigate the consequences of shifting quark masses such that the states are no longer restricted to certain C-parities, but only by J^P. Then, a priori, one can no longer distinguish exotic or conventional states. In order to identify signatures of the different states to look for experimentally, we provide the behavior of masses, leptonic decay constants, and orbital-angular-momentum decomposition of such mesons, as well as the constellations in which they could be found. Most prominently, we consider the case of charged quasi-exotic excitations of the pion.

    hep-phhep-exEPJA(2017)·17 citations
15. 15*

    Strong-field Breit-Wheeler pair production in short laser pulses: Relevance of spin effects

    M. J. A. Jansen🇩🇪 · J. Z. Kamiński🇵🇱 · K. Krajewska🇵🇱 · C. Müller🇩🇪

    Production of electron-positron pairs in the collision of a high-energy photon with a high-intensity few-cycle laser pulse is studied. By utilizing the frameworks of laser-dressed spinor and scalar quantum electrodynamics, a comparison between the production of pairs of Dirac and Klein-Gordon particles is drawn. Positron energy spectra and angular distributions are presented for various laser parameters. We identify conditions under which predictions from Klein-Gordon theory either closely resemble or largely differ from those of the proper Dirac theory. In particular, we address the question to which extent the relevance of spin effects is influenced by the short duration of the laser pulse.

    hep-phphysics.atom-phPRD(2016)·43 citations
16. 16*

    Proton structure in high-energy high-multiplicity p-p collisions

    Stanislaw D. Glazek🇵🇱 · Patryk Kubiczek🇵🇱

    A few-body proton image, expected to be derivable from QCD in the renormalization group procedure for effective particles, is used within the Monte Carlo Glauber model to calculate the anisotropy coefficients in the initial collision-state of matter in high-energy high-multiplicity proton-proton interaction events. We estimate the ridge-like correlations in the final hadronic state by assuming their proportionality to the initial collision-state anisotropy. In our estimates, some distinct few-body proton structures appear capable of accounting for the magnitude of p-p ridge effect, with potentially discernible differences in dependence on multiplicity.

    hep-phFew Body Syst.(2016)·9 citations
17. 17*

    Search for time-independent Lorentz violation using muon neutrino to muon antineutrino transitions in MINOS

    P. Adamson · I. Anghel · A. Aurisano · G. Barr · M. Bishai · A. Blake · G. J. Bock · D. Bogert · S. V. Cao · T. J. Carroll · C. M. Castromonte · R. Chen and 108 other authors

    Data from the MINOS experiment has been used to search for mixing between muon neutrinos and muon antineutrinos using a time-independent Lorentz-violating formalism derived from the Standard-Model Extension (SME). MINOS is uniquely capable of searching for muon neutrino-antineutrino mixing given its long baseline and ability to distinguish between neutrinos and antineutrinos on an event-by-event basis. Neutrino and antineutrino interactions were observed in the MINOS Near and Far Detectors from an exposure of 10.56$\times 10^{20}$ protons-on-target from the NuMI neutrino-optimized beam. No evidence was found for such transitions and new, highly stringent limits were placed on the SME coefficients governing them. We place the first limits on the SME parameters $(c_L{)}_{\mu \mu }^{TT}$ and $(c_L{)}_{\tau \tau }^{TT}$ at $-8.4\times 10^{-23}<(c_L{)}_{\mu \mu }^{TT}<8.0\times 10^{-23}$ and $-8.0\times 10^{-23}<(c_L{)}_{\tau \tau }^{TT}<8.4\times 10^{-23}$, and the world's best limits on the ${\tilde{g}}_{\mu \overline{\mu }}^{ZT}$ and ${\tilde{g}}_{\tau \overline{\tau }}^{ZT}$ parameters at $|{\tilde{g}}_{\mu \overline{\mu }}^{ZT}|<3.3\times 10^{-23}$ and $|{\tilde{g}}_{\tau \overline{\tau }}^{ZT}|<3.3\times 10^{-23}$, all limits quoted at $3\sigma$.

    ↳ hep-exhep-ph0 citations
18. 18*

    $K$-essence model from the mechanical approach point of view: coupled scalar field and the late cosmic acceleration

    Mariam Bouhmadi-López🇪🇸 · K. Sravan Kumar🇵🇹 · João Marto🇵🇹 · João Morais🇪🇸 · Alexander Zhuk🇺🇦

    In this paper, we consider the Universe at the late stage of its evolution and deep inside the cell of uniformity. At these scales, we can consider the Universe to be filled with dust-like matter in the form of discretely distributed galaxies, a $K$-essence scalar field, playing the role of dark energy, and radiation as matter sources. We investigate such a Universe in the mechanical approach. This means that the peculiar velocities of the inhomogeneities (in the form of galaxies) as well as the fluctuations of the other perfect fluids are non-relativistic. Such fluids are designated as coupled because they are concentrated around the inhomogeneities. In the present paper, we investigate the conditions under which the $K$-essence scalar field with the most general form for its action can become coupled. We investigate at the background level three particular examples of the $K$-essence models: (i) the pure kinetic $K$-essence field, (ii) a $K$-essence with a constant speed of sound and (iii) the $K$-essence model with the Lagrangian $bX+c{X}^2-V(\varphi )$. We demonstrate that if the $K$-essence is coupled, all these $K$-essence models take the form of multicomponent perfect fluids where one of the component is the cosmological constant. Therefore, they can provide the late-time cosmic acceleration and be simultaneously compatible with the mechanical approach.

    ↳ gr-qcastro-ph.COhep-phhep-thJCAP(2016)·11 citations
19. 19*

    Fermion self-energy in magnetized chirally asymmetric QED matter

    D.O. Rybalka🇺🇸

    The fermion self-energy is calculated for a cold QED plasma with chiral chemical potential in a magnetic field. It is found that a momentum shift parameter dynamically generated in such a plasma leads to a modification of the chiral magnetic effect current. It is argued that the momentum shift parameter can be relevant for the evolution of magnetic field in the chirally asymmetric primordial plasma in the early Universe.

    ↳ nucl-thhep-phhep-thJ.Phys.G(2016)·0 citations
20. 20*

    Review of Nucleon Decay Searches at Super-Kamiokande

    Volodymyr Takhistov (for the Super-Kamiokande Collaboration)🇺🇸

    Baryon number violation appears in many contexts. It is a requirement for baryogenesis and is a consequence of Grand Unified Theories (GUTs), which predict nucleon decay. Nucleon decay searches provide the most direct way to test baryon number conservation and also serve as a unique probe of GUT scale physics around $10^{14-16}$ GeV. Such energies cannot be reached directly by accelerators. However, they can be explored indirectly at large underground water Cherenkov (WC) experiments, which due to the size of their fiducial volume are highly sensitive to nucleon decays. We review searches for baryon number violating processes at the state of the art WC detector, the Super-Kamiokande. Analyses of the typically dominant non-SUSY and SUSY nucleon decay channels such as $p\to (e^{+},{\mu }^{+}){\pi }^0$ and $p\to \nu K^{+}$, as well as more exotic searches, will be discussed. Presented studies set the world's best limits, which circumvent the allowed parameter space of theoretical models

    ↳ hep-exhep-ph85 citations
21. 21*

    Goldilocks Models of Higher-Dimensional Inflation (including modulus stabilization)

    C.P. Burgess🇨🇦 · Jared J.H. Enns🇨🇦 · Peter Hayman🇨🇦 · Subodh P. Patil🇨🇭

    We explore the mechanics of inflation in simplified extra-dimensional models involving an inflaton interacting with the Einstein-Maxwell system in two extra dimensions. The models are Goldilocks-like in that they are just complicated enough to include a mechanism to stabilize the extra-dimensional size, yet simple enough to solve the full 6D field equations using basic tools. The solutions are not limited to the effective 4D regime with H << m_KK (the latter referring to the mass splitting of the Kaluza-Klein excitations) because the full 6D Einstein equations are solved. This allows an exploration of inflationary physics in a controlled regime away from the usual 4D lamp-post. The inclusion of modulus stabilization is important as experience with string models teaches that this is usually what makes models fail: stabilization energies dominate the shallow potentials required by slow roll and open up directions to evolve that are steeper than those of the putative inflationary direction. We explore three representative inflationary scenarios within this simple setup. In one the radion is trapped in an inflaton-dependent local minimum whose non-zero energy drives inflation. Inflation ends as this energy relaxes to zero when the inflaton finds its minimum. The others involve power-law solutions during inflation. One is an attractor whose features are relatively insensitive to initial conditions but whose slow-roll parameters cannot be arbitrarily small; the other is not an attractor but can roll much more slowly, until eventually decaying to the attractor. These solutions can satisfy H > m_KK, but when they do standard 4D fluctuation calculations need not apply. When in a 4D regime the solutions predict eta ~ 0 hence r ~ 0.11 when n_s ~ 0.96 and so are ruled out if tensor modes remain unseen. Analysis of general parameters is difficult without a full 6D fluctuation calculation.

    ↳ gr-qcastro-ph.COhep-phhep-thJCAP(2016)·10 citations
22. 22*

    The $B\to K^{\ast }$ form factors on the lattice

    Andria Agadjanov (Bonn U. and Bonn U., HISKP)🇩🇪 · Véronique Bernard (Orsay, IPN)🇫🇷 · Ulf-G. Meißner (Bonn U. and Bonn U., HISKP and IAS, Julich and Julich, Forschungszentrum and JCHP, Julich)🇩🇪 · Akaki Rusetsky (Bonn U. and Bonn U., HISKP)🇩🇪

    The extraction of the $B\to K^{\ast }$ transition form factors from lattice data is studied, applying non-relativistic effective field theory in a finite volume. The possible mixing of $\pi K$ and $\eta K$ states is taken into account. The two-channel analogue of the Lellouch-Lüscher formula is reproduced. Due to the resonance nature of the $K^{\ast }$, an equation is derived, which allows to determine the form factors at the pole position in a process-independent manner. The infinitely-narrow width approximation of the results is discussed.

    ↳ hep-lathep-phNPB(2016)·44 citations
23. 23*

    Sub-threshold charm production in nuclear collisions

    J. Steinheimer🇩🇪 · A. Botvina🇩🇪 · M. Bleicher🇩🇪

    We present the first predictions for sub-threshold open charm and charmonium production in nuclear collisions. The production mechanism is driven by multi-step scatterings of nucleons and their resonance states, accumulating sufficient energy for the production of $J/\Psi$, ${\Lambda }_c+\overline{D}$ and $D+\overline{D}$. Our results are of particular importance for the CBM experiment at FAIR, as they indicate that already at the SIS100 accelerator one can expect a significant number of charmed hadrons to be produced. This opens new possibilities to explore charm dynamics and the formation of charmed nuclei.

    ↳ nucl-thhep-phPRC(2017)·32 citations
24. 24*

    Review of Searches for Rare Processes and Physics Beyond the Standard Model at HERA

    David M. South🇩🇪 · Monica Turcato🇩🇪

    The electron-proton collisions collected by the H1 and ZEUS experiments at HERA comprise a unique particle physics data set, and a comprehensive range of measurements has been performed to provide new insight into the structure of the proton. The high centre of mass energy at HERA has also allowed rare processes to be studied, including the production of W and Z bosons and events with multiple leptons in the final state. The data have also opened up a new domain to searches for physics beyond the Standard Model including contact interactions, leptoquarks, excited fermions and a number of supersymmetric models. This review presents a summary of such results, where the analyses reported correspond to an integrated luminosity of up to 1 fb^-1, representing the complete data set recorded by the H1 and ZEUS experiments.

    ↳ hep-exhep-phEPJC(2016)·15 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.