Wed·May 24, 2017Wednesday·May 24, 2017

1. 01*

   Is Renormalization in QCD Necessary at High Energy Colliders ?

   Gouranga C. Nayak🇺🇸

   In this paper by using the path integral formulation of the background field method of QCD in the presence of SU(3) pure gauge background field we simultaneously prove the renormalization of ultra violet (UV) divergences and the factorization of infrared (IR) and collinear divergences in QCD at all orders in coupling constant. We prove that although perturbative QCD is renormalizable but due to confinement in QCD it is not necessary to renormalize QCD to study hadrons production at high energy colliders. This is consistent with the fact that the partons are not directly experimentally observed but the hadrons are directly experimentally observed.

   hep-phnucl-th19 citations
2. 02*

   A global fit of the MSSM with GAMBIT

   The GAMBIT Collaboration: Peter Athron🇦🇺 · Csaba Balázs🇦🇺 · Torsten Bringmann🇳🇴 · Andy Buckley🇬🇧 · Marcin Chrząszcz🇨🇭 · Jan Conrad🇸🇪 · Jonathan M. Cornell🇨🇦 · Lars A. Dal🇳🇴 · Joakim Edsjö🇸🇪 · Ben Farmer🇸🇪 · Paul Jackson🇦🇺 · Abram Krislock🇳🇴 and 12 other authors

   We study the seven-dimensional Minimal Supersymmetric Standard Model (MSSM7) with the new GAMBIT software framework, with all parameters defined at the weak scale. Our analysis significantly extends previous weak-scale, phenomenological MSSM fits, by adding more and newer experimental analyses, improving the accuracy and detail of theoretical predictions, including dominant uncertainties from the Standard Model, the Galactic dark matter halo and the quark content of the nucleon, and employing novel and highly-efficient statistical sampling methods to scan the parameter space. We find regions of the MSSM7 that exhibit co-annihilation of neutralinos with charginos, stops and sbottoms, as well as models that undergo resonant annihilation via both light and heavy Higgs funnels. We find high-likelihood models with light charginos, stops and sbottoms that have the potential to be within the future reach of the LHC. Large parts of our preferred parameter regions will also be accessible to the next generation of direct and indirect dark matter searches, making prospects for discovery in the near future rather good.

   hep-phastro-ph.COEPJC(2017)·154 citations
3. 03*

   ColliderBit: a GAMBIT module for the calculation of high-energy collider observables and likelihoods

   Csaba Balázs🇦🇺 · Andy Buckley🇬🇧 · Lars A. Dal🇳🇴 · Ben Farmer🇸🇪 · Paul Jackson🇦🇺 · Abram Krislock🇳🇴 · Anders Kvellestad🇸🇪 · Daniel Murnane🇦🇺 · Antje Putze🇫🇷 · Are Raklev🇳🇴 · Christopher Rogan🇺🇸 · Aldo Saavedra🇦🇺 and 3 other authors

   We describe ColliderBit, a new code for the calculation of high energy collider observables in theories of physics beyond the Standard Model (BSM). ColliderBit features a generic interface to BSM models, a unique parallelised Monte Carlo event generation scheme suitable for large-scale supercomputer applications, and a number of LHC analyses, covering a reasonable range of the BSM signatures currently sought by ATLAS and CMS. ColliderBit also calculates likelihoods for Higgs sector observables, and LEP searches for BSM particles. These features are provided by a combination of new code unique to ColliderBit, and interfaces to existing state-of-the-art public codes. ColliderBit is both an important part of the GAMBIT framework for BSM inference, and a standalone tool for efficiently applying collider constraints to theories of new physics.

   hep-phhep-exEPJC(2017)·102 citations
4. 04*

   DarkBit: A GAMBIT module for computing dark matter observables and likelihoods

   Torsten Bringmann🇳🇴 · Jan Conrad🇸🇪 · Jonathan M. Cornell🇨🇦 · Lars A. Dal🇳🇴 · Joakim Edsjö🇸🇪 · Ben Farmer🇸🇪 · Felix Kahlhoefer🇩🇪 · Anders Kvellestad🇸🇪 · Antje Putze🇫🇷 · Christopher Savage🇸🇪 · Pat Scott🇬🇧 · Christoph Weniger🇳🇱 · Martin White🇦🇺 · Sebastian Wild (The GAMBIT Dark Matter Workgroup)🇩🇪

   We introduce DarkBit, an advanced software code for computing dark matter constraints on various extensions to the Standard Model of particle physics, comprising both new native code and interfaces to external packages. This release includes a dedicated signal yield calculator for gamma-ray observations, which significantly extends current tools by implementing a cascade decay Monte Carlo, as well as a dedicated likelihood calculator for current and future experiments (gamlike). This provides a general solution for studying complex particle physics models that predict dark matter annihilation to a multitude of final states. We also supply a direct detection package that models a large range of direct detection experiments (DDcalc), and provides the corresponding likelihoods for arbitrary combinations of spin-independent and spin-dependent scattering processes. Finally, we provide custom relic density routines along with interfaces to DarkSUSY, micrOMEGAs, and the neutrino telescope likelihood package nuLike. DarkBit is written in the framework of the Global And Modular Beyond the Standard Model Inference Tool (GAMBIT), providing seamless integration into a comprehensive statistical fitting framework that allows users to explore new models with both particle and astrophysics constraints, and a consistent treatment of systematic uncertainties. In this paper we describe its main functionality, provide a guide to getting started quickly, and show illustrative examples for results obtained with DarkBit (both as a standalone tool and as a GAMBIT module). This includes a quantitative comparison between two of the main dark matter codes (DarkSUSY and micrOMEGAs), and application of DarkBit's advanced direct and indirect detection routines to a simple effective dark matter model.

   hep-phastro-ph.COastro-ph.IMEPJC(2017)·174 citations
5. 05*

   CEPC Precision of Electroweak Oblique Parameters and Weakly Interacting Dark Matter: the Scalar Case

   Chengfeng Cai🇨🇳 · Zhao-Huan Yu🇦🇺 · Hong-Hao Zhang🇨🇳

   We investigate the sensitivity to weakly interacting scalar dark matter from future determination of electroweak oblique parameters in the Circular Electron-Positron Collider (CEPC) project. As illuminating examples, three dark matter models with scalar electroweak multiplets are studied. The multiplet couplings to the standard model Higgs doublet can break the mass degeneracy among the components, leading to nonzero contributions to oblique parameters. The dark matter candidate in these model is either a CP-even or CP-odd scalar, whose trilinear coupling to the Higgs boson could induce direct detection signals. For some moderate coupling values, we find that the CEPC sensitivity can be better than current direct detection experiments, exploring up to a TeV mass scale.

   hep-phhep-exNPB(2017)·29 citations
6. 06*

   Status of the scalar singlet dark matter model

   The GAMBIT Collaboration: Peter Athron🇦🇺 · Csaba Balázs🇦🇺 · Torsten Bringmann🇳🇴 · Andy Buckley🇬🇧 · Marcin Chrząszcz🇨🇭 · Jan Conrad🇸🇪 · Jonathan M. Cornell🇨🇦 · Lars A. Dal🇳🇴 · Joakim Edsjö🇸🇪 · Ben Farmer🇸🇪 · Paul Jackson🇦🇺 · Felix Kahlhoefer🇩🇪 and 14 other authors

   One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a ${\mathbb{Z}}_2$ symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above $\sim$1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.

   hep-phastro-ph.COEPJC(2017)·271 citations
7. 07*

   FlavBit: A GAMBIT module for computing flavour observables and likelihoods

   Florian U. Bernlochner🇩🇪 · Marcin Chrzaszcz🇨🇭 · Lars A. Dal🇳🇴 · Ben Farmer🇸🇪 · Paul Jackson🇦🇺 · Anders Kvellestad🇸🇪 · Farvah Mahmoudi🇫🇷 · Antje Putze🇫🇷 · Christopher Rogan🇺🇸 · Pat Scott🇬🇧 · Nicola Serra🇨🇭 · Christoph Weniger🇳🇱 · Martin White (The GAMBIT Flavour Workgroup)🇦🇺

   Flavour physics observables are excellent probes of new physics up to very high energy scales. Here we present FlavBit, the dedicated flavour physics module of the global-fitting package GAMBIT. FlavBit includes custom implementations of various likelihood routines for a wide range of flavour observables, including detailed uncertainties and correlations associated with LHCb measurements of rare, leptonic and semileptonic decays of B and D mesons, kaons and pions. It provides a generalised interface to external theory codes such as SuperIso, allowing users to calculate flavour observables in and beyond the Standard Model, and then test them in detail against all relevant experimental data. We describe FlavBit and its constituent physics in some detail, then give examples from supersymmetry and effective field theory illustrating how it can be used both as a standalone library for flavour physics, and within GAMBIT.

   hep-phhep-exphysics.data-anEPJC(2017)·73 citations
8. 08*

   Global fits of GUT-scale SUSY models with GAMBIT

   The GAMBIT Collaboration: Peter Athron🇦🇺 · Csaba Balázs🇦🇺 · Torsten Bringmann🇳🇴 · Andy Buckley🇬🇧 · Marcin Chrząszcz🇨🇭 · Jan Conrad🇸🇪 · Jonathan M. Cornell🇨🇦 · Lars A. Dal🇳🇴 · Joakim Edsjö🇸🇪 · Ben Farmer🇸🇪 · Paul Jackson🇦🇺 · Abram Krislock🇳🇴 and 13 other authors

   We present the most comprehensive global fits to date of three supersymmetric models motivated by grand unification: the Constrained Minimal Supersymmetric Standard Model (CMSSM), and its Non-Universal Higgs Mass generalisations NUHM1 and NUHM2. We include likelihoods from a number of direct and indirect dark matter searches, a large collection of electroweak precision and flavour observables, direct searches for supersymmetry at LEP and Runs I and II of the LHC, and constraints from Higgs observables. Our analysis improves on existing results not only in terms of the number of included observables, but also in the level of detail with which we treat them, our sampling techniques for scanning the parameter space, and our treatment of nuisance parameters. We show that stau co-annihilation is now ruled out in the CMSSM at more than 95\% confidence. Stop co-annihilation turns out to be one of the most promising mechanisms for achieving an appropriate relic density of dark matter in all three models, whilst avoiding all other constraints. We find high-likelihood regions of parameter space featuring light stops and charginos, making them potentially detectable in the near future at the LHC. We also show that tonne-scale direct detection will play a largely complementary role, probing large parts of the remaining viable parameter space, including essentially all models with multi-TeV neutralinos.

   hep-phastro-ph.COEPJC(2017)·155 citations
9. 09*

   SpecBit, DecayBit and PrecisionBit: GAMBIT modules for computing mass spectra, particle decay rates and precision observables

   The GAMBIT Models Workgroup: Peter Athron🇦🇺 · Csaba Balázs🇦🇺 · Lars A. Dal🇳🇴 · Joakim Edsjö🇸🇪 · Ben Farmer🇸🇪 · Tomás E. Gonzalo🇳🇴 · Anders Kvellestad🇸🇪 · James McKay🇬🇧 · Antje Putze🇫🇷 · Chris Rogan🇺🇸 · Pat Scott🇬🇧 · Christoph Weniger🇳🇱 · Martin White🇦🇺

   We present the GAMBIT modules SpecBit, DecayBit and PrecisionBit. Together they provide a new framework for linking publicly available spectrum generators, decay codes and other precision observable calculations in a physically and statistically consistent manner. This allows users to automatically run various combinations of existing codes as if they are a single package. The modular design allows software packages fulfilling the same role to be exchanged freely at runtime, with the results presented in a common format that can be easily passed to downstream dark matter, collider and flavour codes. These modules constitute an essential part of the broader GAMBIT framework, a major new software package for performing global fits. In this paper we present the observable calculations, data, and likelihood functions implemented in the three modules, as well as the conventions and assumptions used in interfacing them with external codes. We also present 3-BIT-HIT, a command-line utility for computing mass spectra, couplings, decays and precision observables in the MSSM, which shows how the three modules can be easily used independently of GAMBIT.

   hep-phEPJC(2018)·69 citations
10. 10*

    Comparison of statistical sampling methods with ScannerBit, the GAMBIT scanning module

    The GAMBIT Scanner Workgroup: Gregory D. Martinez🇺🇸 · James McKay🇬🇧 · Ben Farmer🇸🇪 · Pat Scott🇬🇧 · Elinore Roebber🇨🇦 · Antje Putze🇫🇷 · Jan Conrad🇸🇪

    We introduce ScannerBit, the statistics and sampling module of the public, open-source global fitting framework GAMBIT. ScannerBit provides a standardised interface to different sampling algorithms, enabling the use and comparison of multiple computational methods for inferring profile likelihoods, Bayesian posteriors, and other statistical quantities. The current version offers random, grid, raster, nested sampling, differential evolution, Markov Chain Monte Carlo (MCMC) and ensemble Monte Carlo samplers. We also announce the release of a new standalone differential evolution sampler, Diver, and describe its design, usage and interface to ScannerBit. We subject Diver and three other samplers (the nested sampler MultiNest, the MCMC GreAT, and the native ScannerBit implementation of the ensemble Monte Carlo algorithm T-Walk) to a battery of statistical tests. For this we use a realistic physical likelihood function, based on the scalar singlet model of dark matter. We examine the performance of each sampler as a function of its adjustable settings, and the dimensionality of the sampling problem. We evaluate performance on four metrics: optimality of the best fit found, completeness in exploring the best-fit region, number of likelihood evaluations, and total runtime. For Bayesian posterior estimation at high resolution, T-Walk provides the most accurate and timely mapping of the full parameter space. For profile likelihood analysis in less than about ten dimensions, we find that Diver and MultiNest score similarly in terms of best fit and speed, outperforming GreAT and T-Walk; in ten or more dimensions, Diver substantially outperforms the other three samplers on all metrics.

    hep-phastro-ph.COastro-ph.IMphysics.data-an+1EPJC(2017)·128 citations
11. 11*

    Probing the No-Scale $\mathcal{F}$-$SU(5)$ One-Parameter Model via Gluino Searches at the LHC2

    Tianjun Li🇨🇳 · James A. Maxin🇺🇸 · Dimitri V. Nanopoulos🇺🇸

    In our recent paper entitled "The return of the King: No-Scale $\mathcal{F}$-$SU(5)$", we showed that the model space supporting the most favorable phenomenology should have been probed in 2016 at the LHC2, with an even further reach into this region of the model in 2017-18. This ideal realm of the one-parameter version of No-Scale $\mathcal{F}$-$SU(5)$ yields a 1.9-2.3 TeV gluino mass at the very same point where the light Higgs boson mass enters its rather narrow experimentally determined range of $m_h=125.09\pm 0.24$ GeV. Given the recent results reported at Moriond 2017 for 36 ${\mathrm{fb}}^{-1}$ of luminosity collected in 2016 at the 13 TeV LHC2, we now update the status of the No-Scale $\mathcal{F}$-$SU(5)$ model space in light of the gluino mass exclusion limits presented by the ATLAS and CMS Collaborations. We illustrate that a resolution could be reached soon as to whether supersymmetry lives in this most critical region of the model space.

    hep-phPLB(2017)·3 citations
12. 12*

    Probing flavor parameters in the scalar sector and new bounds for the fermion sector

    R. Gaitán🇲🇽 · J.H. Montes de Oca🇲🇽 · J.A. Orduz-Ducuara🇲🇽

    In this paper we study the Flavor-Changing mediated by Higgs boson within Two-Higgs Doublet Model-III context. We explore the parameter space and, considering recent results, find new limits for the model parameters. We also obtain the total Higgs decay width and the branching ratios for different channels taking limits for the $t\to cV$ and $b\to s\gamma$ processes. Considering different constraints, we estimate the branching ratio for the $h\to t_{}^{\ast }c$ in the model as well as the bounds for the $b\to s\gamma$, $h\to \mu \tau$ and $h\to \gamma Z.$ Considering the quark top decays to $W\bar{b},$ we obtained $Br(h\to Wc\bar{b})\sim 10^{-3}$.

    hep-phPTEP(2017)·3 citations
13. 13*

    What is a parton shower?

    Zoltan Nagy🇩🇪 · Davison E. Soper🇺🇸

    We consider idealized parton shower event generators that treat parton spin and color exactly, leaving aside the choice of practical approximations for spin and color. We investigate how the structure of such a parton shower generator is related to the structure of QCD. We argue that a parton shower with splitting functions proportional to ${\alpha }_s$ can be viewed not just as a model, but as the lowest order approximation to a shower that is defined at any perturbative order. To support this argument, we present a formulation for a parton shower at order ${\alpha }_s^k$ for any $k$. Since some of the input functions needed are specified by their properties but not calculated, this formulation does not provide a useful recipe for an order ${\alpha }_s^k$ parton shower algorithm. However, in this formulation we see how the operators that generate the shower are related to operators that specify the infrared singularities of QCD.

    hep-phPRD(2018)·69 citations
14. 14*

    The Geometric Origin of the CP Phase

    H. Fanchiotti🇦🇷 · C.A. García Canal🇦🇷 · V. Vento🇪🇸

    The complex phase present in CP-violating systems such as neutral kaons is shown to be of geometrical origin. It is also concluded that the complex phase of the Cabibbo--Kobayashi--Maskawa (CKM) matrix is a Berry-like phase.

    hep-ph3 citations
15. 15*

    Non-relativistic approximate numerical ideal-magneto hydrodynamics of (1+1) D transverse flow in Bjorken scenario

    M. Haddadi Moghaddam🇮🇷 · B. Azadegan🇮🇷 · A. F. Kord🇮🇷 · W. M. Alberico🇮🇹

    In this study, we investigate the impact of the magnetic field on the evolution of the transverse flow of QGP matter in the magneto-hydrodynamic (MHD) framework. We assume that the magnetic field is perpendicular to the reaction plane and then we solve the coupled Maxwell and conservation equations in (1+1D) transverse flow, within the Bjorken scenario. We consider a QGP with infinite electrical conductivity. First, the magnetic effects on the QGP medium at mid-rapidity are investigated at leading order; then the time and space dependence of the energy density, velocity and magnetic field in the transverse plane of the ideal magnetized hot plasma are obtained.

    hep-phEPJC(2018)·13 citations
16. 16*

    The photon PDF from high-mass Drell Yan data at the LHC using xFitter

    Francesco Giuli🇬🇧

    In this contribution, we review the results of the recent paper "The photon PDF from high-mass Drell Yan data at the LHC" (arXiv:1701.08553), where a determination of the photon PDF from fits to recent ATLAS measurements of high-mass Drell-Yan dilepton production at centre-of-mass energy of 8 TeV is presented.

    hep-phPoS(2018)·2 citations
17. 17*

    Differential single jet inclusive production at Next-to-Next-to-Leading Order in QCD

    James Currie🇬🇧 · E.W.N. Glover🇬🇧 · Aude Gehrmann-De Ridder🇨🇭 · Thomas Gehrmann🇨🇭 · Alexander Huss🇨🇭 · Joao Pires🇩🇪

    In this talk we present the recent calculation in all partonic channels of the fully differential single jet inclusive cross section at Next-to-Next-to-Leading Order in QCD. We discuss the size and shape of the perturbative corrections as a function of the functional form of the renormalisation and factorisation scales and compare the predictions at NLO and NNLO to the available ATLAS 7 TeV data. We find significant effects at low-$p_T$ due to changes in the functional form of the scale choice whereas at high-$p_T$ the two most common scale choices in the literature give identical results and the perturbative corrections lead to a substantial reduction in the scale dependence of the theoretical prediction at NNLO.

    hep-ph4 citations
18. 18*

    Spontaneous breakdown of charge in the MSSM and in the NMSSM: Possibilities and Implications

    Jyotiranjan Beuria🇮🇳 · AseshKrishna Datta🇮🇳

    We study the possibilities and the implications of a spontaneous breakdown of charge in the MSSM and in the $Z_3$-symmetric NMSSM. The breakdown is triggered by the charged states of the Higgs doublets acquiring vacuum expectation values. In the MSSM, it is known that the presence of a charge conserving minimum for the tree-level Higgs potential precludes a deeper (global) charge-breaking minimum. We find that the inclusion of radiative correction to the potential does not alter the situation while a deeper charge-conserving minimum could arise, albeit with no major practical consequences. In the NMSSM scenario, a charge-breaking global minimum, with or without an accompanying charge-conserving deeper minimum, could appear even with the tree-level Higgs potential thanks to the presence of a charge-neutral scalar state which transforms as a singlet under the Standard Model gauge group. Use of the NMSSM Higgs potential that includes both quantum and thermal corrections and the requirement of a viable (stable or long-lived) vacuum that breaks the electroweak symmetry, along with its compatibility with the latest Higgs data, lead to nontrivial constraints on the NMSSM parameter space.

    hep-phJHEP(2017)·3 citations
19. 19*

    Spectroscopy, Decay properties and Regge trajectories of the $B$ and $B_s$ mesons

    Virendrasinh Kher🇮🇳 · Nayneshkumar Devlani🇮🇳 · Ajay Kumar Rai🇮🇳

    A Gaussian wave function is used for detailed study of mass spectra of the $B$ and $B_S$ mesons using a Cornell potential incorporated with a $\mathcal{O}(1/m)$ correction in the potential energy term and expansion of the kinetic energy term up to a $\mathcal{O}\left({\mathbf{p}}^{10}\right)$ for relativistic correction of the Hamiltonian. The predicted excited states for the $B$ and $B_s$ mesons are in very good agreement with results obtained by experiment. We assigned the $B_2(5747)$ and $B_{s2}(5840)$ as $1^3{p}_2$ state, the $B_1(5721)$ and $B_{s1}(5830)$ as $1p_1$ state, the $B_0(5732)$ as $1^3{p}_0$ state, the $B_{s1}(5850)$ as $1p_1^{{}^{\prime }}$ state and the $B(5970)$ as $2^3{S}_1$ state. We investigate the Regge trajectories in the $(J,M^2)$ and $(n_r,M^2)$ planes with their corresponding parameters. Branching ratio for leptonic and radiative-leptonic decays are estimated for the $B$ and $B_S$ mesons. Our results are in good agreement with experimental observation as well as outcomes of other theoretical models.

    hep-phCPC(2017)·38 citations
20. 20*

    Radiative neutrino mass in an alternative $U(1{)}_{B-L}$ gauge symmetry

    Takaaki Nomura🇰🇷 · Hiroshi Okada🇹🇼

    We propose a neutrino model in which neutrino masses are generated at one loop level and three right-handed fermions have non-trivial charges under $U(1{)}_{B-L}$ gauge symmetry in no conflict with anomaly cancellation. After the spontaneously symmetry breaking, a remnant $Z_2$ symmetry is induced and plays an role in assuring the stability of dark matter candidate.

    hep-phNPB(2019)·35 citations
21. 21*

    Limiting Majoron self-interactions from Gravitational waves experiments

    Andrea Addazi🇨🇳 · Antonino Marciano🇨🇳

    We show how Majoron models may be tested/limited in gravitational waves experiments. In particular, the Majoron self-interaction potential may induce a first order phase transition, producing gravitational waves from bubble collisions. We dubbed such a new scenario {\it violent Majoron model}, because it would be associated to a violent phase transition in the early Universe. Sphaleron constraints can be avoided if the global $U(1{)}_{B-L}$ is broken at scales lower than the electroweak scale, provided that the B-L spontaneously breaking scale is lower than $10\mathrm{TeV}$ in order to satisfy the cosmological mass density bound. The possibility of a sub-electroweak phase transition is practically unconstrained by cosmological bounds and it may be detected within the sensitivity of next generation of gravitational waves experiments: eLISA, DECIGO and BBO. We also comment on the possible detection in CEPC collider, where Majorons's production can be observed from Higgs' portals in missing transverse energy channels.

    hep-phgr-qcCPC(2018)·19 citations
22. 22*

    New explicit expressions for Dirac bilinears

    Cédric Lorcé (Ecole polytechnique, CPHT)🇫🇷

    We derive new explicit expressions for the Dirac bilinears based on a generic representation of the massive Dirac spinors with canonical polarization. These bilinears depend on a direction $n$ in Minkowski space which specifies the form of dynamics. We argue that such a dependence is unavoidable in a relativistic theory with spin, since it originates from Wigner rotation effects. Contrary to most of the expressions found in the literature, our ones are valid for all momenta and canonical polarizations of the spinors. As a by-product, we also obtain a generic explicit expression for the covariant spin vector.

    hep-phhep-thnucl-thPRD(2018)·44 citations
23. 23*

    New light mediators for the $R_K$ and $R_{K^{\ast }}$ puzzles

    Alakabha Datta🇺🇸 · Jacky Kumar🇮🇳 · Jiajun Liao🇺🇸 · Danny Marfatia🇺🇸

    The measurements of $R_K$ and $R_K^{\ast }$ provide hints for the violation of lepton universality. However, it is generally difficult to explain the $R_{K^{\ast }}$ measurement in the low $q^2$ range, $0.045\le q^2\le 1.1$ GeV${}^2$. Light mediators offer a solution by making the Wilson coefficients $q^2$ dependent. We check if new lepton nonuniversal interactions mediated by a scalar ($S$) or vector particle ($Z^{\prime }$) of mass between $10-200$ MeV can reproduce the data. We find that a 25 MeV $Z^{\prime }$ with a $q^2$-dependent $b-s$ coupling and that couples to the electron but not the muon can explain all three anomalies in conjunction with other measurements. A similar 25 MeV $S$ provides a good fit to all relevant data except $R_{K^{\ast }}$ in the low $q^2$ bin. A 25 MeV $Z^{\prime }$ with a $q^2$-dependent $b-s$ coupling and that couples to the muon but not the electron provides a good fit to the combination of the $R_K$ and $R_{K^{\ast }}$ data, but does not fit $R_{K^{\ast }}$ in the low $q^2$ bin well.

    hep-phhep-exPRD(2018)·76 citations
24. 24*

    Higgs-photon resonances

    Bogdan A. Dobrescu🇺🇸 · Patrick J. Fox🇺🇸 · John Kearney🇺🇸

    We study models that produce a Higgs boson plus photon ($h^0\gamma$) resonance at the LHC. When the resonance is a $Z^{\prime }$ boson, decays to $h^0\gamma$ occur at one loop. If the $Z^{\prime }$ boson couples at tree-level to quarks, then the $h^0\gamma$ branching fraction is typically of order $10^{-5}$ or smaller. Nevertheless, there are models that would allow the observation of $Z^{\prime }\to h^0\gamma$ at $\sqrt{s}=13$ TeV with a cross section times branching fraction larger than 1 fb for a $Z^{\prime }$ mass in the 200--450 GeV range, and larger than 0.1 fb for a mass up to 800 GeV. The 1-loop decay of the $Z^{\prime }$ into lepton pairs competes with $h^0\gamma$, even if the $Z^{\prime }$ couplings to leptons vanish at tree level. We also present a model in which a $Z^{\prime }$ boson decays into a Higgs boson and a pair of collimated photons, mimicking an $h^0\gamma$ resonance. In this model, the $h^0\gamma$ resonance search would be the discovery mode for a $Z^{\prime }$ as heavy as 2 TeV. When the resonance is a scalar, although decay to $h^0\gamma$ is forbidden by angular momentum conservation, the $h^0$ plus collimated photons channel is allowed. We comment on prospects of observing an $h^0\gamma$ resonance through different Higgs decays, on constraints from related searches, and on models where $h^0$ is replaced by a nonstandard Higgs boson.

    hep-phhep-exEPJC(2017)·18 citations
25. 25*

    The transverse momentum distribution of hadrons within jets

    Zhong-Bo Kang🇺🇸 · Xiaohui Liu🇨🇳 · Felix Ringer🇺🇸 · Hongxi Xing🇺🇸

    We study the transverse momentum distribution of hadrons within jets, where the transverse momentum is defined with respect to the standard jet axis. We consider the case where the jet substructure measurement is performed for an inclusive jet sample $pp\to \text{jet}+X$. We demonstrate that this observable provides new opportunities to study transverse momentum dependent fragmentation functions (TMDFFs) which are currently poorly constrained from data, especially for gluons. The factorization of the cross section is obtained within Soft Collinear Effective Theory (SCET), and we show that the relevant TMDFFs are the same as for the more traditional processes semi-inclusive deep inelastic scattering (SIDIS) and electron-positron annihilation. Different than in SIDIS, the observable for the in-jet fragmentation does not depend on TMD parton distribution functions which allows for a cleaner and more direct probe of TMDFFs. We present numerical results and compare to available data from the LHC.

    hep-phhep-exnucl-exnucl-thJHEP(2017)·115 citations
26. 26*

    A Fourth Exception in the Calculation of Relic Abundances

    Raffaele Tito D'Agnolo🇺🇸 · Duccio Pappadopulo🇺🇸 · Joshua T. Ruderman🇺🇸

    We propose that the dark matter abundance is set by the decoupling of inelastic scattering instead of annihilations. This coscattering mechanism is generically realized if dark matter scatters against states of comparable mass from the thermal bath. Coscattering points to dark matter that is exponentially lighter than the weak scale and has a suppressed annihilation rate, avoiding stringent constraints from indirect detection. Dark matter upscatters into states whose late decays can lead to observable distortions to the blackbody spectrum of the cosmic microwave background.

    hep-phastro-ph.COPRL(2017)·147 citations
27. 27*

    Inflation with $f(R,\varphi )$ in Jordan frame

    Jose Mathew🇮🇳 · Joseph P Johnson🇮🇳 · S. Shankaranarayanan🇮🇳

    We consider an $f(R)$ action that is non-minimally coupled to a massive scalar field. The model closely resembles scalar-tensor theory and by conformal transformation can be transformed to Einstein frame. To avoid the ambiguity of the frame dependence, we obtain an exact analytical solution in Jordan frame and show that the model leads to a period of accelerated expansion with an exit. Further, we compute the scalar and tensor power spectrum for the model and compare them with observations.

    ↳ gr-qcastro-ph.COhep-phGen.Rel.Grav.(2018)·12 citations
28. 28*

    A kinetic regime of hydrodynamic fluctuations and long time tails for a Bjorken expansion

    Yukinao Akamatsu🇯🇵 · Aleksas Mazeliauskas🇩🇪 · Derek Teaney🇺🇸

    We develop a set of kinetic equations for hydrodynamic fluctuations which are equivalent to nonlinear hydrodynamics with noise. The hydro-kinetic equations can be coupled to existing second order hydrodynamic codes to incorporate the physics of these fluctuations, which become dominant near the critical point. We use the hydro-kinetic equations to calculate the modifications of energy momentum tensor by thermal fluctuations from the earliest moments and at late times in Bjorken expansion. The solution to the kinetic equations precisely determines the coefficient of the first fractional power ($\propto {\tau }^{-3/2}$) in the energy momentum tensor gradient expansion. Numerically, we find that the contribution to the longitudinal pressure from hydrodynamic fluctuations is comparable to the second order hydrodynamic terms for typical medium parameters used to simulate heavy ion collisions.

    ↳ nucl-thhep-phnucl-exNPA(2017)·4 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.