Tue·Nov 29, 2016Tuesday·November 29, 2016

1. 01*

   Dynamics of the cosmological relaxation after reheating

   Kiwoon Choi🇰🇷 · Hyungjin Kim🇰🇷 · Toyokazu Sekiguchi🇰🇷

   We examine if the cosmological relaxation mechanism, which was proposed recently as a new solution to the hierarchy problem, can be compatible with high reheating temperature well above the weak scale. As the barrier potential disappears at high temperature, the relaxion rolls down further after the reheating, which may ruin the successful implementation of the relaxation mechanism. It is noted that if the relaxion is coupled to a dark gauge boson, the new frictional force arising from dark gauge boson production can efficiently slow down the relaxion motion, which allows the relaxion to be stabilized after the electroweak phase transition for a wide range of model parameters, while satisfying the known observational constraints.

   hep-phPRD(2017)·60 citations
2. 02*

   Pinning down the large-x gluon with NNLO top-quark pair differential distributions

   Michał Czakon🇩🇪 · Nathan P. Hartland🇳🇱 · Alexander Mitov🇬🇧 · Emanuele R. Nocera🇬🇧 · Juan Rojo🇳🇱

   Top-quark pair production at the LHC is directly sensitive to the gluon PDF at large x. While total cross-section data is already included in several PDF determinations, differential distributions are not, because the corresponding NNLO calculations have become available only recently. In this work we study the impact on the large-x gluon of top-quark pair differential distributions measured by ATLAS and CMS at $\sqrt{s}=8$ TeV. Our analysis, performed in the NNPDF3.0 framework at NNLO accuracy, allows us to identify the optimal combination of LHC top-quark pair measurements that maximize the constraints on the gluon, as well as to assess the compatibility between ATLAS and CMS data. We find that differential distributions from top-quark pair production provide significant constraints on the large-x gluon, comparable to those obtained from inclusive jet production data, and thus should become an important ingredient for the next generation of global PDF fits.

   hep-phhep-exJHEP(2017)·98 citations
3. 03*

   Resummation of Transverse Momentum Distributions in Distribution Space

   Markus A. Ebert🇩🇪 · Frank J. Tackmann🇩🇪

   Differential spectra in observables that resolve additional soft or collinear QCD emissions exhibit Sudakov double logarithms in the form of logarithmic plus distributions. Important examples are the total transverse momentum $q_T$ in color-singlet production, N-jettiness (with thrust or beam thrust as special cases), but also jet mass and more complicated jet substructure observables. The all-order logarithmic structure of such distributions is often fully encoded in differential equations, so-called (renormalization group) evolution equations. We introduce a well-defined technique of distributional scale setting, which allows one to treat logarithmic plus distributions like ordinary logarithms when solving these differential equations. In particular, this allows one (through canonical scale choices) to minimize logarithmic contributions in the boundary terms of the solution, and to obtain the full distributional logarithmic structure from the solution's evolution kernel directly in distribution space. We apply this technique to the $q_T$ distribution, where the two-dimensional nature of convolutions leads to additional difficulties (compared to one-dimensional cases like thrust), and for which the resummation in distribution (or momentum) space has been a long-standing open question. For the first time, we show how to perform the RG evolution fully in momentum space, thereby directly resumming the logarithms $[{\ln }^n(q_T^2/Q^2)/q_T^2{]}_{+}$ appearing in the physical $q_T$ distribution. The resummation accuracy is then solely determined by the perturbative expansion of the associated anomalous dimensions.

   hep-phJHEP(2017)·114 citations
4. 04*

   SUSY Meets Her Twin

   Andrey Katz🇨🇭 · Alberto Mariotti🇧🇪 · Stefan Pokorski🇵🇱 · Diego Redigolo🇮🇱 · Robert Ziegler🇩🇪

   We investigate the general structure of mirror symmetry breaking in the Twin Higgs scenario. We show, using the IR effective theory, that a significant gain in fine tuning can be achieved if the symmetry is broken hardly. We emphasize that weakly coupled UV completions can naturally accommodate this scenario. We analyze SUSY UV completions and present a simple Twin SUSY model with a tuning of around 10% and colored superpartners as heavy as 2 TeV. The collider signatures of general Twin SUSY models are discussed with a focus on the extended Higgs sectors.

   hep-phJHEP(2017)·65 citations
5. 05*

   Twist-4 contributions to semi-inclusive deeply inelastic scatterings with polarized beam and target

   Shu-yi Wei🇨🇳 · Yu-kun Song🇨🇳 · Kai-bao Chen🇨🇳 · Zuo-tang Liang🇨🇳

   We present for the first time the complete twist-4 result for the semi-inclusive deeply inelastic scattering $e^{-}N\to e^{-}qX$ with polarized electron and proton beams at the tree level of pQCD. The calculations have been carried out using the formulism obtained after collinear expansion where the multiple gluon scattering are taken into account and gauge links are obtained automatically in a systematical way. The results show in particular that there are twist-4 contributions to all the eight twist-2 structure functions for $e^{-}N\to e^{-}hX$ that correspond to the eight twist-2 transverse momentum dependent parton distribution functions. Such higher twist effects could be very significant and therefore have important impacts on extracting these three-dimensional parton distribution functions from the asymmetry data on $e^{-}N\to e^{-}hX$. We suggest also an approximate way for a rough estimation of such higher twist contributions.

   hep-phPRD(2017)·43 citations
6. 06*

   Is the exotic $0^{--}$ glueball a pure gluon state ?

   Alexandr Pimikov🇨🇳 · Hee-Jung Lee🇰🇷 · Nikolai Kochelev🇷🇺 · Pengming Zhang🇨🇳

   We present a new calculation of the mass and width of the exotic $0^{--}$ glueball in the framework of the QCD sum rules. We next construct a new current which couples to a pure $0^{--}$ gluon state and derive consistent and stable sum rules. A previously used current in this approach was shown to be inconsistent. We obtain for this state a mass $M_G=6.3_{-1.1}^{+0.8}$ GeV and an upper limit for the total width ${\Gamma }_G\le 235$ MeV. These values can be used as an important guide for the experimental search of this exotic state. We argue that the mixing of this glueball state with $0^{--}$ tetraquark is very small. Therefore, the exotic $0^{--}$ glueball can be considered as a pure gluon state.

   hep-phPRD(2017)·19 citations
7. 07*

   Strong Sector in non-minimal SUSY model

   Antonio Costantini🇮🇹

   We investigate the squark sector of a supersymmetric theory with an extended Higgs sector. We give the mass matrices of stop and sbottom, comparing the Minimal Supersymmetric Standard Model (MSSM) case and the non-minimal case. We discuss the impact of the extra superfields on the decay channels of the stop searched at the LHC.

   hep-phEPJ Web Conf.(2016)·0 citations
8. 08*

   Photon emission in QGP using AdS/QCD at finite chemical potential

   Miguel Angel Martin Contreras🇨🇴 · Jose Maria Rolando Roldan🇨🇴

   We calculate the photon emission rate and the electrical conductivity of the QGP at finite temperature and finite chemical potential using AdS/QCD approximations in an AdS Reissner Nordstrom background. To do so, we supposed the medium properties to be encoded in a geometric background. The results obtained in the hard wall and soft wall model are consistent with the observed phenomenology and they also in agree with other holographic results, as the D3/D7 or the Sakai Sugimoto models, suggesting the universality of AdS/CFT conjecture as tool to explore QCD.

   hep-ph0 citations
9. 09*

   The quasi-two-body decays $B_{(s)}\to (D_{(s)},{\bar{D}}_{(s)})\rho \to (D_{(s)},{\bar{D}}_{(s)})\pi \pi$ in the perturbative QCD factorization approach

   Ai-Jun Ma🇨🇳 · Ya Li🇨🇳 · Wen-Fei Wang🇨🇳 · Zhen-Jun Xiao🇨🇳

   In this paper, we studied the $B_{(s)}\to (D_{(s)},{\bar{D}}_{(s)})\rho \to (D_{(s)},{\bar{D}}_{(s)})\pi \pi$ decays by employing a framework for the quasi-two-body decays in the perturbative QCD (PQCD) factorization approach. We use the two-pion distribution amplitudes ${\Phi }_{\pi \pi }$, which contains both resonant and nonresonant contributions from the pion pair, to describe the final state interactions (FSIs) between the pions in the resonant region. We found that (a) for all considered decays, the PQCD predictions for their branching ratios based on the quasi-two-body and the two-body framework agree well with each other due to $\mathcal{B}(\rho \to \pi \pi )\approx 100\%$; For $B^{+}\to \overline{D^0}{\rho }^{+}\to \overline{D^0}{\pi }^{+}{\pi }^0$ and other four considered decay modes, the PQCD predictions do agree well with the measured values within errors; (b) the great difference between the PQCD predictions for $\mathcal{B}(B\to \bar{D}\rho \to \bar{D}\pi \pi )$ and $\mathcal{B}(B\to D\rho \to D\pi \pi )$ can be understood by the strong CKM suppression factor $R_{\mathrm{CKM}}\approx 3\times 10^{-4}$; (c) for the $B_s\to D\rho \to D\pi \pi$ and $B_s\to \bar{D}\rho \to \bar{D}\pi \pi$ decays, however, the PQCD predictions of $R_{s1}\approx 0.13$ and $R_{s2}\approx 0.14$ do agree very well with the moderate CKM suppression factor $R_{\mathrm{CKM}}^s\approx 0.14$; and (d) the PQCD predictions for the ratios $R_{D\rho }$ and the strong phase difference $\cos {\delta }_{D\rho }$ of the three $B\to \bar{D}\rho$ decay modes agree well with the LHCb measurements within one standard deviation.

   hep-phNPB(2017)·35 citations
10. 10*

    Analytical solution to DGLAP integro-differential equation in a simple toy-model with a fixed gauge coupling

    Gustavo Alvarez🇩🇪 · Gorazd Cvetic🇨🇱 · Bernd A. Kniehl🇩🇪 · Igor Kondrashuk🇨🇱 · Ivan Parra-Ferrada🇨🇱

    We consider a simple model for QCD dynamics in which DGLAP integro-differential equation may be solved analytically. This is a gauge model which possesses dominant evolution of gauge boson (gluon) distribution and in which the gauge coupling does not run. This may be $\mathcal{N}=4$ supersymmetric gauge theory with softly broken supersymmetry, other finite supersymmetric gauge theory with lower level of supersymmetry, or topological Chern-Simons field theories. We maintain only one term in the splitting function of unintegrated gluon distribution and solve DGLAP analytically for this simplified splitting function. The solution is found by use of the Cauchy integral formula. The solution restricts form of the unintegrated gluon distribution as function of momentum transfer and of Bjorken $x$. Then we consider an almost realistic splitting function of unintegrated gluon distribution as an input to DGLAP equation and solve it by the same method which we have developed to solve DGLAP equation for the toy-model. We study a result obtained for the realistic gluon distribution and find a singular Bessel-like behaviour in the vicinity of the point $x=0$ and a smooth behaviour in the vicinity of the point

    hep-phmath-phmath.MPQuantum Rep.(2023)·7 citations
11. 11*

    A Potential Model Approach in the Study of Static and Dynamic properties of Heavy-Light Quark-Antiquark Systems

    Sabyasachi Roy🇮🇳 · D K Choudhury🇮🇳

    We report some approximate analytic form of meson wave function constructed upon solving Schrodinger equation with linear plus Coulomb type Cornell potential. With this wave function, we study Isgur-Wise function and its derivatives for heavy-light mesons in the infinite heavy quark mass limit. We also explore the elastic form factors, charge radii and decay constants of pseudoscalar mesons in this QCD inspired quark model approach.

    hep-phQuant.Matt.(2016)·6 citations
12. 12*

    Lectures on Soft-Collinear Effective Theory

    Andrey Grozin🇷🇺

    Introductory lectures on SCET mainly following the first chapters of arXiv:1410.1892

    hep-ph4 citations
13. 13*

    Tau lepton production and decays: perspective of multi-dimensional distributions and Monte Carlo methods

    Z. Was🇵🇱

    Status of tau lepton decay Monte Carlo generator TAUOLA, its main applications and recent developments are reviewed. It is underlined, that in recent efforts on development of new hadronic currents, the multi-dimensional nature of distributions of the experimental data must be taken with a great care: lesson from comparison and fits to the BaBar and Belle data is recalled. It was found, that as in the past at a time of comparisons with CLEO and ALEPH data, proper fitting, to as detailed as possible representation of the experimental data, is essential for appropriate developments of models of tau decay dynamic. This multi-dimensional nature of distributions is also important for observables where tau leptons are used to constrain experimental data. In later part of the presentation,use of the TAUOLA program for phenomenology of W,Z,H decays at LHC is addressed, in particular in the context of the Higgs boson parity measurements. Some new results, relevant for QED lepton pair emission are mentioned as well.

    hep-phNucl.Part.Phys.Proc.(2017)·2 citations
14. 14*

    The signatures of doubly charged leptons in future linear colliders

    Yu-Chen Guo🇨🇳 · Chong-Xing Yue🇨🇳 · Zhi-Cheng Liu🇨🇳

    We discuss the production of the doubly charged leptons in future linear electron positron colliders, such as the International Linear Collider and Compact Linear Collider. Such states are introduced in extended weak-isospin multiplets by composite models. We discuss the production cross section of $e^{-}\gamma \to L^{--}{W}^{+}$ and carry out analyses for hadronic, semi-leptonic and pure leptonic channels based on the full simulation performance of the Silicon Detector. The 3- and 5-sigma statistical significance exclusion curves are provided in the model parameter space. It is found that the hadronic channel could offer the most possible detectable signature.

    hep-phJ.Phys.G(2017)·12 citations
15. 15*

    Curvaton as dark matter with secondary inflation

    Jinn-Ouk Gong🇰🇷 · Naoya Kitajima🇰🇷 · Takahiro Terada🇰🇷

    We consider a novel cosmological scenario in which a curvaton is long-lived and plays the role of cold dark matter (CDM) in the presence of a short, secondary inflation. Non-trivial evolution of the large scale cosmological perturbation in the curvaton scenario can affect the duration of the short term inflation, resulting in the inhomogeneous end of inflation. Non-linear parameters of the curvature perturbation are predicted to be fNL ~ 5/4 and gNL ~ 0. The curvaton abundance can be well diluted by the short-term inflation and accordingly, it does not have to decay into the Standard Model particles. Then the curvaton can account for the present CDM with the isocurvature perturbation being sufficiently suppressed because both the adiabatic and CDM isocurvature perturbations have the same origin. As an explicit example, we consider the thermal inflation scenario and a string axion as a candidate for this curvaton-dark matter. We further discuss possibilities to identify the curvaton-dark matter with the QCD axion.

    hep-phastro-ph.COJCAP(2017)·9 citations
16. 16*

    On the Color Dipole Picture

    Dieter Schildknecht🇩🇪

    We give a brief representation of the theoretical results from the color dipole picture, covering the total photoabsorption cross section, high-energy $J/\psi$ photoproduction with respect to recent experimental data from the LHCb Collaboration at CERN, and ultra-high energy neutrino scattering, relevant for the ICE-CUBE experiment.

    hep-phAIP Conf.Proc.(2017)·0 citations
17. 17*

    Charged Higgs Boson Searches at the LHC via Multiple $b\bar{b}{W}^{\pm }$ Final States

    Stefano Moretti🇬🇧 · Rui Santos🇵🇹 · Pankaj Sharma🇦🇺

    We review the prospects of the Large Hadron Collider in accessing heavy charged Higgs boson signals in $b\bar{b}{W}^{\pm }$ final states, wherein the contributing channels can be $H^{+}\to t\bar{b}$, $h{W}^{\pm }$, $H{W}^{\pm }$ and $A{W}^{\pm }$. In particular, we devise a selection strategy which optimizes their global yield. We consider a 2-Higgs Doublet Model Type-II and we assume as production mode $bg\to t{H}^{-}$ + c.c., the dominant one over the range $M_{H^{\pm }}\ge 480$ GeV, as dictated by $b\to s\gamma$ constraints. Possibilities of detection are found to be significant for various Run 2 energies and luminosities.

    hep-phPoS(2016)·3 citations
18. 18*

    Vector resonances at LHC Run II in composite 2HDM

    Stefano Di Chiara🇪🇪 · Matti Heikinheimo🇫🇮 · Kimmo Tuominen🇫🇮

    We consider a model where the electroweak symmetry breaking is driven by strong dynamics, resulting in an electroweak doublet scalar condensate, and transmitted to the standard model matter fields via another electroweak doublet scalar. At low energies the effective theory therefore shares features with a type-I two Higgs doublet model. However, important differences arise due to the rich composite spectrum expected to contain new vector resonances accessible at the LHC. We carry out a systematic analysis of the vector resonance signals at LHC and find that the model remains viable, but will be tightly constrained by direct searches as the projected integrated luminosity, around 200 fb${}^{-1}$, of the current run becomes available.

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

    Dark matter physics in neutrino specific two Higgs doublet model

    Seungwon Baek🇰🇷 · Takaaki Nomura🇰🇷

    Although the seesaw mechanism is a natural explanation for the small neutrino masses, there are cases when the Majorana mass terms for the right-handed neutrinos are not allowed due to symmetry. In that case, if neutrino-specific Higgs doublet is introduced, neutrinos become Dirac particles and their small masses can be explained by its small VEV. We show that the same symmetry, which we assume a global $U(1{)}_X$, can also be used to explain the stability of dark matter. In our model, a new singlet scalar breaks the global symmetry spontaneously down to a discrete $Z_2$ symmetry. The dark matter particle, lightest $Z_2$-odd fermion, is stabilized. We discuss the phenomenology of dark matter: relic density, direct detection, and indirect detection. We find that the relic density can be explained by a novel Goldstone boson channel or by resonance channel. In the most region of parameter space considered, the direct detections is suppressed well below the current experimental bound. Our model can be further tested in indirect detection experiments such as FermiLAT gamma ray searches or neutrinoless double beta decay experiments.

    hep-phJHEP(2017)·11 citations
20. 20*

    Nonabelian Higgs models: paving the way for asymptotic freedom

    Holger Gies🇩🇪 · Luca Zambelli🇩🇪

    Asymptotically free renormalization group trajectories can be constructed in nonabelian Higgs models with the aid of generalized boundary conditions imposed on the renormalized action. We detail this construction within the languages of simple low-order perturbation theory, effective field theory, as well as modern functional renormalization group equations. We construct a family of explicit scaling solutions using a controlled weak-coupling expansion in the ultraviolet, and obtain a standard Wilsonian RG relevance classification of perturbations about scaling solutions. We obtain global information about the quasi-fixed function for the scalar potential by means of analytic asymptotic expansions and numerical shooting methods. Further analytical evidence for such asymptotically free theories is provided in the large-N limit. We estimate the long-range properties of these theories, and identify initial/boundary conditions giving rise to a conventional Higgs phase.

    hep-phhep-thPRD(2017)·27 citations
21. 21*

    Aspects of Leptonic Flavour Mixing

    Ferruccio Feruglio🇮🇹

    Since the discovery of neutrino oscillations many ideas have been put forward to explain the special features of the leptonic mixing and the differences with respect to the quark sector. In this talk I review some of these proposals, emphasizing especially their predictability. In the light of the new data, I first revisit fixed-point relations among mixing angles and phases. Then I briefly comment on radiative neutrino masses. Finally I discuss the role of flavour symmetries. Given the very many existing models I focus on two classes of models. On the one hand I illustrate the ability of models based on a generalization of the anarchy idea in reproducing the main features of both the quark and the lepton spectrum, also in a GUT framework. On the other hand I discuss less ambitious but more predictive models based on discrete flavour symmetries, centered on the properties of the leptonic mixing matrix.

    hep-phJ.Phys.Conf.Ser.(2017)·1 citation
22. 22*

    On the IceCube Result on ${\bar{\nu }}_{\mu }\to {\bar{\nu }}_s$ Oscillations

    S. T. Petcov🇮🇹

    We elucidate the mechanism of enhancement of the ${\bar{\nu }}_{\mu }\to {\bar{\nu }}_s$ transitions at small mixing angles of Earth-core-crossing neutrinos, which is at the basis of the recent result of the IceCube experiment on atmospheric muon anti-neutrino oscillations into sterile anti-neutrino.

    hep-phInt.J.Mod.Phys.A(2017)·11 citations
23. 23*

    Event Shape Sorting: selecting events with similar evolution

    Boris Tomasik🇸🇰 · Renata Kopecna🇩🇪

    We present novel method for the organisation of events. The method is based on comparing event-by-event histograms of a chosen quantity Q that is measured for each particle in every event. The events are organised in such a way that those with similar shape of the Q-histograms end-up placed close to each other. We apply the method on histograms of azimuthal angle of the produced hadrons in ultrarelativsitic nuclear collisions. By selecting events with similar azimuthal shape of their hadron distribution one chooses events which are likely that they underwent similar evolution from the initial state to the freeze-out. Such events can more easily be compared to theoretical simulations where all conditions can be controlled. We illustrate the method on data simulated by the AMPT model.

    ↳ physics.data-anhep-exhep-phnucl-ex+1EPJ Web Conf.(2017)·0 citations
24. 24*

    Flow anisotropy due to momentum deposition in ultra-relativistic nuclear collisions

    Boris Tomasik🇸🇰 · Martin Schulc🇨🇿

    Minijets and jets are produced in large numbers in nuclear collisions at TeV energies, so that there are many of them in a single fireball. They deposit non-negligible amount of momentum and energy into the hydrodynamically expanding bulk and cause anisotropies of the expansion. Moreover, due to their multiple production in a single event the resulting anisotropies are correlated with the collision geometry and thus contribute positively also to event-averaged anisotropies in non-central collisions. Using simulations with three-dimensional ideal hydrodynamic model we demonstrate the importance of this effect. It must be taken into account if conclusions about the properties of the hot matter are to be drawn.

    ↳ nucl-thhep-phEPJ Web Conf.(2017)·0 citations
25. 25*

    Heating of galactic gas by dark matter annihilation in ultracompact minihalos

    Hamish A. Clark🇦🇺 · Nikolas Iwanus🇦🇺 · Pascal J. Elahi🇦🇺 · Geraint F. Lewis🇦🇺 · Pat Scott🇬🇧

    The existence of substructure in halos of annihilating dark matter would be expected to substantially boost the rate at which annihilation occurs. Ultracompact minihalos of dark matter (UCMHs) are one of the more extreme examples of this. The boosted annihilation can inject significant amounts of energy into the gas of a galaxy over its lifetime. Here we determine the impact of the boost factor from UCMH substructure on the heating of galactic gas in a Milky Way-type galaxy, by means of N-body simulation. If $1\%$ of the dark matter exists as UCMHs, the corresponding boost factor can be of order $10^5$. For reasonable values of the relevant parameters (annihilation cross section $3\times 10^{-26}{\text{cm}}^3{\text{s}}^{-1}$, dark matter mass 100 GeV, 10% heating efficiency), we show that the presence of UCMHs at the 0.1% level would inject enough energy to eject significant amounts of gas from the halo, potentially preventing star formation within $\sim$1 kpc of the halo centre.

    ↳ astro-ph.COastro-ph.HEhep-phJCAP(2017)·17 citations
26. 26*

    Hadronically decaying heavy dark matter and high-energy neutrino limits

    M.Yu. Kuznetsov🇷🇺

    We consider dark matter consisting of long--living particles with masses $10^7\lesssim M\lesssim 10^{16}$ GeV decaying through hadronic channel as a source of high energy neutrino. Using recent data on high energy neutrino from IceCube and Pierre Auger experiments we derive the upper-limits on neutrino flux from dark matter decay and constraints on dark matter parameter space. For the dark matter masses of order $10^8$ GeV the constraints derived are slightly stronger than those obtained for the same dark matter model using the high energy gamma-ray limits.

    ↳ astro-ph.HEhep-phJETP Lett.(2017)·21 citations
27. 27*

    Some Relations for Quark Confinement and Chiral Symmetry Breaking in QCD

    Hideo Suganuma🇯🇵 · Takahiro M. Doi (Kyoto U.)🇯🇵 · Krzysztof Redlich🇵🇱 · Chihiro Sasaki (Wroclaw U.)🇵🇱

    We analytically study the relation between quark confinement and spontaneous chiral-symmetry breaking in QCD. In terms of the Dirac eigenmodes, we derive some formulae for the Polyakov loop, its fluctuations, and the string tension from the Wilson loop. We also investigate the Polyakov loop in terms of the eigenmodes of the Wilson, the clover and the domain wall fermion kernels, respectively. For the confinement quantities, the low-lying Dirac/fermion eigenmodes are found to give negligible contribution, while they are essential for chiral symmetry breaking. These relations indicate no direct one-to-one correspondence between confinement and chiral symmetry breaking in QCD, which seems to be natural because confinement is realized independently of the quark mass.

    ↳ hep-thhep-lathep-phEPJ Web Conf.(2017)·3 citations
28. 28*

    Gravitational closure of matter field equations

    Maximilian Düll🇩🇪 · Frederic P. Schuller🇩🇪 · Nadine Stritzelberger🇬🇧 · Florian Wolz🇨🇦

    The requirement that both the matter and the geometry of a spacetime canonically evolve together, starting and ending on shared Cauchy surfaces and independently of the intermediate foliation, leaves one with little choice for diffeomorphism-invariant gravitational dynamics that can provide consistent evolution equations to the coefficients of a given system of matter field equations. Concretely, we show how starting from any linear local matter field equations whose principal polynomial satisfies three physicality conditions, one may calculate coefficient functions which then enter an otherwise immutable set of countably many linear homogeneous partial differential equations. Any solution of these so-called gravitational closure equations then provides a Lagrangian density for any type of tensorial geometry that features ultralocally in the initially specified matter Lagrangian density. Thus the given system of matter field equations is indeed closed by the so obtained gravitational equations. In contrast to previous work, we build the theory on a suitable associated bundle encoding the canonical configuration degrees of freedom, which allows to include necessary constraints on the geometry in practically tractable fashion. By virtue of the presented mechanism, one thus can practically calculate, rather than having to postulate, the gravitational theory that is required by specific matter field dynamics. For the special case of standard model matter one obtains general relativity.

    ↳ gr-qchep-phhep-thPRD(2018)·24 citations
29. 29*

    Fine-tuning challenges for the matter bounce scenario

    Aaron M. Levy🇺🇸

    A bouncing universe with a long period of contraction during which the average density is pressureless (the same equation of state as matter) as cosmologically observable scales exit the Hubble horizon has been proposed as an explanation for producing a nearly scale-invariant spectrum of adiabatic scalar perturbations. A well-known problem with this scenario is that, unless suppressed, the energy density associated with anisotropy grows faster than that of the pressureless matter, so the matter-like phase is unstable. Previous models introduce an ekpyrotic phase after the matter-like phase to prevent the anisotropy from generating chaotic mixmaster behavior. In this work, though, we point out that, unless the anisotropy is suppressed first, the matter-like phase will never start and that suppressing the anisotropy requires extraordinary, exponential fine-tuning.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2017)·23 citations
30. 30*

    Overview of the vector-like quark searches with the LHC data collected by the ATLAS detector

    J. P. Araque (for the ATLAS Collaboration)🇵🇹

    In 2012 the discovery of the Higgs boson by the ATLAS and CMS collaborations set a milestone in particle physics by finding the missing piece of the Standard Model. Nonetheless some questions are still open: the origin of the mass of the neutrino and finding the missing candidate for dark matter are some examples. One of the main issues with the Standard Model is the hierarchy problem which appears when trying to go to high energy scales at which the theory cannot accommodate corrections large enough to explain the observed nature. Vector-like quarks appear naturally in some non-supersymmetric models which try to find a solution for this issue. The different searches for vector-like quarks within the ATLAS Collaboration using data collected at a centre-of-mass energy of 8 and 13~TeV with integrated luminosities of $20.3\mathrm{f}{\mathrm{b}}^{-1}$ (8~TeV) and $3.2\mathrm{f}{\mathrm{b}}^{-1}$ and $14.7\mathrm{f}{\mathrm{b}}^{-1}$ (13~TeV) are discussed.

    ↳ hep-exhep-ph5 citations
31. 31*

    Excesses of Cosmic Ray Spectra from A Single Nearby Source

    Wei Liu🇨🇳 · Xiao-Jun Bi🇨🇳 · Su-Jie Lin🇨🇳 · Bing-Bing Wang🇨🇳 · Peng-Fei Yin🇨🇳

    Growing evidence reveals universal hardening on various cosmic ray spectra, e.g. proton, positron, as well as antiproton fraction. Such universality may indicate they have a common origin. In this paper, we argue that these widespread excesses can be accounted for by a nearby supernova remnant surrounded by a giant molecular cloud. Secondary cosmic rays ($\mathrm{p}$, ${\mathrm{e}}^{+}$) are produced through the collisions between the primary cosmic ray nuclei from this supernova remnant and the molecular gas. Different from the background, which is produced by the ensemble of large amount of sources in the Milky Way, the local injected spectrum can be harder. The time-dependent transport of particles would make the propagated spectrum even harder. Under this scenario, the anomalies of both primary ($\mathrm{p}$, ${\mathrm{e}}^{-}$) and secondary (${\mathrm{e}}^{+}$, $\bar{\mathrm{p}}/p$) cosmic rays can be properly interpreted. We further show that the TeV to sub-PeV anisotropy of proton is consistent with the observations if the local source is relatively young and lying at the anti-Galactic center direction.

    ↳ astro-ph.HEhep-phPRD(2017)·60 citations
32. 32*

    Anomalous Dimensions and the Renormalizability of the Four-Fermion Interaction

    Philip D. Mannheim🇺🇸

    We show that when the dynamical dimension of the $\bar{\psi }\psi$ operator is reduced from three to two in a fermion electrodynamics with scaling, a $g(\bar{\psi }\psi {)}^2+g(\bar{\psi }i{\gamma }^5\psi {)}^2$ four-fermion interaction which is dressed by this electrodynamics becomes renormalizable. In the fermion-antifermion scattering amplitude every term in an expansion to arbitrary order in $g$ is found to diverge as just a single ultraviolet logarithm (i.e. no log squared or higher), and is thus made finite by a single subtraction. While not necessary for renormalizability per se, the reduction in the dimension of $\bar{\psi }\psi$ to two leads to dynamical chiral symmetry breaking in the infrared, with the needed subtraction then automatically being provided by the theory itself through the symmetry breaking mechanism, with there then being no need to introduce the subtraction by hand. Since the vector and axial vector currents are conserved, they do not acquire any anomalous dimension, with the four-fermion $(\bar{\psi }{\gamma }^{\mu }\psi {)}^2$ and $(\bar{\psi }{\gamma }^{\mu }{\gamma }^5\psi {)}^2$ interactions instead having to be controlled by the standard Higgs mechanism.

    ↳ hep-thhep-phPLB(2017)·5 citations
33. 33*

    Nucleon spin and quark content at the physical point

    C. Alexandrou (Univ. of Cyprus and The Cyprus Inst.)🇨🇾 · M. Constantinou🇨🇾 · K. Hadjiyiannakou🇨🇾 · Ch. Kallidonis🇨🇾 · G. Koutsou (The Cyprus Inst.)🇨🇾 · K. Jansen🇩🇪 · Ch. Wiese (DESY-Zeuthen)🇩🇪 · A. Vaquero Avilés-Casco (INFN-Milan)🇮🇹

    We present results on the spin and quark content of the nucleon using $N_f=2$ twisted mass clover-improved fermion simulations with a pion mass close to its physical value. We use recently developed methods to obtain accurate results for both connected and disconnected contributions. We provide results for the axial charge, quark and gluon momentum fraction as well as the light, strange and charm $\sigma$-terms.

    ↳ hep-lathep-phnucl-thPoS(2016)·12 citations
34. 34*

    Non-equilibrium dilepton production in hadronic transport approaches

    Jan Staudenmaier🇩🇪 · Janus Weil🇩🇪 · Hannah Petersen🇩🇪

    In this work the non-equilibrium dilepton production from a hadronic transport approach (SMASH) is presented. The dilepton emission from the hadronic stage is of interest for current HADES results measured at GSI in the beam energy range from 1.25 - 3.5 GeV. Also at high collision energies (RHIC/LHC) the later dilute stages of the reaction are dominated by hadronic dynamics. The newly developed hadronic transport approach called SMASH (=Simulating Many Accelerated Strongly-interacting Hadrons) is introduced first. After explaining the basic interaction mechanisms, a comparison of elementary cross sections for pion production to experimental data is shown. The dilepton production within SMASH is explained in detail. The main contribution to the dilepton spectra in the low energy regime of GSI/FAIR/RHIC-BES originates from resonance decays. Results of the dilepton production with SMASH such as invariant mass spectra are shown.

    ↳ nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2017)·6 citations

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