Wed·Nov 18, 2015Wednesday·November 18, 2015

1. 01*

   Multiphoton amplitudes and generalized LKF transformation in Scalar QED

   Naser Ahmadiniaz🇲🇽 · Adnan Bashir🇲🇽 · Christian Schubert🇲🇽

   We apply the worldline formalism to amplitudes in scalar quantum electrodynamics (QED) involving open scalar lines, with an emphasis on their non-perturbative gauge dependence. At the tree-level, we study the scalar propagator interacting with any number of photons in configuration space as well as in momentum space. At one-loop we rederive, in an efficient way, the off-shell vertex in an arbitrary dimension and any covariant gauge. Generalizing the Landau-Khalatnikov-Fradkin transformation (LKFT) for the non-perturbative propagator, we find simple non-perturbative transformation rules for arbitrary x-space amplitudes under a change of the covariant gauge parameter in terms of conformal cross ratios.

   hep-phhep-thPRD(2016)·40 citations
2. 02*

   Atmospheric Neutrino Oscillations for Earth Tomography

   Walter Winter🇩🇪

   Modern proposed atmospheric neutrino oscillation experiments, such as PINGU in the Antarctic ice or ORCA in Mediterranean sea water, aim for precision measurements of the oscillation parameters including the ordering of the neutrino masses. They can, however, go far beyond that: Since neutrino oscillations are affected by the coherent forward scattering with matter, neutrinos can provide a new view on the interior of the earth. We show that the proposed atmospheric oscillation experiments can measure the lower mantle density of the earth with a precision at the level of a few percent, including the uncertainties of the oscillation parameters and correlations among different density layers. While the earth's core is, in principle, accessible by the angular resolution, new technology would be required to extract degeneracy-free information.

   hep-phhep-exphysics.geo-phNPB(2016)·59 citations
3. 03*

   Muon $g-2$ in the Aligned Two Higgs Doublet Model

   Tao Han🇺🇸 · Sin Kyu Kang🇰🇷 · Joshua Sayre🇺🇸

   We study the Two-Higgs-Doublet Model with the aligned Yukawa sector (A2HDM) in light of the observed excess measured in the muon anomalous magnetic moment. We take into account the existing theoretical and experimental constraints with up-to-date values and demonstrate that a phenomenologically interesting region of parameter space exists. With a detailed parameter scan, we show a much larger region of viable parameter space in this model beyond the limiting case Type X 2HDM as obtained before. It features the existence of light scalar states with masses $3$ GeV $\lesssim m_H^{}\lesssim 50$ GeV, or $10$ GeV $\lesssim m_A^{}\lesssim 130$ GeV, with enhanced couplings to tau leptons. The charged Higgs boson is typically heavier, with $200$ GeV $\lesssim m_{H^{+}}^{}\lesssim 630$ GeV. The surviving parameter space is forced into the CP-conserving limit by EDM constraints. Some Standard Model observables may be significantly modified, including a possible new decay mode of the SM-like Higgs boson to four taus. We comment on future measurements and direct searches for those effects at the LHC as tests of the model.

   hep-phJHEP(2016)·64 citations
4. 04*

   Light 't Hooft Top Partners

   Giacomo Cacciapaglia (IPN, Lyon)🇫🇷 · Alberto Parolini (KIAS, Seoul)🇰🇷

   Vector-like quarks, usually dubbed top partners, are a common presence in composite Higgs models. Being composite objects, their mass is expected to be of the order of their inverse size, that is the condensation scale of the new strong interactions. Light top partners, while not being a generic prediction, are however often considered in phenomenological models. We suggest that their lightness may be due to the matching of global 't Hooft anomalies of the underlying theory. We check this mechanism in explicit models showing that, in one case, composite fermions with the quantum numbers of the top quark obtain a mass which is controlled by a soft breaking term and can be made parametrically small.

   hep-phhep-thPRD(2016)·13 citations
5. 05*

   Higgs coupling measurements at the LHC

   Christoph Englert🇬🇧 · Roman Kogler🇩🇪 · Holger Schulz🇬🇧 · Michael Spannowsky🇬🇧

   Due to the absence of tantalising hints for new physics during the LHC's run 1, the extension of the Higgs sector by dimension six operators will provide the new phenomenological standard for searches of non-resonant extensions of the Standard Model. Using all dominant and subdominant Higgs production mechanisms at the LHC, we compute the constraints on Higgs physics-relevant dimension six operators in a global and correlated fit. We show in how far these constraints can be improved by new Higgs channels becoming accessible at higher energy and luminosity, both through inclusive cross sections as well as through highly sensitive differential distributions. This allows us to discuss the sensitivity to new effects in the Higgs sector that can be reached at the LHC if direct hints for physics beyond the SM remain elusive and the impact of these constraints on well-motivated BSM scenarios.

   hep-phEPJC(2016)·124 citations
6. 06*

   Jet-Images -- Deep Learning Edition

   Luke de Oliveira🇺🇸 · Michael Kagan🇺🇸 · Lester Mackey🇺🇸 · Benjamin Nachman🇺🇸 · Ariel Schwartzman🇺🇸

   Building on the notion of a particle physics detector as a camera and the collimated streams of high energy particles, or jets, it measures as an image, we investigate the potential of machine learning techniques based on deep learning architectures to identify highly boosted W bosons. Modern deep learning algorithms trained on jet images can out-perform standard physically-motivated feature driven approaches to jet tagging. We develop techniques for visualizing how these features are learned by the network and what additional information is used to improve performance. This interplay between physically-motivated feature driven tools and supervised learning algorithms is general and can be used to significantly increase the sensitivity to discover new particles and new forces, and gain a deeper understanding of the physics within jets.

   hep-phphysics.data-anstat.MLJHEP(2016)·399 citations
7. 07*

   Tetraquark Production in Double Parton Scattering

   F. Carvalho🇧🇷 · E.R. Cazaroto🇧🇷 · V.P. Gonçalves🇧🇷 · F.S. Navarra🇧🇷

   We develop a model to study tetraquark production in hadronic collisions. We focus on double parton scattering and formulate a version of the color evaporation model for the production of the $X(3872)$ and of the $T_{4c}$ tetraquark, a state composed by the $c\bar{c}c\bar{c}$ quarks. We find that the production cross section grows rapidly with the collision energy $\sqrt{s}$ and make predictions for the forthcoming higher energy data of the LHC.

   hep-phPRD(2016)·48 citations
8. 08*

   Muon g$-$2 in two-Higgs-doublet models

   Eung Jin Chun🇰🇷

   Updating various theoretical and experimental constraints on the four different types of two-Higgs-doublet models (2HDMs), we find that only the ``lepton-specific" (or ``type X") 2HDM can explain the present muon g$-$2 anomaly in the parameter region of large $\tan \beta$, a light CP-odd boson, and heavier CP-even and charged bosons which are almost degenerate. The severe constraints on the models come mainly from the consideration of vacuum stability and perturbativity, the electroweak precision data, the $b$-quark observables like $B_S\to \mu \mu$, the precision measurements of the lepton universality as well as the 125 GeV boson property observed at the LHC.

   hep-phEPJ Web Conf.(2016)·15 citations
9. 09*

   A Study of Quasi-parton Distribution Functions in the Diquark Spectator Model

   Leonard Gamberg🇺🇸 · Zhong-Bo Kang🇺🇸 · Ivan Vitev🇺🇸 · Hongxi Xing🇺🇸

   To facilitate lattice QCD calculations of nucleon structute, a set of quasi-parton distributions were recently introduced. These quasi-PDFs were shown to reduce to standard PDFs when the nucleon is boosted to high energies, $P_z\to \infty$. Since taking such limit is not feasible in lattice simulations, it is essential to provide guidance for what values of $P_z$ the quasi-PDFs are good approximations of standard PDFs. Within the framework of the spectator diquark model, we evaluate both the up and down quarks' quasi-PDFs and standard PDFs for all leading-twist distributions (unpolarized distribution $f_1$, helicity distribution $g_1$, and transversity distribution $h_1$). We find that, for intermediate parton momentum fractions $x$, quasi-PDFs are good approximations to standard PDFs (within $20-30\%$) when $P_z\gtrsim 1.5-2$ GeV. On the other hand, for large $x\sim 1$ much larger $P_z>4$ GeV is necessary to obtain a satisfactory agreement between the two sets. We further find that the Soffer positivity bound does not hold in general for quasi-PDFs.

   hep-phnucl-thPoS(2015)·10 citations
10. 10*

    Decays of Charmed Vector Mesons --- eta-pi^0 mixing as an origin of isospin non-conservation ---

    Kunihiko Terasaki🇯🇵

    Pion emitting decays and radiative ones of D^{*+,0} and D_s^{*+} are studied. As the result, the full-width of D^{*0} is predicted, by assuming the isospin symmetry. In addition, the isospin non-conserving D_s^{*+} --> D_s^+ pi^0 decay is investigated under the assumption that it proceeds through the eta-pi^0 mixing.

    hep-ph3 citations
11. 11*

    Critical Behavior and Dimension Crossover of Pion Superfluidity

    Ziyue Wang🇨🇳 · Pengfei Zhuang🇨🇳

    We investigate the critical behavior of pion superfluidity in the frame of functional renormalization group. By solving the flow equation in the SU(2) linear sigma model with pion superfluidity at finite temperature and isospin density, and making comparison with the fixed point analysis of the flow diagram in a general $O(N)$ model at zero temperature and density but with continuous dimension, the pion superfluidity is a second order phase transition subject to a $O(2)$ universality class with a dimension crossover from $d_{\text{eff}}=4$ to $d_{\text{eff}}=3$. The usually used large $N$ expansion gives a temperature independent critical exponent $\beta$ and agrees with the renormalization group only at zero temperature.

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

    Symmetry-Improved 2PI Approach to the Goldstone-Boson IR Problem of the SM Effective Potential

    Apostolos Pilaftsis🇬🇧 · Daniele Teresi🇧🇪

    The effective potential of the Standard Model (SM), from three loop order and higher, suffers from infra-red (IR) divergences arising from quantum effects due to massless would-be Goldstone bosons associated with the longitudinal polarizations of the W and Z bosons. Such IR pathologies also hinder accurate evaluation of the two-loop threshold corrections to electroweak quantities, such as the vacuum expectation value of the Higgs field. However, these divergences are an artifact of perturbation theory, and therefore need to be consistently resummed in order to obtain a IR-safe effective potential. The so-called Two-Particle-Irreducible (2PI) effective action provides a rigorous framework to consistently perform such resummations, without the need to resort to ad hoc subtractions or running into the risk of over-counting contributions. By considering the recently proposed symmetry-improved 2PI formalism, we address the problem of the Goldstone-boson IR divergences of the SM effective potential in the gaugeless limit of the theory. In the same limit, we evaluate the IR-safe symmetry-improved 2PI effective potential, after taking into account quantum loops of chiral fermions, as well as the renormalization of spurious custodially breaking effects triggered by fermionic Yukawa interactions. Finally, we compare our results with those obtained with other methods presented in the literature.

    hep-phhep-thNPB(2016)·32 citations
13. 13*

    Energy loss of $B$ and $D$ mesons in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV

    Kapil Saraswat🇮🇳 · Prashant Shukla🇮🇳 · Venktesh Singh🇮🇳

    We present the calculations of collisional and radiative energy loss of $B$ and $D$ mesons in the medium produced in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The nuclear modification factor $R_{AA}$ of $B$ and $D$ mesons including shadowing and energy loss are calculated and compared with the measured data. While the $D$ meson $R_{AA}$ can be described in terms of the radiative energy loss alone, both the collisional as well as radiative energy loss are required to explain the $B$ meson measurements.

    hep-phnucl-thPoS(2015)·1 citation
14. 14*

    Testing the light dark matter scenario of the MSSM at the LHC

    Junjie Cao🇨🇳 · Yangle He🇨🇳 · Liangliang Shang🇨🇳 · Wei Su🇨🇳 · Yang Zhang🇨🇳

    In the light dark matter (DM) scenario of the MSSM, the DM relic density puts non-trivial requirements on the spectrum of supersymmetric particles. As a result, the direct search for multi-lepton signals at the LHC has great impact on the scenario. In this work, we concentrate on the searches for sleptons and electroweak-inos at the LHC, and investigate the constraints on the light DM scenario from the 8 TeV LHC data as well as the capability of the 14 TeV LHC to test the scenario. We first get the samples of the scenario by scanning the vast parameter space of the MSSM and considering some easily available constraints, such as those from the DM relic density, the LUX experiment and the Higgs searches at colliders. Then for the surviving samples, we simulate the $2l+E_T^{miss}$ signal from slepton pair production process and the $2l+E_T^{miss}$ and $3l+E_T^{miss}$ signals from chargino and neutralino associated production processes at both the 8 TeV LHC and the 14 TeV LHC. Our simulations indicate that the 8 TeV LHC has excluded a sizable portion of the samples, and the 14 TeV LHC can be even much more powerful in testing the scenario. For example, in case that no multi-lepton signals are observed at the 14 TeV LHC, most samples of the light DM scenario will be excluded, especially a lower limit on the lightest neutralino mass will be set at 42 GeV and 44 GeV with 30 $f{b}^{-1}$ and 100 $f{b}^{-1}$ data respectively, and this limit can be further pushed up to $55\mathrm{GeV}$ with 300 $f{b}^{-1}$ data.

    hep-phJHEP(2016)·36 citations
15. 15*

    Concurrent tests of Lorentz invariance in $\beta$-decay experiments

    K.K. Vos🇳🇱 · H.W. Wilschut🇳🇱 · R.G.E. Timmermans🇳🇱

    Modern experiments on neutron and allowed nuclear $\beta$ decay search for new semileptonic interactions, beyond the ``left-handed'' electroweak force. We show that ongoing and planned $\beta$-decay experiments, with isotopes at rest and in flight, can be exploited as sensitive tests of Lorentz invariance. The variety of correlations that involve the nuclear spin, the direction of the emitted $\beta$ particle, and the recoil direction of the daughter nucleus allow for relatively simple experiments that give direct bounds on Lorentz violation. The pertinent observables are decay-rate asymmetries and their dependence on sidereal time. We discuss the potential of several asymmetries that together cover a large part of the parameter space for Lorentz violation in the gauge sector. High counting statistics is required.

    hep-phhep-exnucl-exnucl-thPRC(2015)·15 citations
16. 16*

    Decaying light particles in the SHiP experiment. III. Signal rate estimates for scalar and pseudoscalar sgoldstinos

    K. O. Astapov🇷🇺 · D. S. Gorbunov🇷🇺

    For supersymmetric extensions of the Standard Model with light sgoldstinos - scalar and pseudoscalar superparthners of goldstino - we estimate the signal rate anticipated at the lately proposed fixed target experiment SHiP utilizing CERN SPS beam of 400 GeV protons. We also place new limits on the model parameters from the similar analysis of the published results of CHARM experiment.

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

    Review of Recent Calculations of the Hadronic Vacuum Polarisation Contribution

    Zhiqing Zhang🇫🇷

    Recent calculations of the hadronic vacuum polarisation contribution are reviewed. The focus is put on the leading-order contribution to the muon magnetic anomaly involving $e^{+}{e}^{-}$ annihilation cross section data as input to a dispersion relation approach. Alternative calculation including tau data is also discussed. The $\tau$ data are corrected for various isospin-breaking sources which are explicitly shown source by source.

    hep-phhep-exEPJ Web Conf.(2016)·11 citations
18. 18*

    Generalized DGLAP evolution

    D. Strozik-Kotlorz🇵🇱 · S. V. Mikhailov🇷🇺 · O. V. Teryaev🇷🇺

    We present progress in development of the truncated Mellin moments approach (TMMA). We show our recent results on the generalization of DGLAP evolution equations and discuss some their applications in spin physics.

    hep-phhep-thJ.Phys.Conf.Ser.(2016)·1 citation
19. 19*

    Analytic form of the two-loop planar five-gluon all-plus-helicity amplitude in QCD

    T. Gehrmann🇨🇭 · J. M. Henn🇺🇸 · N. A. Lo Presti🇨🇭

    Virtual two-loop corrections to scattering amplitudes are a key ingredient to precision physics at collider experiments. We compute the full set of planar master integrals relevant to five-point functions in massless QCD, and use these to derive an analytical expression for the two-loop five-gluon all-plus-helicity amplitude. After subtracting terms that are related to the universal infrared and ultraviolet pole structure, we obtain a remarkably simple and compact finite remainder function, consisting only of dilogarithms.

    hep-phhep-thPRL(2016)·215 citations
20. 20*

    Spectrum-doubled Heavy Vector Bosons at the LHC

    Thomas Appelquist🇺🇸 · Yang Bai🇺🇸 · James Ingoldby🇺🇸 · Maurizio Piai🇬🇧

    We study a simple effective field theory incorporating six heavy vector bosons together with the standard-model field content. The new particles preserve custodial symmetry as well as an approximate left-right parity symmetry. The enhanced symmetry of the model allows it to satisfy precision electroweak constraints and bounds from Higgs physics in a regime where all the couplings are perturbative and where the amount of fine-tuning is comparable to that in the standard model itself. We find that the model could explain the recently observed excesses in di-boson processes at invariant mass close to 2 TeV from LHC Run 1 for a range of allowed parameter space. The masses of all the particles differ by no more than roughly 10%. In a portion of the allowed parameter space only one of the new particles has a production cross section large enough to be detectable with the energy and luminosity of Run 1, both via its decay to WZ and to Wh, while the others have suppressed production rates. The model can be tested at the higher-energy and higher-luminosity run of the LHC even for an overall scale of the new particles higher than 3 TeV.

    hep-phhep-exJHEP(2016)·10 citations
21. 21*

    Monopole-Antimonopole Scattering

    Tanmay Vachaspati🇺🇸

    We numerically study the head-on scattering of a 't Hooft-Polyakov magnetic monopole and antimonopole for a wide range of parameters. In contrast to the scattering of a $\lambda {\varphi }^4$ kink and antikink in 1+1 dimensions, we find that the monopole and antimonopole annihilate even when scattered at relativistic velocities. If the monopole and antimonopole have a relative twist, there is a repulsive force between them and they can initially be reflected. However, in every case we have examined, the reflected monopoles remain bound and eventually annihilate. We also calculate the magnetic helicity in the aftermath of monopole-antimonopole annihilation and confirm the conversion of relative twist to magnetic helicity as discussed earlier in the electroweak case.

    ↳ hep-thhep-phPRD(2016)·17 citations
22. 22*

    Large Field Inflation and Gravitational Entropy

    Nemanja Kaloper🇺🇸 · Matthew Kleban🇺🇸 · Albion Lawrence🇺🇸 · Martin S. Sloth🇩🇰

    Large field inflation can be sensitive to perturbative and nonperturbative quantum corrections that spoil slow roll. A large number $N$ of light species in the theory, which occur in many string constructions, can amplify these problems. One might even worry that in a de Sitter background, light species will lead to a violation of the covariant entropy bound at large $N$. If so, requiring the validity of the covariant entropy bound could limit the number of light species and their couplings, which in turn could severely constrain axion-driven inflation. Here we show that there is no such problem when we correctly renormalize models with many light species, taking the {\it physical} Planck scale to be $M_{pl}^2\gtrsim N{\mathcal{M}}_{UV}^2$, where ${\mathcal{M}}_{UV}$ is the cutoff for the QFT coupled to semiclassical quantum gravity. The number of light species then cancels out of the gravitational entropy of de Sitter or near-de Sitter backgrounds at leading order. Working in detail with $N$ scalar fields in de Sitter space, renormalized to one loop order, we show that the gravitational entropy automatically obeys the covariant entropy bound. Furthermore, while the axion decay constant is a strong coupling scale for the axion dynamics, we show that it is {\it not} in general the cutoff of 4d semiclassical gravity. After renormalizing the two point function of the inflaton, we note that it is also controlled by scales much below the cutoff. We revisit $N$-flation and KKLT-type compactifications in this light, and show that they are perfectly consistent with the covariant entropy bound. Thus, while quantum gravity might yet spoil large field inflation, holographic considerations in the semiclassical theory do not obstruct it.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2016)·38 citations
23. 23*

    Beginning inflation in an inhomogeneous universe

    William E. East🇺🇸 · Matthew Kleban🇺🇸 · Andrei Linde🇺🇸 · Leonardo Senatore🇺🇸

    Using numerical solutions of the full Einstein field equations coupled to a scalar inflaton field in 3+1 dimensions, we study the conditions under which a universe that is initially expanding, highly inhomogeneous and dominated by gradient energy can transition to an inflationary period. If the initial scalar field variations are contained within a sufficiently flat region of the inflaton potential, and the universe is spatially flat or open on average, inflation will occur following the dilution of the gradient and kinetic energy due to expansion. This is the case even when the scale of the inhomogeneities is comparable to the initial Hubble length, and overdense regions collapse and form black holes, because underdense regions continue expanding, allowing inflation to eventually begin. This establishes that inflation can arise from highly inhomogeneous initial conditions and solve the horizon and flatness problems, at least as long as the variations in the scalar field do not include values that exceed the inflationary plateau.

    ↳ hep-thastro-ph.COgr-qchep-phJCAP(2016)·213 citations
24. 24*

    Updated Constraints and Forecasts on Primordial Tensor Modes

    Giovanni Cabass🇮🇹 · Luca Pagano🇮🇹 · Laura Salvati🇮🇹 · Martina Gerbino🇸🇪 · Elena Giusarma🇺🇸 · Alessandro Melchiorri🇮🇹

    We present new, tight, constraints on the cosmological background of gravitational waves (GWs) using the latest measurements of CMB temperature and polarization anisotropies provided by the Planck, BICEP2 and Keck Array experiments. These constraints are further improved when the GW contribution $N_{\mathrm{eff}}^{\mathrm{GW}}$ to the effective number of relativistic degrees of freedom $N_{\mathrm{eff}}$ is also considered. Parametrizing the tensor spectrum as a power law with tensor-to-scalar ratio $r$, tilt $n_{\mathrm{t}}$ and pivot $0.01{\mathrm{Mpc}}^{-1}$, and assuming a minimum value of $r=0.001$, we find $r<0.089$, $n_{\mathrm{t}}=1.7_{-2.0}^{+2.1}$ ($95\%\mathrm{CL}$, no $N_{\mathrm{eff}}^{\mathrm{GW}}$) and $r<0.082$, $n_{\mathrm{t}}=-0.05_{-0.87}^{+0.58}$ ($95\%\mathrm{CL}$, with $N_{\mathrm{eff}}^{\mathrm{GW}}$). When the recently released $95\mathrm{GHz}$ data from Keck Array are added to the analysis, the constraints on $r$ are improved to $r<0.067$ ($95\%\mathrm{CL}$, no $N_{\mathrm{eff}}^{\mathrm{GW}}$), $r<0.061$ ($95\%\mathrm{CL}$, with $N_{\mathrm{eff}}^{\mathrm{GW}}$). We discuss the limits coming from direct detection experiments such as LIGO-Virgo, pulsar timing (European Pulsar Timing Array) and CMB spectral distortions (FIRAS). Finally, we show future constraints achievable from a COrE-like mission: if the tensor-to-scalar ratio is of order $10^{-2}$ and the inflationary consistency relation $n_{\mathrm{t}}=-r/8$ holds, COrE will be able to constrain $n_{\mathrm{t}}$ with an error of $0.16$ at $95\%\mathrm{CL}$. In the case that lensing $B$-modes can be subtracted to $10\%$ of their power, a feasible goal for COrE, these limits will be improved to $0.11$ at $95\%\mathrm{CL}$.

    ↳ astro-ph.COhep-phPRD(2016)·83 citations
25. 25*

    Backreaction of particle production on false vacuum decay

    Cyril Lagger🇦🇺

    As originally described by Rubakov, particles are produced during the tunneling of a metastable quantum field. We propose to extend his formalism to compute the backreaction of these particles on the semiclassical decay probability of the field. The idea is to integrate out the external bath of particles by computing the reduced density matrix of the system. Following this approach, we derive an explicit correction factor in the specific case of scalar particle production in flat spacetime. In this given framework, we conclude that the backreaction is ultraviolet finite and enhances the decay rate. Moreover, in the weak production limit, the backreaction factor is directly given by one half of the total number of created particles. In order to estimate the importance of this correction, we apply our formalism to a toy model potential which allows us to consider both the decay of a homogeneous bounce and the nucleation of a thin-wall bubble. In the former case, the impact of the created particles is parameter dependent and we exhibit a reasonable choice of variables for which ones the backreaction is significant. In the latter case, we conclude that the backreaction is always negligible.

    ↳ hep-thhep-phPRD(2016)·1 citation
26. 26*

    Inverse Magnetic/Shear Catalysis

    Brett McInnes🇸🇬

    It is well known that very large magnetic fields are generated when the Quark-Gluon Plasma is formed during peripheral heavy-ion collisions. Lattice, holographic, and other studies strongly suggest that these fields may, for observationally relevant field values, induce "inverse magnetic catalysis", signalled by a lowering of the critical temperature for the chiral/deconfinement transition. The theoretical basis of this effect has recently attracted much attention; yet so far these investigations have not included another, equally dramatic consequence of the peripheral collision geometry: the QGP acquires a large angular momentum vector, parallel to the magnetic field. Here we use holographic techniques to argue that the angular momentum can also, independently, have an effect on transition temperatures, and we obtain a rough estimate of the relative effects of the presence of both a magnetic field and an angular momentum density. We find that the shearing angular momentum reinforces the effect of the magnetic field at low values of the baryonic chemical potential, but that it can actually decrease that effect at high chemical potentials.

    ↳ hep-thhep-phnucl-thNPB(2016)·29 citations
27. 27*

    Wormholes supported by phantom energy from Shan-Chen cosmological fluids

    D Wang🇨🇳 · Xin-He Meng🇨🇳

    The firm observational confirmation of the late-time acceleration of the universe expansion has proposed a major challenge to the theoretical foundations of cosmology and the explanation of the acceleration mechanism requires the introduction of either a simply cosmological constant, or of a mysterious dark energy component (time dependent or modified gravities), filling the universe and dominating its current expansionary evolution. Universally given that the universe is permeated by a dark energy fluid, therefore, we should also investigate the astrophysical scale properties from the dark energy effects. In the present paper, the exact solutions of spherically-symmetrical Einstein field equations describing wormholes supported by phantom energy that violates the null energy condition from Shan-Chen fluid description are obtained. We have considered the important case that the model parameter $\psi \approx 1$ which corresponds to the `` saturation effect ", and this regime corresponds to an effective form of `` asymptotic freedom " for the fluids, but occurring at cosmological rather than subnuclear scales. Then we investigate the allowed range values of the model parameters $g$ and $\omega$ when the space-time metrics describe wormholes and discuss the possible singularities of the solutions, finding that the obtained spacetimes are geodesically complete. Moreover, we construct two traversable wormholes through matching our obtained interior solutions to the exterior Schwarzschild solutions and calculate out the total mass of the wormhole when the wormhole throat size $r\le a$ or $r\le b$, respectively. Finally, we acquire that the surface stress-energy $\sigma$ is zero and the surface tangential pressure $\wp$ is positive when discussing the surface stresses of the solutions and analyze the traversable wormholes.

    ↳ gr-qcastro-ph.COhep-phhep-thEPJC(2016)·35 citations
28. 28*

    Top and EW Physics at the LHeC

    Zhiqing Zhang (for the LHeC Study Group)🇫🇷

    The LHeC is a proposed upgrade of the LHC to study $ep/eA$ collisions in the TeV regime, by adding a 60 GeV electron beam through an energy recovery linac. In $ep$, high precision top and electroweak physics can be performed, such as measurements of anomalous top couplings, light quark couplings to the $Z$ boson and the energy dependence of the weak mixing angle ${\sin }^2{\theta }_W$, for which simulation studies are presented.

    ↳ hep-exhep-phPoS(2015)·10 citations
29. 29*

    HERA Inclusive Neutral and Charged Current Cross Sections and a New PDF Fit, HERAPDF 2.0

    Zhiqing Zhang (for the H1 and ZEUS Collaborations)🇫🇷

    In this talk, I present the brand new results from the H1 and ZEUS Collaborations on the combination of all previously published inclusive deep inelastic cross sections at HERA for neutral and charged current $e^{\pm }p$ scattering for zero beam polarisation and the corresponding parton distributions functions, HERAPDF 2.0, at up to next-to-next-to-leading order (NNLO). The results also include a new precise determination at next-to-leading order (NLO) of the strong coupling constant ${\alpha }_s(M_Z^2)=0.1184\pm 0.0016$ (excluding scale uncertainties) based on a simultaneous fit to the combined inclusive cross section data and jet production data.

    ↳ hep-exhep-phActa Phys.Polon.Supp.(2015)·25 citations
30. 30*

    General Analysis of Dark Radiation in Sequestered String Models

    Michele Cicoli🇮🇹 · Francesco Muia🇮🇹

    We perform a general analysis of axionic dark radiation produced from the decay of the lightest modulus in the sequestered LARGE Volume Scenario. We discuss several cases depending on the form of the Kahler metric for visible sector matter fields and the mechanism responsible for achieving a de Sitter vacuum. The leading decay channels which determine dark radiation predictions are to hidden sector axions, visible sector Higgses and SUSY scalars depending on their mass. We show that in most of the parameter space of split SUSY-like models squarks and sleptons are heavier than the lightest modulus. Hence dark radiation predictions previously obtained for MSSM-like cases hold more generally also for split SUSY-like cases since the decay channel to SUSY scalars is kinematically forbidden. However the inclusion of string loop corrections to the Kahler potential gives rise to a parameter space region where the decay channel to SUSY scalars opens up, leading to a significant reduction of dark radiation production. In this case, the simplest model with a shift-symmetric Higgs sector can suppress the excess of dark radiation $\Delta N_{eff}$ to values as small as 0.14, in perfect agreement with current experimental bounds. Depending on the exact mass of the SUSY scalars all values in the range 0.14 $\lesssim \Delta N_{eff}\lesssim$ 1.6 are allowed. Interestingly dark radiation overproduction can be avoided also in the absence of a Giudice-Masiero coupling.

    ↳ hep-thastro-ph.COhep-phJHEP(2015)·52 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.