Thu·Dec 17, 2015Thursday·December 17, 2015

1. 01*

   Higgs production in heavy quark annihilation through next-to-next-to-leading order QCD

   Robert V. Harlander🇩🇪

   The total inclusive cross section for charged and neutral Higgs production in heavy-quark annihilation is presented through NNLO QCD. It is shown that, aside from an overall factor, the partonic cross section is independent of the initial-state quark flavors, and that any interference terms involving two different Yukawa couplings vanish. A simple criterion for defining the central renormalization and factorization scale is proposed. Its application to the $b\bar{b}H$ process yields results which are compatible with the values usually adopted for this process. Remarkably, we find little variation in these values for the other initial-state quark flavors. Finally, we disentangle the impact of the different parton luminosities from genuine hard NNLO effects and find that, for the central scales, a naive rescaling by the parton luminosities approximates the full result remarkably well.

   hep-phEPJC(2016)·30 citations
2. 02*

   The LHC diphoton resonance and dark matter

   Yann Mambrini🇫🇷 · Giorgio Arcadi🇫🇷 · Abdelhak Djouadi🇫🇷

   A Higgs-like resonance with a mass of approximately 750 GeV has recently been observed at the LHC in its diphoton decay. If this state is not simply a statistical fluctuation which will disappear with more data, it will have important implications not only for particle physics but also for cosmology. In this note, we analyze the implications of such a resonance for the dark matter (DM). Assuming a spin 1/2 DM particle, we first verify that indeed the correct relic density can be obtain for a wide range of the particle mass and weak scale coupling that are compatible with present data. We then show that the combination of near future direct and indirect detection experiments will allow to probe the CP-nature of the mediator resonance, i.e. check whether it is a scalar or a pseudoscalar like particle.

   hep-phastro-ph.HEPLB(2016)·216 citations
3. 03*

   Di-photon excess illuminates Dark Matter

   Mihailo Backovic🇧🇪 · Alberto Mariotti🇧🇪 · Diego Redigolo🇫🇷

   We propose a simplified model of dark matter with a scalar mediator to accommodate the di-photon excess recently observed by the ATLAS and CMS collaborations. Decays of the resonance into dark matter can easily account for a relatively large width of the scalar resonance, while the magnitude of the total width combined with the constraint on dark matter relic density lead to sharp predictions on the parameters of the Dark Sector. Under the assumption of a rather large width, the model predicts a signal consistent with ~300 GeV dark matter particle in channels with large missing energy. This prediction is not yet severely bounded by LHC Run I searches and will be accessible at the LHC Run II in the jet plus missing energy channel with more luminosity. Our analysis also considers astrophysical constraints, pointing out that future direct detection experiments will be sensitive to this scenario.

   hep-phhep-exJHEP(2016)·217 citations
4. 04*

   Numerical Evaluation of Two-Loop Integrals in FDR

   Tom Zirke🇩🇪

   We present a method to numerically evaluate infrared-finite one- and two-loop integrals within the Four-Dimensional Regularization/Renormalization approach, in which a small mass serves as regulator. Typical integrals exhibit a logarithmic dependence on this mass, which we extract with the aid of suitable subtraction terms that can easily be integrated analytically until the logarithmic structure is revealed. As first physical applications to test the method, we calculate QCD corrections to the decay rates of scalar and pseudoscalar Higgs bosons into two photons in the limit of an infinite top-quark mass as well as to the $\rho$ parameter.

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

   Scenarii for interpretations of the LHC diphoton excess: two Higgs doublets and vector-like quarks and leptons

   Andrei Angelescu🇫🇷 · Abdelhak Djouadi🇫🇷 · Grégory Moreau🇫🇷

   An evidence for a diphoton resonance at a mass of 750 GeV has been observed in the data collected at the LHC run at a center of mass energy of 13 TeV. We explore several interpretations of this signal in terms of Higgs-like resonances in a two-Higgs doublet model and its supersymmetric incarnation, in which the heavier CP-even and CP-odd states present in the model are produced in gluon fusion and decay into two photons through top quark loops. We show that one cannot accommodate the observed signal in the minimal versions of these models and that an additional particle content is necessary. We then consider the possibility that vector-like quarks or leptons strongly enhance the heavy Higgs couplings to photons and eventually gluons, without altering those of the already observed 125 GeV state.

   hep-phPLB(2016)·254 citations
6. 06*

   Footprints of New Strong Dynamics via Anomaly and the 750 GeV Diphoton

   Yuichiro Nakai🇺🇸 · Ryosuke Sato🇮🇱 · Kohsaku Tobioka🇮🇱

   The chiral anomaly provides a smoking-gun evidence of a new confining gauge theory. Motivated by a reported event excess in a diphoton invariant mass distribution at the LHC, we discuss a scenario that a pseudo-Nambu-Goldstone (pNG) boson of a new QCD-like theory is produced by gluon fusion and decays into a pair of the standard model gauge bosons. Despite the strong dynamics, the production cross section and the decay widths are determined by anomaly matching condition. The excess can be explained by the pNG boson with mass of around 750 GeV. The model also predicts exotic hadrons such as a color octet scalar and baryons. Some of them are within the reach of the LHC experiment.

   hep-phhep-exPRL(2016)·213 citations
7. 07*

   Rays of light from the LHC

   Simon Knapen🇺🇸 · Tom Melia🇺🇸 · Michele Papucci🇺🇸 · Kathryn Zurek🇺🇸

   We consider models for the di-photon resonance observed at ATLAS (with 3.6 fb^{-1}) and CMS (with 2.6 fb^{-1}). We find there is no conflict between the signal reported at 13 TeV, and the constraints from both experiments at 8 TeV with 20.3 fb^{-1}. We make a simple argument for why adding only one new resonance to the standard model (SM) is not sufficient to explain the observation. We explore four viable options: (i): resonance production and decay through loops of messenger fermions or scalars; (ii): a resonant messenger which decays to the di-photon resonance + X; (iii): an edge configuration where A -> B gamma -> C gamma gamma, and (iv): Hidden Valley-like models where the resonance decays to a pair of very light (sub-GeV) states, each of which in turn decays to a pair of collimated photons that cannot be distinguished from a single photon. Since in each case multiple new states have been introduced, a wealth of signatures is expected to ensue at Run-2 of LHC.

   hep-phPRD(2016)·251 citations
8. 08*

   Knocking on New Physics' door with a Scalar Resonance

   Dario Buttazzo🇨🇭 · Admir Greljo🇨🇭 · David Marzocca🇨🇭

   We speculate about the origin of the recent excess at ~750 GeV in diphoton resonance searches observed by the ATLAS and CMS experiments using the first 13 TeV data. Its interpretation as a new scalar resonance produced in gluon fusion and decaying to photons is consistent with all relevant exclusion bounds from the 8 TeV LHC run. We provide a simple phenomenological framework to parametrize the properties of the new resonance and show in a model-independent way that, if the scalar is produced in gluon fusion, additional new colored and charged particles are required. Finally, we discuss some interpretations in various concrete setups, such as a singlet (pseudo-) scalar, composite Higgs, and the MSSM.

   hep-phhep-exEPJC(2016)·236 citations
9. 09*

   Diphoton Signatures from Heavy Axion Decays at the CERN Large Hadron Collider

   Apostolos Pilaftsis🇬🇧

   Recently, the LHC collaborations, ATLAS and CMS, have announced an excess in the diphoton channel with local significance of about $3\sigma$ around an invariant mass distribution of $\sim 750$ GeV, after analyzing new data collected at centre-of-mass energies of $\sqrt{s}=13\mathrm{TeV}$. We present a possible physical interpretation of such a signature, within the framework of a minimal UV-complete model with a massive singlet pseudo-scalar state $a$ that couples to a new TeV-scale coloured vector-like fermion $F$, whose hypercharge quantum number is a non-zero integer. The pseudo-scalar state $a$ might be a heavy pseudo-Goldstone boson, such as a heavy axion, which decays into two photons and whose mass lies around the excess region. The mass of the CP-odd state $a$ and its coupling to $F$ may be due to non-perturbative effects, which can break the original Goldstone shift symmetry dynamically. The possible role that the heavy axion $a$ can play in the radiative generation of a seesaw Majorana scale and in the solution to the so-called strong CP problem is briefly discussed.

   hep-phPRD(2016)·194 citations
10. 10*

    What is the gamma gamma resonance at 750 GeV?

    Roberto Franceschini🇨🇭 · Gian F. Giudice🇨🇭 · Jernej F. Kamenik🇸🇮 · Matthew McCullough🇨🇭 · Alex Pomarol🇪🇸 · Riccardo Rattazzi🇨🇭 · Michele Redi🇮🇹 · Francesco Riva🇨🇭 · Alessandro Strumia🇨🇭 · Riccardo Torre🇨🇭

    Run 2 LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. We analyse the data in terms of a new boson, extracting information on its properties and exploring theoretical interpretations. Scenarios covered include a narrow resonance and, as preliminary indications suggest, a wider resonance. If the width indications persist, the new particle is likely to belong to a strongly-interacting sector. We also show how compatibility between Run 1 and Run 2 data is improved by postulating the existence of an additional heavy particle, whose decays are possibly related to dark matter.

    hep-phhep-exJHEP(2016)·400 citations
11. 11*

    First interpretation of the 750 GeV di-photon resonance at the LHC

    Stefano Di Chiara🇪🇪 · Luca Marzola🇪🇪 · Martti Raidal🇪🇪

    We scrutinise the evidences recently reported by the ATLAS and CMS collaborations for compatible 750 GeV resonances which appear in the di-photon channels of the two experiments in both the 8 TeV and 13 TeV datasets. Similar resonances in di-boson, di-lepton, di-jet and $t\bar{t}$ final states are instead not detected. After discussing the properties and the compatibility of the reported signals, we study the implications on the physics beyond the Standard Model with particular emphasis on possible scalar extensions of the theory such as singlet extensions and the two Higgs doublet models. We also analyse the significance of the new experimental indications within the frameworks of the minimal supersymmetric standard model and of technicolour models. Our results show that a simple effective singlet extension of the SM achieves phenomenological viability with a minimal number of free parameters. The minimal supersymmetric model and the two Higgs doublet model, on the other hand, cannot explain the 750 GeV di-photon excess. Compatibility with the observed signal requires the extension of the particle content of these models, for instance by heavy vector quarks in the case of the two Higgs doublet model.

    hep-phhep-exPRD(2016)·219 citations
12. 12*

    SUSY's Ladder: Reframing Sequestering at Large Volume

    Matthew Reece🇺🇸 · Wei Xue🇺🇸

    Theories with approximate no-scale structure, such as the Large Volume Scenario, have a distinctive hierarchy of multiple mass scales in between TeV gaugino masses and the Planck scale, which we call SUSY's Ladder. This is a particular realization of Split Supersymmetry in which the same small parameter suppresses gaugino masses relative to scalar soft masses, scalar soft masses relative to the gravitino mass, and the UV cutoff or string scale relative to the Planck scale. This scenario has many phenomenologically interesting properties, and can avoid dangers including the gravitino problem, flavor problems, and the moduli-induced LSP problem that plague other supersymmetric theories. We study SUSY's Ladder using a superspace formalism that makes the mysterious cancelations in previous computations manifest. This opens the possibility of a consistent effective field theory understanding of the phenomenology of these scenarios, based on power-counting in the small ratio of string to Planck scales. We also show that four-dimensional theories with approximate no-scale structure enforced by a single volume modulus arise only from two special higher-dimensional theories: five-dimensional supergravity and ten-dimensional type IIB supergravity. This gives a phenomenological argument in favor of ten dimensional ultraviolet physics which is different from standard arguments based on the consistency of superstring theory.

    hep-phhep-thJHEP(2016)·19 citations
13. 13*

    Electroweak Naturalness and Deflected Mirage Mediation

    Vernon Barger🇺🇸 · Lisa L. Everett🇺🇸 · Todd S. Garon🇺🇸

    We investigate the question of electroweak naturalness within the deflected mirage mediation (DMM) framework for supersymmetry breaking in the minimal supersymmetric standard model (MSSM). The class of DMM models considered are nine-parameter theories that fall within the general classification of the 19-parameter phenomenological MSSM (pMSSM). Our results show that these DMM models have regions of parameter space with very low electroweak fine-tuning, at levels comparable to the pMSSM. These parameter regions should be probed extensively in the current LHC run.

    hep-phPRD(2016)·7 citations
14. 14*

    Inhomogeneous chiral phases in two-flavor quark matter

    Hiroaki Abuki🇯🇵

    We present a systematic study of the phase structure of QCD in a generalized Ginzburg-Landau framework. We find, going up in density, a strongly interacting matter might go through the "pion crystal", an exotic inhomogeneous chiral phase before reaching the full restoration of symmetry.

    hep-phActa Astron.Sin.Suppl.(2015)·0 citations
15. 15*

    A new dynamics of electroweak symmetry breaking with classically scale invariance

    Naoyuki Haba🇯🇵 · Hiroyuki Ishida🇯🇵 · Noriaki Kitazawa🇯🇵 · Yuya Yamaguchi🇯🇵

    We propose a new dynamics of the electroweak symmetry breaking in a classically scale invariant version of the standard model. The scale invariance is broken by the condensations of additional fermions under a strong coupling dynamics. The electroweak symmetry breaking is triggered by negative mass squared of the elementary Higgs doublet, which is dynamically generated through the bosonic seesaw mechanism. We introduce a real pseudo-scalar singlet field interacting with additional fermions and Higgs doublet in order to avoid massless Nambu-Goldstone bosons from the chiral symmetry breaking in a strong coupling sector. We investigate the mass spectra and decay rates of these pseudo-Nambu-Goldstone bosons, and show they can decay fast enough without cosmological problems. We further evaluate the energy dependences of the couplings between elementary fields perturbatively, and find that our model is the first one which realizes the flatland scenario with the dimensional transmutation by the strong coupling dynamics. Similarly to the conventional flatland model with Coleman-Weinberg mechanism, the electroweak vacuum in our model is meta-stable.

    hep-phPLB(2016)·37 citations
16. 16*

    An $S_4$ model inspired from self-complementary neutrino mixing

    Xinyi Zhang🇨🇳

    We build an $S_4$ model for neutrino masses and mixings based on the self-complementary (SC) neutrino mixing pattern. The SC mixing is constructed from the self-complementarity relation plus ${\delta }_{\mathrm{CP}}=-\frac{\pi }{2}$. We elaborately construct the model at a percent level of accuracy to reproduce the structure given by the SC mixing. After performing a numerical study on the model's parameter space, we find that in the case of normal ordering, the model can give predictions on the observables that are compatible with their $3\sigma$ ranges, and give predictions for the not-yet observed quantities like the lightest neutrino mass $m_1\in [0.003,0.010]$ eV and the Dirac CP violating phase ${\delta }_{\mathrm{CP}}\in [256.72^{\circ },283.33^{\circ }]$.

    hep-phJ.Phys.G(2018)·9 citations
17. 17*

    Novel Perspectives from Light-Front QCD, Superconformal Algebra, and Light-Front Holography

    Stanley J. Brodsky🇺🇸

    Light-Front Quantization -- Dirac's "Front Form" -- provides a physical, frame-independent formalism for hadron dynamics and structure. Observables such as structure functions, transverse momentum distributions, and distribution amplitudes are defined from the hadronic LFWFs. One obtains new insights into the hadronic mass scale, the hadronic spectrum, and the functional form of the QCD running coupling in the nonperturbative domain using light-front holography. In addition, superconformal algebra leads to remarkable supersymmetric relations between mesons and baryons. I also discuss evidence that the antishadowing of nuclear structure functions is non-universal, i.e., flavor dependent, and why shadowing and antishadowing phenomena may be incompatible with the momentum and other sum rules for the nuclear parton distribution functions.

    hep-phBled Workshops Phys.(2015)·0 citations
18. 18*

    High Energy Hadron Spin Flip Amplitude

    O.V. Selyugin🇷🇺

    The high energy part of the hadron spin flip amplitude is examined in the framework of the new high energy general structure (HEGS) model of the elastic hadron scattering at high energies. The different forms of the hadron spin flip amplitude are compared in the impact parameters representation. It is shown that the existing experimental data of the proton-proton and proton-antiproton elastic scattering at high energy in the region of the diffraction minimum and at large momentum transfer give support in the presence of the energy-independent part of the hadron spin flip amplitude with the momentum dependence proposed in the works by Galynskii-Kuraev.

    hep-phhep-exPhys.Part.Nucl.Lett.(2016)·7 citations
19. 19*

    Pinning down QCD-matter shear viscosity in A+A collisions via EbyE fluctuations using pQCD + saturation + hydrodynamics

    H. Niemi🇩🇪 · K. J. Eskola🇫🇮 · R. Paatelainen🇪🇸 · K. Tuominen🇫🇮

    We compute the initial energy densities produced in ultrarelativistic heavy-ion collisions from NLO perturbative QCD using a saturation conjecture to control soft particle production, and describe the subsequent space-time evolution of the system with hydrodynamics, event by event. The resulting centrality dependence of the low-$p_T$ observables from this pQCD + saturation + hydro ("EKRT") framework are then compared simultaneously to the LHC and RHIC measurements. With such an analysis we can test the initial state calculation, and constrain the temperature dependence of the shear viscosity-to-entropy ratio $\eta /s$ of QCD matter. Using these constraints from the current RHIC and LHC measurements we then predict the charged hadron multiplicities and flow coefficients for the 5.023 TeV Pb+Pb collisions.

    hep-phnucl-thNPA(2016)·7 citations
20. 20*

    Effects of Goldstone Bosons on Gamma-Ray Bursts

    Huitzu Tu🇹🇼 · Kin-Wang Ng🇹🇼

    Gamma-ray bursts (GRBs) are the most energetic explosion events in the universe. An amount of gravitational energy of the order of the rest-mass energy of the Sun is released from a small region, within seconds or longer. This should lead to the formation of a fireball of temperature in the MeV range, consisting of electrons/positrons, photons, and a small fraction of baryons. We exploit the potential of GRB fireballs for being a laboratory for testing particle physics beyond the Standard Model, where we find that Weinberg's Higgs portal model serves as a good candidate for this purpose. Due to the resonance effects, the Goldstone bosons can be rapidly produced by electron-positron annihilation process in the initial fireballs of the gamma-ray bursts. On the other hand, the mean free path of the Goldstone bosons is larger than the size of the GRB initial fireballs, so they are not coupled to the GRB's relativistic flow and can lead to significant energy loss. Using generic values for the GRB initial fireball energy, temperature, radius, expansion rate, and baryon number density, we find that the GRB bounds on the parameters of Weinberg's Higgs portal model are indeed competitive to current laboratory constraints.

    hep-phastro-ph.HEJCAP(2016)·5 citations
21. 21*

    Heavy-flavour production in high-energy d-Au and p-Pb collisions

    Andrea Beraudo🇮🇹 · Arturo De Pace🇮🇹 · Marco Monteno🇮🇹 · Marzia Nardi🇮🇹 · Francesco Prino🇮🇹

    Soft-hadron measurements in high-energy collisions of small systems like p-Pb and d-Au show peculiar qualitative features (long-range rapidity correlations, flattening of the $p_T$-spectra with increasing hadron mass and centrality, non-vanishing Fourier harmonics in the azimuthal particle distributions) suggestive of the formation of a strongly-interacting medium displaying a collective behaviour, with a hydrodynamic flow as a response to the pressure gradients in the initial conditions. Hard observables (high-$p_T$ jet and hadron spectra) on the other hand, within the current large systematic uncertainties, appear only midly modified with the respect to the benchmark case of minimum-bias p-p collisions. What should one expect for heavy-flavour particles, initially produced in hard processes but tending, in the nucleus-nucleus case, to approach kinetic equilibrium with the rest of the medium? This is the issue we address in the present study, showing how the current experimental findings are compatible with a picture in which the formation of a hot medium even in proton-nucleus collisions modifies the propagation and hadronization of heavy-flavour particles.

    hep-phnucl-exnucl-thJHEP(2016)·76 citations
22. 22*

    High-precision ${\alpha }_s$ measurements from LHC to FCC-ee

    David d'Enterria · Peter Z. Skands (eds.) · S. Alekhin · A. Banfi · S. Bethke · J. Blümlein · K.G. Chetyrkin · D. d'Enterria · G. Dissertori · X. Garcia i Tormo · A. H. Hoang · M. Klasen and 21 other authors

    This document provides a writeup of all contributions to the workshop on "High precision measurements of ${\alpha }_s$: From LHC to FCC-ee" held at CERN, Oct. 12--13, 2015. The workshop explored in depth the latest developments on the determination of the QCD coupling ${\alpha }_s$ from 15 methods where high precision measurements are (or will be) available. Those include low-energy observables: (i) lattice QCD, (ii) pion decay factor, (iii) quarkonia and (iv) $\tau$ decays, (v) soft parton-to-hadron fragmentation functions, as well as high-energy observables: (vi) global fits of parton distribution functions, (vii) hard parton-to-hadron fragmentation functions, (viii) jets in $e^{\pm }$p DIS and $\gamma$-p photoproduction, (ix) photon structure function in $\gamma$-$\gamma$, (x) event shapes and (xi) jet cross sections in $e^{+}{e}^{-}$ collisions, (xii) W boson and (xiii) Z boson decays, and (xiv) jets and (xv) top-quark cross sections in proton-(anti)proton collisions. The current status of the theoretical and experimental uncertainties associated to each extraction method, the improvements expected from LHC data in the coming years, and future perspectives achievable in $e^{+}{e}^{-}$ collisions at the Future Circular Collider (FCC-ee) with $\mathcal{O}$(1--100 ab${}^{-1}$) integrated luminosities yielding 10${}^{12}$ Z bosons and jets, and 10${}^8$ W bosons and $\tau$ leptons, are thoroughly reviewed. The current uncertainty of the (preliminary) 2015 strong coupling world-average value, ${\alpha }_s(m_Z)$ = 0.1177 $\pm$ 0.0013, is about 1\%. Some participants believed this may be reduced by a factor of three in the near future by including novel high-precision observables, although this opinion was not universally shared. At the FCC-ee facility, a factor of ten reduction in the ${\alpha }_s$ uncertainty should be possible, mostly thanks to the huge Z and W data samples available.

    hep-phhep-ex96 citations
23. 23*

    Lifetime of the eta' meson at low temperature

    E. Perotti (Uppsala U.)🇸🇪 · C. Niblaeus (Stockholm U.)🇸🇪 · S. Leupold (Uppsala U.)🇸🇪

    This work constitutes one part of an investigation of the low-temperature changes of the properties of the eta' meson. In turn these properties are strongly tied to the U(1)_A anomaly of Quantum Chromodynamics. The final aim is to explore the interplay of the chiral anomaly and in-medium effects. We determine the lifetime of an eta' meson being at rest in a strongly interacting medium as a function of the temperature. To have a formally well-defined low-energy limit we use in a first step Chiral Perturbation Theory for a large number of colors. We determine the pertinent scattering amplitudes in leading and next-to-leading order. In a second step we include resonances that appear in the same mass range as the eta' meson. The resonances are introduced such that the low-energy limit remains unchanged and that they saturate the corresponding low-energy constants. This requirement fixes all coupling constants. We find that the width of the eta' meson is significantly increased from about 200 keV in vacuum to about 10 MeV at a temperature of 120 MeV.

    hep-phnucl-thNPA(2016)·0 citations
24. 24*

    Pion and $\eta$-meson mass splitting at the two-flavour chiral crossover

    Markus Heller🇮🇹 · Mario Mitter🇩🇪

    We study the splitting in the screening mass of pions and the $\eta$-meson across the chiral crossover. This splitting is determined by the 't Hooft determinant. We use results for the renormalisation group scale dependence of the 't Hooft determinant obtained within the functional renomalisation group in quenched QCD with two flavours. The scale dependence of the 't Hooft determinant is mapped to its temperature dependence with the help of a Polyakov-quark-meson model. As a result we obtain the temperature dependence of the splitting in the screening mass of pions and the $\eta$-meson.

    hep-phPRD(2016)·21 citations
25. 25*

    Distinguishing b-quark and gluon jets with a tagged b-hadron

    Dorival Goncalves🇬🇧 · Frank Krauss🇬🇧 · Robin Linten🇬🇧

    Based on the knowledge of the QCD radiation pattern, observables to distinguish jets containing one and two $b$-hadrons are discussed. A simple method is used to combine pairs of the most sensitive observables, girth, number of charged tracks and the energy or momentum fraction of the leading $b$-hadron with respect to the jet, into one discriminator. Their efficiencies, on particle level, are estimated and found to improve the performance and the robustness of the observables in different momentum slices.

    hep-phPRD(2016)·17 citations
26. 26*

    Antilinearity Rather than Hermiticity as a Guiding Principle for Quantum Theory

    Philip D. Mannheim🇺🇸

    Currently there is much interest in Hamiltonians that are not Hermitian but instead possess an antilinear $PT$ symmetry, since such Hamiltonians can still lead to the time-independent evolution of scalar products, and can still have an entirely real energy spectrum. However, such theories can also admit of energy spectra in which energies come in complex conjugate pairs, and can even admit of Hamiltonians that cannot be diagonalized at all. Hermiticity is just a particular realization of $PT$ symmetry, with $PT$ symmetry being the more general. These $PT$ theories are themselves part of an even broader class of theories, theories that can be characterized by possessing some general antilinear symmetry, as that requirement alone is a both necessary and sufficient condition for the time-independent evolution of scalar products, with all the different realizations of the $PT$ symmetry program then being obtained. Use of complex Lorentz invariance allows us to show that the antilinear symmetry is uniquely specified to be $CPT$, with the $CPT$ theorem thus being extended to the non-Hermitian case. For theories that are separately charge conjugation invariant, the results of the $PT$-symmetry program then follow. We show that in order to construct the correct classical action needed for a path integral quantization one must impose $CPT$ symmetry on each classical path, a requirement that has no counterpart in any Hermiticity condition since Hermiticity of a Hamiltonian is only definable after the quantization has been performed and the quantum Hilbert space has been constructed. We show that whether or not a $CPT$-invariant Hamiltonian is Hermitian is a property of the solutions to the theory and not of the Hamiltonian itself. Thus Hermiticity never needs to be postulated at all.

    ↳ hep-thhep-phquant-phJ.Phys.A(2018)·54 citations
27. 27*

    The Gamma-Ray Luminosity Function of Millisecond Pulsars and Implications for the GeV Excess

    Dan Hooper🇺🇸 · Gopolang Mohlabeng🇺🇸

    It has been proposed that a large population of unresolved millisecond pulsars (MSPs) could potentially account for the excess of GeV-scale gamma-rays observed from the region surrounding the Galactic Center. The viability of this scenario depends critically on the gamma-ray luminosity function of this source population, which determines how many MSPs Fermi should have already detected as resolved point sources. In this paper, we revisit the gamma-ray luminosity function of MSPs, without relying on uncertain distance measurements. Our determination, based on a comparison of models with the observed characteristics of the MSP population, suggests that Fermi should have already detected a significant number of sources associated with such a hypothesized Inner Galaxy population. We cannot rule out a scenario in which the MSPs residing near the Galactic Center are systematically less luminous than those present in the Galactic Plane or within globular clusters.

    ↳ astro-ph.HEastro-ph.COastro-ph.GAhep-phJCAP(2016)·65 citations
28. 28*

    Fluctuations of conserved charges in relativistic heavy ion collisions: An introduction

    Masayuki Asakawa🇯🇵 · Masakiyo Kitazawa🇯🇵

    Bulk fluctuations of conserved charges measured by event-by-event analysis in relativistic heavy ion collisions are observables which are believed to carry significant amount of information on the hot medium created by the collisions. Active studies have been done recently experimentally, theoretically, and on the lattice. In particular, non-Gaussianity of the fluctuations has acquired much attention recently. In this review, we give a pedagogical introduction to these issues, and survey recent developments in this field of research. Starting from the definition of cumulants, basic concepts in fluctuation physics, such as thermal fluctuations in statistical mechanics and time evolution of fluctuations in diffusive systems, are described. Phenomena which are expected to occur in finite temperature and/or density QCD matter and their measurement by event-by-event analyses are also elucidated.

    ↳ nucl-thhep-phnucl-exPPNP(2016)·166 citations
29. 29*

    Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data

    C. Adolph🇩🇪 · M. Aghasyan🇮🇹 · R. Akhunzyanov🇷🇺 · M.G. Alexeev · G.D. Alexeev · A. Amoroso🇮🇹 · V. Andrieux🇫🇷 · N.V. Anfimov🇷🇺 · V. Anosov🇷🇺 · W. Augustyniak🇵🇱 · A. Austregesilo🇩🇪 · C.D.R. Azevedo🇵🇹 and 209 other authors

    Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality $Q^2>1(\mathrm{GeV}/c{)}^2$. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/$c$ polarised muon beam impinging on a polarised ${}^6$LiD target. By analysing the full range in hadron transverse momentum $p_{\mathrm{T}}$, the different $p_{\mathrm{T}}$-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation $\Delta g/g$ is evaluated at leading order in pQCD at a hard scale of ${\mu }^2=⟨Q^2⟩=3(\mathrm{GeV}/c{)}^2$. It is determined in three intervals of the nucleon momentum fraction carried by gluons, $x_{\mathrm{g}}$, covering the range $0.04<x_{\mathrm{g}}<0.28$~ and does not exhibit a significant dependence on $x_{\mathrm{g}}$. The average over the three intervals, $⟨\Delta g/g⟩=0.113\pm 0.038_{(stat.)}\pm 0.036_{(syst.)}$ at $⟨x_{\mathrm{g}}⟩\approx 0.10$, suggests that the gluon polarisation is positive in the measured $x_{\mathrm{g}}$ range.

    ↳ hep-exhep-phEPJC(2017)·29 citations
30. 30*

    Interference of Dark Matter Solitons and Galactic Offsets

    Angel Paredes🇪🇸 · Humberto Michinel🇪🇸

    By performing numerical simulations, we discuss the collisional dynamics of stable solitary waves in the Schrodinger-Poisson equation. In the framework of a model in which part or all of dark matter is a Bose-Einstein condensate of ultralight axions, we show that these dynamics can naturally account for the relative displacement between dark and ordinary matter in the galactic cluster Abell 3827, whose recent observation is the first empirical evidence of dark matter interactions beyond gravity. The essential assumption is the existence of solitonic galactic cores in the kiloparsec scale. For this reason, we present simulations with a benchmark value of the axion mass $m_a=2\times 10^{-24}$ eV, which is somewhat lower than the one preferred for cosmological structure formation if the field is all of dark matter ($m_a\approx 10^{-22}$eV). We argue that future observations might bear out or falsify this coherent wave interpretation of dark matter offsets.

    ↳ astro-ph.COhep-phnlin.PSPhys.Dark Univ.(2016)·65 citations
31. 31*

    Introductory lectures on lattice QCD at nonzero baryon number

    Gert Aarts (Swansea University)🇬🇧

    These lecture notes contain an elementary introduction to lattice QCD at nonzero chemical potential. Topics discussed include chemical potential in the continuum and on the lattice; the sign, overlap and Silver Blaze problems; the phase boundary at small chemical potential; imaginary chemical potential; and complex Langevin dynamics. An incomplete overview of other approaches is presented as well. These lectures are meant for postgraduate students and postdocs with an interest in extreme QCD. A basic knowledge of lattice QCD is assumed but not essential. Some exercises are included at the end.

    ↳ hep-lathep-phnucl-thJ.Phys.Conf.Ser.(2016)·233 citations
32. 32*

    Equation of state for cold and dense heavy QCD

    Jonas Glesaaen🇩🇪 · Mathias Neuman🇩🇪 · Owe Philipsen🇩🇪

    A previously derived three-dimensional effective lattice theory describing the thermodynamics of QCD with heavy quarks in the cold and dense region is extended through order $\sim u^5{\kappa }^8$ in the combined character and hopping expansion of the original four-dimensional Wilson action. The systematics of the effective theory is investigated to determine its range of validity in parameter space. We demonstrate the severe cut-off effects due to lattice saturation, which afflict any lattice results at finite baryon density independent of the sign problem or the quality of effective theories, and which have to be removed by continuum extrapolation. We then show how the effective theory can be solved analytically by means of a linked cluster expansion, which is completely unaffected by the sign problem, in quantitative agreement with numerical simulations. As an application, we compute the cold nuclear equation of state of heavy QCD. Our continuum extrapolated result is consistent with a polytropic equation of state for non-relativistic fermions.

    ↳ hep-lathep-phnucl-thJHEP(2016)·32 citations
33. 33*

    The sensitivity of R_pA to color recombination effects

    Korinna Christina Zapp🇨🇭 · Guilherme Milhano🇵🇹 · Urs Achim Wiedemann🇨🇭

    In hadronization models with color recombination, partons are allowed to regroup into color singlet structures that are different from those determined by the perturbative parton shower. This aims at modeling the possibility that soft interactions of partons with the underlying event can change color connections. If such an effect is at play in proton-proton collisions, it may be expected to be enhanced in proton-nucleus collisions due to the higher color charge density in the underlying event. Here, we provide a qualitative argument that color recombination effects could lead to a multiplicity dependent hardening of single inclusive hadron spectra that dies out very weakly with increasing transverse momentum. We present results of a (conservative) model implementation in the cluster hadronization model of the SHERPA event generator. In this model, we find that color recombination effects harden indeed the single inclusive hadron spectra without affecting the jet spectra, but that this effect does not depend significantly on underlying event activity. We explain this model feature and we argue why, in general, data on proton-nucleus collisions can help to constrain hadronization models used in proton-proton event generators.

    ↳ nucl-thhep-phNPA(2016)·0 citations
34. 34*

    DBI scalar field theory for QGP hydrodynamics

    Horatiu Nastase🇧🇷

    A way to describe the hydrodynamics of the quark-gluon plasma using a DBI action is proposed, based on the model found by Heisenberg for high energy scattering of nucleons. The expanding plasma is described as a shockwave in a DBI model for a real scalar standing in for the pion, and I show that one obtains a fluid description in terms of a relativistic fluid that near the shock is approximately ideal ($\eta \simeq 0$) and conformal. One can introduce an extra term inside the square root of the DBI action that generates a shear viscosity term in the energy-momentum tensor near the shock, as well as a bulk viscosity, and regulates the behaviour of the energy density at the shock, making it finite. The resulting fluid satisfies the relativistic Navier-Stokes equation with $u^{\mu },\rho ,P,\eta$ defined in terms of $\varphi$ and its derivatives. One finds a relation between the parameters of the theory and the QGP thermodynamics, $\text{a}/{\text{b}}^2=\eta /(sT)$, and by fixing $\text{a}$ and $\text{b}$ from usual (low multiplicity) particle scattering, one finds $T\propto m_{\pi }$.

    ↳ hep-thhep-phnucl-thPRD(2016)·7 citations
35. 35*

    ETHOS - An Effective Theory of Structure Formation: From dark particle physics to the matter distribution of the Universe

    Francis-Yan Cyr-Racine (1 and 2)🇬🇧 · Kris Sigurdson (3 and 4)🇺🇸 · Jesus Zavala (5)🇩🇰 · Torsten Bringmann (6)🇳🇴 · Mark Vogelsberger (7)🇬🇧 · Christoph Pfrommer (8) ((1) Harvard, (2) Caltech, (3) IAS Princeton, (4) UBC, (5) Dark Cosmology Centre, (6) UIO, (7) MIT, (8) HITS)🇩🇪

    We formulate an effective theory of structure formation (ETHOS) that enables cosmological structure formation to be computed in almost any microphysical model of dark matter physics. This framework maps the detailed microphysical theories of particle dark matter interactions into the physical effective parameters that shape the linear matter power spectrum and the self-interaction transfer cross section of non-relativistic dark matter. These are the input to structure formation simulations, which follow the evolution of the cosmological and galactic dark matter distributions. Models with similar effective parameters in ETHOS but with different dark particle physics would nevertheless result in similar dark matter distributions. We present a general method to map an ultraviolet complete or effective field theory of low energy dark matter physics into parameters that affect the linear matter power spectrum and carry out this mapping for several representative particle models. We further propose a simple but useful choice for characterizing the dark matter self-interaction transfer cross section that parametrizes self-scattering in structure formation simulations. Taken together, these effective parameters in ETHOS allow the classification of dark matter theories according to their structure formation properties rather than their intrinsic particle properties, paving the way for future simulations to span the space of viable dark matter physics relevant for structure formation.

    ↳ astro-ph.COastro-ph.GAhep-phhep-thPRD(2016)·306 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.