Thu·Jul 23, 2015Thursday·July 23, 2015

1. 01*

   Fluctuations and the rapidity dependence of charged particles spectra in fixed centrality bins in p$A$ collisions

   Larry McLerran🇺🇸 · Michal Praszalowicz🇵🇱

   We argue that large fluctuations in the saturation momentum are necessary to explain the ATLAS and ALICE data on pA collisions measured at the LHC. Using a form for the distribution of fluctuations motivated by theoretical studies of the non-linear evolution equations for the Color Glass Condensate, we find a remarkably good agreement between theory and the measured distributions. If the saturation momentum fluctuates, we argue that the cross section for a proton probe should also fluctuate, consistent with previous observations. Finally we discuss these results and their possible consistency with what is known about multiplicity fluctuations in such collisions, and attempts to describe the ridge effect from properties of the initial state.

   hep-phnucl-thAnnals Phys.(2016)·17 citations
2. 02*

   Initial-state cold nuclear matter energy loss effects on inclusive jet production in p+A collisions at RHIC and LHC

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

   Recent measurements of the centrality and rapidity dependence of single inclusive jet production in p+Pb collisions at the LHC have revealed large and non-trivial nuclear modification of the production cross section for this process. In this paper, we explore to what extent such nuclear modification can be understood by the framework of standard cold nuclear matter effects, in particular initial-state cold nuclear matter energy loss. We demonstrate quantitatively that theoretical calculations which include medium-induced radiative corrections can describe rather reasonably the attenuation of the jet production yields in the large transverse momentum region in d+Au collisions at RHIC and p+Pb collisions at the LHC for central to semi-central collisions. We further show that the observed scaling behavior of the nuclear modification factor as a function of the total jet energy $p_T\cosh (y)$ for various rapidity intervals has a natural explanation in the picture of cold nuclear matter energy loss. On the other hand, the observed enhancement in peripheral collisions is not described in this picture and could have a different origin.

   hep-phnucl-exnucl-thPRC(2015)·53 citations
3. 03*

   Higgs relaxation and the matter-antimatter asymmetry of the universe

   Alexander Kusenko🇯🇵

   The recent measurement of the Higgs boson mass implies a relatively slow rise of the Standard Model Higgs potential at large scales, and a possible second minimum at even larger scales. Consequently, the Higgs field may develop a large vacuum expectation value during inflation. The relaxation of the Higgs field from its large postinflationary value to the minimum of the effective potential represents an important stage in the evolution of the universe. During this epoch, the time-dependent Higgs condensate can create an effective chemical potential for the lepton number, leading to a generation of the lepton asymmetry in the presence of some large right-handed Majorana neutrino masses. Electroweak sphalerons redistribute this asymmetry between leptons and baryons. Higgs relaxation leptogenesis can explain the observed matter-antimatter asymmetry of the universe even if the Standard Model is valid up to the scale of inflation, and any new physics is suppressed by that high scale.

   hep-ph1 citation
4. 04*

   Low Scale Composite Higgs Model and 1.8 $\sim$ 2 TeV Diboson Excess

   Ligong Bian🇨🇳 · Da Liu🇨🇳 · Jing Shu🇨🇳

   We consider a simple solution to explain the recent diboson excess observed by ATALS and CMS Collaborations in models with custodial symmetry $SU(2{)}_L\times SU(2{)}_R\to SU(2{)}_c$. The $SU(2{)}_L$ triplet vector boson $\rho$ with mass range of $1.8\sim 2$ TeV would be produced through the Drell-Yan process with sizable diboson decay branching to account for the excess. The other $SU(2{)}_L\times SU(2{)}_R$ bidoublet axial vector boson $a$ would cancel all deviations of electroweak obervables induced by $\rho$ even if the SM fermions mix with some heavy vector like (composite) fermions which couple to $\rho$ ("non-universally partially composite"), therefore allows arbitrary couplings between each SM fermion and $\rho$. We present our model in the "General Composite Higgs" framework with $SO(5)\times U(1{)}_X\to SO(4)\times U(1{)}_X$ breaking at scale $f$ and demand the first Weinberg sum rule and positive gauge boson form factors as the theoretical constraints. We find that our model can fit the diboson excess very well if the left-handed SM light quarks, charged leptons and tops have zero, zero/moderately small and moderate/large composite components for reasonable values of $g_{\rho }$ and $f$. The correlation between tree level $S$ parameter and the $h\to Z\gamma$ suggest a large $a$ contribution to $h\to Z\gamma$ and it is indeed a $\mathcal{O}(1)$ effect in our parameter space which provides a strong hint for our scenario if this diboson excess is confirmed by the $13\sim 14$ TeV LHC Run II.

   hep-phInt.J.Mod.Phys.A(2018)·32 citations
5. 05*

   Influence of clustering and hadron potentials on the rapidity distribution of protons from the UrQMD model

   Qingfeng Li🇨🇳 · Yongjia Wang🇨🇳 · Xiaobao Wang🇨🇳 · Caiwan Shen🇨🇳 · Marcus Bleicher🇩🇪

   The Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model supplemented by potentials for both pre-formed hadrons and confined baryons (called UrQMD/M) are used to describe rapidity distributions of both the E895 proton data at AGS energies and the NA49 net proton data at SPS energies. With the help of a coalescence afterburner using only one parameter set of ($R_0$, $P_0$)=(3.8 fm, 0.3 GeV$/$c), both sets of experimental data can be described fairly well except for a small discrepancy seen for the net protons at mid-rapidity from heavy ion collisions (HICs) at high SPS energies. Furthermore, in contrast to the logarithmic dependence with beam energy at SIS energies there are still about 10$\%$ of protons in clusters from central HICs at the beam energy of $80$ GeV$/$nucleon.

   hep-phnucl-th7 citations
6. 06*

   Bounds on Higgs-Portal models from the LHC Higgs data

   Kingman Cheung🇹🇼 · P. Ko🇰🇷 · Jae Sik Lee🇰🇷 · Po-Yan Tseng🇹🇼

   In a number of Higgs-portal models, an $SU(2)$ isospin-singlet scalar boson generically appears at the electroweak scale and can mix with the Standard Model (SM) Higgs boson with a mixing angle $\alpha$. This singlet scalar boson can have renormalizable couplings to a pair of dark matter particles, vectorlike leptons or quarks, or new gauge bosons, thereby modifying the Higgs signal strengths in a nontrivial way. In this work, we perform global fits to such models using the most updated LHC Higgs-boson data and discuss the corresponding implications on Higgs-portal-type models. In particular we find that the current LHC Higgs-boson data slightly favors the SM over the Higgs-portal singlet-scalar models, which has to be further examined using the upcoming LHC Higgs-boson data. Finally the Higgs-portal models are constrained as follows: $\cos \alpha \gtrsim 0.86$ and $\Delta {\Gamma }_{\mathrm{tot}}\lesssim 1.9$ MeV at 95 \% CL.

   hep-phhep-exJHEP(2015)·52 citations
7. 07*

   Axino dark matter with low reheating temperature

   Leszek Roszkowski🇵🇱 · Sebastian Trojanowski🇵🇱 · Krzysztof Turzynski🇵🇱

   We examine axino dark matter in the regime of a low reheating temperature T_R after inflation and taking into account that reheating is a non-instantaneous process. This can have a significant effect on the dark matter abundance, mainly due to entropy production in inflaton decays. We study both thermal and non-thermal production of axinos in the context of the MSSM with ten free parameters. We identify the ranges of the axino mass and the reheating temperature allowed by the LHC and other particle physics data in different models of axino interactions. We confront these limits with cosmological constraints coming the observed dark matter density, large structures formation and big bang nucleosynthesis. We find a number of differences in the phenomenologically acceptable values of the axino mass and the reheating temperature relative to previous studies. In particular, an upper bound on the axino mass becomes dependent on T_R, reaching a maximum value at T_R~10^2 GeV. If the lightest ordinary supersymmetric particle is a wino or a higgsino, we obtain lower a limit of approximately 10 GeV for the reheating temperature. We demonstrate also that entropy production during reheating affects the maximum allowed axino mass and lowest values of the reheating temperature.

   hep-phastro-ph.COJHEP(2015)·13 citations
8. 08*

   Gluon PDF constraints from the ratio of forward heavy quark production at the LHC at \sqrt{S}=7 and 13 TeV

   Matteo Cacciari🇫🇷 · Michelangelo L. Mangano🇨🇭 · Paolo Nason🇮🇹

   We discuss production of charm and bottom quarks at forward rapidity in pp collisions at the LHC, updating the QCD predictions for the run at \sqrt{S}=13 TeV. We show that, while the absolute rates suffer from large theoretical systematics, dominated by scale uncertainties, the increase relative to the rates precisely measured at 7 TeV can be predicted with an accuracy of a few percent, sufficient to highlight the sensitivity to the gluon distribution function.

   hep-phhep-exEPJC(2015)·191 citations
9. 09*

   Heavy concerns about the light axino explanation of the 3.5 keV X-ray line

   Stefano Colucci🇩🇪 · Herbi K. Dreiner🇩🇪 · Florian Staub🇨🇭 · Lorenzo Ubaldi🇮🇱

   An unidentified 3.5 keV line from X-ray observations of galaxy clusters has been reported recently. Although still under scrutiny, decaying dark matter could be responsible for this signal. We investigate whether an axino with a mass of 7 keV could explain the line, keeping the discussion as model independent as possible. We point out several obstacles, which were overlooked in the literature, and which make the axino an unlikely candidate. The only viable scenario predicts a light metastable neutralino, with a mass between 0.1 and 10 GeV and a lifetime between $10^{-3}$ and $10^4$ s.

   hep-phastro-ph.COastro-ph.HEPLB(2015)·9 citations
10. 10*

    Determining $V_{tb}$ at Electron-Positron Colliders

    Qing-Hong Cao🇨🇳 · Bin Yan🇨🇳

    Verifying $V_{tb}\simeq 1$ is critical to test the three generation assumption of the Standard Model. So far our best knowledge of $V_{tb}$ is inferred either from the $3\times 3$ unitarity of CKM matrix or from single top-quark productions upon the assumption of universal weak couplings. The unitarity could be relaxed in new physics models with extra heavy quarks and the universality of weak couplings could also be broken if the $Wtb$ coupling is modified in new physics models. In this work we propose to measure $V_{tb}$ in the process of $e^{+}{e}^{-}\to t\bar{t}$ without prior knowledge of the number of fermion generations or the strength of the $Wtb$ coupling. Using an effective Lagrangian approach, we perform a model-independent analysis of the interactions among electroweak gauge bosons and the third generation quarks, i.e. the $Wtb$, $Zt\bar{t}$ and $Zb\bar{b}$ couplings. The electroweak symmetry of the Standard Model specifies a pattern of deviations of the $Z$-$t_L$-$t_L$ and $W$-$t_L$-$b_L$ couplings after one imposes the known experimental constraint on the $Z$-$b_L$-$b_L$ coupling. We demonstrate that, making use of the predicted pattern and the accurate measurements of top-quark mass and width from the energy threshold scan experiments, one can determine $V_{tb}$ from the cross section and the forward-backward asymmetry of top-quark pair production at an {\it unpolarized} electron-positron collider.

    hep-phPRD(2015)·34 citations
11. 11*

    Lepton number violation as a key to low-scale leptogenesis

    Asmaa Abada🇫🇷 · Giorgio Arcadi🇫🇷 · Valerie Domcke🇮🇹 · Michele Lucente🇫🇷

    We explore the possibility of having a successful leptogenesis through oscillations between new sterile fermion states added to the Standard Model field content in a well motivated framework, naturally giving rise to the required mass splitting between the sterile states through a small total lepton number violation. We propose a framework with only two sterile states forming a pseudo-Dirac state, in which their mass difference as well as the smallness of the neutrino masses are due to two sources of lepton number violation with $\Delta L=2$, corresponding to an Inverse Seesaw framework extended by a Linear Seesaw mass term. We also explore the pure Inverse Seesaw mechanism in its minimal version, requiring at least four new sterile states in order to comply with neutrino data. Our analytical and numerical studies reveal that one can have a successful leptogenesis at the temperature of the electroweak scale through oscillations between the two sterile states with a "natural" origin of the strong degeneracy in their mass spectrum. We also revisit the analytical expression of the baryon asymmetry of the Universe in the weak washout regime of this framework.

    hep-phJCAP(2015)·89 citations
12. 12*

    High energy photon production in strong colliding laser beams

    Michael Kuchiev🇦🇺 · Julian Ingham🇦🇺

    The collision of two intense, low-frequency laser beams is considered. The $e^{-}{e}^{+}$ pairs created in this field are shown to exhibit recollisions, which take place at high energy accumulated due to the wiggling of fermions. The resulting $e^{-}{e}^{+}$ annihilation produces high energy photons, or heavy particles. The coherent nature of the laser field provides strong enhancement of the probability of these events. Analytical and numerical results are outlined.

    hep-ph0 citations
13. 13*

    Testing the minimal $S_4$ model of neutrinos with the Dirac and Majorana phases

    Yusuke Shimizu🇯🇵 · Morimitsu Tanimoto🇯🇵

    We propose two new simple lepton flavor models in the framework of the $S_4$ flavor symmetry. The neutrino mass matrices, which are given by two complex parameters, lead to the inverted mass hierarchy. The charged lepton mass matrix has the 1-2 lepton flavor mixing, which gives the non-vanishing reactor angle ${\theta }_{13}$. These models predict the Dirac phase and the Majorana phases, which are testable in the future experiments. The predicted magnitudes of the effective neutrino mass for the neutrino-less double beta decay are in the regions as $32\text{meV}\lesssim |m_{ee}|\lesssim 49\text{meV}$ and $34\text{meV}\lesssim |m_{ee}|\lesssim 59\text{meV}$, respectively. These values are close to the expected reaches of the coming experiments. The total sum of the neutrino masses are predicted in both models as $0.0952\text{eV}\lesssim \sum m_i\lesssim 0.101\text{eV}$ and $0.150\text{eV}\lesssim \sum m_i\lesssim 0.160\text{eV}$, respectively.

    hep-phhep-exJHEP(2015)·7 citations
14. 14*

    Predictions for Leptonic Mixing Angle Correlations and Non-trivial Dirac CP Violation from $A_5$ with Generalised CP Symmetry

    Jessica Turner🇬🇧

    Using discrete flavour group, $A_5$, combined with generalised CP, we study the mixing parameter correlations which arise from breaking to residual symmetries in the neutrino, $G_{\nu }={\mathbb{Z}}_2\times \text{CP}$, and charged lepton sectors, $G_e={\mathbb{Z}}_2$. By focusing on patterns that agree with current experimental data we demonstrate that non-trivial leptonic phases are predicted and discuss a number of distinctive correlations between mixing parameters.

    hep-phPRD(2015)·62 citations
15. 15*

    ZZ production at the LHC: fiducial cross sections and distributions in NNLO QCD

    Massimiliano Grazzini🇨🇭 · Stefan Kallweit🇩🇪 · Dirk Rathlev🇨🇭

    We consider QCD radiative corrections to the production of four charged leptons in the ZZ signal region at the LHC. We report on the complete calculation of the next-to-next-to-leading order (NNLO) corrections to this process in QCD perturbation theory. Numerical results are presented for $\sqrt{s}=8$ TeV, using typical selection cuts applied by the ATLAS and CMS collaborations. The NNLO corrections increase the NLO fiducial cross section by about $15\%$, and they have a relatively small impact on the shape of the considered kinematical distributions. In the case of the $\Delta \Phi$ distribution of the two Z candidates, the NNLO corrections improve the agreement of the theoretical prediction with the CMS data.

    hep-phhep-exPLB(2015)·282 citations
16. 16*

    Froggatt-Nielsen meets Mordell-Weil: A Phenomenological Survey of Global F-theory GUTs with U(1)s

    Sven Krippendorf🇬🇧 · Sakura Schafer-Nameki🇬🇧 · Jin-Mann Wong🇬🇧

    In F-theory, U(1) gauge symmetries are encoded in rational sections, which generate the Mordell-Weil group of the elliptic fibration of the compactification space. Recently the possible U(1) charges for global SU(5) F-theory GUTs with smooth rational sections were classified arXiv:1504.05593 [hep-th]. In this paper we utilize this classification to probe global F-theory models for their phenomenological viability. After imposing an exotic-free MSSM spectrum, anomaly cancellation (related to hypercharge flux GUT breaking in the presence of U(1) gauge symmetries), absence of dimension four and five proton decay operators and other R-parity violating couplings, and the presence of at least the third generation top Yukawa coupling, we generate the remaining quark and lepton Yukawa textures by a Froggatt-Nielsen mechanism. In this process we require that the dangerous couplings are forbidden at leading order, and when re-generated by singlet vevs, lie within the experimental bounds. We scan over all possible configurations, and show that only a small class of U(1) charge assignments and matter distributions satisfy all the requirements. The solutions give rise to the exact MSSM spectrum with realistic quark and lepton Yukawa textures, which are consistent with the CKM and PMNS mixing matrices. We also discuss the geometric realization of these models, and provide pointers to the class of elliptic fibrations with good phenomenological properties.

    ↳ hep-thhep-phJHEP(2015)·32 citations
17. 17*

    Neutrino emissivity in the quark-hadron mixed phase of neutron stars

    William M. Spinella (1,2)🇺🇸 · Fridolin Weber (2,3)🇺🇸 · Gustavo A. Contrera (4,5,6)🇦🇷 · Milva G. Orsaria (4,6) ((1) Computational Science Research Center San Diego State University, San Diego, CA, USA, (2) Department of Physics, San Diego State University, San Diego, CA, USA, (3) Center for Astrophysics and Space Sciences, University of California San Diego, La Jolla, CA, USA, (4) CONICET, Rivadavia 1917, Buenos Aires, Argentina, (5) IFLP, CONICET - Dpto. de Fisica, UNLP, La Plata, Argentina, (6) Grupo de Gravitacion, Astrofisica y Cosmologia, Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosqu, La Plata, Argentina.)🇦🇷

    Numerous theoretical studies using various equation of state models have shown that quark matter may exist at the extreme densities in the cores of high-mass neutron stars. It has also been shown that a phase transition from hadronic matter to quark matter would result in an extended mixed phase region that would segregate phases by net charge to minimize the total energy of the phase, leading to the formation of a crystalline lattice. The existence of quark matter in the core of a neutron star may have significant consequences for its thermal evolution, which for thousands of years is facilitated primarily by neutrino emission. In this work we investigate the effect a crystalline quark-hadron mixed phase can have on the neutrino emissivity from the core. To this end we calculate the equation of state using the relativistic mean-field approximation to model hadronic matter and a nonlocal extension of the three-flavor Nambu-Jona-Lasinio model for quark matter. Next we determine the extent of the quark-hadron mixed phase and its crystalline structure using the Glendenning construction, allowing for the formation of spherical blob, rod, and slab rare phase geometries. Finally we calculate the neutrino emissivity due to electron-lattice interactions utilizing the formalism developed for the analogous process in neutron star crusts. We find that the contribution to the neutrino emissivity due to the presence of a crystalline quark-hadron mixed phase is substantial compared to other mechanisms at fairly low temperatures ($\lesssim 10^9$ K) and quark fractions ($\lesssim 30\%$), and that contributions due to lattice vibrations are insignificant compared to static-lattice contributions.

    ↳ nucl-thastro-ph.HEhep-phEPJA(2016)·18 citations
18. 18*

    Evanescent Effects Can Alter Ultraviolet Divergences in Quantum Gravity without Physical Consequences

    Zvi Bern🇺🇸 · Clifford Cheung🇺🇸 · Huan-Hang Chi🇺🇸 · Scott Davies🇺🇸 · Lance Dixon🇺🇸 · Josh Nohle🇺🇸

    Evanescent operators such as the Gauss-Bonnet term have vanishing perturbative matrix elements in exactly D=4 dimensions. Similarly, evanescent fields do not propagate in D=4; a three-form field is in this class, since it is dual to a cosmological-constant contribution. In this Letter, we show that evanescent operators and fields modify the leading ultraviolet divergence in pure gravity. To analyze the divergence, we compute the two-loop identical-helicity four-graviton amplitude and determine the coefficient of the associated (non-evanescent) R^3 counterterm studied long ago by Goroff and Sagnotti. We compare two pairs of theories that are dual in D=4: gravity coupled to nothing or to three-form matter, and gravity coupled to zero-form or to two-form matter. Duff and van Nieuwenhuizen showed that, curiously, the one-loop conformal anomaly --- the coefficient of the Gauss-Bonnet operator --- changes under p-form duality transformations. We concur, and also find that the leading R^3 divergence changes under duality transformations. Nevertheless, in both cases the physical renormalized two-loop identical-helicity four-graviton amplitude can be chosen to respect duality. In particular, its renormalization-scale dependence is unaltered.

    ↳ hep-thgr-qchep-phPRL(2015)·99 citations
19. 19*

    Towards a realistic astrophysical interpretation of the gamma-ray Galactic center excess

    Daniele Gaggero🇮🇹 · Marco Taoso🇫🇷 · Alfredo Urbano🇮🇹 · Mauro Valli🇮🇹 · Piero Ullio🇮🇹

    A spherical-symmetric gamma-ray emission from the central region of the Galaxy has been recently identified in Fermi-LAT data, and initially associated to dark matter particle annihilations. Guided by the evidence for a high gas density in the inner kpc of the Galaxy correlated with a very large Supernova rate, and hence with ongoing cosmic-ray acceleration, we investigate instead the possibility of addressing this excess in terms of ordinary cosmic-ray sources and standard steady-state diffusion. We alter the source term, and consistently the correlated gamma-ray emissions, in the context of a template-fitting analysis. We focus on a region of interest (ROI) defined as: $|l|<20^{\circ };2^{\circ }<|b|<20^{\circ },$ with $l$ and $b$ the Galactic longitude and latitude coordinates. We analyze in detail the overall goodness of the fit of our framework, and perform a detailed direct comparison against data examining profiles in different directions. Remarkably, the test statistic of the fit related to our scenario turns out to be as good as the Dark Matter one in the ROI here considered.

    ↳ astro-ph.HEhep-phJCAP(2015)·105 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.