Fri·Sep 11, 2015Friday·September 11, 2015

1. 01*

   Closing up on Dark Sectors at Colliders: from 14 to 100 TeV

   Philip Harris🇨🇭 · Valentin V. Khoze🇬🇧 · Michael Spannowsky🇬🇧 · Ciaran Williams🇺🇸

   We investigate the reach of the LHC Run 2 and that of a future circular hadron collider with up to 100 TeV centre of mass energy for the exploration of potential Dark Matter sectors. These dark sectors are conveniently and broadly described by simplified models. The simplified models we consider provide microscopic descriptions of interactions between the Standard Model partons and the dark sector particles mediated by the four basic types of messenger fields: scalar, pseudo-scalar, vector or axial-vector. Our analysis extends and updates the previously available results for the LHC at 8 and 14 TeV to 100 TeV for models with all four messenger types. We revisit and improve the analysis at 14 TeV, by studying a variety of analysis techniques, concluding that the most discriminating variables correspond to the missing transverse energy and the azimuthal angle between jets in the final state. Going to 100 TeV, the limits on simplified models of Dark Matter are enhanced significantly, in particular for heavier mediators and dark sector particles, for which the available phase space at the LHC is restricted. The possibility of a 100 TeV collider provides an unprecedented coverage of the dark sector basic parameters and a unique opportunity to pin down the particle nature of Dark Matter and its interactions with the Standard Model.

   hep-phhep-exPRD(2016)·43 citations
2. 02*

   CT14QED PDFs from Isolated Photon Production in Deep Inelastic Scattering

   Carl Schmidt🇺🇸 · Jon Pumplin🇺🇸 · Daniel Stump🇺🇸 · C.-P. Yuan🇺🇸

   We describe the implementation of Quantum Electrodynamic (QED) evolution at Leading Order (LO) along with Quantum Chromodynamic (QCD) evolution at Next-to-Leading Order (NLO) in the CTEQ-TEA Global analysis package. The inelastic contribution to the photon Parton Distribution Function (PDF) is described by a two-parameter ansatz, coming from radiation off the valence quarks, and based on the CT14 NLO PDFs. Setting the two parameters to be equal allows us to completely specify the inelastic photon PDF in terms of the inelastic momentum fraction carried by the photon, $p_0^{\gamma }$, at the initial scale $Q_0=1.295$ GeV. We obtain constraints on the photon PDF by comparing with ZEUS data~\cite{Chekanov:2009dq} on the production of isolated photons in deep inelastic scattering, $ep\to e\gamma +X$. For this comparison we present a new perturbative calculation of the process that consistently combines the photon-initiated contribution with the quark-initiated contribution. Comparison with the data allows us to put a constraint at the 90\% confidence level of $p_0^{\gamma }\lesssim 0.14\%$ for the inelastic photon PDF at the initial scale of $Q_0=1.295$ GeV in the one-parameter radiative ansatz. The resulting inelastic CT14QED PDFs will be made available to the public. In addition, we also provide CT14QEDinc PDFs, in which the {\em inclusive} photon PDF at the scale $Q_0$ is defined by the sum of the inelastic photon PDF and the elastic photon distribution obtained from the Equivalent Photon Approximation.

   hep-phPRD(2016)·174 citations
3. 03*

   Quasiparticle equation of state for anisotropic hydrodynamics

   Mubarak Alqahtani🇺🇸 · Mohammad Nopoush🇺🇸 · Michael Strickland🇺🇸

   We present a new method for imposing a realistic equation of state in anisotropic hydrodynamics. The method relies on the introduction of a single finite-temperature quasiparticle mass which is fit to lattice data. By taking moments of the Boltzmann equation, we obtain a set of coupled partial differential equations which can be used to describe the 3+1d spacetime evolution of an anisotropic relativistic system. We then specialize to the case of a 0+1d system undergoing boost-invariant Bjorken expansion and subject to the relaxation-time approximation collisional kernel. Using this setup, we compare results obtained using the new quasiparticle equation of state method with those obtained using the standard method for imposing the equation of state in anisotropic hydrodynamics. We demonstrate that the temperature evolution obtained using the two methods is nearly identical and that there are only small differences in the pressure anisotropy. However, we find that there are significant differences in the evolution of the bulk pressure correction.

   hep-phnucl-thPRC(2015)·75 citations
4. 04*

   Upper bounds on sparticle masses from naturalness or how to disprove weak scale supersymmetry

   Howard Baer🇺🇸 · Vernon Barger🇺🇸 · Michael Savoy🇺🇸

   While it is often stated that the notion of electroweak (EW) naturalness in supersymmetric models is subjective, fuzzy and model-dependent, here we argue the contrary: electroweak naturalness can be elevated to a {\it principle} which is both objective and predictive. We demonstrate visually when too much fine-tuning sets in at the electroweak scale which corresponds numerically to the measure \Delta_{BG}~\Delta_{EW}> 30. While many constrained SUSY models are already excluded by this value, we derive updated upper bounds on sparticle masses within the two-extra parameter non-universal Higgs model (NUHM2). We confirm the classic Barbieri-Giudice (BG) result that \Delta_{BG}<30 implies mu <350 GeV. However, by combining dependent soft terms which appear as multiples of m_{3/2} in supergravity models, then we obtain m(gluino)< 4 TeV as opposed to the BG result that m(gluino)<350 GeV. We compare the NUHM2 results to a similar scan in the pMSSM with 19 weak scale parameters. In the pMSSM with complete one-loop scalar potential plus dominant two-loop terms, then a m(gluino)<7 TeV bound is found. Our tabulation of upper bounds provides a target for experimenters seeking to discover or else falsify the existence of weak scale supersymmetry. In an Appendix, we show contributions to the naturalness measure from one-loop contributions to the weak scale scalar potential.

   hep-phPRD(2016)·101 citations
5. 05*

   Electroweak Baryogenesis in a Scalar-Assisted Vector-Like Fermion Model

   Ming-Lei Xiao🇺🇸 · Jiang-Hao Yu🇺🇸

   We extend the standard model to a scalar-assisted vector-like fermion model to realize electroweak baryogenesis. The extended Cabbibo-Kobayashi-Maskawa matrix, due to the mixing among the vector-like quark and the standard model quarks, provides additional sources of the CP violation. Together with the enhancement from large vector-like quark mass, a large enough baryon-to-photon ratio could be obtained. The strongly first-order phase transition could be realized via the potential barrier which separate the broken minimum and the symmetric minimum in the scalar potential. We investigate in detail the one-loop temperature-dependent effective potential, and perform a random parameter scan to study the allowed parameter region that satisfies the strongly first order phase transition criteria $v_c\ge T_c$. Several distinct patterns of phase transition are classified and discussed. Among these patterns, large trilinear mass term between the Higgs boson and the scalar is preferred, for it controls the width of the potential barrier. Our results indicate large quartic scalar couplings, and moderate mixing angle between the Higgs boson and the new scalar. This parameter region could be further explored at the Run 2 LHC.

   hep-phPRD(2016)·14 citations
6. 06*

   Stop-Catalyzed Baryogenesis Beyond the MSSM

   Andrey Katz🇨🇭 · Maxim Perelstein🇺🇸 · Michael J. Ramsey-Musolf🇺🇸 · Peter Winslow🇺🇸

   Non-minimal supersymmetric models that predict a tree-level Higgs mass above the Minimal Supersymmetric Standard Model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. We also introduce a gauge-invariant analysis framework that may generalize to other scenarios in which interactions outside the gauge sector drive the electroweak phase transition.

   hep-phPRD(2015)·48 citations
7. 07*

   Jet Quenching from QCD Evolution

   Yang-Ting Chien🇺🇸 · Alexander Emerman🇺🇸 · Zhong-Bo Kang🇺🇸 · Grigory Ovanesyan🇺🇸 · Ivan Vitev🇺🇸

   Recent advances in soft-collinear effective theory with Glauber gluons have led to the development of a new method that gives a unified description of inclusive hadron production in reactions with nucleons and heavy nuclei. We show how this approach, based on the generalization of the DGLAP evolution equations to include final-state medium-induced parton showers, can be combined with initial-state effects for applications to jet quenching phenomenology. We demonstrate that the traditional parton energy loss calculations can be regarded as a special soft-gluon emission limit of the general QCD evolution framework. We present phenomenological comparison of the SCET${}_{\mathrm{G}}$-based results on the suppression of inclusive charged hadron and neutral pion production in $\sqrt{s_{NN}}=2.76$ TeV lead-lead collisions at the Large Hadron Collider to experimental data. We also show theoretical predictions for the upcoming $\sqrt{s_{NN}}\simeq 5.1$ TeV Pb+Pb run at the LHC.

   hep-phnucl-exnucl-thPRD(2016)·142 citations
8. 08*

   Multi-particle long-range rapidity correlations from fluctuation of the fireball longitudinal shape

   Adam Bzdak🇵🇱 · Piotr Bozek🇵🇱

   We calculate the genuine long-range multi-particle rapidity correlation functions, $C_n(y_1,...,y_n)$ for $n=3,4,5,6$, originating from fluctuations of the fireball longitudinal shape. In these correlation functions any contribution from the short-range two-particle correlations, and in general up to $(n-1)$-particle in $C_n$, is suppressed. The information about the fluctuating fireball shape in rapidity is encoded in the cumulants of coefficients of the orthogonal polynomial expansion of particle distributions in rapidity.

   hep-phhep-exnucl-thPRC(2016)·20 citations
9. 09*

   Cosmological bounds of sterile neutrinos in a $SU(3{)}_C\otimes SU(3{)}_L\otimes SU(3{)}_R\otimes U(1{)}_N$ model as dark matter candidates

   Cesar P. Ferreira🇧🇷 · Marcelo M. Guzzo🇧🇷 · Pedro C. de Holanda🇧🇷

   We study sterile neutrinos in an extension of the standard model, based on the gauge group $SU(3{)}_C\otimes SU(3{)}_L\otimes SU(3{)}_R\otimes U(1{)}_N$, and use this model to illustrate how to apply cosmological limits to thermalized particles that decouple while relativistic. These neutrinos, $N_{aL}$, can be dark matter candidates, with a keV mass range arising rather naturally in this model. We analyse the cosmological limits imposed by $N_{eff}$ and dark matter abundance on these neutrinos. Assuming that these neutrinos have roughly equal masses and are not CDM, we conclude that the $N_{eff}$ experimental value can be satisfied in some cases and the abundance constraint implies that these neutrinos are hot dark matter. With this information, we give upper bounds on the Yukawa coupling between the sterile neutrinos and a scalar field, the possible values of the VEV of this scalar field and lower bounds to the mass of one gauge boson of the model.

   hep-phBraz.J.Phys.(2016)·14 citations
10. 10*

    Pentaquarks and strange tetraquark mesons

    V.V. Anisovich🇷🇺 · M.A. Matveev🇷🇺 · A.V. Sarantsev🇩🇪 · A.N. Semenova🇷🇺

    We consider the interplay of the pentaquark states and strange tetraquark states in the decay ${\Lambda }_b^0\to K^{-}J/\psi p$. Possible existence of ($cs\bar{c}\bar{u}$)-states is taken up and their manifestation in the $K^{-}J/\psi$-channel is discussed. It is emphasised that these exotic mesons can imitate broad bumps in the in the $pJ/\psi$-channel.

    hep-phMod.Phys.Lett.A(2015)·15 citations
11. 11*

    Update of the MCSANC Monte Carlo Integrator, v.1.20

    A. Arbuzov🇷🇺 · D. Bardin🇷🇺 · S. Bondarenko🇷🇺 · P. Christova🇷🇺 · L. Kalinovskaya🇷🇺 · U. Klein🇬🇧 · V. Kolesnikov🇷🇺 · L. Rumyantsev🇷🇺 · R. Sadykov🇷🇺 · A. Sapronov🇷🇺

    This article presents new features of the MCSANC v.1.20 program, a Monte Carlo tool for calculation of the next-to-leading order electroweak and QCD corrections to various Standard Model processes. The extensions concern implementation of Drell--Yan-like processes and include a systematic treatment of the photon-induced contribution in proton--proton collisions and electroweak corrections beyond NLO approximation. There are also technical improvements such as calculation of the forward-backward asymmetry for the neutral current Drell--Yan process. The updated code is suitable for studies of the effects due to EW and QCD radiative corrections to Drell--Yan (and several other) processes at the LHC and for forthcoming high energy proton--proton colliders.

    hep-phJETP Lett.(2016)·53 citations
12. 12*

    Strong Couplings of Charmed Mesons and Quarkonia

    Wolfgang Lucha🇦🇹 · Dmitri Melikhov🇷🇺 · Hagop Sazdjian🇫🇷 · Silvano Simula🇮🇹

    We extract the strong coupling constants of three mesons, each of which is composed of either two charm quarks or one charm quark and one light (i.e., $u$, $d$, or $s$) quark, from the matrix elements for the transitions of two of these mesons induced by appropriate quark currents within the framework of a relativistic dispersion approach to the constituent-quark picture of mesons. Among others, we also analyse the impact of the violation of the SU(3) flavour symmetry by the quark masses. In the case of mesons containing one light quark, we observe, in two respects, discrepancies between our findings and the predictions of QCD sum rules: our strong couplings exceed considerably the ones emerging from QCD sum rules, and, in our approach, the replacement of a light quark by a strange quark entails, in contrast to QCD sum rules, a reduction of the magnitudes of the strong couplings.

    hep-phnucl-thPoS(2015)·1 citation
13. 13*

    The Relation between the Perturbative QCD Scale ${\Lambda }_s$ and Hadronic Masses from Light-Front Holography

    A. Deur🇺🇸 · S. J. Brodsky🇺🇸 · G. F. de Teramond🇨🇷

    QCD is well understood at short distances where perturbative calculations are feasible. Establishing an explicit analytic connection between the short-distance regime and the large-distance physics of quark confinement has been a long-sought goal. A major challenge is to relate the scale ${\Lambda }_s$ underlying the evolution of the QCD coupling in the perturbative regime to the masses of hadrons. We show here how new theoretical insights into the behavior of QCD at large distances leads to such a relation. The resulting prediction for ${\Lambda }_s$ in the $\overline{MS}$ scheme agrees well with experimental measurements. Conversely, the relation can be used to predict the masses of hadrons composed of light quarks with the measured value of ${\Lambda }_s$ as the sole parameter. We also use "light-front holography" to determine the analytic form of ${\alpha }_s(Q^2)$ at small $Q^2$.

    hep-phNucl.Part.Phys.Proc.(2016)·2 citations
14. 14*

    Hard Diffraction in Pythia 8

    Christine O. Rasmussen🇸🇪

    We present an overview of the options for diffraction implemented in the general--purpose event generator Pythia 8. We review the existing model for low-- and high--mass soft diffraction and present a new model for hard diffraction in pp and ppbar collisions. Both models uses the Pomeron approach pioneered by Ingelman and Schlein, factorising the single diffractive cross section into a Pomeron flux and a Pomeron PDF. The model for hard diffraction is implemented as a part of the multiparton interactions framework, thereby introducing a dynamical rapidity gap survival probability that explicitly breaks factorisation.

    hep-phActa Phys.Polon.Supp.(2015)·1 citation
15. 15*

    $J/\Psi {\rm Y}$ Production at LHC

    A. V. Luchinsky🇷🇺

    Inclusive production of ${\rm Y}J/\psi$ pair in proton-proton interation at LHCb is considered. This process is forbidden at leading order of perturbation theory, so such channels as double parton scattering, ${\chi }_b{\chi }_c$ pair production with subsequent radiative decays of $P$-wave quarkonia, contributions of color-octet states, and NLO corrections are studied in details. For all these channels we present theoretical predictions of total cross sections at LHCb and distributions over different kinematical variables. According to presented in the paper results, double parton interaction gives main contribution to the cross section of the considered reaction.

    hep-ph1 citation
16. 16*

    3-flavor and 4-flavor implications of the latest T2K and NO$\nu$A electron (anti-)neutrino appearance results

    Antonio Palazzo🇩🇪

    The two long-baseline experiments T2K and NO$\nu$A have recently presented new findings. T2K has shown the first ${\bar{\nu }}_e$ appearance data while NO$\nu$A has released the first ${\nu }_e$ appearance results. These data are of particular importance because they allow us to probe for the first time in a direct (or manifest) way the leptonic CP-violation. In fact, it is the first time that a hint of CP-violation arises from the comparison of the observations of neutrinos and antineutrinos. We consider the implications of such new results both for the standard 3-flavor framework and for the non-standard 3+1 scheme involving one sterile neutrino species. The 3-flavor analysis shows a consolidation of the previous trends, namely a slight preference for $\sin \delta <0$, disfavoring CP conservation ($\delta =0,\pi$) with a statistical significance close to $90\%$ C.L., and a mild preference (at more than 68\% C.L.) for the normal hierarchy. In a 3+1 framework, the data constrain two CP-phases (${\delta }_{13}\equiv \delta$ and ${\delta }_{14}$), which exhibit a slight preference for the common value ${\delta }_{13}\simeq {\delta }_{14}\simeq -\pi /2$. Interestingly, in the enlarged four neutrino scheme the preference for the normal hierarchy found within the 3-flavor framework completely disappears. This indicates that light sterile neutrinos may constitute a potential source of fragility in the capability of the two LBL experiments of discriminating the neutrino mass hierarchy.

    hep-phhep-exPLB(2016)·54 citations
17. 17*

    Temporal Instability Enables Neutrino Flavor Conversions Deep Inside Supernovae

    Basudeb Dasgupta (Tata Inst., Mumbai)🇮🇳 · Alessandro Mirizzi (Bari U. & INFN Bari)🇮🇹

    We show that a self-interacting neutrino gas can spontaneously acquire a non-stationary pulsating component in its flavor content, with a frequency that can exactly cancel the "multi-angle" refractive effects of dense matter. This can then enable homogeneous and inhomogeneous flavor conversion instabilities to exist even at large neutrino and matter densities, where the system would have been stable if the evolution were strictly stationary. Large flavor conversions, especially close to a supernova core, are possible via this novel mechanism. This may have important consequences for the explosion dynamics, nucleosynthesis, as well as for neutrino observations of supernovae.

    hep-phastro-ph.HEastro-ph.SRPRD(2015)·84 citations
18. 18*

    Dispersion-theoretical analysis of the D^+ --> K^- pi^+ pi^+ Dalitz plot

    Franz Niecknig🇩🇪 · Bastian Kubis🇩🇪

    We study the Dalitz plot of the Cabibbo-favored charmed-meson decay $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ using dispersion theory. The formalism respects all constraints from analyticity and unitarity, and consistently describes final-state interactions between all three decay products. We employ pion-pion and pion-kaon phase shifts as input, and fit the pertinent subtraction constants to Dalitz plot data by the CLEO and FOCUS collaborations. Phase motions of resonant as well as nonresonant amplitudes are discussed, which should provide crucial input for future studies of CP violation in similar three-body charm decays.

    hep-phhep-exJHEP(2015)·84 citations
19. 19*

    Thermal and non-thermal charmed meson production in heavy ions collisions at the LHC

    I.P. Lokhtin🇷🇺 · A.V. Belyaev🇷🇺 · G.Kh. Eyyubova🇷🇺 · G. Ponimatkin🇨🇿 · E.Yu. Pronina🇷🇺

    The phenomenological analysis of the LHC data on transverse momentum spectrum and elliptic flow of $J/\psi$ and D mesons in PbPb collisions at center-of-mass energy 2.76 TeV per nucleon pair is presented. The charmed meson production pattern in PbPb collisions may be reproduced by two-component model HYDJET++ including thermal and non-thermal components. The significant part of D-mesons is found to be in a kinetic equilibrium with the created medium, while $J/\psi$-mesons are not.

    hep-phJ.Phys.Conf.Ser.(2016)·3 citations
20. 20*

    Photon and dilepton spectra from nonlinear QED effects in supercritical magnetic fields induced by heavy-ion collisions

    Koichi Hattori🇯🇵 · Kazunori Itakura🇯🇵

    We discuss properties of photons in extremely strong magnetic fields induced by the relativistic heavy-ion collisions. We investigate the vacuum birefringence, the real-photon decay, and the photon splitting which are all forbidden in the ordinary vacuum, but become possible in strong magnetic fields. These effects potentially give rise to anisotropies in photon and dilepton spectra.

    hep-phastro-ph.HEnucl-thNucl.Part.Phys.Proc.(2016)·3 citations
21. 21*

    Hanbury-Brown-Twiss measurements at large rapidity separations, or can we measure the proton radius in p-A collisions?

    T. Altinoluk🇪🇸 · N. Armesto🇪🇸 · G. Beuf🇮🇱 · A. Kovner🇺🇸 · M. Lublinsky🇮🇱

    We point out that current calculations of inclusive two-particle correlations in p-A collisions based on the Color Glass Condensate approach exhibit a contribution from Hanbury-Brown-Twiss correlations. These HBT correlations are quite distinct from the standard ones, in that they are apparent for particles widely separated in rapidity. The transverse size of the emitter which is reflected in these correlations is the gluonic size of the proton. This raises an interesting possibility of measuring the proton size directly by the HBT effect of particle pairs produced in p-A collisions.

    hep-phnucl-thPLB(2016)·35 citations
22. 22*

    Implications of the CMS search for W_R on Grand Unification

    Triparno Bandyopadhyay (Calcutta Univ)🇮🇳 · Biswajoy Brahmachari (Vidyasagar Evening Coll)🇮🇳 · Amitava Raychaudhuri (Calcutta Univ)🇮🇳

    The CMS experiment at the Large Hadron Collider has reported a 2.8$\sigma$ excess in the $(2e)(2jets)$ channel around 2.1 TeV. Interpretation of this data is reconsidered in terms of the production of a right-handed weak gauge boson, $W_R$, of the left-right symmetric model and in an $SO(10)$ grand unified theory abiding by the Extended Survival Hypothesis. The left-right symmetric model can be consistent with this excess if (a) the heavy right-handed neutrino has a mass near $W_R$, or (b) if $g_L\ne g_R$, or (c) the right-handed CKM matrix is nontrivial. Combinations of the above possibilities are also viable. A $W_R$ with a mass in the TeV region if embedded in $SO(10)$ is not compatible with $g_L=g_R$. Rather, it implies $0.64\le g_R/g_L\le 0.78$. Further, a unique symmetry-breaking route -- the order being left-right discrete symmetry breaking first, followed by $SU(4{)}_C$ and finally $SU(2{)}_R$ -- to the standard model is picked out. The $L\leftrightarrow R$ discrete symmetry has to be broken at around $10^{16}$ GeV. The grand unification scale is pushed to $10^{18}$ GeV making the detection of proton decay in ongoing searches rather unlikely. The $SU(4{)}_C$ breaking scale can be at its allowed lower limit of $10^6$ GeV so that $n-\bar{n}$ oscillation or flavour changing processes such as $K_L\to \mu e$ and $B_{d,s}\to \mu e$ may be detectable. The Higgs scalar multiplets responsible for $SO(10)$ symmetry breaking at various stages are uniquely identified so long as one adheres to a minimalist principle. We also remark, {\em en passant}, about a partially unified Pati-Salam model.

    hep-phJHEP(2016)·32 citations
23. 23*

    Lepton Flavour Violation in Composite Higgs Models

    Ferruccio Feruglio🇮🇹 · Paride Paradisi🇮🇹 · Andrea Pattori🇨🇭

    We discuss in detail the constraints on partial compositeness coming from flavour and CP violation in the leptonic sector. In a first part we present a formulation of partial compositeness in terms of a flavour symmetry group and a set of spurions, whose background values specify the symmetry breaking pattern. In such a framework we construct the complete set of dimension-six operators describing lepton flavour violation and CP violation. By exploiting the existing bounds, we derive limits on the compositeness scale in different scenarios, characterised by increasing restrictions on the spurion properties. We confirm that in the most general case the compositeness scale should lie well-above 10 TeV. However, if in the composite sector mass parameters and Yukawa couplings are universal, such a bound can be significantly lowered, without necessarily reproducing the case of minimal flavour violation. The most sensitive processes are decays of charged leptons either of radiative type or into three charged leptons, muon to electron conversion in nuclei and the electric dipole moment of the electron. In a second part we explicitly compute the Wilson coefficients of the relevant dimension-six operators in the so-called two-site model, embodying the symmetry breaking pattern discussed in our first part, and we compare the results with those of the general spurion analysis.

    hep-phEPJC(2015)·33 citations
24. 24*

    Assisted dynamical Schwinger effect: pair production in a pulsed bifrequent field

    A.D. Panferov🇷🇺 · S.A. Smolyansky🇷🇺 · A. Otto🇩🇪 · B. Kaempfer🇩🇪 · D. Blaschke🇷🇺 · L. Juchnowski🇵🇱

    Electron-positron pair production by the superposition of two laser pulses with different frequencies and amplitudes is analyzed as a particular realization of the assisted dynamic Schwinger effect. It is demonstrated that, within a non-perturbative kinetic equation framework, an amplification effect is conceivable for certain parameters. When both pulses have wavelengths longer than the Compton wavelength, the residual net density of produced pairs is determined by the resultant field strength. The number of pairs starts to grow rapidly if the wavelength of the high-frequency laser component gets close to the Compton wavelength.

    ↳ quant-phhep-phphysics.opticsEur.Phys.J.D(2016)·35 citations
25. 25*

    Contemporary continuum QCD approaches to excited hadrons

    Bruno El-Bennich🇧🇷 · Eduardo Rojas🇨🇴

    Amongst the bound states produced by the strong interaction, radially excited meson and nucleon states offer an important phenomenological window into the long-range behavior of the coupling constant in Quantum Chromodynamics. We here report on some technical details related to the computation of the bound state's eigenvalue spectrum in the framework of Bethe-Salpeter and Faddeev equations.

    ↳ nucl-thhep-lathep-phnucl-exEPJ Web Conf.(2016)·4 citations
26. 26*

    Three Lectures on Hadron Physics

    Craig D. Roberts🇺🇸

    These lectures explain that comparisons between experiment and theory can expose the impact of running couplings and masses on hadron observables and thereby aid materially in charting the momentum dependence of the interaction that underlies strong-interaction dynamics. The series begins with a primer on continuum QCD, which introduces some of the basic ideas necessary in order to understand the use of Schwinger functions as a nonperturbative tool in hadron physics. It continues with a discussion of confinement and dynamical symmetry breaking (DCSB) in the Standard Model, and the impact of these phenomena on our understanding of condensates, the parton structure of hadrons, and the pion electromagnetic form factor. The final lecture treats the problem of grand unification; namely, the contemporary use of Schwinger functions as a symmetry-preserving tool for the unified explanation and prediction of the properties of both mesons and baryons. It reveals that DCSB drives the formation of diquark clusters in baryons and sketches a picture of baryons as bound-states with Borromean character. Planned experiments are capable of validating the perspectives outlined in these lectures.

    ↳ nucl-thhep-lathep-phnucl-exJ.Phys.Conf.Ser.(2016)·71 citations
27. 27*

    Known Radio Pulsars Do Not Contribute to the Galactic Center Gamma-Ray Excess

    Tim Linden🇺🇸

    Observations using the Fermi Large Area Telescope (Fermi-LAT) have found a significant gamma-ray excess surrounding the center of the Milky Way (GC). One possible interpretation of this excess invokes gamma-ray emission from an undiscovered population of either young or recycled pulsars densely clustered throughout the inner kiloparsec of the Milky Way. While these systems, by construction, have individual fluxes that lie below the point source sensitivity of the Fermi-LAT, they may already be observed in multiwavelength observations. Notably the Australia Telescope National Facility (ATNF) catalog of radio pulsars includes 270 sources observed in the inner 10 degrees around the GC. We calculate the gamma-ray emission observed from these 270 sources and obtain three key results: (1) point source searches in the GC region produce a plethora of highly significant gamma-ray "hotspots", compared to searches far from the Galactic plane, (2) there is no statistical correlation between the positions of these gamma-ray hotspots and the locations of ATNF pulsars, and (3) the spectrum of the most statistically significant gamma-ray hotspots is substantially softer than the spectrum of the GC gamma-ray excess. These results place strong constraints on models where young pulsars produce the majority of the gamma-ray excess, and disfavor some models where millisecond pulsars produce the gamma-ray excess.

    ↳ astro-ph.HEastro-ph.GAhep-phPRD(2016)·19 citations
28. 28*

    Investigating dark matter substructure with pulsar timing: II. Improved limits on small-scale cosmology

    Hamish A. Clark🇦🇺 · Geraint F. Lewis🇦🇺 · Pat Scott🇬🇧

    Ultracompact Minihalos (UCMHs) have been proposed as a type of dark matter sub-structure seeded by large-amplitude primordial perturbations and topological defects. UCMHs are expected to survive to the present era, allowing constraints to be placed on their cosmic abundance using observations within our own Galaxy. Constraints on their number density can be linked to conditions in the early universe that impact structure formation, such as increased primordial power on small scales, generic weak non-Gaussianity, and the presence of cosmic strings. We use new constraints on the abundance of UCMHs from pulsar timing to place generalised limits on the parameters of each of these cosmological scenarios. At some scales, the limits are the strongest to date, exceeding those from dark matter annihilation. Our new limits have the added advantage of being independent of the particle nature of dark matter, as they are based only on gravitational effects.

    ↳ astro-ph.COgr-qchep-phMNRAS(2016)·33 citations
29. 29*

    Large-N QCD and the Veneziano Amplitude

    Adi Armoni🇬🇧

    We consider four scalar mesons scattering in large-Nc QCD. Using the worldline formalism we show that the scattering amplitude can be written as a formal sum over Wilson loops. The AdS/CFT correspondence maps this sum into a sum over string worldsheets in a confining background. We then argue that for well separated mesons the sum is dominated by flat space configurations. Under additional assumptions about the dual string path integral we obtain the Veneziano amplitude.

    ↳ hep-thhep-lathep-phPLB(2016)·5 citations
30. 30*

    Charm and bottom quark masses on the lattice

    Andrew T. Lytle🇬🇧

    Lattice determinations of quark mass have made significant progress in the last few years. I will review recent advances in calculations of charm and bottom mass, which are near to achieving percent-level precision and with fully controlled systematics. Precise knowledge of these parameters is of particular interest for precision Higgs studies at future accelerators.

    ↳ hep-lathep-ph3 citations
31. 31*

    Photoproduction of $J/\psi$ mesons in peripheral and semi-central heavy ion collisions

    Mariola Kłusek-Gawenda🇵🇱 · Antoni Szczurek🇵🇱

    We calculate total and differential cross sections for $J/\psi$ photoproduction in ultrarelativistic lead-lead collisions at the LHC energy $\sqrt{s_{NN}}=2.76$ TeV. In the present approach we use a simple model based on vector dominance picture and multiple scattering of the hadronic ($c\bar{c}$) state in a cold nucleus as an example. In our analysis we use both the classical mechanics and quantum (Glauber) formulae for calculating ${\sigma }_{tot}(J/\psi Pb)$ which is a building block of our model. We compare our UPC results with ALICE and CMS data. For semi-central collisions ($b<R_A+R_B$) a modification of the photon flux seems necessary. We discuss different physics motivated approximations. We try to estimate the cross sections for different centrality bins and for $J/\psi$ mesons emitted in forward rapidity range ($2.5<y<4$) corresponding to recent ALICE experimental results. Reasonable results are obtained but open questions are discussed.

    ↳ nucl-thhep-exhep-phPRC(2016)·62 citations
32. 32*

    Production of unstable heavy neutrinos in proto-neutron stars

    C. Albertus🇪🇸 · M. Masip🇪🇸 · M. A. Pérez-García🇪🇸

    We discuss the production of a class of heavy sterile neutrinos ${\nu }_h$ in proto-neutron stars. The neutrinos, of mass around $50$ MeV, have a negligible mixing with the active species but relatively large dimension-5 electromagnetic couplings. In particular, a magnetic dipole moment $\mu \approx 10^{-6}$ GeV${}^{-1}$ implies that they are thermally produced through $e^{+}{e}^{-}\to {\bar{\nu }}_h{\nu }_h$ in the early phase of the core collapse, whereas a heavy--light transition moment ${\mu }_{\mathrm{tr}}\approx 10^{-8}$ GeV${}^{-1}$ allows their decay ${\nu }_h\to {\nu }_i\gamma$ with a lifetime around $10^{-3}$ s. This type of electromagnetic couplings has been recently proposed to explain the excess of electron-like events in baseline experiments. We show that the production and decay of these heavy neutrinos would transport energy from the central regions of the star to distances $d\approx 400$ km, providing a very efficient mechanism to enhance the supernova shock front and heat the material behind it.

    ↳ astro-ph.HEastro-ph.SRhep-phPLB(2015)·9 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.