Tue·Aug 18, 2015Tuesday·August 18, 2015

1. 01*

   The $q_T$ subtraction method for top quark production at hadron colliders

   Roberto Bonciani🇮🇹 · Stefano Catani🇮🇹 · Massimiliano Grazzini🇨🇭 · Hayk Sargsyan🇨🇭 · Alessandro Torre🇨🇭

   We consider QCD radiative corrections to top-quark pair production at hadron colliders. We use the $q_T$ subtraction formalism to perform a fully-differential computation for this process. Our calculation is accurate up to the next-to-leading order in QCD perturbation theory and it includes all the flavour off-diagonal partonic channels at the next-to-next-to-leading order. We present a comparison of our numerical results with those obtained with the publicly available numerical programs MCFM and Top++.

   hep-phEPJC(2015)·101 citations
2. 02*

   Top-Yukawa effects on the $\beta$-function of the strong coupling in the SM at four-loop level

   M. F. Zoller🇩🇪

   We present analytical results for the QCD $\beta$-function extended to the gaugeless limit of the unbroken phase of the Standard Model at four-loop level. Apart from the strong coupling itself we include the top-Yukawa contribution and the Higgs self-coupling. We observe a non-naive ${\gamma }_5$ contribution at order $y_t^4{g}_s^4$, a feature not encountered in lower loop orders.

   hep-phJHEP(2016)·55 citations
3. 03*

   Baryogenesis from Symmetry Principle

   Chee Sheng Fong🇧🇷

   In this work, a formalism based on symmetry which allows one to express asymmetries of all the particles in terms of conserved charges is developed. The manifestation of symmetry allows one to easily determine the viability of a baryogenesis scenario and also to identity the different roles played by the symmetry. This formalism is then applied to the standard model and its supersymmetric extension, which constitute two important foundations for constructing models of baryogenesis.

   hep-phPLB(2016)·23 citations
4. 04*

   Leptogenesis in GeV scale seesaw models

   P. Hernández🇪🇸 · M.Kekic🇪🇸 · J. López-Pavón🇮🇹 · J. Racker🇪🇸 · N. Rius🇪🇸

   We revisit the production of leptonic asymmetries in minimal extensions of the Standard Model that can explain neutrino masses, involving extra singlets with Majorana masses in the GeV scale. We study the quantum kinetic equations both analytically, via a perturbative expansion up to third order in the mixing angles, and numerically. The analytical solution allows us to identify the relevant CP invariants, and simplifies the exploration of the parameter space. We find that sizeable lepton asymmetries are compatible with non-degenerate neutrino masses and measurable active-sterile mixings.

   hep-phJHEP(2015)·85 citations
5. 05*

   Inclusive tau lepton hadronic decay in vector and axial-vector channels within dispersive approach to QCD

   A.V.Nesterenko🇷🇺

   The dispersive approach to QCD, which properly embodies the intrinsically nonperturbative constraints originating in the kinematic restrictions on relevant physical processes and extends the applicability range of perturbation theory towards the infrared domain, is briefly overviewed. The study of OPAL (update 2012) and ALEPH (update 2014) experimental data on inclusive tau lepton hadronic decay in vector and axial-vector channels within dispersive approach is presented.

   hep-phAIP Conf.Proc.(2016)·13 citations
6. 06*

   Neutrino Masses and Deviation from Tri-bimaximal mixing in \Delta(27) model with Inverse Seesaw Mechanism

   M. Abbas🇪🇬 · S. Khalil🇪🇬 · A. Rashed🇪🇬 · A. Sil🇮🇳

   We propose a scheme, based on \Delta(27) flavor symmetry and supplemented by other discrete symmetries and inverse seesaw mechanism, where both the light neutrino masses and the deviation from tri-bimaximal mixing matrix can be linked to the source of lepton number violation. The hierarchies of the charged leptons are explained. We find that the quark masses including their hierarchies and the mixing can also be constructed in a similar way.

   hep-phPRD(2016)·29 citations
7. 07*

   Predictions for the Top-Quark Forward-Backward Asymmetry at High Invariant Pair Mass Using the Principle of Maximum Conformality

   Sheng-Quan Wang🇨🇳 · Xing-Gang Wu🇨🇳 · Zong-Guo Si🇨🇳 · Stanley J. Brodsky🇺🇸

   The D0 collaboration at FermiLab has recently measured the top-quark pair forward-backward asymmetry in $\bar{p}p\to t\bar{t}X$ reactions as a function of the $t\bar{t}$ invariant mass $M_{t\bar{t}}$. The D0 result for $A_{\mathrm{FB}}(M_{t\bar{t}}>650\mathrm{GeV})$ is smaller than $A_{\mathrm{FB}}(M_{t\bar{t}})$ obtained for small values of $M_{t\bar{t}}$, which may indicate an "increasing-decreasing" behavior for $A_{\mathrm{FB}}(M_{t\bar{t}}>M_{\mathrm{cut}})$. This behavior is not explained using conventional renormalization scale-setting, even by a next-to-next-to-leading order (N${}^2$LO) QCD calculation -- one predicts a monotonically increasing behavior. In the conventional scale-setting method, one simply guesses a single renormalization scale ${\mu }_r$ for the argument of the QCD running coupling and then varies it over an arbitrary range. However, the conventional method has inherent difficulties. ...... In contrast, if one fixes the scale using the Principle of Maximum Conformality (PMC), the resulting pQCD predictions are renormalization-scheme independent since all of the scheme-dependent $\{{\beta }_i\}$-terms in the QCD perturbative series are resummed into the QCD running couplings at each order. ...... In this paper we show that if one applies the PMC to determine the top versus anti-top quark forward-backward asymmetry by properly using the pQCD predictions up to N${}^2$LO level, one obtains the predictions without renormalization scheme or scale ambiguities. ...... In addition, the PMC prediction for $A_{\mathrm{FB}}(M_{t\bar{t}}>M_{\mathrm{cut}})$ shows an "increasing-decreasing" behavior for increasing values of $M_{\mathrm{cut}}$ which is not observed in the NLO and N${}^2$LO predictions for $A_{\mathrm{FB}}(M_{t\bar{t}}>M_{\mathrm{cut}})$ with conventional scale-setting. This behavior could be tested by the future more precise measurements at the LHC.

   hep-phhep-exPRD(2016)·17 citations
8. 08*

   Two-photon exchange correction in elastic unpolarized electron-proton scattering at small momentum transfer

   O. Tomalak🇩🇪 · M. Vanderhaeghen (JGU Mainz)🇩🇪

   We evaluate the two-photon exchange (TPE) correction to the unpolarized elastic electron-proton scattering at small momentum transfer $Q^2$. We account for the inelastic intermediate states approximating the double virtual Compton scattering by the unpolarized forward virtual Compton scattering. The unpolarized proton structure functions are used as input for the numerical evaluation of the inelastic contribution. Our calculation reproduces the leading terms in the $Q^2$ expansion of the TPE correction and goes beyond this approximation by keeping the full $Q^2$ dependence of the proton structure functions. In the range of small momentum transfer, our result is in good agreement with the empirical TPE fit to existing data.

   hep-phnucl-thPRD(2016)·51 citations
9. 09*

   Streched String with Self-Interaction at the Hagedorn Point: Spatial Sizes and Black Hole

   Yachao Qian🇺🇸 · Ismail Zahed🇺🇸

   We analyze the length, mass and spatial distribution of a discretized transverse string in $D_{\perp }$ dimensions with fixed end-points near its Hagedorn temperature. We suggest that such a string may dominate the (holographic) Pomeron kinematics for dipole-dipole scattering at intermediate and small impact parameters. Attractive self-string interactions cause the transverse string size to contract away from its diffusive size, a mechanism reminiscent of the string-black-hole transmutation. The string shows sizable asymmetries in the transverse plane that translate to primordial azimuthal asymmetries in the stringy particle production in the Pomeron kinematics for current pp and pA collisions at collider energies.

   hep-phhep-thPRD(2015)·9 citations
10. 10*

    XYZ: four-quark states?

    A. Pilloni🇮🇹

    The observation of many unexpected states decaying into heavy quarkonia has challenged the usual Q-Qbar interpretation. We will discuss the nature of some of the charmonium-like resonances recently observed by BES III and LHCb, and their identication according to the compact tetraquark model. We also commment the production of light nuclei in hadron collisions and the relevance for the physics of the X(3872).

    hep-phNuovo Cim.C(2016)·6 citations
11. 11*

    Pentaquarks from intrinsic charms in ${\Lambda }_b$ decays

    Y.K. Hsiao🇹🇼 · C.Q. Geng🇨🇳

    We study the three-body ${\Lambda }_b$ decays of ${\Lambda }_b\to J/\psi pM$ with $M=K^{-}$ and ${\pi }^{-}$. The two new states ${\mathcal{P}}_{c1}\equiv {\mathcal{P}}_c(4380{)}^{+}$ and ${\mathcal{P}}_{c2}\equiv {\mathcal{P}}_c(4450{)}^{+}$ observed recently as the resonances in the $J/\psi p$ invariant mass spectrum of ${\Lambda }_b\to J/\psi p{K}^{-}$ can be identified to consist of five quarks, $uudc\bar{c}$, being consistent with the existence of the pentaquark states. We argue that, in the doubly charmful ${\Lambda }_b$ decays of ${\Lambda }_b\to J/\psi p{K}^{-}$ through $b\to c\bar{c}s$, apart from those through the non-resonant ${\Lambda }_b\to p{K}^{-}$ and resonant ${\Lambda }_b\to {\Lambda }^{\ast }\to p{K}^{-}$ transitions, the third contribution with the non-factorizable effects is not the dominant part for the resonant ${\Lambda }_b\to K^{-}{\mathcal{P}}_{c1,c2},{\mathcal{P}}_{c1,c2}\to J/\psi p$ processes, such that we propose that the ${\mathcal{P}}_{c1,c2}$ productions are mainly from the charmless ${\Lambda }_b$ decays through $b\to \bar{u}us$, in which the $c\bar{c}$ content in ${\mathcal{P}}_{c1,c2}$ arises from the intrinsic charms within the ${\Lambda }_b$ baryon. We hence predict the observables related to the branching ratios and the direct CP violating asymmetries to be $\mathcal{B}({\Lambda }_b\to {\pi }^{-}({\mathcal{P}}_{c1,c2}\to )J/\psi p)/\mathcal{B}({\Lambda }_b\to K^{-}({\mathcal{P}}_{c1,c2}\to )J/\psi p)=0.8\pm 0.1$, ${\mathcal{A}}_{CP}({\Lambda }_b\to {\pi }^{-}({\mathcal{P}}_{c1,c2}\to )J/\psi p)=(-3.9\pm 0.2)\%$, and ${\mathcal{A}}_{CP}({\Lambda }_b\to K^{-}({\mathcal{P}}_{c1,c2}\to )J/\psi p)=(5.8\pm 0.2)\%$, which can alleviate the inconsistency between the theoretical expectations from the three contributions in the doubly charmful ${\Lambda }_b$ decays and the observed data.

    hep-phhep-exnucl-thPLB(2015)·30 citations
12. 12*

    Nontopological Soliton in the Polyakov Quark Meson Model

    Jinshuang Jin🇨🇳 · Hong Mao🇨🇳

    Within a mean field approximation, we study a nontopological soliton solution of the Polyakov quark-meson model in the presence of a fermionic vacuum term with two flavors at finite temperature and density. The profile of the effective potential exhibits a stable soliton solution below a critical temperature $T\le T_{\chi }^c$ for both the crossover and the first-order phase transitions, and these solutions are calculated here with appropriate boundary conditions. However, it is found that only if $T\le T_d^c$,the energy of the soliton $M_N$ is less than the energy of the three free constituent quarks $3M_q$. As $T>T_d^c$, there is an instant delocalization phase transition from hadron matter to quark matter. The phase diagram together with the location of a critical end point (CEP) has been obtained in $T$ and $\mu$ plane. We notice that two critical temperatures always satisfy $T_d^c\le T_{\chi }^c$. Finally, we present and compare the result of thermodynamic pressure at zero chemical potential with lattice data.

    hep-phnucl-thPRC(2016)·8 citations
13. 13*

    Comparative analysis of the ${\Lambda }_b\to \Lambda {\ell }^{+}{\ell }^{-}$ decay in the SM, SUSY and RS model with custodial protection

    K. Azizi🇹🇷 · A. T. Olgun🇹🇷 · Z. Tavukoglu🇹🇷

    We comparatively analyze the rare ${\Lambda }_b\to \Lambda {\ell }^{+}{\ell }^{-}$ channel in standard model, supersymmetry and Randall-Sundrum model with custodial protection (RS${}_c$). Using the parametrization of the matrix elements entering the low energy effective Hamiltonian in terms of form factors, we calculate the corresponding differential decay width and lepton forward-backward asymmetry in these models. We compare the results obtained with the most recent data from LHCb as well as lattice QCD results on the considered quantities. It is obtained that the standard model, with the form factors calculated in light-cone QCD sum rules, can not reproduce some experimental data on the physical quantities under consideration but the supersymmetry can do it. The RS${}_c$ model predictions are roughly the same as the standard model and there are no considerable differences between the predictions of these two models. In the case of differential decay rate, the data in the range $4$ GeV${}^2/$c${}^4\le$ $q^2\le 6$ GeV${}^2/$c${}^4$ can not be described by any of the considered models.

    hep-phPRD(2015)·9 citations
14. 14*

    The Pion-Cloud Contribution to the Electromagnetic Nucleon Form Factors

    Daniel Kupelwieser🇦🇹 · Wolfgang Schweiger🇦🇹

    We study the electromagnetic structure of the nucleon within a hybrid constituent-quark model that comprises, in addition to the $3q$ valence component, also a $3q$+$\pi$ non-valence component. To this aim we employ a Poincaré-invariant multichannel formulation based on the point-form of relativistic quantum mechanics. With a simple 3-quark wave function for the bare nucleon, i.e. the $3q$-component, we obtain reasonable results for the nucleon form factors and predict the meson-cloud contribution to be significant only below $Q^2\lesssim 0.5$\,GeV${}^2$ amounting to about 10\% for $Q^2\to 0$, in accordance with the findings of other authors.

    hep-phnucl-thEPJ Web Conf.(2016)·4 citations
15. 15*

    Confronting the real scalar septuplet minimal dark matter model with vacuum stability, perturbativity, and Type-I and Type-III seesaws

    Chengfeng Cai🇨🇳 · Ze-Min Huang🇨🇳 · Zhaofeng Kang · Zhao-Huan Yu🇨🇳 · Hong-Hao Zhang🇨🇳

    We study a real scalar septuplet model which has a neutral component regarded as a dark matter particle candidate. The calculation of its thermal relic abundance without (with) the Sommerfeld effect suggests that the observed value corresponds to the mass of the dark matter particle $m_0\gtrsim 8.8(25)\mathrm{TeV}$. Two extra quartic couplings ${\lambda }_2$ and ${\lambda }_3$ introduced in this model affect the running of other couplings, and hence the vacuum stability and the perturbativity up to the Planck scale. Therefore, the vacuum stability and the perturbativity conditions can constrain these couplings into a narrow region in the ${\lambda }_2$-${\lambda }_3$ plane. Other constraints from $h\to \gamma \gamma$, electroweak oblique parameters, and direct and indirect DM searches are also investigated. Moreover, we survey the vacuum stability and the perturbativity in the model combining the septuplet with the Type-I or Type-III seesaw. The running of couplings is further altered when the energy scale goes above the seesaw scale. In the Type-I case, when the seesaw scale $\sim 10^{15}\mathrm{GeV}$, the vacuum stability condition makes the acceptable region in the ${\lambda }_2$-${\lambda }_3$ plane much narrower. In the Type-III case, if the seesaw scale is $\lesssim 52\mathrm{TeV}$ or $\gtrsim 10^{15}\mathrm{GeV}$, the acceptable region vanishes.

    hep-ph1 citation
16. 16*

    Vector meson spectral function and dilepton rate in the presence of strong entanglement effect between the chiral and the Polyakov loop dynamics

    Chowdhury Aminul Islam🇮🇳 · Sarbani Majumder🇮🇳 · Munshi G. Mustafa🇮🇳

    In this work we have re-explored our earlier study on the vector meson spectral function and its spectral property in the form of dilepton rate in a two-flavour Polyakov loop extended Nambu-Jona-Lasinio (PNJL) model in presence of a strong entanglement between the chiral and Polyakov loop dynamics. The entanglement considered here is generated through the four-quark scalar type interaction in which the coupling strength depends on the Polyakov loop and runs with temperature and chemical potential. The entanglement effect is also considered for the four-quark vector type interaction in the same manner. We observe that the entanglement effect relatively enhances the color degrees of freedom due to the running of the both scalar and vector couplings. This modifies the vector meson spectral function and thus the spectral property such as the dilepton production rate in low invariant mass also gets modified.

    hep-phnucl-thPRD(2015)·7 citations
17. 17*

    The Effective MSSM

    Archil Kobakhidze🇦🇺 · Matthew Talia🇦🇺

    We suggest an effective field theory framework to discuss deviations from the minimal supersymmetric Standard Model (MSSM) which is based on an alternative arrangement of the gauge-Higgs sector. In this effective MSSM (EffMSSM) nonlinearly realised $SU(2)\times U(1)$ gauge sector is described by an $SU(2)\times U(1)$-valued massive vector superfield, which contains a neutral CP-even and charged Higgs fields, while another neutral CP-even Higgs and the neutral CP-odd Higgs fields are residing in an $SU(2)\times U(1)$-singlet chiral superfield. Although the new theory contains the same particle content as the conventional MSSM, the unconventional representation of superfields allows for new type of interactions, which may lead to a significant modification of the phenomenology. As an illustrative example we consider EffMSSM with modified Higgs and electroweak gauge sector augmented by gaugino soft supersymmetry breaking masses, $M_i(i=1,2,3)$ and the Standard Higgs soft-breaking masses, $m_{H_u}=m_{H_d}$ and $B_{\mu }$, and point out distinct features in the Higgs and gaugino sectors as compared to MSSM. In particular, we show that the lightest neutral CP-even Higgs boson with mass $\sim 125$ GeV can be easily accommodated within EffMSSM.

    hep-phhep-thPLB(2015)·3 citations
18. 18*

    Improving parton distribution uncertainties in a W mass measurement at the LHC

    Zack Sullivan🇺🇸 · Seth Quackenbush🇺🇸

    We reexamine the dominant contribution of parton distribution function (PDF) uncertainties to the W mass measurement, and determine their contribution is +-39(30) MeV when running the Large Hadron Collider at 7(13) TeV. We find that spurious correlations in older PDF sets led to over-optimistic assumptions regarding normalization to Z observables. In order to understand the origin of the large uncertainties we break down the contribution of the PDF errors into effects at the hard matrix element level, in showering, and in sensitivity to finite detector resolutions. Using CT10, CT10W, and charm enhanced PDF sets in comparison to older PDF sets, we develop a robust analysis that examines correlations between transverse mass reconstructions of W and Z decays (scaled by cos ${\theta }_W$) to leptons. We find that central leptons (|${\eta }_l$| < 1.3) from W and Z bosons carry the most weight in reducing the PDF uncertainty, and estimate a PDF error of +10/-12 MeV is achievable in a W mass measurement at the LHC. Further reductions of the W mass uncertainty will require improved fits to the parton distribution functions.

    hep-phhep-ex0 citations
19. 19*

    Axion Induced Oscillating Electric Dipole Moment of the Electron

    Christopher T. Hill🇺🇸

    A cosmic axion, via the electromagnetic anomaly, induces an oscillating electric dipole for the electron of frequency $m_a$ and strength $\sim$(few)$\times 10^{-32}$ e-cm, two orders of magnitude above the nucleon, and within a few orders of magnitude of the present standard model constant limit. We give a detailed study of this phenomenon via the interaction of the cosmic axion, through the electromagnetic anomaly, with particular emphasis on the decoupling limit of the axion, ${\partial }_{t}a(t)\propto m_a\to 0$. The analysis is subtle, and we find the general form of the action involves a local contact interaction and a nonlocal contribution, analogous to the "transverse current" in QED, that enforces the decoupling limit. We carefully derive the effective action in the Pauli-Schroedinger non-relativistic formalism, and in Georgi's heavy quark formalism adapted to the "heavy electron" ($m_e>>m_a$). We compute the electric dipole radiation emitted by free electrons, magnets and currents, immersed in the cosmic axion field, and discuss experimental configurations that may yield a detectable signal.

    hep-phastro-ph.COhep-exhep-thPRD(2016)·32 citations
20. 20*

    From Pentaquarks to Dibaryons in Lambda_b(5620) decays

    L. Maiani🇮🇹 · A.D. Polosa🇮🇹 · V. Riquer🇮🇹

    Pentaquarks and dibaryons are natural possibilities if diquarks are used as the building blocks to assemble hadrons. In this short note, motivated by the very recent discovery of two pentaquark states, we highlight some possible channels to search for dibaryons in Lambda_b(5620) decays.

    hep-phPLB(2015)·31 citations
21. 21*

    Eight Ultra-faint Galaxy Candidates Discovered in Year Two of the Dark Energy Survey

    The DES Collaboration: A. Drlica-Wagner🇺🇸 · K. Bechtol🇺🇸 · E. S. Rykoff🇺🇸 · E. Luque🇧🇷 · A. Queiroz🇧🇷 · Y.-Y. Mao🇺🇸 · R. H. Wechsler🇺🇸 · J. D. Simon🇺🇸 · B. Santiago🇧🇷 · B. Yanny🇺🇸 · E. Balbinot🇬🇧 · S. Dodelson🇺🇸 and 64 other authors

    We report the discovery of eight new ultra-faint dwarf galaxy candidates in the second year of optical imaging data from the Dark Energy Survey (DES). Six of these candidates are detected at high confidence, while two lower-confidence candidates are identified in regions of non-uniform survey coverage. The new stellar systems are found by three independent automated search techniques and are identified as overdensities of stars, consistent with the isochrone and luminosity function of an old and metal-poor simple stellar population. The new systems are faint (Mv > -4.7 mag) and span a range of physical sizes (17 pc < $r_{1/2}$ < 181 pc) and heliocentric distances (25 kpc < D < 214 kpc). All of the new systems have central surface brightnesses consistent with known ultra-faint dwarf galaxies (\mu < 27.5 mag arcsec${}^{-2}$). Roughly half of the DES candidates are more distant, less luminous, and/or have lower surface brightnesses than previously known Milky Way satellite galaxies. Most of the candidates are found in the southern part of the DES footprint close to the Magellanic Clouds. We find that the DES data alone exclude (p < 0.001) a spatially isotropic distribution of Milky Way satellites and that the observed distribution can be well, though not uniquely, described by an association between several of the DES satellites and the Magellanic system. Our model predicts that the full sky may hold ~100 ultra-faint galaxies with physical properties comparable to the DES satellites and that 20-30% of these would be spatially associated with the Magellanic Clouds.

    ↳ astro-ph.GAastro-ph.HEastro-ph.IMhep-phApJ(2015)·378 citations
22. 22*

    Simulating the Universe(s) III: Observables for the full bubble collision spacetime

    Matthew C. Johnson🇨🇦 · Carroll L. Wainwright🇺🇸 · Anthony Aguirre🇺🇸 · Hiranya V. Peiris🇬🇧

    This is the third paper in a series establishing a quantitative relation between inflationary scalar field potential landscapes and the relic perturbations left by the collision between bubbles produced during eternal inflation. We introduce a new method for computing cosmological observables from numerical relativity simulations of bubble collisions in one space and one time dimension. This method tiles comoving hypersurfaces with locally-perturbed Friedmann-Robertson-Walker coordinate patches. The method extends previous work, which was limited to the spacetime region just inside the future light cone of the collision, and allows us to explore the full bubble-collision spacetime. We validate our new methods against previous work, and present a full set of predictions for the comoving curvature perturbation and local negative spatial curvature produced by identical and non-identical bubble collisions, in single scalar field models of eternal inflation. In both collision types, there is a non-zero contribution to the spatial curvature and cosmic microwave background quadrupole. Some collisions between non-identical bubbles excite wall modes, giving extra structure to the predicted temperature anisotropies. We comment on the implications of our results for future observational searches. For non-identical bubble collisions, we also find that the surfaces of constant field can readjust in the presence of a collision to produce spatially infinite sections that become nearly homogeneous deep into the region affected by the collision. Contrary to previous assumptions, this is true even in the bubble into which the domain wall is accelerating.

    ↳ hep-thastro-ph.COhep-phJCAP(2016)·17 citations
23. 23*

    Master integrals for the four-loop Sudakov form factor

    Rutger Boels🇩🇪 · Bernd A. Kniehl🇩🇪 · Gang Yang🇩🇪

    The light-like cusp anomalous dimension is a universal function in the analysis of infrared divergences. In maximally ($\mathcal{N}=4$) supersymmetric Yang-Mills theory (SYM) in the planar limit, it is known, in principle, to all loop orders. The non-planar corrections are not known in any theory, with the first appearing at the four-loop order. The simplest quantity which contains this correction is the four-loop two-point form factor of the stress tensor multiplet. This form factor was largely obtained in integrand form in a previous work for $\mathcal{N}=4$ SYM, up to a free parameter. In this work, a reduction of the appearing integrals obtained by solving integration-by-parts (IBP) identities using a modified version of Reduze is reported. The form factor is shown to be independent of the remaining parameter at integrand level due to an intricate pattern of cancellations after IBP reduction. Moreover, two of the integral topologies vanish after reduction. The appearing master integrals are cross-checked using independent algebraic-geometry techniques explored in the Mint package. The latter results provide the basis of master integrals applicable to generic form factors, including those in Quantum Chromodynamics. Discrepancies between explicitly solving the IBP relations and the MINT approach are highlighted. Remaining bottlenecks to completing the computation of the four-loop non-planar cusp anomalous dimension in $\mathcal{N}=4$ SYM and beyond are identified.

    ↳ hep-thhep-phmath-phmath.MPNPB(2016)·51 citations
24. 24*

    Event-by-event distribution of magnetic field energy over initial fluid energy density in $\sqrt{s_{\mathrm{NN}}}$= 200 GeV Au-Au collisions

    Victor Roy🇩🇪 · Shi Pu🇩🇪

    We estimate the event-by-event (e-by-e) distribution of the ratio ($\sigma$) of the magnetic field energy to the fluid energy density in the transverse plane of Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV. A Monte-Carlo (MC) Glauber model is used to calculate the $\sigma$ in the transverse plane for impact parameter b=0, 12 fm at time ${\tau }_i\sim$0.5 fm. The fluid energy density is obtained by using Gaussian smoothing with two different smoothing parameter ${\sigma }_g$=0.25 , 0.5 fm. For $b=0\mathrm{fm}$ collisions $\sigma$ is found to be $\ll$ 1 in the central region of the fireball and $\sigma \gtrsim$ 1 at the periphery. For b=12 fm collisions $\sigma \gtrsim$ 1. The e-by-e correlation between $\sigma$ and the fluid energy density ($\epsilon$) is studied. We did not find strong correlation between $\sigma$ and $\epsilon$ at the centre of the fireball, whereas they are mostly anti-correlated at the periphery of the fireball.

    ↳ nucl-thhep-phPRC(2015)·73 citations
25. 25*

    Observable Signatures of a Classical Transition

    Matthew C. Johnson🇨🇦 · Wei Lin🇨🇦

    Eternal inflation arising from a potential landscape predicts that our universe is one realization of many possible cosmological histories. One way to access different cosmological histories is via the nucleation of bubble universes from a metastable false vacuum. Another way to sample different cosmological histories is via classical transitions, the creation of pocket universes through the collision between bubbles. Using relativistic numerical simulations, we examine the possibility of observationally determining if our observable universe resulted from a classical transition. We find that classical transitions produce spatially infinite, approximately open Friedman-Robertson-Walker universes. The leading set of observables in the aftermath of a classical transition are negative spatial curvature and a contribution to the Cosmic Microwave Background temperature quadrupole. The level of curvature and magnitude of the quadrupole are dependent on the position of the observer, and we determine the possible range of observables for two classes of single-scalar field models. For the first class, where the inflationary phase has a lower energy than the vacuum preceding the classical transition, the magnitude of the observed quadrupole generally falls to zero with distance from the collision while the spatial curvature grows to a constant. For the second class, where the inflationary phase has a higher energy than the vacuum preceding the classical transition, the magnitude of the observed quadrupole generically falls to zero with distance from the collision while the spatial curvature grows without bound. We find that the magnitude of the quadrupole and curvature grow with increasing centre of mass energy of the collision, and explore variations of the parameters in the scalar field lagrangian.

    ↳ astro-ph.COhep-phhep-thJCAP(2016)·6 citations
26. 26*

    ND^(*) and NB^(*) interactions in a chiral quark model

    Dan Yang🇨🇳 · Jing Liu🇨🇳 · Dan Zhang🇨🇳

    ND and ND^* interactions become a hot topic after the observation of new charmed hadrons \Sigma_c(2800) and \Lambda_c(2940)^+. In this letter, we have preliminary investigated S-wave ND and ND^* interactions with possible quantum numbers in the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving the resonating group method equation. The numerical results show that the interactions between N and D or N and D^* are both attractive, which are mainly from \sigma exchanges between light quarks. Further bound-state studies indicate the attractions are strong enough to form ND or ND^* molecules, except for (ND)_{J=3/2} and (ND^*)_{J=3/2} in the chiral SU(3) quark model. In consequence ND system with J=1/2 and ND^* system with J=3/2 in the extended SU(3) quark model could correspond to the observed \Sigma_c(2800) and \Lambda_c(2940)^+, respectively. Naturally, the same method can be applied to research NB and NB^* interactions, and similar conclusions obtained, i.e. NB and NB^* attractive forces may achieve bound states, except for (NB^*)_{J=3/2} in the chiral SU(3) quark model. Meanwhile, S partial wave phase shifts of ND^{(*)} and NB^{(*)} elastic scattering are illustrated, which are qualitatively consistent with results from bound state problem.

    ↳ nucl-thhep-ph5 citations
27. 27*

    Heavy flavor in relativistic heavy-ion collisions

    E. L. Bratkovskaya🇩🇪 · T. Song🇩🇪 · H. Berrehrah🇩🇪 · D. Cabrera🇩🇪 · J. M. Torres-Rincon🇫🇷 · L. Tolos🇪🇸 · W. Cassing🇩🇪

    We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the PYTHIA event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM), which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross sections are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into $D$ mesons through coalescence and/or fragmentation. The hadronized $D$ mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavy-quark spin symmetry. The nuclear modification factor $R_{AA}$ and the elliptic flow $v_2$ of $D^0$ mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at $\sqrt{s_{NN}}$ =200 GeV and to the ALICE data for Pb+Pb collisions at $\sqrt{s_{NN}}$ =2.76 TeV. We find that in the PHSD the energy loss of $D$ mesons at high $p_T$ can be dominantly attributed to partonic scattering while the actual shape of $R_{AA}$ versus $p_T$ reflects the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the $R_{AA}$ at low $p_T$ and enhances the $D$-meson elliptic flow $v_2$.

    ↳ nucl-thhep-phJ.Phys.Conf.Ser.(2016)·5 citations
28. 28*

    Ultra-diffuse cluster galaxies as key to the MOND cluster conundrum

    Mordehai Milgrom🇮🇱

    MOND reduces greatly the mass discrepancy in clusters of galaxies, but does leave a consistent global discrepancy of about a factor of two. It has been proposed, within the minimalist and purist MOND, that clusters harbor some indigenous, yet-undetected, cluster baryonic (dark) matter (CBDM). Its total amount has to be comparable with that of the observed hot gas. Following an initial discovery by van Dokkum & al. (2015a), Koda & al. (2015) have recently identified more than a thousand ultra-diffuse galaxy-like objects (UDGs) in the Coma cluster. Robustness of the UDGs to tidal disruption seems to require, within Newtonian dynamics, that they are much more massive than their observed stellar component. Here, I propound that a considerable fraction of the CBDM is internal to UDGs, which endows them with robustness. The rest of the CBDM objects formed in now-disrupted kin of the UDGs, and is dispersed in the intracluster medium. While the discovery of cluster UDGs is not in itself a resolution of the MOND cluster conundrum, it lends greater qualitative plausibility to CBDM as its resolution, for reasons I discuss. Alternatively, if the UDGs are only now falling into Coma, their large size and very low surface brightness could result from the adiabatic inflation due to the MOND external-field effect, as described in Brada & Milgrom (2000). I also consider briefly solutions to the conundrum that invoke more elaborate extensions of purist MOND, e.g., that in clusters, the MOND constant takes up larger-than-canonical values of the MOND constant.

    ↳ astro-ph.GAgr-qchep-phMNRAS(2015)·18 citations
29. 29*

    Reply to Comment on "Reevaluation of the parton distribution of strange quarks in the nucleon"

    E.C. Aschenauer🇺🇸 · H.E. Jackson🇺🇸 · S. Joosten🇺🇸 · K. Rith🇩🇪 · G. Schnell🇪🇸 · C. Van Hulse (for the HERMES Collaboration)🇪🇸

    A Comment on the recently published reevaluation of the polarization-averaged parton distribution of strange quarks in the nucleon using final data on the multiplicities of charged kaons in semi-inclusive deep-inelastic scattering is reviewed. Important features of the comparison of one-dimensional projections of the multidimensional HERMES data are pointed out. A test of the leading-order extraction of xS(x) using the difference between charged-kaon multiplicities is repeated. The results are consistent with leading-order predictions within the uncertainties in the input data, and do not invalidate the earlier extraction of xS(x).

    ↳ hep-exhep-phPRD(2015)·17 citations
30. 30*

    Fluid/gravity correspondence: A nonconformal realization in compactified D4 branes

    Chao Wu🇨🇳 · Yidian Chen🇨🇳 · Mei Huang🇨🇳

    We develop the framework of boundary derivative expansion (BDE) formalism of fluid/gravity correspondence in compactified D4-brane system, which is a nonconformal background used in top-down holographic QCD models. Such models contain the D4-D6 model and the Sakai-Sugimoto (SS) model, with the background of the compactified black D4 branes under the near horizon limit. By using the dimensional reduction technique, we derive a 5D Einstein gravity minimally coupled with 3 scalar fields from the 10D D4-brane background. Following the BDE formalism of fluid/gravity correspondence in the conformal background, we directly derive all the first order transport coefficients for nonconformal gluonic matter. The results of the ratio of the bulk to shear viscosity and the sound speed agree with those obtained from the Green-Kubo method. This agreement guarantees the validity of the BDE formalism of fluid/gravity duality in the nonconformal D-brane background, which can be used to calculate the second order transport coefficients in nonconformal background.

    ↳ hep-thhep-phPRD(2016)·12 citations
31. 31*

    The case for mixed dark matter from sterile neutrinos

    Louis Lello🇺🇸 · Daniel Boyanovsky🇺🇸

    Sterile neutrinos are SU(2) singlets that mix with active neutrinos via a mass matrix, its diagonalization leads to mass eigenstates that couple via standard model vertices. We study the cosmological production of heavy neutrinos via standard model charged and neutral current vertices under a minimal set of assumptions: i) the mass basis contains a hierarchy of heavy neutrinos, ii) these have very small mixing angles with the active (flavor) neutrinos, iii) standard model particles, including light (active-like) neutrinos are in thermal equilibrium. The same weak interaction processes that produce active-like neutrinos also produce the heavier species. We introduce the kinetic equations that describe their production, freeze out and decay and discuss the various processes that lead to their production in a wide range of temperatures assessing their feasibility as dark matter candidates. We identify processes in which finite temperature collective excitations lead to the production of the heavy species. As a specific example, we consider the production of heavy neutrinos from pion decay shortly after the QCD crossover including finite temperature corrections to the pion form factors and mass. We consider the different decay channels that allow for the production of heavy neutrinos showing that their frozen distribution functions exhibit effects from "kinematic entanglement" and argue for their viability as mixed dark matter candidates. We discuss abundance, phase space density and stability constraints and argue that heavy neutrinos with lifetime $\tau >1/H_0$ freeze out of local thermal equilibrium, and \emph{conjecture} that those with lifetimes $\tau \ll 1/H_0$ may undergo cascade decay into lighter DM candidates and/or inject non-LTE neutrinos into the cosmic neutrino background. We provide a comparison with non-resonant production via active-sterile mixing.

    ↳ astro-ph.COhep-phJCAP(2016)·12 citations
32. 32*

    Recent results on the nucleon resonance spectrum and structure from the CLAS detector

    Victor Mokeev🇺🇸 · Inna Aznauryan🇦🇲 · Volker Burkert🇺🇸 · Ralf Gothe🇺🇸

    The CLAS detector at Jefferson Lab has provided the dominant part of all available worldwide data on exclusive meson electroproduction off protons in the resonance region. New results on the ${\gamma }_{v}p{N}^{\ast }$ transition amplitudes (electrocouplings) are available from analyses of the CLAS data and will be presented. Their impact on understanding of hadron structure will be discussed emphasizing the credible access to the dressed quark mass function that has been achieved for the first time by a combined analysis of the experimental results on the electromagnetic nucleon elastic and $N\to N^{\ast }$ transition form factors. We will also discuss further convincing evidences for a new baryon state $N^{{}^{\prime }}(1720)3/2^{+}$ found in a combined analysis of charged double pion photo- and electroproduction cross sections off the protons.

    ↳ nucl-exhep-phEPJ Web Conf.(2016)·22 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.