Fri·Jul 15, 2016Friday·July 15, 2016

1. 01*

   LHC diphoton excess in a left-right symmetric model with minimal dark matter

   Sanjib Kumar Agarwalla🇮🇳 · Kirtiman Ghosh🇮🇳 · Ayon Patra🇮🇳

   We construct a model containing a viable dark matter candidate, in the framework of left-right symmetry, which can explain both width and cross-section of the observed 750 GeV diphoton excess at the LHC. We introduce a fermion quintuplet whose neutral component can be a possible dark matter candidate, whereas the charged components enhance the loop induced coupling of a 750 GeV singlet scalar with a pair of photons. We study the photo-production of the singlet scalar and its various decay modes, successfully addressing both the ATLAS and the CMS diphoton excess.

   hep-ph8 citations
2. 02*

   Finite-temperature modification of heavy particle decay and dark matter annihilation

   Martin Beneke🇩🇪 · Francesco Dighera🇩🇪 · Andrzej Hryczuk🇳🇴

   We apply the operator product expansion (OPE) technique to the decay and annihilation of heavy particles in a thermal medium with temperature below the heavy particle mass, m_chi. This allows us to explain two interesting observations made before: a) that the leading thermal correction to the decay width of a charged particle is the same multiplicative factor of the zero-temperature width for a two-body decay and muon decay, and b) that the leading thermal correction to fermionic dark matter annihilation arises only at order T^4/m_chi^4. The OPE further considerably simplifies the computation and factorizes it into model-independent matrix elements in the thermal background, and short-distance coefficients to be computed in zero-temperature field theory.

   hep-phJHEP(2016)·11 citations
3. 03*

   Two-loop Dirac neutrino mass and WIMP dark matter

   Cesar Bonilla🇪🇸 · Ernest Ma🇺🇸 · Eduardo Peinado🇲🇽 · Jose W.F. Valle🇪🇸

   We propose a "scotogenic" mechanism relating small neutrino mass and cosmological dark matter. Neutrinos are Dirac fermions with masses arising only in two--loop order through the sector responsible for dark matter. Two triality symmetries ensure both dark matter stability and strict lepton number conservation at higher orders. A global spontaneously broken U(1) symmetry leads to a physical $Diracon$ that induces invisible Higgs decays which add up to the Higgs to dark matter mode. This enhances sensitivities to spin-independent WIMP dark matter search below $m_h/2$.

   hep-phhep-thPLB(2016)·114 citations
4. 04*

   Suppressed $B\to PV$ CP asymmetry: CPT constraint

   J.H. Alvarenga Nogueira🇧🇷 · I. Bediaga🇧🇷 · T. Frederico🇧🇷 · P.C. Magalhães🇧🇷 · J. Molina Rodriguez🇧🇷

   Charge Parity asymmetry in charmless B meson decays is a key issue to be understood. Many theoretical calculations have been performed using short distance factorization approaches which, in general, do not take into account the CPT invariance constraint. For each channel with CP violation there is an equal amount of CP asymmetry in another channel or other channels, with an opposite sign. This happens if these channels are coupled through final state interactions (FSI). In the specific process $B\to PV$, involving one pseudo-scalar and one vector particle in the final state, we argue that the CP asymmetry, inherent from a short distance mechanism, could be suppressed due to the CPT constraint. In this case, we propose a sensitive and practical experimental method to identify even a small CP asymmetry, which provides the values for $A_{CP}$ without the need for an amplitude analysis. This method, if applied directly to data, will enable to extract the CP asymmetry information in a model independent way and check to which extend the suggested suppression due to the CPT constraint is verified.

   hep-phhep-exPRD(2016)·19 citations
5. 05*

   X(16.7) Production in Electron-Position Collision

   Jun Jiang · Long-Bin Chen · Yi Liang · Cong-Feng Qiao

   The anomaly found in the excited ${}^8\text{Be}$ nuclear transition to its ground state is attributed to a spin-1 gauge boson $X(16.7)$. To hunt for this boson, we propose two traps: $e^{+}{e}^{-}\to X\gamma$ and $J/\psi \to X\gamma$, both following with $X\to e^{+}{e}^{-}$ decay. We adopt the "vector minus axial-vector" interaction hypothesis. Analysis on the $X(16.7)$ decay length, production rates, differential distribution with respect to the $e^{+}{e}^{-}$ invariant-mass spectrum, and the signal-to-noise ratios (SNR) after the smearing at BESIII detector are discussed in detail. Given the coupling strength of $X$ to vector/axial-vector currents $g_f^{v/a}\sim 10^{-3}$ at BESIII: (1) there would be about $6000$ $X$ measurable events per year in electron-positron collision, yet with a large background after smearing, (2) while in $J/\psi$ decays, we find that the axial-vector current may come into play, though merely 52 events may appear, the SNR are inspiring even after smearing.

   hep-ph24 citations
6. 06*

   Heavy quark potential and jet quenching parameter in a D-instanton background

   Zi-qiang Zhang🇨🇳 · De-fu Hou🇨🇳 · Gang Chen🇨🇳

   Using the AdS/CFT correspondence, we study the heavy quark potential and the jet quenching parameter in the near horizon limit of D3-D(-1) background. The results are compared with those of conformal cases. It is shown that the presence of instantons tends to suppress the heavy quark potential and enhance the jet quenching parameter.

   hep-phEPJA(2016)·8 citations
7. 07*

   Construction of a Model of Monopolium and its Search via Multi-Photon Channels at LHC

   Neil D. Barrie🇦🇺 · Akio Sugamoto🇯🇵 · Kimiko Yamashita🇯🇵

   A model of monopolium is constructed based on an electromagnetic dual formulation of Zwanziger and lattice gauge theory. To cope with the strong coupling nature of the magnetic charge, for which the monopole is confined, $U(1)$ lattice gauge theory is applied. The monopole is assumed to have a finite-sized inner structure based on a 't Hooft-Polyakov like solution in which the magnetic charge is uniformly distributed on the surface of a sphere. The monopole and antimonopole potential becomes linear plus Coulomb outside the sphere and is constant inside. Numerical estimation gives two kinds of solutions: One which has a small binding energy, and hence the para-($J=0$) and ortho-($J=1$) monopoliums have degenerate masses. For the parameter choices considered, they both have $\mathcal{O}(1-10)$ TeV masses and are very short-lived. The other solution has a small monopole mass and large binding energy, with an illustrative example of parameter choices giving a 750 GeV para-monopolium and 1.4 TeV ortho-monopolium. The production rate of the former is one order of magnitude smaller than the announced enhancement, but they may be the target of future LHC searches and the 100 TeV colliders.

   hep-phhep-exhep-thPTEP(2016)·18 citations
8. 08*

   Unravelling the physical meaning of the Jaffe-Manohar decomposition of the nucleon spin

   Masashi Wakamatsu🇯🇵

   A general consensus now is that there are two physically inequivalent complete decompositions of the nucleon spin, i.e. the decomposition of the canonical type and that of mechanical type. The well-known Jaffe-Manohar decomposition is of the former type. Unfortunately, there is a wide-spread misbelief that this decomposition matches the partonic picture, which states that motion of quarks in the nucleon is approximately free. In the present monograph, we reveal that this understanding is not necessarily correct and that the Jaffe-Manohar decomposition is not such a decomposition, which natively reflects the intrinsic (or static) orbital angular momentum structure of the nucleon.

   hep-phhep-exnucl-thPRD(2016)·12 citations
9. 09*

   On the constituent counting rules for hard exclusive processes involving multiquark states

   Feng-Kun Guo🇨🇳 · Ulf-G. Meißner🇩🇪 · Wei Wang🇨🇳

   At high energies, the cross section of a hard exclusive process at finite scattering angle falls off as a negative power of the center-of-mass energy $\sqrt{s}$. If all involved quark-gluon compositions undergo hard momentum transfers, the scaling of the fall-off is determined by the underlying valence structures of the initial and final states, known as the constituent counting rules. It was argued in the literature that the counting rules are a powerful tool to determine the valence degrees of freedom inside multiquark states when applied to exclusive production processes. However, we demonstrate that for hadrons with hidden flavors the naive application of the constituent counting rules is problematic, since it is not mandatory for all components to participate the hard scattering at the scale $\sqrt{s}$. The correct scaling rules can be obtained easily by using effective field theory. A few examples involving the $Z_c(3900{)}^{\pm }$ and $X(3872)$ are discussed.

   hep-phhep-exCPC(2017)·18 citations
10. 10*

    Heavy quark production in $pA$ collisions: the double parton scattering contribution

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

    In this paper we estimate the double parton scattering (DPS) contribution for the heavy quark production in $pA$ collisions at the LHC. The cross sections for the charm and bottom production are estimated using the dipole approach and taking into account the saturation effects, which are important for high energies and for the scattering with a large nucleus. We compare the DPS contribution with the single parton scattering one and demonstrate that in the case of charm production both are similar in the kinematical range probed by the LHC. Predictions for the rapidity range analysed by the LHCb Collaboration are also presented. Our results indicate that the study of the DPS contribution for the heavy quark production in $pPb$ collisions at the LHC is feasible and can be useful to probe the main assumptions of the approach.

    hep-phnucl-thMod.Phys.Lett.A(2018)·12 citations
11. 11*

    A new B-L model without right-handed neutrinos

    Sudhanwa Patra🇮🇳 · Werner Rodejohann🇩🇪 · Carlos E. Yaguna🇩🇪

    We propose and study a novel extension of the Standard Model based on the B-L gauge symmetry that can account for dark matter and neutrino masses. In this model, right-handed neutrinos are absent and the gauge anomalies are canceled instead by four chiral fermions with fractional B-L charges. After the breaking of $U(1{)}_{B-L}$, these fermions arrange themselves into two Dirac particles, the lightest of which is automatically stable and plays the role of the dark matter. We determine the regions of the parameter space consistent with the observed dark matter density and show that they can be partially probed via direct and indirect dark matter detection or collider searches at the LHC. Neutrino masses, on the other hand, can be explained by a variant of the type-II seesaw mechanism involving one of the two scalar fields responsible for the dark matter mass.

    hep-phJHEP(2016)·59 citations
12. 12*

    Gauged $U(1{)}_{L_{\mu }-L_{\tau }}$ model in light of muon $g-2$ anomaly, neutrino mass and dark matter phenomenology

    Sudhanwa Patra🇮🇳 · Soumya Rao🇦🇺 · Nirakar Sahoo🇮🇳 · Narendra Sahu🇮🇳

    Gauged $U(1{)}_{L_{\mu }-L_{\tau }}$ model has been advocated for a long time in light of muon $g-2$ anomaly, which is a more than $3\sigma$ discrepancy between the experimental measurement and the standard model prediction. We augment this model with three right-handed neutrinos $(N_e,N_{\mu },N_{\tau })$ and a vector-like singlet fermion $(\chi )$ to explain simultaneously the non-zero neutrino mass and dark matter content of the Universe, while satisfying anomalous muon $g-2$ constraints. It is shown that in a large parameter space of this model we can explain positron excess, observed at PAMELA, Fermi-LAT and AMS-02, through dark matter annihilation, while satisfying the relic density and direct detection constraints.

    hep-phNPB(2017)·78 citations
13. 13*

    Quark mass dependence of H-dibaryon in $\Lambda \Lambda$ scattering

    Yasuhiro Yamaguchi🇯🇵 · Tetsuo Hyodo🇯🇵

    We study the quark mass dependence of the H-dibaryon in the strangeness $S=-2$ baryon-baryon scattering. A low-energy effective field theory is used to describe the coupled-channel scattering, in which the quark mass dependence is incorporated so as to reproduce the lattice QCD data by the HAL QCD collaboration in the SU(3) limit. We point out the existence of the Castillejo-Dalitz-Dyson (CDD) pole in the $\Lambda \Lambda$ scattering amplitude below the threshold in the SU(3) limit, which may cause the Ramsauer-Townsend effect near the $N\Xi$ threshold at the physical point. The H-dibaryon is unbound at the physical point, and a resonance appears just below the $N\Xi$ threshold. As a consequence of the coupled-channel dynamics, the pole associated with the resonance is not continuously connected to the bound state in the SU(3) limit. Through the extrapolation in quark masses, we show that the unitary limit of the $\Lambda \Lambda$ scattering is achieved between the physical point and the SU(3) limit. We discuss the possible realization of the "H-matter" in the unphysical quark mass region.

    hep-phnucl-thPRC(2016)·25 citations
14. 14*

    Deuteron electromagnetic structure functions and polarization properties in soft-wall AdS/QCD

    Thomas Gutsche🇩🇪 · Valery E. Lyubovitskij🇩🇪 · Ivan Schmidt🇨🇱

    We apply a soft-wall AdS/QCD approach to the description of deuteron structure functions and tensor polarized properties. Present work is a completion of our previous study on electromagnetic form factors. By the appropriate choice of two couplings in the effective action we are able to reproduce both the form factors and structure functions in full consistency with model-independent constraints set by perturbative QCD. Our framework is based on a five-dimensional action in AdS space formulated in terms of vector fields dual to the deuteron and the electromagnetic fields. The AdS fields depend on four Minkowski and one holographic coordinate $z$. The scale dependence of the form factors and structure functions is consistent with quark counting rules implying the $1/Q^{10}$ behavior of the charge form factor $G_C(Q^2)$, structure functions $A(Q^2)$ and $B(Q^2)$, and the $1/Q^{12}$ behavior of the magnetic $G_M(Q^2)$ and quadrupole $G_Q(Q^2)$ form factors.

    hep-phPRD(2016)·27 citations
15. 15*

    Light sterile neutrinos from a late phase transition

    Luca Vecchi🇮🇹

    Light sterile neutrinos represent a well-motivated extension of the 3-neutrino paradigm. However, the impressive agreement between standard cosmology and data casts doubts on their existence. Here we present a class of scenarios that robustly avoids this tension. In these models the sterile neutrinos are light, chiral states of a new sector interacting with the Standard Model via the right-handed neutrino portal and, crucially, active-sterile neutrino oscillations require a phase transition in the hidden sector. We explore the hidden-couplings/critical-temperature plane and identify regions where several sterile neutrinos can be accommodated. A late phase transition is usually preferred and may also ward off a potential threat posed by the formation of topologically stable defects.

    hep-phPRD(2016)·15 citations
16. 16*

    Diphoton resonance at the ILC

    Junping Tian🇯🇵 · Keisuke Fujii🇯🇵 · Hiroshi Yokoya🇰🇷

    In this paper we study the direct production of the diphoton resonance $X$ which has been suggested by 2015 data at the LHC, in $e^{+}{e}^{-}\to X\gamma /XZ$ processes at the ILC. We derive an analytic expression for the scattering amplitudes of these processes, and present a comprehensive analysis for determining the properties of $X$ at the ILC. A realistic simulation study for $e^{+}{e}^{-}\to X\gamma$ is performed based on the full detector simulation to demonstrate the capabilities of the ILC experiment. Complementary to the searches at the LHC, prospects of the measurement of the absolute values of production cross-section are obtained for the ILC using recoil technique without assuming decay modes of $X$. In addition, we have studied the searches for $X\to \mathrm{invisible}$ and $X\to b\bar{b}$ modes, which are challenging at the LHC, and found that these decay modes can be discovered with high significance if their branching ratios are large enough.

    hep-phhep-exPRD(2016)·6 citations
17. 17*

    Resonance production in Pomeron-Pomeron collisions at the LHC

    R.Schicker🇩🇪 · R.Fiore🇮🇹 · L.Jenkovszky🇺🇦

    A model for Pomeron-Pomeron total cross section in the resonance region $\sqrt{M^2}\le$ 5 GeV is presented. This model is based on Regge poles from the Pomeron and two different $f$ trajectories, and includes the isolated f${}_0(500)$ resonance in the region $\sqrt{M^2}\lesssim 1$ GeV. A slowly varying background is included. The presented Pomeron-Pomeron cross section is not directly measurable, but is an essential ingredient for calculating exclusive resonance production at the LHC.

    hep-phPoS(2016)·0 citations
18. 18*

    Chiral Gravitational Waves from Chiral Fermions

    Mohamed M. Anber🇨🇭 · Eray Sabancilar🇨🇭

    We report on a new mechanism that leads to the generation of primordial chiral gravitational waves, and hence, the violation of the parity symmetry in the Universe. We show that nonperturbative production of fermions with a definite helicity is accompanied by the generation of chiral gravitational waves. This is a generic and model-independent phenomenon that can occur during inflation, reheating and radiation eras, and can leave imprints in the cosmic microwave background polarization and may be observed in future ground- and space-based interferometers. We also discuss a specific model where chiral gravitational waves are generated via the production of light chiral fermions during pseudoscalar inflation.

    ↳ hep-thastro-ph.COgr-qchep-phPRD(2017)·19 citations
19. 19*

    Production of $\Lambda \Lambda$ and $\overline{\Lambda \text{n}}$ in central Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV within a covariant coalescence model

    Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳

    We study the production of $\Lambda \Lambda$ and $\overline{\Lambda \text{n}}$ exotic states in central Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV at LHC via both hadron and quark coalescence within a covariant coalescence model with a blast-wave-like parametrization for the phase-space configurations of constituent particles at freezeout. In the hadron coalescence, the two states are considered as molecular states while they are considered as six-quark states in the quark coalescence.For $\overline{\Lambda \text{n}}$, we find that the yields of both molecular and six-quark states are much larger than the experimental upper-limits. For $\Lambda \Lambda$, while the molecule-state yield is much larger than the experimental upper-limits, the six-quark-state yield could be lower than the upper-limits. The higher molecule-state yields are mainly due to the large contribution of short-lived strong resonance decays into (anti-)nucleons and (anti-)$\Lambda$ which can significantly enhance the molecule-state yields of $\Lambda \Lambda$ and $\overline{\Lambda \text{n}}$ via hadron coalescence. Our results suggest that the current experimental measurement at LHC cannot exclude the existence of the $\Lambda \Lambda$ as an exotic six-quark state, and if $\Lambda \Lambda$ is a six-quark state, it is then on the brink of being discovered.

    ↳ nucl-thhep-phnucl-exPRC(2016)·14 citations
20. 20*

    Complex heavy-quark potential and Debye mass in a gluonic medium from lattice QCD

    Yannis Burnier🇨🇭 · Alexander Rothkopf🇩🇪

    We improve and extend our study of the complex in-medium heavy quark potential and its Debye mass $m_D$ in a gluonic medium with a finer scan around the deconfinement transition and newly generated ensembles closer to the thermodynamic limit. On the lattices with larger physical volume, Re[V] shows signs of screening, i.e. a finite $m_D$, only in the deconfined phase, reminiscent of a genuine phase transition. Consistently Im[V] exhibits nonzero values also only above $T_C$. We compare the behavior of Re[V] with the color singlet free-energies that have been used historically to extract the Debye mass. An effective coupling constant is computed to assess the residual influence of the confining part of the potential at $T>0$. Our previous finding of a gradual screening of Re[V] around $T_C$ on finer lattices is critically reassessed and interpreted to originate from finite volume artifacts that affect the deployed $\beta =7$, ${\xi }_b=3.5$ parameter set at $N_s=32$.

    ↳ hep-lathep-phnucl-thPRD(2017)·57 citations
21. 21*

    Chiral symmetry restoration in heavy-ion collisions at intermediate energies

    A. Palmese🇩🇪 · W. Cassing🇩🇪 · E. Seifert🇩🇪 · T. Steinert🇩🇪 · P. Moreau🇩🇪 · E. L. Bratkovskaya🇩🇪

    We study the effect of the chiral symmetry restoration (CSR) on heavy-ion collisions observables in the energy range $\sqrt{s_{NN}}$=3-20 GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach. The PHSD includes the deconfinement phase transition as well as essential aspects of CSR in the dense and hot hadronic medium, which are incorporated in the Schwinger mechanism for the hadronic particle production. We adopt different parametrizations of the nuclear equation of state from the non-linear $\sigma -\omega$ model, which enter in the computation of the quark scalar density for the CSR mechanism, in order to estimate the uncertainty in our calculations.

    ↳ nucl-thhep-phPRC(2016)·86 citations
22. 22*

    Multi-Skyrmions with orientational moduli

    Fabrizio Canfora🇨🇱 · Gianni Tallarita🇨🇱

    We analyze the mechanism of condensation of orientational moduli (as introduced in [25]) on multi-Skyrmionic configurations of the four-dimensional Skyrme model. The present analysis reveals interesting novel features. First of all, the orientational moduli tend to decrease the repulsive interactions between Skyrmions, the effect decreasing with the increase of the Baryon number. Moreover, in the case of a single Skyrmion, the appearance of moduli is energetically favorable if finite volume effects are present. Otherwise, in the usual flat topologically trivial case, it is not. In the low energy theory these solutions can be interpreted as Skyrmions with additional isospin degrees of freedom.

    ↳ hep-thhep-phnucl-thPRD(2016)·20 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.