Tue·Feb 23, 2016Tuesday·February 23, 2016

1. 01*

   String Consistency, Heavy Exotics, and the 750 GeV Diphoton Excess at the LHC: Addendum

   Mirjam Cvetic🇺🇸 · James Halverson🇺🇸 · Paul Langacker🇺🇸

   We study models with heavy exotics that account for the LHC $750$ GeV diphoton excess in light of current vector-like quark bounds. Utilizing only exotics that may appear in three-stack and four-stack D-brane models, we show that a narrow width diphoton excess can be accounted for while evading existing bounds if multiple exotics are added, with vector-like leptons of mass $M_L\lesssim 375$ GeV and vector-like quarks with masses up to $\simeq 3$ TeV. However, a large width $(\Gamma /M\sim 0.06)$, as suggested by the ATLAS data, cannot be easily accommodated in this framework. Renormalization group equations with GUT-scale boundary conditions show that these supersymmetric models are perturbative and stable. Type IIA compactifications on toroidal orbifolds allow for $O(10)$ Yukawa couplings in the ultraviolet.

   hep-ph22 citations
2. 02*

   Automation of NLO processes and decays and POWHEG matching in WHIZARD

   J. Reuter🇩🇪 · B. Chokoufe🇩🇪 · A. Hoang🇦🇹 · W. Kilian🇩🇪 · M. Stahlhofen🇩🇪 · T. Teubner🇬🇧 · C. Weiss🇩🇪

   We give a status report on the automation of next-to-leading order processes within the Monte Carlo event generator WHIZARD, using GoSam and OpenLoops as provider for one-loop matrix elements. To deal with divergences, WHIZARD uses automated FKS subtraction, and the phase space for singular regions is generated automatically. NLO examples for both scattering and decay processes with a focus on e+e- processes are shown. Also, first NLO-studies of observables for collisions of polarized leptons beams, e.g. at the ILC, will be presented. Furthermore, the automatic matching of the fixed-order NLO amplitudes with emissions from the parton shower within the POWHEG formalism inside WHIZARD will be discussed. We also present results for top pairs at threshold in lepton collisions, including matching between a resummed threshold calculation and fixed-order NLO. This allows the investigation of more exclusive differential observables.

   hep-phJ.Phys.Conf.Ser.(2016)·18 citations
3. 03*

   Solving the Strong CP Problem with High-Colour Quarks and Composite Axion

   Archil Kobakhidze🇦🇺

   I propose a new axionic solution to the strong CP problem which involves a hypothetical vector-like quark(s) in a high-colour representation of the conventional QCD. There are two distinct scenarios. If the current mass of the exotic quark is zero, the strong CP phase can be trivially rotated away. The high-colour quark is `hidden' in various bounds states, the lightest being the composite axion field, with properties similar to the standard invisible axion. If the high-colour quark acquire a non-zero current mass due to the spontaneous chiral symmetry breaking, the composite axion can be heavy, while the strong CP phase is still cancelling out in the vacuum. The phenomenology and cosmological implications of the heavy composite axion differs drastically from the standard invisible axion.

   hep-ph8 citations
4. 04*

   Excited State Mass spectra of Singly Charmed Baryons

   Zalak Shah🇮🇳 · Kaushal Thakkar🇮🇳 · Ajay Kumar Rai🇮🇳 · P. C. Vinodkumar🇮🇳

   Mass spectra of excited states of the singly charmed baryons are calculated using the hypercentral description of three body system. The baryon consist of a charm quark and light quarks (u, d and s) are studied in the framework of QCD motivated constituent quark model. The form of confinement potential is hyper coloumb plus power potential with potential index $\nu$, varying from 0.5 to 2.0. The first order correction to the confinement potential is also incorporated in this approach. The radial as well as orbital excited state masses of ${\Sigma }_c^{++},{\Sigma }_c^{+},{\Sigma }_c^0,{\Xi }_c^{+},{\Xi }_c^0,{\Lambda }_c^{+},{\Omega }_c^0$ baryons, are reported in this paper. We have incorporated spin-spin, spin-orbit and tensor interactions perturbatively in the present study. The semi-electronic decay of ${\Omega }_c$ and ${\Xi }_c$ are also calculated using the spectroscopic parameters of these baryons. The computed results are compared with other theoretical predictions as well as with the available experimental observations. We also construct the Regge trajectory in ($n_r$, $M^2$) and (J, $M^2$) plane for these baryons.

   hep-phEPJA(2016)·102 citations
5. 05*

   Perturbative Unitarity Bounds in Composite 2-Higgs Doublet Models

   Stefania De Curtis🇮🇹 · Stefano Moretti🇬🇧 · Kei Yagyu🇬🇧 · Emine Yildirim🇬🇧

   We study bounds from perturbative unitarity in a Composite 2-Higgs Doublet Model (C2HDM) based on the spontaneous breakdown of a global symmetry $SO(6)\to SO(4)\times SO(2)$ at the compositeness scale $f$. The eight pseudo Nambu-Goldstone Bosons (pNGBs) emerging from such a dynamics are identified as two isospin doublet Higgs fields. We calculate the $S$-wave amplitude for all possible 2-to-2-body elastic (pseudo)scalar boson scatterings at energy scales $\sqrt{s}$ reachable at the Large Hadron Collider (LHC) and beyond it, including the longitudinal components of weak gauge boson states as the corresponding pNGB states. In our calculation, the Higgs potential is assumed to have the same form as that in the Elementary 2-Higgs Doublet Model (E2HDM) with a discrete $Z_2$ symmetry, which is expected to be generated at the one-loop level via the Coleman-Weinberg (CW) mechanism. We find that the $S$-wave amplitude matrix can be block-diagonalized with maximally $2\times 2$ submatrices in a way similar to the E2HDM case as long as we only keep the contributions from $\mathcal{O}(\xi s)$ and $\mathcal{O}({\xi }^0{s}^0)$ in the amplitudes, where $\xi =v_{\text{SM}}^2/f^2$ and $v_{\text{SM}}^{}\simeq 246$ GeV, which is an appropriate approximation for our analysis. By requiring the C2HDM to satisfy perturbative unitarity at energies reachable by the LHC, we derive bounds on its parameters such as $\xi$ and the masses of extra Higgs bosons present in the scenario alongside the Standard Model (SM)-like Higgs state discovered in 2012.

   hep-phPRD(2016)·30 citations
6. 06*

   Inverse magnetic catalysis and confinement within a contact interaction model for quarks

   Aftab Ahmad🇲🇽 · Alfredo Raya🇲🇽

   We evaluate the impact of an external magnetic field on the chiral symmetry and confinement-deconfinement transition temperatures by using a vector-vector contact interaction model for quarks regularized so as to include an explicit confining scale in the corresponding gap equation. Exploring the evolution of the chiral condensate and the confining scale with temperature $T$ and magnetic field strength $eB$ ($e$ represents the fundamental electric charge), we determine the pseudo-critical temperatures for the chiral ($T_c^{\chi }$) and deconfinement ($T_c^c$) transitions from their inflection points, respectively. By construction, $T_c^{\chi }=T_c^c$ in the chiral limit. Within a mean field approximation, we observe the magnetic catalysis phenomenon, characterized by a rising behavior of $T_c^{\chi }$ and $T_c^c$ with growing $eB$. Considering a lattice inspired running coupling which monotonically decreases with $eB$, inverse magnetic catalysis takes place in our model. We explore the role of the magnetic field in the traits of the confinement-deconfinement transition described by the model. Our findings are also in agreement with predictions derived from effective models of strong interactions.

   hep-phJ.Phys.G(2016)·37 citations
7. 07*

   Probing the R-parity violating supersymmetric effects in the exclusive b\to c\ell^-\bar{\nu}_\ell decays

   Jie Zhu🇨🇳 · Hua-Min Gan🇨🇳 · Ru-Min Wang🇨🇳 · Ying-Ying Fan🇨🇳 · Qin Chang🇨🇳 · Yuan-Guo Xu🇨🇳

   Motivated by recent results from the LHCb, BABAR and Belle collaborations on B\to D^{(*)}\ell^-\bar{\nu}_\ell decays, which significantly deviate from the Standard Model and hint the possible new physics beyond the Standard Model, we probe the R-parity violating supersymmetric effects in B^-_c\to \ell^-\bar{\nu}_\ell and B\to D^{(*)}\ell^-\bar{\nu}_\ell decays. We find that (i) \mathcal{B}(B^-_c\to e^- \bar{\nu}_e) and \mathcal{B}(B^-_c\to\mu^-\bar{\nu}_\mu) are sensitive to the constrained slepton exchange couplings; (ii) the normalized forward-backward asymmetries of B\to De^-\bar{\nu}_{e} decays have been greatly affected by the constrained slepton exchange couplings, and their signs could be changed; (iii) all relevant observables in the exclusive b\to c\tau^-\bar{\nu}_\tau decays and the ratios \mathcal{R}(D^{(*)}) are sensitive to the slepton exchange coupling, \mathcal{R}(D^*) could be enhanced by the constrained slepton exchange coupling to reach each 95\% confidence level experimental range from BABAR, Belle and LHCb, but it could not reach the lower limit of the 95\% confidence level experimental average. Our results in this work could be used to probe R-parity violating effects, and will correlate with searches for direct supersymmetric signals at the running LHCb and the forthcoming Belle-II.

   hep-phPRD(2016)·49 citations
8. 08*

   Scalar model of SU(N) glueball à la Heisenberg

   Vladimir Dzhunushaliev🇰🇿 · Vladimir Folomeev🇰🇬

   Nonperturbative model of glueball is studied. The model is based on the nonperturbative quantization technique suggested by Heisenberg. 2- and 4-point Green functions for a gauge potential are expressed in terms of two scalar fields. The first scalar field describes quantum fluctuations of the subgroup $SU(n)\subset SU(N)$, and the second one describes quantum fluctuations of the coset $SU(N)/SU(n)$. An effective Lagrangian for the scalar fields is obtained. The coefficients for all terms in the Lagrangian are calculated, and it is shown that they depend on $\dim SU(n),\dim SU(N)$. It is demonstrated that a spherically symmetric solution describing the glueball does exist.

   hep-phhep-th0 citations
9. 09*

   Inverse Magnetic Catalysis in Nambu--Jona-Lasinio Model beyond Mean Field

   Shijun Mao🇨🇳

   We study inverse magnetic catalysis in the Nambu--Jona-Lasinio model beyond mean field approximation. The feed-down from mesons to quarks is embedded in an effective coupling constant at finite temperature and magnetic field. While the magnetic catalysis is still the dominant effect at low temperature, the meson dressed quark mass drops down with increasing magnetic field at high temperature due to the dimension reduction of the Goldstone mode in the Pauli-Villars regularization scheme.

   hep-phhep-thPLB(2016)·98 citations
10. 10*

    Size of Shell Universe in Light of Fermi GBM Transient Associated with GW150914

    Merab Gogberashvili🇬🇪 · Alexander Sakharov🇨🇭 · Edward Sarkisyan-Grinbaum🇨🇭

    The possible gamma ray burst occurred in location and temporal consistence with gravitational wave event GW150914, as reported by Fermi Gamma-ray Burst Monitor (GBM), offers a new way of constraining models with extra dimensions. Using the time delay in arrival of the gamma ray transient observed by Fermi GBM relative to the gravitational waves event triggered by the LIGO detectors we investigate the size of the spherical brane-universe expanding in multi-dimensional space-time. It is shown that a joint observation of gravitational waves in association with gamma ray burst can provide a very stringent bound on the spatial curvature of the brain.

    hep-phastro-ph.COgr-qchep-thPLB(2016)·3 citations
11. 11*

    Approximate degeneracy of heavy-light mesons with the same $L$

    Takayuki Matsuki🇯🇵 · Qi-Fang Lü🇨🇳 · Yubing Dong🇨🇳 · Toshiyuki Morii🇯🇵

    Careful observation of the experimental spectra of heavy-light mesons tells us that heavy-light mesons with the same angular momentum $L$ are almost degenerate. The estimate is given how much this degeneracy is broken in our relativistic potential model, and it is analytically shown that expectation values of a commutator between the lowest order Hamiltonian and ${\vec{L}}^2$ are of the order of $1/m_Q$ with a heavy quark mass $m_Q$. It turns out that nonrelativistic approximation of heavy quark system has a rotational symmetry and hence degeneracy among states with the same $L$. This feature can be tested by measuring higher orbitally and radially excited heavy-light meson spectra for $D/D_s/B/B_s$ in LHCb and forthcoming BelleII.

    hep-phhep-exnucl-thPLB(2016)·8 citations
12. 12*

    Rotating quark-gluon plasma in relativistic heavy ion collisions

    Yin Jiang🇺🇸 · Zi-Wei Lin🇺🇸 · Jinfeng Liao🇺🇸

    We study the rotational collective motion of the quark-gluon plasma in relativistic heavy ion collisions using the widely-adopted AMPT (A Multi-Phase Transport) model. The global angular momentum, the average vorticity carried by the quark-gluon plasma, and the locally defined vorticity fields are computed for Au+Au collisions, with detailed information of their time evolution, spatial distribution, as well as the dependence on beam energy and collision centrality.

    hep-phnucl-thPRC(2016)·321 citations
13. 13*

    Composite (pseudo) scalar contributions to muon g-2

    Deog Ki Hong🇰🇷 · Du Hwan Kim🇰🇷

    We have calculated the composite (pseudo) scalar contributions to the anomalous magnetic moment of muons in models of walking technicolor. By the axial or scale anomaly the light scalars such as techni-dilaton, techni-pions or techni-eta have anomalous couplings to two-photons, which make them natural candidates for the recent 750 GeV resonance excess, observed at LHC. Due to the anomalous couplings, their contributions to muon (g-2) are less suppressed and might explain the current deviation in muon (g-2) measurements from theory.

    hep-phPLB(2016)·15 citations
14. 14*

    Consequences of an Abelian $Z^{\prime }$ for neutrino oscillations and dark matter

    Ryan Plestid🇨🇦

    The Standard Model's accidental and anomaly-free currents: $B-L$, $L_e-L_{\mu }$, $L_e-L_{\tau }$, and $L_{\mu }-L_{\tau }$, could be indicative of a hidden gauge structure beyond the Standard Model. Additionally, neutrino masses can be generated by a dimension-5 operator that generically breaks all of these symmetries. It is therefore important to investigate the compatibility of a gauged $U^{\prime }(1)$ and neutrino phenomenology. We consider gauging each of the symmetries above with a minimal extended matter content. This includes the $Z^{\prime }$, an order parameter to break the $U^{\prime }(1)$, and three right-handed neutrinos. We find all but $B-L$ require additional matter content to explain the measured neutrino oscillation parameters. We also discuss the compatibility of the measured neutrino textures with a non-thermal dark matter production mechanism involving the decay of the $Z^{\prime }$. Finally, we present a parametric relation that implies that a sterile neutrino dark matter candidate should not be expected to contribute to neutrino masses beyond ten parts per million.

    hep-phastro-ph.COPRD(2016)·9 citations
15. 15*

    Dynamically Emergent Flavor in a Confining Theory with Unbroken Chiral Symmetry

    M. Shifman🇺🇸

    I discuss "truncated" QCD studied recently by Glozman et al. through numerical simulations. For two flavors it was observed that truncation restores the full chiral U(2)\times U(2) symmetry of the Lagrangian. Moreover, additional enhancement of the above symmetry connecting representations with distinct Lorentz spins was observed. I argue that the chiral symmetry restoration in a confining theory could entail emergent (extra) dynamical flavors which would show up in the spectrum of color-singlet particles provided their mass \neq 0. As an example, I consider truncated QCD with a single massless Dirac quark. Assuming the validity of the above observations,I demonstrate how a dynamical SU(2)_{fl} symmetry could emerge for massive spin-1 mesons without contradicting general principles.

    hep-phhep-thPRD(2016)·9 citations
16. 16*

    Low mass Drell-Yan production of lepton pairs at forward directions at the LHC: a hybrid approach

    Wolfgang Schäfer🇵🇱 · Antoni Szczurek🇵🇱

    We discuss Drell-Yan production of dileptons at high energies in forward rapidity region in a hybrid high-energy approach. This approach uses unintegrated gluon distributions in one proton and collinear quark/antiquark distributions in the second proton. Corresponding momentum-space formula for the differential cross sections in high-energy approximation has been derived and will be presented. The relation to the commonly used dipole approach is discussed. We conclude and illustrate that some results of the dipole approaches are too approximate, as far as kinematics is considered, and in fact cannot be used when comparing with real experimental data. We find that the dipole formula is valid only in very forward/backward rapidity regions ($|y|>$ 5) that cannot be studied experimentally in the moment. We performed calculations of some differential cross sections for low-mass dilepton production by the LHCb and ATLAS collaborations. In distinction to most of dipole approaches, we include all of the four Drell-Yan structure functions, although the impact of interference structure functions is rather small for the relevant experimental cuts. We find that both side contributions ($g+q/\bar{q}$ and $q/\bar{q}+g$) have to be included even for the LHCb rapidity coverage which is in contradiction with what is usually done in the dipole approach. We present results for different unintegrated gluon distributions from the literature (some of them include saturation effects). We see no clear hints of saturation even at small $M_{ll}$ when comparing with the LHCb data.

    hep-phPRD(2016)·23 citations
17. 17*

    Electromagnetic spectral properties and Debye screening of a strongly magnetized hot medium

    Aritra Bandyopadhyay🇮🇳 · Chowdhury Aminul Islam🇮🇳 · Munshi G. Mustafa🇮🇳

    We have evaluated the electromagnetic spectral function and its spectral properties by computing the one-loop photon polarization tensor in presence of magnetic field, particularly in a strong field approximation compared to the thermal scale. When the magnetic scale is higher than the thermal scale the lowest Landau level (LLL) becomes effectively (1+1) dimensional strongly correlated system that provides a kinematical threshold based on the mass scale. Beyond this threshold the photon strikes the LLL and the spectral strength starts with a high value due to the dimensional reduction and then falls off with increase of the photon energy due to LLL dynamics in a strong field approximation. This strongly enhances the dilepton rate over the thermal perturbative leading order (Born) rate at very low invariant mass. We have also investigated the electromagnetic screening by computing the Debye screening mass and it depends distinctively on three different scales (mass of the quasiquark, temperature and the magnetic field strength) of a hot magnetized system. The mass dependence of the Debye screening supports the occurrence of a magnetic catalysis effect in the strong field approximation.

    hep-phnucl-thPRD(2016)·102 citations
18. 18*

    On the hidden charm pentaquark-s in ${\Lambda }_b\to J/\psi K^{-}p$ decay

    L. Roca🇪🇸 · E. Oset🇪🇸

    In a previous work we presented a theoretical analysis of the ${\Lambda }_b\to J/\psi K^{-}p$ reaction from where a recent experiment by the LHCb collaboration at CERN claimed the existence of two hidden charm pentaquarks, $P_c(4380{)}^{+}$ and $P_c(4450{)}^{+}$. In that work we focused only on the $\Lambda (1405)$ and $P_c(4450{)}^{+}$ signals and discussed the possible explanation of this pentaquark state within the picture of a dynamical meson-baryon molecule made up mostly from ${\bar{D}}^{\ast }{\Sigma }_c$ and ${\bar{D}}^{\ast }{\Sigma }_c^{\ast }$ components. In the present work we improve upon the previous one by considering the total $K^{-}p$ and $J/\psi p$ data including all the relevant resonances contributing to the spectra, and discuss the possible nature of both $P_c(4380{)}^{+}$ and $P_c(4450{)}^{+}$. We also discuss several important topics, like the effect of the contact term in the reaction, the viability of reproducing the data without the $P_c(4380{)}^{+}$ and the possible quantum numbers assignment to these pentaquarks.

    hep-phEPJC(2016)·39 citations
19. 19*

    Four-jet production in single- and double-parton scattering within high-energy factorization

    Krzysztof Kutak🇵🇱 · Rafal Maciula🇵🇱 · Mirko Serino🇵🇱 · Antoni Szczurek🇵🇱 · Andreas van Hameren🇵🇱

    We perform a first study of 4-jet production in a complete high-energy factorization (HEF) framework. We include and discuss contributions from both single-parton scattering (SPS) and double-parton scattering (DPS). The calculations are performed for kinematical situations relevant for two experimental measurements (ATLAS and CMS) at the LHC. We compare our results to those reported by the ATLAS and CMS collaborations for different sets of kinematical cuts. The results of the HEF approach are compared with their counterparts for collinear factorization. For symmetric cuts the DPS HEF result is considerably smaller than the one obtained with collinear factorization. The mechanism leading to this difference is of kinematical nature. We conclude that an analysis of inclusive 4-jet production with asymmetric $p_T$-cuts below 50 GeV would be useful to enhance the DPS contribution relative to the SPS contribution. In contrast to the collinear approach, the HEF approach nicely describes the distribution of the $\Delta S$ variable, which involves all four jets and their angular correlations.

    hep-phhep-exJHEP(2016)·63 citations
20. 20*

    Electromagnetic instability induced by neutrino interaction

    Jitesh R. Bhatt🇮🇳 · Manu George🇮🇳

    We consider the generation and evolution of magnetic field in a primordial plasma at temperature T < 1 MeV in presence of asymmetric neutrino background i.e. the number densities of right- handed and left-handed neutrinos are not same. Semi-classical equations of motion of a charged fermion are derived using the effective low-energy Lagrangian. It is shown that the spin degree of freedom of the charged fermion couples with the neutrino background. Using this kinetic equation we study the collective modes of the plasma. We find that there exist an unstable mode. This instability is closely related with the instability induced by chiral-anomaly in high temperature T > 80 TeV plasma where right and left-handed electrons are out of equilibrium. We find that at the temperatures below the neutrino decoupling the instability can produce magnetic field of 10 Gauss in the Universe. We discuss cosmological implications of the results.

    hep-phInt.J.Mod.Phys.D(2016)·4 citations
21. 21*

    Induced Gravity II: Grand Unification

    Martin B Einhorn🇺🇸 · D R Timothy Jones🇺🇸

    As an illustration of a renormalizable, asymptotically-free model of induced gravity, we consider an $SO(10)$ gauge theory interacting with a real scalar multiplet in the adjoint representation. We show that dimensional transmutation can occur, spontaneously breaking $SO(10)$ to $SU(5)\otimes U(1),$ while inducing the Planck mass and a positive cosmological constant, all proportional to the same scale $v$. All mass ratios are functions of the values of coupling constants at that scale. Below this scale (at which the Big Bang may occur), the model takes the usual form of Einstein-Hilbert gravity in de Sitter space plus calculable corrections. We show that there exist regions of parameter space in which the breaking results in a local minimum of the effective action, and a {\bf positive} dilaton $(mass{)}^2$ from two-loop corrections associated with the conformal anomaly. Furthermore, unlike the singlet case we considered previously, some minima lie within the basin of attraction of the ultraviolet fixed point. Moreover, the asymptotic behavior of the coupling constants also lie within the range of convergence of the Euclidean path integral, so there is hope that there will be candidates for sensible vacua. Although open questions remain concerning unitarity of all such renormalizable models of gravity, it is not obvious that, in curved backgrounds such as those considered here, unitarity is violated. In any case, any violation that may remain will be suppressed by inverse powers of the reduced Planck mass.

    ↳ hep-thgr-qchep-phJHEP(2016)·34 citations
22. 22*

    Understanding the negative binomial multiplicity fluctuations in relativistic heavy ion collisions

    Hao-jie Xu🇨🇳

    By deriving a general expression for multiplicity distribution (a conditional probability distribution) in statistical model, we demonstrate the mismatches between experimental measurements and previous theoretical calculations on multiplicity fluctuations. From the corrected formula, we develop an improved baseline measure for multiplicity distribution under Poisson approximation in statistical model to replace the traditional Poisson expectations. We find that the ratio of the mean multiplicity to the corresponding reference multiplicity are crucial to systemically explaining the measured scale variances of total charge distributions in different experiments, as well as understanding the centrality resolution effect observed in experiment. The improved statistical expectations, albeit simple, work well in describing the negative binomial multiplicity distribution measured in experiments, e.g. the cumulants (cumulant products) of total (net) electric charge distributions.

    ↳ nucl-thhep-phnucl-ex6 citations
23. 23*

    Evaluation of the CHY Gauge Amplitude

    C.S. Lam🇨🇦 · York-Peng Yao🇺🇸

    The Cachazo-He-Yuan (CHY) formula for $n$-gluon scattering is known to give the same amplitude as the one obtained from Feynman diagrams, though the former contains neither vertices nor propagators explicitly. The equivalence was shown by indirect means, not by a direct evaluation of the $(n-3)$-dimensional integral in the CHY formula. The purpose of this paper is to discuss how such a direct evaluation can be carried out. There are two basic difficulties in the calculation: how to handle the large number of terms in the reduced Pfaffian, and how to carry out the integrations in the presence of a $\sigma$-dependence much more complicated than the Parke-Taylor form found in a CHY double-color scalar amplitude. We have solved both of these problems, and have formulated a method that can be applied to any $n$. Many examples are provided to illustrate these calculations.

    ↳ hep-thhep-phPRD(2016)·59 citations
24. 24*

    Search for a gamma-ray line feature from a group of nearby Galaxy clusters with Fermi LAT Pass 8 data

    Yun-Feng Liang🇨🇳 · Zhao-Qiang Shen🇨🇳 · Xiang Li🇨🇳 · Yi-Zhong Fan🇨🇳 · Xiaoyuan Huang🇩🇪 · Shi-Jun Lei🇨🇳 · Lei Feng🇨🇳 · En-Wei Liang🇨🇳 · Jin Chang🇨🇳

    Galaxy clusters are the largest gravitationally bound objects in the universe and may be suitable targets for indirect dark matter searches. With 85 months of Fermi-LAT Pass 8 publicly available data, we analyze the gamma-ray emission in the directions of 16 nearby Galaxy Clusters with an unbinned likelihood analysis. No globally statistically-significant $\gamma -$ray line feature is identified and a tentative line signal may be present at $\sim 43$ GeV. The 95\% confidence level upper limits on the velocity-averaged cross section of dark matter particles annihilating into double $\gamma -$rays (i.e., $⟨\sigma v{⟩}_{\chi \chi \to \gamma \gamma }$) are derived. Unless very optimistic boost factors of dark matter annihilation in these Galaxy Clusters have been assumed, such constraints are much weaker than the bounds set by the Galactic $\gamma -$ray data.

    ↳ astro-ph.HEastro-ph.COhep-phPRD(2016)·70 citations
25. 25*

    SU(2) Gauge Theory with Two Fundamental Flavours: a Minimal Template for Model Building

    Rudy Arthur🇩🇰 · Vincent Drach🇨🇭 · Martin Hansen🇩🇰 · Ari Hietanen🇩🇰 · Claudio Pica🇩🇰 · Francesco Sannino🇩🇰

    We investigate the continuum spectrum of the SU(2) gauge theory with $N_f=2$ flavours of fermions in the fundamental representation. This model provides a minimal template which is ideal for a wide class of Standard Model extensions featuring novel strong dynamics that range from composite (Goldstone) Higgs theories to several intriguing types of dark matter candidates, such as the SIMPs. We improve our previous lattice analysis [1] by adding more data at light quark masses, at two additional lattice spacings, by determining the lattice cutoff via a Wilson flow measure of the $w_0$ parameter, and by measuring the relevant renormalisation constants non-perturbatively in the RI'-MOM scheme. Our results for the lightest isovector states in the vector and axial channels, in units of the pseudoscalar decay constant, are $m_V/F_{\mathrm{PS}}\sim 13.1(2.2)$ and $m_A/F_{\mathrm{PS}}\sim 14.5(3.6)$ (combining statistical and systematic errors). In the context of the composite (Goldstone) Higgs models, our result for the spin-one resonances are $m_V>3.2(5)$ TeV and $m_A>3.6(9)$ TeV, which are above the current LHC constraints. In the context of dark matter models, for the SIMP case our results indicate the occurrence of a compressed spectrum at the required large dark pion mass, which implies the need to include the effects of spin-one resonances in phenomenological estimates.

    ↳ hep-lathep-phhep-thPRD(2016)·114 citations
26. 26*

    Constraints on $s-\bar{s}$ asymmetry of the proton in chiral effective theory

    X.G. Wang🇦🇺 · Chueng-Ryong Ji🇺🇸 · W. Melnitchouk🇺🇸 · Y. Salamu🇨🇳 · A.W. Thomas🇦🇺 · P. Wang🇨🇳

    We compute the $s-\bar{s}$ asymmetry in the proton in chiral effective theory, using phenomenological constraints based upon existing data. Unlike previous meson cloud model calculations, which accounted for kaon loop contributions with on-shell intermediate states alone, this work includes off-shell terms and contact interactions, which impact the shape of the $s-\bar{s}$ difference. We identify a valence-like component of $s(x)$ which is balanced by a $\delta$-function contribution to $\bar{s}(x)$ at $x=0$, so that the integrals of $s$ and $\bar{s}$ over the experimentally accessible region $x>0$ are not equal. Using a regularization procedure that preserves chiral symmetry and Lorentz invariance, we find that existing data limit the integrated value of the second moment of the asymmetry to the range $-0.07\times 10^{-3}\le ⟨x(s-\bar{s})⟩\le 1.12\times 10^{-3}$ at a scale of $Q^2=1$GeV${}^2$. This is too small to account for the NuTeV anomaly and of the wrong sign to enhance it.

    ↳ nucl-thhep-lathep-phPLB(2016)·27 citations
27. 27*

    Examining nuclear effects in neutrino interactions with transverse kinematic imbalance

    Luke Pickering🇬🇧

    We present a Monte Carlo truth study examining nuclear effects in charged-current neutrino interactions using observables constructed in the transverse plane. Three distributions are introduced that show very weak dependence on neutrino flux and its associated uncertainty. Measurements comparing these distributions between quasi-elastic-like and single charged pion final states will provide new constraints of nuclear effects. It is suggested that the on-axis position in the NuMI beam provides the correct flux to take advantage of this reduced energy dependence in measuring nuclear effect-generated transverse imbalances.

    ↳ hep-exhep-phnucl-thJPS Conf.Proc.(2016)·10 citations
28. 28*

    Excited hadrons and the analytical structure of bound-state interaction kernels

    Bruno El-Bennich🇧🇷 · Gastão Krein🇧🇷 · Eduardo Rojas🇨🇴 · Fernando E. Serna🇧🇷

    We highlight Hermiticity issues in bound-state equations whose kernels are subject to a highly asymmetric mass and momentum distribution and whose eigenvalue spectrum becomes complex for radially excited states. We trace back the presence of imaginary components in the eigenvalues and wave functions to truncation artifacts and suggest how they can be eliminated in the case of charmed mesons. The solutions of the gap equation in the complex plane, which play a crucial role in the analytic structure of the Bethe-Salpeter kernel, are discussed for several interaction models and qualitatively and quantitatively compared to analytic continuations by means of complex-conjugate pole models fitted to real solutions.

    ↳ nucl-thhep-lathep-phnucl-exFew Body Syst.(2016)·37 citations
29. 29*

    Hidden in the background: a local approach to CMB anomalies

    Juan C. Bueno Sanchez🇨🇴

    We investigate a framework aiming to provide a common origin for the large-angle anomalies detected in the Cosmic Microwave Background (CMB), which are hypothesized as the result of the statistical inhomogeneity developed by different isocurvature fields of mass $m\sim H$ present during inflation. The inhomogeneity arises as the combined effect of $(i)$ the initial conditions for isocurvature fields (obtained after a fast-roll stage finishing many $e$-foldings before cosmological scales exit the horizon), $(ii)$ their inflationary fluctuations and $(iii)$ their coupling to other degrees of freedom. Our case of interest is when these fields (interpreted as the precursors of large-angle anomalies) leave an observable imprint only in isolated patches of the Universe. When the latter intersect the last scattering surface, such imprints arise in the CMB. Nevertheless, due to their statistically inhomogeneous nature, these imprints are difficult to detect, for they become hidden in the background similarly to the Cold Spot. We then compute the probability that a single isocurvature field becomes inhomogeneous at the end of inflation and find that, if the appropriate conditions are given (which depend exclusively on the preexisting fast-roll stage), this probability is at the percent level. Finally, we discuss several mechanisms (including the curvaton and the inhomogeneous reheating) to investigate whether an initial statistically inhomogeneous isocurvature field fluctuation might give rise to some of the observed anomalies. In particular, we focus on the Cold Spot, the power deficit at low multipoles and the breaking of statistical isotropy.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2016)·6 citations
30. 30*

    Time Reversal Invariance Violating and Parity Conserving effects in Proton Deuteron Scattering

    Young-Ho Song🇰🇷 · Rimantas Lazauskas🇫🇷 · Vladimir Gudkov🇺🇸

    Time reversal invariance violating parity conserving (TVPC) effects are calculated for elastic proton deuteron scattering with proton energies up to $2$MeV. Distorted Wave Born Approximation is employed to estimate TVPC matrix elements, based on hadronic wave functions, obtained by solving three-body Faddeev-Merkuriev equations in configuration space with realistic potentials.

    ↳ nucl-thhep-phPRC(2016)·2 citations
31. 31*

    Physics case for a polarised target for AFTER@LHC

    J.P. Lansberg · M. Anselmino · R. Arnaldi · S.J. Brodsky · V. Chambert · J.P. Didelez · M.G Echevarria · E.G. Ferreiro · F. Fleuret · Y. Gao · B. Genolini · C. Hadjidakis and 18 other authors

    We review a number of ideas put forward in favour of the use of a polarised target along with the proposed idea of a fixed-target experiment using the LHC beams -- AFTER@LHC. A number of recent studies have shown that single transverse-spin asymmetries (STSAs) are large enough to be precisely measured in the region accessible with AFTER@LHC, in particular as regards the Drell-Yan process as well as single-pion, isolated-photon and jet production. AFTER@LHC with a polarised target would also be the ideal experimental set-up to measure the gluon Sivers effect via a number of original quarkonium STSA studies. We discuss first figures-of-merit based on simulations for AFTER@LHC with a polarised target.

    ↳ nucl-exhep-exhep-phnucl-thPoS(2016)·18 citations
32. 32*

    The infinite turn and speculative explanations in cosmology

    Reza Tavakol (QMUL)🇬🇧 · Fabio Gironi (UCD)🇮🇪

    Infinity, in various guises, has been invoked recently in order to `explain' a number of important questions regarding observable phenomena in science, and in particular in cosmology. Such explanations are by their nature speculative. Here we introduce the notions of relative infinity, closure, and economy of explanation and ask: to what extent explanations involving relative or real constructed infinities can be treated as reasonable?

    ↳ physics.hist-phastro-ph.COgr-qchep-ph0 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.