Thu·Feb 11, 2016Thursday·February 11, 2016

1. 01*

   Constraints on large-$x$ parton distributions from new weak boson production and deep-inelastic scattering data

   A. Accardi🇺🇸 · L. T. Brady🇺🇸 · W. Melnitchouk🇺🇸 · J. F. Owens🇺🇸 · N. Sato🇺🇸

   We present a new set of leading twist parton distribution functions, referred to as "CJ15", which take advantage of developments in the theoretical treatment of nuclear corrections as well as new data. The analysis includes for the first time data on the free neutron structure function from Jefferson Lab, and new high-precision charged lepton and W-boson asymmetry data from Fermilab. These significantly reduce the uncertainty on the d/u ratio at large values of x and provide new insights into the partonic structure of bound nucleons.

   hep-phnucl-thPRD(2016)·375 citations
2. 02*

   BCJ Identities and $d$-Dimensional Generalized Unitarity

   Amedeo Primo🇮🇹 · William J. Torres Bobadilla🇮🇹

   We present a set of relations between one-loop integral coefficients for dimensionally regulated QCD amplitudes. Within dimensional regularization, the combined use of color-kinematics duality and integrand reduction yields the existence of relations between the integrand residues of partial amplitudes with different orderings of the external particles. These relations can be established for the cut-constructible contributions as well for the ones responsible for rational terms. Starting from the general parametrization of one-loop residues and applying Laurent expansion in order to extract the coefficients of the amplitude decomposition in terms of master integrals, we show that the full set of relations can be obtained by considering BCJ identities between d-dimensional tree-levels. We provide explicit examples for multi-gluon scattering amplitudes at one-loop.

   hep-phhep-thJHEP(2016)·28 citations
3. 03*

   Small neutrino masses from gravitational $\theta$-term

   Gia Dvali🇩🇪 · Lena Funcke🇩🇪

   We present how a neutrino condensate and small neutrino masses emerge from a topological formulation of gravitational anomaly. We first recapitulate how a gravitational $\theta$-term leads to the emergence of a new bound neutrino state analogous to the ${\eta }^{\prime }$ meson of QCD. Then we show the consequent formation of a neutrino vacuum condensate, which effectively generates small neutrino masses. Afterwards we outline several phenomenological consequences of our neutrino mass generation model. The cosmological neutrino mass bound vanishes since we predict the neutrinos to be massless until the phase transition in the late Universe, $T\sim \mathrm{meV}$. Deviations from an equal flavor rate due to enhanced neutrino decays in extraterrestrial neutrino fluxes can be observed in future IceCube data. The current cosmological neutrino background only consists of the lightest neutrinos, which, due to enhanced neutrino-neutrino interactions, either bind up, form a superfluid, or completely annihilate into massless bosons. Strongly coupled relic neutrinos could provide a contribution to cold dark matter in the late Universe, together with the new proposed particles and topological defects, which may have formed during neutrino condensation. These enhanced interactions could also be a source of relic neutrino clustering in our Galaxy, which possibly makes the overdense cosmic neutrino background detectable in the KATRIN experiment. The neutrino condensate provides a mass for the hypothetical $B-L$ gauge boson, leading to a gravity-competing force detectable in short-distance measurements. Gravitational waves detections have the potential to probe our neutrino mass generation mechanism.

   hep-phastro-ph.COgr-qchep-thPRD(2016)·140 citations
4. 04*

   Rare Top Decays in Minimal and Non-minimal Universal Extra Dimension

   Ujjal Kumar Dey🇮🇳 · Tapoja Jha🇮🇳

   The flavour changing decays of the top quark are severely suppressed in the Standard Model by virtue of the Glashow-Iliopoulos-Maiani mechanism. Many beyond Standard Model extensions predict the decay rates at a level that is observable in the LHC. We perform a complete one-loop calculation of the flavour changing top quark decays $t\to c\gamma$ and $t\to ch$ in the universal extra dimensional model. Apart from considering the decay rates in the minimal version of the model, we also calculate the rates in the non-minimal scenario where the presence of boundary localised terms interestingly modify the set-up. We find that the decay rates in the minimal variant of the model do not change much from their Standard Model values. In the non-minimal version of this model, these decay rates can be higher for specific choices of the boundary localised parameters for a certain range of inverse compactification radius. But these model parameters lead to Kaluza-Klein particle masses that are in tension with various searches at the LHC.

   hep-phPRD(2016)·38 citations
5. 05*

   Gravitational effects on the Higgs field within the Solar System

   Franco D. Albareti🇪🇸 · Antonio L. Maroto🇪🇸 · Francisco Prada🇪🇸

   The Higgs mechanism predicts, apart from the existence of a new scalar boson, the presence of a constant Higgs field that permeates all of space. The vacuum expectation value (VEV) of this field is affected by quantum corrections which are mainly generated by the self-interactions and couplings of the Higgs field to gauge bosons and heavy quarks. In this work we show that gravity can affect, in a non-trivial way, these quantum corrections through the finite parts of the one-loop contributions to the effective potential. In particular, we consider the corrections generated by the Standard Model Higgs self-interactions in slowly-varying weak gravitational backgrounds. The obtained results amount to the existence of non-negligible inhomogeneities in the Higgs VEV. Such inhomogeneities translate into spatial variations of the particle masses, and in particular of the proton-to-electron mass ratio. We find that these Higgs perturbations in our Solar System are controlled by the Eddington parameter, and are absent in pure General Relativity. Yet, they may be present in modified gravity theories. This predicted effect may be constrained by atomic clocks or high-resolution spectroscopic measurements, which could allow to improve current limits on modifications of Einstein's gravity.

   hep-phastro-ph.COgr-qc0 citations
6. 06*

   A 750 GeV Diphoton Signal from a Very Light Pseudoscalar in the NMSSM

   Ulrich Ellwanger🇫🇷 · Cyril Hugonie🇫🇷

   The excess of events in the diphoton final state near 750 GeV observed by ATLAS and CMS can be explained within the NMSSM near the R-symmetry limit. Both scalars beyond the Standard Model Higgs boson have masses near 750 GeV, mix strongly, and share sizeable production cross sections in association with b-quarks as well as branching fractions into a pair of very light pseudoscalars. Pseudoscalars with a mass of ~ 210 MeV decay into collimated diphotons, whereas pseudoscalars with a mass of ~ 500-550 MeV can decay either into collimated diphotons or into three pi^0 resulting in collimated photon jets. Various such scenarios are discussed; the dominant constraints on the latter scenario originate from bounds on radiative Upsilon decays, but they allow for a signal cross section up to 6.7 fb times the acceptance for collimated multiphotons to pass as a single photon.

   hep-phJHEP(2016)·58 citations
7. 07*

   Long-range contributions to double beta decay revisited

   J.C. Helo🇨🇱 · M. Hirsch🇪🇸 · T. Ota🇯🇵

   We discuss the systematic decomposition of all dimension-7 (d=7) lepton number violating operators. These d=7 operators produce momentum enhanced contributions to the long-range part of the neutrinoless double beta decay amplitude and thus are severely constrained by existing half-live limits. In our list of possible models one can find contributions to the long-range amplitude discussed previously in the literature, such as the left-right symmetric model or scalar leptoquarks, as well as some new models not considered before. The d=7 operators generate Majorana neutrino mass terms either at tree-level, 1-loop or 2-loop level. We systematically compare constraints derived from the mass mechanism to those derived from the long-range double beta decay amplitude and classify our list of models accordingly. We also study one particular example decomposition, which produces neutrino masses at 2-loop level, can fit oscillation data and yields a large contribution to the long-range double beta decay amplitude, in some detail.

   hep-phJHEP(2016)·22 citations
8. 08*

   Multi-particle correlations in transverse momenta from statistical clusters

   Andrzej Bialas🇵🇱 · Adam Bzdak🇵🇱

   We evaluate $n$-particle ($n=2,3,4,5$) transverse momentum correlations for pions and kaons following from the decay of statistical clusters. These correlation functions could provide strong constraints on a possible existence of thermal clusters in the process of particle production.

   hep-phhep-exnucl-exPLB(2016)·0 citations
9. 09*

   On the precision of a data-driven estimate of hadronic light-by-light scattering in the muon g-2: pseudoscalar-pole contribution

   Andreas Nyffeler🇩🇪

   The evaluation of the numerically dominant pseudoscalar-pole contribution to hadronic light-by-light scattering in the muon g-2 involves the pseudoscalar-photon transition form factor F_{P gamma^* gamma^*}(-Q_1^2, -Q_2^2) with P = pi^0, eta, eta^\prime and, in general, two off-shell photons with spacelike momenta Q_{1,2}^2. We show, in a largely model-independent way, that for pi^0 (eta, eta^\prime) the region of photon momenta below about 1 (1.5) GeV gives the main contribution to hadronic light-by-light scattering. We then discuss how the precision of current and future measurements of the single- and double-virtual transition form factor in different momentum regions impacts the precision of a data-driven estimate of this contribution to hadronic light-by-light scattering. Based on Monte Carlo simulations for a planned first measurement of the double-virtual form factor at BESIII, we find that for the pi^0, eta, eta^\prime-pole contributions a precision of 14\%, 23\%, 15\% seems feasible. Further improvements can be expected from other experimental data and also from the use of dispersion relations for the different form factors themselves.

   hep-phPRD(2016)·123 citations
10. 10*

    Transverse-momentum resummation of colorless final states at the NNLL+NNLO

    Marius Wiesemann🇨🇭

    We present a general framework that allows to compute the resummed transverse-momentum distribution of a system of colorless particles. The implementation is fully differential in the degrees of freedom of the final-state system. As a first application, we consider the transverse-momentum spectrum of ZZ and WW boson pairs produced in hadron collisions, where we resum the logarithmically enhanced contributions due to multiple soft-gluon emission at small transverse momenta to all orders in perturbation theory. We exploit the most advanced perturbative information for the ZZ and WW production processes that is available at present by combining next-to-next-to-leading order QCD corrections with next-to-next-to-leading logarithmic resummation.

    hep-phPoS(2016)·4 citations
11. 11*

    Gluon TMDs in quarkonium production

    Andrea Signori (Vrije U., Amsterdam & NIKHEF, Amsterdam)🇳🇱

    I report on our investigations into the impact of (un)polarized transverse momentum dependent parton distribution functions (TMD PDFs or TMDs) for gluons at hadron colliders, especially at A Fixed Target Experiment at the LHC (AFTER@LHC). In the context of high energy proton-proton collisions, we look at final states with low mass (e.g. ${\eta }_b$) in order to investigate the nonperturbative part of TMD PDFs. We study the factorization theorem for the $q_T$ spectrum of ${\eta }_b$ produced in proton-proton collisions relying on the effective field theory approach, defining the tools to perform phenomenological investigations at next-to-next-to-leading log (NNLL) and next-to-leading order (NLO) accuracy in the perturbation theory. We provide predictions for the unpolarized cross section and comment on the possibility of extracting nonperturbative information about the gluon content of the proton once data at low transverse momentum are available.

    hep-phFew Body Syst.(2016)·20 citations
12. 12*

    Improved empirical parametrizations of the ${\gamma }^{\ast }N\to N(1535)$ transition amplitudes and the Siegert's theorem

    G. Ramalho🇧🇷

    Some empirical parametrizations of the ${\gamma }^{\ast }N\to N(1535)$ transition amplitudes violates the Siegert's theorem, that relates the longitudinal and the transverse amplitudes, in the pseudo-threshold limit (nucleon and resonance at rest). In the case of the electromagnetic transition from the nucleon (mass $M$) to the resonance $N(1525)$ (mass $M_R$), the Siegert's theorem is sometimes expressed by the relation $|\mathbf{q}|A_{1/2}=\lambda S_{1/2}$ in the pseudo-threshold limit, when the photon momentum $|\mathbf{q}|$ vanishes, and $\lambda =\sqrt{2}(M_R-M)$. In this article, we argue that the Siegert's theorem should be expressed by the relation $A_{1/2}=\lambda \frac{S_{1/2}}{|\mathbf{q}|}$, in the limit $|\mathbf{q}|\to 0$. This result is a consequence of the relation $S_{1/2}\propto |\mathbf{q}|$, when $|\mathbf{q}|\to 0$, as suggested by the analysis of the transition form factors and by the orthogonality between the nucleon and $N(1535)$ states. We propose then new empirical parametrizations for the ${\gamma }^{\ast }N\to N(1535)$ helicity amplitudes, that are consistent with the data and the Siegert's theorem. The proposed parametrization follow closely the MAID2007 parametrization, except for a small deviation in the amplitudes $A_{1/2}$ and $S_{1/2}$ when $Q^2<1.5$ GeV${}^2$.

    hep-phhep-exnucl-exnucl-thPLB(2016)·21 citations
13. 13*

    Progress in the calculation of nucleon transition form factors

    Gernot Eichmann🇩🇪

    We give a brief account of the Dyson-Schwinger and Faddeev-equation approach and its application to nucleon resonances and their transition form factors. We compare the three-body with the quark-diquark approach and present a quark-diquark calculation for the low-lying nucleon resonances including scalar, axialvector, pseudoscalar and vector diquarks. We also discuss the timelike structure of transition form factors and highlight the advantages of form factors over helicity amplitudes.

    hep-phnucl-thFew Body Syst.(2016)·14 citations
14. 14*

    A Lorentz Violating Theory: Its Nonminimal Extension in the Photon Sector

    Soner Albayrak🇹🇷

    The relentless efforts of the physics community has not yet availed us the solution of how to unify the Quantum Mechanics with General Relativity, a puzzle that has engaged the minds of the physicists for almost a century. The insufficiency of today's and foreseeable future's technology for a direct reach into the Planck energies at which the fundamental theory, the Quantum Theory of Gravity, lies has lead to the search of the low energy effects of that fundamental Planck level theory irregardless of the details of it. In this thesis, one of the leading candidates of such an exotic effect, that is the violation of Lorentz and CPT symmetries is analyzed. The action level effective field theoretical framework for such an analysis called Standard Model Extension has already been in the literature for the last two decades; here, the nonminimal photon sector of such a framework is examined from a quantum field theoretical point of view. All possible polarization vectors for different kinds of CPT violations, the generic forms of the dispersion relations that these polarization vectors satisfy, and the corresponding propagators of the photon field are explicitly calculated. Special models of Lorentz violations are introduced, and a particular one called vacuum orthogonal model is analyzed extensively. It is found that this particular form of Lorentz violation cannot induce any effects that is detectable in the vacuum propagation of the photon. Isotropic and leading order cases of the Lorentz violation is studied and this found result is explicitly shown.

    hep-phhep-th0 citations
15. 15*

    Fundamental Constants as Monitors of the Universe

    Rodger I. Thompson🇺🇸

    Astronomical observations have a unique ability to determine the laws of physics at distant times in the universe. They, therefore, have particular relevance in answering the basic question as to whether the laws of physics are invariant with time. The dimesionless fundamental constants, such as the proton to electron mass ratio and the fine structure constant are key elements in the investigation. If they vary with time then the answer is clearly that the laws of physics are not invariant with time and significant new physics must be developed to describe the universe. Limits on their variance, on the other hand, constrains the parameter space available to new physics that requires a variation with time of basic physical law. There are now observational constraints on the time variation of the proton to electron mass ratio mu at the 1.E-7 level. Constraints on the variation of the fine structure constant alpha are less rigorous, 1E-5, but are imposed at higher redshift. The implications of these limits on new cosmologies that require rolling scalar fields has already had its first investigations. Here we address the implications on basic particle physics. The proton to electron mass ratio is obviously dependent on the particle physics parameters that set the mass of the proton and the electron. To first order the ratio is dependent on a combination of the Quantum Chromodynamic scale, the Yukawa couplings, and the Higgs Vacuum Expectation Value. Here that relationship is quantitative defined for the first time. When coupled with previous determinations of the relation of the fine structure constant to the same parameters two constraints exist on the fractional variation of these parameters with time. A third independent constraint involving only the three parameters could set the stage for constraints on their individual fractional variation.

    ↳ astro-ph.COhep-ph2 citations
16. 16*

    WIMP detection and slow ion dynamics in carbon nanotube arrays

    G. Cavoto🇮🇹 · E.N.M. Cirillo🇮🇹 · F. Cocina🇮🇹 · J. Ferretti🇮🇹 · A.D. Polosa🇮🇹

    Large arrays of aligned carbon nanotubes (CNTs), open at one end, could be used as target material for the directional detection of weakly interacting dark matter particles (WIMPs). As a result of a WIMP elastic scattering on a CNT, a carbon ion might be injected in the body of the array and propagate through multiple collisions within the lattice. The ion may eventually emerge from the surface with open end CNTs, provided that its longitudinal momentum is large enough to compensate energy losses and its transverse momentum approaches the channeling conditions in a single CNT. Therefore, the angle formed between the WIMP wind apparent orientation and the direction of parallel carbon nanotube axes must be properly chosen. We focus on very low ion recoil kinetic energies, related to low mass WIMPs (~ 10 GeV) where most of the existing experiments have low sensitivity. Relying on some exact results on two-dimensional lattices of circular obstacles, we study the low energy ion motion in the transverse plane with respect to CNT directions. New constraints are obtained on how to devise the CNT arrays to maximize the detection efficiency.

    ↳ physics.ins-detastro-ph.IMhep-phEPJC(2016)·35 citations
17. 17*

    Can one measure the Cosmic Neutrino Background?

    Amand Faessler🇩🇪 · Rastislav Hodak🇨🇿 · Sergey Kovalenko🇨🇱 · Fedor Simkovic🇸🇰

    The Cosmic Microwave Background (CMB) yields information about our Universe at around 380 000 years after the Big Bang (BB). Due to the weak interaction of the neutrinos with matter the Cosmic Neutrino Background (CNB) should give information about a much earlier time of our Universe, around one second after the Big Bang. Probably the most promising method to `see' the Cosmic Neutrino Background is the capture of the electron neutrinos from the Background by Tritium, which then decays into 3He and an electron with the energy of the the Q-value = 18.562 keV plus the electron neutrino rest mass. The `KArlsruhe TRItium Neutrino' (KATRIN) experiment, which is in preparation, seems presently the most sensitive proposed method for measuring the electron antineutrino mass. At the same time KATRIN can also look by the reaction: electron neutrino (~1.95 Kelvin) + 3H --> 3He + e- (with the energy Q = 18.6 keV + electron neutrino mass). The capture of the Cosmic Background Neutrinos (CNB) should show in the electron spectrum as a peak by the electron neutrino rest mass above Q. Here the possibility to see the CNB with KATRIN is studied. A detection of the CNB by KATRIN seems not to be possible at the moment. But KATRIN should be able to determine an upper limit for the local electron neutrino density of the CNB.

    ↳ nucl-thhep-phphysics.ins-detIJMPE(2017)·24 citations
18. 18*

    Charm production in high multiplicity pp events

    K. Werner🇫🇷 · B. Guiot🇫🇷 · Iu. Karpenko🇺🇦 · T. Pierog🇩🇪 · G. Sophys🇫🇷

    Recent experimental studies of the multiplicity dependence of heavy quark (HQ) production in proton-proton collisions at 7 TeV showed a strong non-linear increase of the HQ multiplicity as a function of the charged particle multiplicity. We try to understand this behavior using the EPOS3 approach. Two issues play an important role: multiple scattering, in particular its impact on multiplicity fluctuations, and the collective hydrodynamic expansion. The results are very robust with respect to many details of the modeling, which means that these data contain valuable information about very basic features of the reaction mechanism in proton-proton collisions.

    ↳ nucl-thastro-ph.HEhep-ph8 citations
19. 19*

    Fate of the Tetraquark Candidate Zc(3900) from Lattice QCD

    Yoichi Ikeda (Nishina Ctr., RIKEN)🇯🇵 · Sinya Aoki (Kyoto U., YITP and Tsukuba U., CCS)🇯🇵 · Takumi Doi (Nishina Ctr., RIKEN)🇯🇵 · Shinya Gongyo (Kyoto U., YITP)🇯🇵 · Tetsuo Hatsuda (Nishina Ctr., RIKEN and Tokyo U., IPMU)🇯🇵 · Takashi Inoue (Nihon U.)🇯🇵 · Takumi Iritani (Stony Brook U.)🇺🇸 · Noriyoshi Ishii (Osaka U., RCNP)🇯🇵 · Keiko Murano (Osaka U., RCNP)🇯🇵 · Kenji Sasaki (Tsukuba U., CCS) (HAL QCD Collaboration)🇯🇵

    The possible exotic meson $Z_c(3900)$, found in $e^{+}{e}^{-}$ reactions, is studied by the method of coupled-channel scattering in lattice QCD. The interaction among $\pi J/\psi$, $\rho {\eta }_c$ and $\bar{D}{D}^{\ast }$ channels is derived from (2+1)-flavor QCD simulations at $m_{\pi }=410$-$700$ MeV. The interaction is dominated by the off-diagonal $\pi J/\psi$-$\bar{D}{D}^{\ast }$ and $\rho {\eta }_c$-$\bar{D}{D}^{\ast }$ couplings, which indicates that the $Z_c(3900)$ is not a usual resonance but a threshold cusp. Semi-phenomenological analyses with the coupled-channel interaction are presented to confirm this conclusion.

    ↳ hep-lathep-exhep-phnucl-thPRL(2016)·131 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.