Fri·Jun 9, 2017Friday·June 9, 2017

1. 01*

   Initial state qqg correlations as a background for the Chiral Magnetic Effect in collision of small systems

   Alex Kovner🇺🇸 · Michael Lublinsky🇮🇱 · Vladimir Skokov🇺🇸

   Motivated by understanding the background to Chiral Magnetic Effect in proton-nucleus collisions from first principles, we compute the three particle correlation in the projectile wave function. We extract the correlations between two quarks and one gluon in the framework of the Color Glass Condensate. This is related to the same-charge correlation of the conventional observable for the Chiral Magnetic Effect. We show that there are two different contributions to this correlation function. One contribution is rapidity-independent and as such can be identified with the pedestal; while the other displays rather strong rapidity dependence. The pedestal contribution and the rapidity-dependent contribution at large rapidity separation between the two quarks result in the negative same charge correlations, while at small rapidity separation the second contribution changes sign. We argue that the computed initial state correlations might be partially responsible for the experimentally observed signal in proton-nucleus collisions.

   hep-phPRD(2017)·9 citations
2. 02*

   The Semi-Hooperon: Gamma-ray and anti-proton excesses in the Galactic Center

   Giorgio Arcadi🇩🇪 · Farinaldo S. Queiroz🇩🇪 · Clarissa Siqueira🇩🇪

   A puzzling excess in gamma-rays at GeV energies has been observed in the center of our galaxy using Fermi-LAT data. Its origin is still unknown, but it is well fitted by Weakly Interacting Massive Particles (WIMPs) annihilations into quarks with a cross section around $10^{-26}\mathrm{c}{\mathrm{m}}^3{\mathrm{s}}^{-1}$ with masses of $20-50$~GeV, scenario which is promptly revisited. An excess favoring similar WIMP properties has also been seen in anti-protons with AMS-02 data potentially coming from the Galactic Center as well. In this work, we explore the possibility of fitting these excesses in terms of semi-annihilating dark matter, dubbed as semi-Hooperon, with the process $\mathrm{WIMP}\mathrm{WIMP}\to \mathrm{WIMP}\mathrm{X}$ being responsible for the gamma-ray excess, where X=h,Z. An interesting feature of semi-annihilations is the change in the relic density prediction compared to the standard case, and the possibility to alleviate stringent limits stemming from direct detection searches. Moreover, we discuss which models might give rise to a successful semi-Hooperon setup in the context of ${\mathcal{Z}}_3$,${\mathcal{Z}}_4$ and extra "dark" gauge symmetries.

   hep-phPLB(2017)·37 citations
3. 03*

   Gravitational waves from non-Abelian gauge fields at a tachyonic transition

   Anders Tranberg🇳🇴 · Sara Tähtinen🇫🇮 · David J. Weir🇫🇮

   We compute the gravitational wave spectrum from a tachyonic preheating transition of a Standard Model-like SU(2)-Higgs system. Tachyonic preheating involves exponentially growing IR modes, at scales as large as the horizon. Such a transition at the electroweak scale could be detectable by LISA, if these non-perturbatively large modes translate into non-linear dynamics sourcing gravitational waves. Through large-scale numerical simulations, we find that the spectrum of gravitational waves does not exhibit such IR features. Instead, we find two peaks corresponding to the Higgs and gauge field mass, respectively. We find that the gravitational wave production is reduced when adding non-Abelian gauge fields to a scalar-only theory, but increases when adding Abelian gauge fields. In particular, gauge fields suppress the gravitational wave spectrum in the IR. A tachyonic transition in the early Universe will therefore not be detectable by LISA, even if it involves non-Abelian gauge fields.

   hep-phhep-latJCAP(2018)·31 citations
4. 04*

   Neutrinoless double beta decay in minimal left-right symmetric model with universal seesaw

   Debasish Borah🇮🇳 · Arnab Dasgupta🇮🇳 · Sudhanwa Patra🇮🇳

   We present a detailed discussion on neutrinoless double beta decay $(0\nu \beta \beta )$ within left-right symmetric models based on the gauge symmetry of type $SU(2{)}_L\times SU(2{)}_R\times U(1{)}_{B-L}$ as well as $SU(3{)}_L\times SU(3{)}_R\times U(1{)}_X$ where fermion masses including that of neutrinos are generated through a universal seesaw mechanism. We find that one or more of the right-handed neutrinos could be as light as a few keV if left-right symmetry breaking occurs in the range of a few TeV to 100 TeV. With such light right-handed neutrinos, we perform a detailed study of new physics contributions to $0\nu \beta \beta$ and constrain the model parameters from the latest experimental bound on such a rare decay process. We find that the new physics contribution to $0\nu \beta \beta$ in such a scenario, particularly the heavy-light neutrino mixing diagrams, can individually saturate the existing experimental bounds, but their contributions to total $0\nu \beta \beta$ half-life cancels each other due to unitarity of the total $6\times 6$ mass matrix. The effective contribution to half-life therefore, arises from the purely left and purely right neutrino and gauge boson mediated diagrams. We find that the parameter space saturating the $0\nu \beta \beta$ bounds remain allowed from the latest experimental bounds on charged lepton flavour violating decays like $\mu \to e\gamma$. We finally include the bounds from cosmology and supernova to constrain the parameter space of the model.

   hep-phInt.J.Mod.Phys.A(2018)·10 citations
5. 05*

   Pentaquarks in semileptonic ${\Lambda }_b$ decays

   Ping Zhou🇨🇳 · Y.K. Hsiao🇨🇳 · C.Q. Geng🇨🇳

   In terms of ${\mathcal{P}}_{c1,c2}={\mathcal{P}}_c(4380,4450{)}^{+}$ as the hidden charm pentaquark states to consist of $c\bar{c}uud$, we study the semileptonic ${\Lambda }_b\to ({\mathcal{P}}_{c1,c2}\to )J/\psi p{\ell }^{-}{\bar{\nu }}_{\ell }$ decays. In our discussion, while the main contribution to ${\Lambda }_b\to K^{-}J/\psi p$ is from the non-perturbative process via the doubly charmful $b\to c\bar{c}s$ transition, we propose that the ${\Lambda }_b\to {\mathcal{P}}_{c1,c2}\to J/\psi p$ transitions are partly contribute to the ${\Lambda }_b\to K^{-}({\mathcal{P}}_{c1,c2}\to )J/\psi p$ decays, in which the required $c\bar{c}$ pair is formed by the sea quarks, intrinsic charm, or both. We predict that $\mathcal{B}({\Lambda }_b\to J/\psi p{\ell }^{-}{\bar{\nu }}_{\ell })=(2.04_{-1.57}^{+4.82},1.75_{-1.35}^{+4.14})\times 10^{-6}$ for $\ell =(e,\mu )$, which are about two orders of magnitude smaller than the observed decay of ${\Lambda }_b\to p\mu {\bar{\nu }}_{\mu }$. We also explore the angular correlations for the $J/\psi p$ and ${\ell }^{-}{\bar{\nu }}_{\ell }$ pairs. Our results of the decay branching ratios and angular asymmetries in ${\Lambda }_b\to J/\psi p{\ell }^{-}{\bar{\nu }}_{\ell }$, accessible to the ongoing experiments at the LHCb, can be used to improve the understanding of the hidden charm pentaquark states.

   hep-phhep-exAnnals Phys.(2017)·5 citations
6. 06*

   On neutrino production of a charmed meson

   J. Wagner🇵🇱 · B. Pire🇫🇷 · L. Szymanowski🇵🇱

   We calculate in the framework of the collinear QCD approach the amplitude for exclusive neutrino-production of a pseudoscalar charmed $D$ meson. This process allows to access gluon and both chiral-odd and chiral-even quark generalized parton distributions (GPDs), which contribute in specific ways to the amplitude for different polarization states of the $W$ boson. The energy dependence of the cross section allows to separate different contributions and the measurement of the azimuthal dependence helps to single out the transversity chiral-odd GPDs contributions. The flavor dependence, and in particular the difference between $D^{+}$ and $D^0$ production rates, allows to test the importance of gluonic contributions. The behaviour of the proton and neutron target cross sections enables to separate the $u$ and $d$ quark contributions. Planned medium and high energy neutrino facilities will thus allow some important progress in the realm of hadronic physics.

   hep-phhep-exnucl-exnucl-thPoS(2018)·1 citation
7. 07*

   A necessary condition for sphaleron process in the presence of anomalous $U(1)$ symmetry

   Y. H. Ahn🇰🇷

   We argue that, in the presence of anomalous $U(1)$ symmetries, the invariance of Lagrangian including the standard model (SM) under the axionic shift symmetries requires a necessary condition ${\sum }_i{\delta }_i^{\mathrm{GS}}\le 2N_f$, where $N_f$ stands for the number of families in the SM and ${\delta }_i^{\mathrm{GS}}$ (Green-Schwarz parameter) characterizes the coupling of the anomalous $U(1)$ gauge boson to the corresponding axion. In turn, we show that in order for the usual $B+L$ violating sphaleron process to be valid a necessary condition ${\sum }_i{\delta }_i^{\mathrm{GS}}<2N_f$ is required, where $B(L)$ stands for the baryon(lepton) number.

   hep-ph0 citations
8. 08*

   Exploring LHC Run 1 and 2 data using the Madala hypothesis

   Stefan von Buddenbrock🇿🇦

   The Standard Model (SM) Higgs boson, with its experimental discovery in 2012, has long been an interesting particle to study with the intention of exploring new physics ideas beyond the SM (BSM). Its properties are still not well understood, and there are several features in LHC Run 1 and Run 2 data which point at the possibility of extensions to the SM Higgs sector. This work explores the Madala hypothesis, which is the introduction of a heavy scalar (the Madala boson) to the SM, in addition to a real scalar $S$ and dark matter (DM) candidate $\chi$. This hypothesis has previously been used to explain several anomalous features observe in the LHC Run 1 data. This work extends the study to Run 2 data, and shows that the particle spectrum predicted in the Madala hypothesis is indeed compatible with LHC data. Further study prospects and striking signatures for searches are presented.

   hep-phJ.Phys.Conf.Ser.(2017)·8 citations
9. 09*

   Sub-GeV Dark Matter Detection with Electron Recoils in Carbon Nanotubes

   G. Cavoto🇮🇹 · F. Luchetta🇮🇹 · A.D. Polosa🇮🇹

   Directional detection of Dark Matter particles (DM) in the MeV mass range could be accomplished by studying electron recoils in large arrays of parallel carbon nanotubes. In a scattering process with a lattice electron, a DM particle might transfer sufficient energy to eject it from the nanotube surface. An external electric field is added to drive the electron from the open ends of the array to the detection region. The anisotropic response of this detection scheme, as a function of the orientation of the target with respect to the DM wind, is calculated, and it is concluded that no direct measurement of the electron ejection angle is needed to explore significant regions of the light DM exclusion plot. A compact sensor, in which the cathode element is substituted with a dense array of parallel carbon nanotubes, could serve as the basic detection unit.

   hep-phphysics.ins-detPLB(2018)·99 citations
10. 10*

    Colorphilic Spin-2 Resonances in the LHC Dijet Channel

    R. Sekhar Chivukula🇺🇸 · Dennis Foren🇺🇸 · Elizabeth H. Simmons🇺🇸

    Experiments at the LHC may yet discover a dijet resonance indicative of Beyond the Standard Model (BSM) physics. In this case, the question becomes: what BSM theories are consistent with the unexpected resonance? One possibility would be a spin-2 object called the colorphilic graviton--a spin-2 color-singlet particle which couples exclusively to the quark and gluon stress-energy tensors. We assess the possibility of this state's discovery in the dijet channel as an s-channel resonance, and report the regions of parameter space where colorphilic gravitons have not yet been excluded by LHC-13 data but still may be discovered in the dijet channel at LHC-14 for integrated luminosities of 0.3, 1, and 3 ab${}^{-1}$. We then delineate which of those regions remain accessible to future collider searches, once one accounts for applicability of the narrow-width approximation, detector mass resolution, and self-consistency according to tree-level partial-wave unitarity. We discover that--despite the strong constraints unitarity imposes on collider searches--the colorphilic graviton remains potentially discoverable in the LHC dijet channel. A means of investigation would be to apply the color discriminant variable (CDV), a dimensionless combination of quantities (cross-section, decay width, and invariant mass) that can be quickly measured after the discovery of a dijet resonance. Previous publications have demonstrated the CDV's utility when applied to theories containing Z', colorons, excited quarks, and diquarks. We extend this analysis to the colorphilic graviton by applying the CDV to the appropriate region of parameter space. We conclude that resolvable, discoverable dijet resonances consistent with colorphilic gravitons span a narrower range of masses than those consistent with leptophobic Z' models, and can be distinguished from those originating from coloron, excited quark, and diquark models.

    hep-phhep-exPhys.Scripta(2018)·5 citations
11. 11*

    Revisiting Large Neutrino Magnetic Moments

    Manfred Lindner🇩🇪 · Branimir Radovčić🇩🇪 · Johannes Welter🇩🇪

    Current experimental sensitivity on neutrino magnetic moments is many orders of magnitude above the Standard Model prediction. A potential measurement of next-generation experiments would therefore strongly request new physics beyond the Standard Model. However, large neutrino magnetic moments generically tend to induce large corrections to the neutrino masses and lead to fine-tuning. We show that in a model where neutrino masses are proportional to neutrino magnetic moments. We revisit, discuss and propose mechanisms that still provide theoretical consistent explanations for a potential measurement of large neutrino magnetic moments. We find only two viable mechanisms to realize large transition magnetic moments for Majorana neutrinos only.

    hep-phhep-exJHEP(2017)·51 citations
12. 12*

    Heavy Baryon-Antibaryon Molecules in Effective Field Theory

    Jun-Xu Lu🇨🇳 · Li-Sheng Geng🇨🇳 · Manuel Pavon Valderrama🇨🇳

    We discuss the effective field theory description of bound states composed of a heavy baryon and antibaryon. This framework is a variation of the ones already developed for heavy meson-antimeson states to describe the $X(3872)$ or the $Z_c$ and $Z_b$ resonances. We consider the case of heavy baryons for which the light quark pair is in S-wave and we explore how heavy quark spin symmetry constrains the heavy baryon-antibaryon potential. The one pion exchange potential mediates the low energy dynamics of this system. We determine the relative importance of pion exchanges, in particular the tensor force. We find that in general pion exchanges are probably non-perturbative for the ${\Sigma }_Q{\bar{\Sigma }}_Q$, ${\Sigma }_Q^{\ast }{\bar{\Sigma }}_Q$ and ${\Sigma }_Q^{\ast }{\bar{\Sigma }}_Q^{\ast }$ systems, while for the ${\Xi }_Q^{\prime }{\bar{\Xi }}_Q^{\prime }$, ${\Xi }_Q^{\ast }{\bar{\Xi }}_Q^{\prime }$ and ${\Xi }_Q^{\ast }{\bar{\Xi }}_Q^{\ast }$ cases they are perturbative If we assume that the contact-range couplings of the effective field theory are saturated by the exchange of vector mesons, we can estimate for which quantum numbers it is more probable to find a heavy baryonium state. The most probable candidates to form bound states are the isoscalar ${\Lambda }_Q{\bar{\Lambda }}_Q$, ${\Sigma }_Q{\bar{\Sigma }}_Q$, ${\Sigma }_Q^{\ast }{\bar{\Sigma }}_Q$ and ${\Sigma }_Q^{\ast }{\bar{\Sigma }}_Q^{\ast }$ and the isovector ${\Lambda }_Q{\bar{\Sigma }}_Q$ and ${\Lambda }_Q{\bar{\Sigma }}_Q^{\ast }$ systems, both in the hidden-charm and hidden-bottom sectors. Their doubly-charmed and -bottom counterparts (${\Lambda }_Q{\Lambda }_Q$, ${\Lambda }_Q{\Sigma }_Q^{(\ast )}$, ${\Sigma }_Q^{(\ast )}{\Sigma }_Q^{(\ast )}$) are also good candidates for binding.

    hep-phhep-exhep-latnucl-thPRD(2019)·55 citations
13. 13*

    Charmonium resonances in the 3.9 GeV/$c^2$ energy region and the $X(3915)/X(3930)$ puzzle

    Pablo G. Ortega🇪🇸 · Jorge Segovia🇩🇪 · David R. Entem🇪🇸 · Francisco Fernández🇪🇸

    An interesting controversy has emerged challenging the widely accepted nature of the $X(3915)$ and the $X(3930)$ resonances, which had initially been assigned to the ${\chi }_{c0}(2P)$ and ${\chi }_{c2}(2P)$ $c\bar{c}$ states, respectively. To unveil their inner structure, the properties of the $J^{PC}=0^{++}$ and $J^{PC}=2^{++}$ charmonium states in the energy region of these resonances are analyzed in the framework of a constituent quark model. Together with the bare $q\bar{q}$ states, threshold effects due to the opening of nearby meson-meson channels are included in a coupled-channels scheme calculation. We find that the structure of both states is dominantly molecular with a probability of bare $q\bar{q}$ states lower than $45\%$. Our results favor the hypothesis that $X(3915)$ and $X(3930)$ resonances arise as different decay mechanisms of the same $J^{PC}=2^{++}$ state. Moreover we found an explanation for the recently discovered $M=3860$ MeV$/c^2$ as a $J^{PC}=0^{++}$ $2P$ state and rediscovery the lost $Y(3940)$ as an additional state in the $J^{PC}=0^{++}$ family.

    hep-phPLB(2018)·70 citations
14. 14*

    Holographic Entanglement Entropy in the QCD Phase Diagram with a Critical Point

    J. Knaute🇩🇪 · B. Kämpfer🇩🇪

    We calculate the holographic entanglement entropy for the holographic QCD phase diagram considered in [Knaute, Yaresko, Kämpfer (2017), arXiv:1702.06731] and explore the resulting qualitative behavior over the temperature-chemical potential plane. In agreement with the thermodynamic result, the phase diagram exhibits the same critical point as the onset of a first-order phase transition curve. We compare the phase diagram of the entanglement entropy to that of the thermodynamic entropy density and find a striking agreement in the vicinity of the critical point. Thus, the holographic entanglement entropy qualifies to characterize different phase structures. The scaling behavior near the critical point is analyzed through the calculation of critical exponents.

    hep-phhep-thPRD(2017)·38 citations
15. 15*

    Holographic description of $SO(5)\to SO(4)$ composite Higgs model

    D. Espriu🇪🇸 · A. Katanaeva🇪🇸

    We study a 5D bottom-up holographic model that is expected to describe the dynamics of the minimal composite Higgs model characterized by a $SO(5)\to SO(4)$ global symmetry breaking pattern. We assume that the fundamental degrees of freedom are scalars transforming under some representation of $SO(5)$ and subject to some unspecified strong interactions. The holographic description presented here is inspired by previous studies performed in the context of QCD and it allows for the consideration of spin one and spin zero resonances. The resulting spectrum leads in a natural way to a variety of resonances. Namely, those transforming under the unbroken $SO(4)$ subgroup exhibit an exact degeneracy between the two Regge trajectories of vector and scalar channels, while the resonances with quantum numbers in the $SO(5)/SO(4)$ coset lie on a trajectory of (heavier) spin one states and a non-degenerated one of scalar resonances where the four lowest lying ones are massless. These correspond to the four Goldstone bosons in 4D associated to the global symmetry breaking pattern. Restrictions derived from the experimental constraints (Higgs couplings, $S$ parameter, etc.) are then implemented and we conclude that the model is able to accommodate vector and scalar resonances with masses in the range 1 TeV to 2 TeV without encountering phenomenological difficulties. Extension to generic models characterized by the breaking pattern $SO(N)\to SO(N^{\prime }<N)$ is straightforward.

    hep-phhep-th7 citations
16. 16*

    Nuclear-bound quarkonia and heavy-flavor hadrons

    G. Krein🇧🇷 · A.W. Thomas🇦🇺 · K. Tsushima🇧🇷

    In our quest to win a deeper understanding of how QCD actually works, the study of the binding of heavy quarkonia and heavy-flavor hadrons to atomic nuclei offers enormous promise. Modern experimental facilities such as FAIR, Jefferson Lab at 12 GeV and J-PARC offer exciting new experimental opportunities to study such systems. These experimental advances are complemented by new theoretical approaches and predictions, which will both guide these experimental efforts and be informed and improved by them. This review will outline the main theoretical approaches, beginning with QCD itself, summarize recent theoretical predictions and relate them both to past experiments and those from which we may expect results in the near future.

    hep-phhep-exnucl-exnucl-thPPNP(2018)·126 citations
17. 17*

    $R_{K^{(\ast )}}$ and related $b\to s\ell \bar{\ell }$ anomalies in minimal flavor violation framework with $Z^{\prime }$ boson

    Cheng-Wei Chiang🇹🇼 · Xiao-Gang He🇨🇳 · Jusak Tandean🇹🇼 · Xing-Bo Yuan🇹🇼

    A recent LHCb measurement of the ratio $R_{K^{\ast }}$ of $B\to K^{\ast }\mu \bar{\mu }$ to $B\to K^{\ast }e\bar{e}$ branching fractions has produced results in mild tension with the standard model (SM). This adds to the known anomalies also induced by the $b\to s\ell \bar{\ell }$ transitions, resulting in a confidence level now as high as 4$\sigma$. We analyze whether the parameter space preferred by all the $b\to s\ell \bar{\ell }$ anomalies is compatible with a heavy $Z^{\prime }$ boson assumed to have nonuniversal couplings to SM fermions dictated by the principle of minimal flavor violation (MFV). We deal with the MFV couplings of the $Z^{\prime }$ to leptons in the context of the type-I seesaw scenario for generating neutrino masses. The flavor-violating $Z^{\prime }$ interactions are subject to stringent constraints from other processes, especially $B$-$\bar{B}$ mixing, charged lepton decays ${\ell }_i\to {\ell }_j{\ell }_k{\bar{\ell }}_l$ occurring at tree level, and the loop induced $\mu \to e\gamma$. We perform scans for parameter regions allowed by various data and predict the ranges for a number of observables. Some of the predictions, such as the branching fractions of lepton-flavor violating $\tau \to 3\mu$, $B\to Ke\mu$, $K_L\to e\mu$, and $Z\to \ell {\ell }^{\prime }$, are not far below their experimental bounds and therefore could be probed by searches in the near future. The viable parameter space depends strongly on the neutrino mass hierarchy, with a preference for the inverted one.

    hep-phhep-exPRD(2017)·73 citations
18. 18*

    Thermalizing sterile neutrino dark matter

    Rasmus S. L. Hansen🇩🇪 · Stefan Vogl🇩🇪

    Sterile neutrinos produced through oscillations are a well motivated dark matter candidate, but recent constraints from observations have ruled out most of the parameter space. We analyze the impact of new interactions on the evolution of keV sterile neutrino dark matter in the early Universe. Based on general considerations we find a mechanism which thermalizes the sterile neutrinos after an initial production by oscillations. The thermalization of sterile neutrinos is accompanied by dark entropy production which increases the yield of dark matter and leads to a lower characteristic momentum. This resolves the growing tensions with structure formation and X-ray observations and even revives simple non-resonant production as a viable way to produce sterile neutrino dark matter. We investigate the parameters required for the realization of the thermalization mechanism in a representative model and find that a simple estimate based on energy- and entropy conservation describes the mechanism well.

    hep-phastro-ph.COPRL(2017)·46 citations
19. 19*

    Multifield Stochastic Particle Production: Beyond a Maximum Entropy Ansatz

    Mustafa A. Amin🇺🇸 · Marcos A. G. Garcia🇺🇸 · Hong-Yi Xie🇺🇸 · Osmond Wen🇺🇸

    We explore non-adiabatic particle production for $N_{\mathrm{f}}$ coupled scalar fields in a time-dependent background with stochastically varying effective masses, cross-couplings and intervals between interactions. Under the assumption of weak scattering per interaction, we provide a framework for calculating the typical particle production rates after a large number of interactions. After setting up the framework, for analytic tractability, we consider interactions (effective masses and cross couplings) characterized by series of Dirac-delta functions in time with amplitudes and locations drawn from different distributions. Without assuming that the fields are statistically equivalent, we present closed form results (up to quadratures) for the asymptotic particle production rates for the $N_{\mathrm{f}}=1$ and $N_{\mathrm{f}}=2$ cases. We also present results for the general $N_{\mathrm{f}}>2$ case, but with more restrictive assumptions. We find agreement between our analytic results and direct numerical calculations of the total occupation number of the produced particles, with departures that can be explained in terms of violation of our assumptions. We elucidate the precise connection between the maximum entropy ansatz (MEA) used in Amin & Baumann (2015) and the underlying statistical distribution of the self and cross couplings. We provide and justify a simple to use (MEA-inspired) expression for the particle production rate, which agrees with our more detailed treatment when the parameters characterizing the effective mass and cross-couplings between fields are all comparable to each other. However, deviations are seen when some parameters differ significantly from others. We show that such deviations become negligible for a broad range of parameters when $N_{\mathrm{f}}\gg 1$.

    ↳ astro-ph.COhep-phhep-thJCAP(2017)·15 citations
20. 20*

    Three--Dimensional parton structure of light nuclei

    Sergio Scopetta🇮🇹 · Alessio Del Dotto🇮🇹 · Leonid Kaptari🇷🇺 · Emanuele Pace🇮🇹 · Matteo Rinaldi🇪🇸 · Giovanni Salmè🇮🇹

    Two promising directions beyond inclusive deep inelastic scattering experiments, aimed at unveiling the three dimensional structure of the bound nucleon, are reviewed, considering in particular the ${}^3$He nucleus. The 3D structure in coordinate space can be accessed through deep exclusive processes, whose non-perturbative part is encoded in generalized parton distributions (GPDs). In this way, the distribution of partons in the transverse plane can be obtained. As an example, coherent deeply virtual Compton scattering (DVCS) off ${}^3$He nuclei, important to access the neutron GPDs, will be discussed. In Impulse Approximation (IA), the sum of two GPDs of ${}^3$He, $H$ and $E$, at low momentum transfer, turns out to be dominated by the neutron contribution. Besides, a technique, able to take into account the nuclear effects included in the Impulse Approximation analysis, has been developed. The spin dependent GPD $\tilde{H}$ of ${}^3$He is also found to be largely dominated, at low momentum transfer, by the neutron contribution. Semi-inclusive deep inelastic scattering processes access the momentum space 3D structure parameterized through transverse momentum dependent parton distributions. A distorted spin-dependent spectral function has been recently introduced for ${}^3$He, in a non-relativistic framework, to take care of the final state interaction between the observed pion and the remnant in semi-inclusive deep inelastic electron scattering off transversely polarized ${}^3$He. The calculation of the Sivers and Collins single spin asymmetries for ${}^3$He, and a straightforward procedure to effectively take into account nuclear dynamics and final state interactions, will be reviewed. The Light-front dynamics generalization of the analysis is also addressed.

    ↳ nucl-thhep-phJ.Phys.Conf.Ser.(2018)·0 citations
21. 21*

    Hamiltonian approach to QCD in Coulomb gauge - a survey of recent results

    H. Reinhardt🇩🇪 · G. Burgio🇩🇪 · D. Campagnari🇩🇪 · E. Ebadati🇩🇪 · J. Heffner🇩🇪 · M. Quandt🇩🇪 · P. Vastag🇩🇪 · H. Vogt🇩🇪

    I report on recent results obtained within the Hamiltonian approach to QCD in Coulomb gauge. Furthermore this approach is compared to recent lattice data, which were obtained by an alternative gauge fixing method and which show an improved agreement with the continuum results. By relating the Gribov confinement scenario to the center vortex picture of confinement it is shown that the Coulomb string tension is tied to the spatial string tension. For the quark sector a vacuum wave functional is used which explicitly contains the coupling of the quarks to the transverse gluons and which results in variational equations which are free of ultraviolet divergences. The variational approach is extended to finite temperatures by compactifying a spatial dimension. The effective potential of the Polyakov loop is evaluated from the zero-temperature variational solution. For pure Yang--Mills theory, the deconfinement phase transition is found to be second order for SU(2) and first order for SU(3), in agreement with the lattice results. The corresponding critical temperatures are found to be $275\mathrm{MeV}$ and $280\mathrm{MeV}$, respectively. When quarks are included, the deconfinement transition turns into a cross-over. From the dual and chiral quark condensate one finds pseudo-critical temperatures of $198\mathrm{MeV}$ and $170\mathrm{MeV}$, respectively, for the deconfinement and chiral transition.

    ↳ hep-thhep-lathep-phAdv.High Energy Phys.(2018)·40 citations
22. 22*

    Origin of Bardeen-Zumino current in lattice models of Weyl semimetals

    E. V. Gorbar🇺🇦 · V. A. Miransky🇨🇦 · I. A. Shovkovy🇺🇸 · P. O. Sukhachov🇨🇦

    For a generic lattice Hamiltonian of the electron states in Weyl semimetals, we calculate the electric charge and current densities in the first order in background electromagnetic and strain-induced pseudoelectromagnetic fields. We show that the resulting expressions for the densities contain contributions of two types. The contributions of the first type coincide with those in the chiral kinetic theory. The contributions of the second type contain the information about the whole Brillouin zone and cannot be reproduced in the chiral kinetic theory. Remarkably, the latter coincide exactly with the Bardeen-Zumino terms that are usually introduced in relativistic quantum field theory in order to define the consistent anomaly. We demonstrate the topological origin of the Bardeen-Zumino (or, equivalently, Chern-Simons) corrections by expressing them in terms of the winding number in the lattice Hamiltonian model.

    ↳ cond-mat.mes-hallhep-phhep-thPRB(2017)·22 citations
23. 23*

    UV complete me: Positivity Bounds for Particles with Spin

    Claudia de Rham🇬🇧 · Scott Melville🇬🇧 · Andrew J. Tolley🇺🇸 · Shuang-Yong Zhou🇬🇧

    For a low energy effective theory to admit a standard local, unitary, analytic and Lorentz-invariant UV completion, its scattering amplitudes must satisfy certain inequalities. While these bounds are known in the forward limit for real polarizations, any extension beyond this for particles with nonzero spin is subtle due to their non-trivial crossing relations. Using the transversity formalism (i.e. spin projections orthogonal to the scattering plane), in which the crossing relations become diagonal, these inequalities can be derived for 2-to-2 scattering between any pair of massive particles, for a complete set of polarizations at and away from the forward scattering limit. This provides a set of powerful criteria which can be used to restrict the parameter space of any effective field theory, often considerably more so than its forward limit subset alone.

    ↳ hep-thgr-qchep-phJHEP(2018)·195 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.