Wed·Nov 2, 2016Wednesday·November 2, 2016

1. 01*

   Introduction to the physics of the total cross-section at LHC: A Review of Data and Models

   Giulia Pancheri🇮🇹 · Yogendra N. Srivastava🇮🇹

   This review describes the development of the physics of hadronic cross sections up to recent LHC results and cosmic ray experiments. We present here a comprehensive review - written with a historical perspective - about total cross-sections from medium to the highest energies explored experimentally and studied through a variety of methods and theoretical models for over sixty years. We begin by recalling the analytic properties of the elastic amplitude and the theorems about the asymptotic behavior of the total cross-section. A discussion of how proton-proton cross-sections are extracted from cosmic rays at higher than accelerator energies and help the study of these asymptotic limits, is presented. This is followed by a description of the advent of particle colliders, through which high energies and unmatched experimental precisions have been attained. Thus the measured hadronic elastic and total cross-sections have become crucial instruments to probe the so called soft part of QCD physics, where quarks and gluons are confined, and have led to test and refine Regge behavior and a number of diffractive models. As the c.m. energy increases, the total cross-section also probes the transition into hard scattering describable with perturbative QCD, the so-called mini-jet region. Further tests are provided by cross-section measurements of gamma p, gamma*p and gamma* gamma* for models based on vector meson dominance, scaling limits of virtual photons at high Q^2 and the BFKL formalism. Models interpolating from virtual to real photons are also tested.

   hep-phEPJC(2017)·70 citations
2. 02*

   A quest for new physics inside the neutron

   B.O. Kerbikov🇷🇺

   The lecture presents an overview of the quest for the new physics in low energy neutron phenomena. In addition to the traditional topics the quantum damping of $n$ $\bar{n}$ oscillations is discussed.

   hep-phnucl-exPhys.Atom.Nucl.(2017)·2 citations
3. 03*

   Baryon asymmetry via leptogenesis in a neutrino mass model with complex scaling

   Rome Samanta🇮🇳 · Mainak Chakraborty🇮🇳 · Probir Roy🇮🇳 · Ambar Ghosal🇮🇳

   Baryogenesis via leptogenesis is investigated in a specific model of light neutrino masses and mixing angles. The latter was proposed on the basis of an assumed complex-extended scaling property of the neutrino Majorana mass matrix $M_{\nu }$, derived with a type-1 seesaw from a Dirac mass matrix $m_D$ and a heavy singlet neutrino Majorana mass matrix $M_R$. One of its important features, highlighted here, is that there is a common source of the origin of a nonzero ${\theta }_{13}$ and the CP violating lepton asymmetry through the imaginary part of $m_D$. The model predicted CP violation to be maximal for the Dirac type and vanishing for the Majorana type. We assume strongly hierarchical mass eigenvalues for $M_R$. The leptonic CP asymmetry parameter ${\epsilon }_1^{\alpha }$ with lepton flavor $\alpha$, originating from the decays of the lightest of the heavy neutrinos $N_1$ (of mass $M_1$) at a temperature $T\sim M_1$, is what matters here with ${\epsilon }_{2,3}^{\alpha }$, originating from the decays of $N_{2,3}$, being washed out. The light leptonic and heavy neutrino number densities (normalized to the entropy density) are evolved via Boltzmann equations down to electroweak temperatures to yield a baryon asymmetry through sphaleronic transitions. The effect of flavored vs. unflavored leptogenesis in the three mass regimes (1) $M_1<10^9$ GeV, (2) $10^9$ GeV $<M_1<$ $10^{12}$ GeV and (3) $M_1>10^{12}$ GeV are numerically worked out for both a normal and an inverted mass ordering of the light neutrinos. Corresponding results on the baryon asymmetry of the universe are obtained, displayed and discussed.

   hep-phJCAP(2017)·13 citations
4. 04*

   Likelihood Analysis of Supersymmetric SU(5) GUTs

   E. Bagnaschi🇩🇪 · J.C. Costa🇬🇧 · K. Sakurai🇬🇧 · M. Borsato🇪🇸 · O. Buchmueller🇬🇧 · R. Cavanaugh🇺🇸 · V. Chobanova🇪🇸 · M. Citron🇬🇧 · A. De Roeck🇨🇭 · M.J. Dolan🇦🇺 · J.R. Ellis🇬🇧 · H. Flächer🇬🇧 and 8 other authors

   We perform a likelihood analysis of the constraints from accelerator experiments and astrophysical observations on supersymmetric (SUSY) models with SU(5) boundary conditions on soft SUSY-breaking parameters at the GUT scale. The parameter space of the models studied has 7 parameters: a universal gaugino mass $m_{1/2}$, distinct masses for the scalar partners of matter fermions in five- and ten-dimensional representations of SU(5), $m_5$ and $m_{10}$, and for the $5$ and $\bar{5}$ Higgs representations $m_{H_u}$ and $m_{H_d}$, a universal trilinear soft SUSY-breaking parameter $A_0$, and the ratio of Higgs vevs $\tan \beta$. In addition to previous constraints from direct sparticle searches, low-energy and flavour observables, we incorporate constraints based on preliminary results from 13 TeV LHC searches for jets + MET events and long-lived particles, as well as the latest PandaX-II and LUX searches for direct Dark Matter detection. In addition to previously-identified mechanisms for bringing the supersymmetric relic density into the range allowed by cosmology, we identify a novel ${\tilde{u}}_R/{\tilde{c}}_R-{\tilde{\chi }}_1^0$ coannihilation mechanism that appears in the supersymmetric SU(5) GUT model and discuss the role of ${\tilde{\nu }}_{\tau }$ coannihilation. We find complementarity between the prospects for direct Dark Matter detection and SUSY searches at the LHC.

   hep-phastro-ph.HEhep-exEPJC(2017)·42 citations
5. 05*

   Radiative Yukawa Couplings in the Simplest Left-Right Symmetric Model

   Emidio Gabrielli🇮🇹 · Luca Marzola🇪🇪 · Martti Raidal🇪🇪

   We revisit a recent solution to the flavor hierarchy problem based on the paradigm that Yukawa couplings are, rather than fundamental constants, effective low energy couplings radiatively generated by interactions in a hidden sector of the theory. In the present paper we show that the setup required by this scenario can be set by gauge invariance alone, provided that the Standard Model gauge group be extended to the left-right symmetric group of $SU(2{)}_L\times SU(2{)}_R\times U(1{)}_Y$. The simplest scheme in which Yukawa couplings are forbidden at the tree-level organises the right-handed fermions into doublets and presents an additional Higgs $SU(2{)}_R$ doublet, responsible for the spontaneous breaking of the $SU(2{)}_R$ gauge sector. The flavor and chiral symmetry breaking induced by the $SU(2{)}_R$ breaking is transferred at the one-loop level to the Standard Model via the dynamics of the hidden sector, which effectively regulates the spread of the effective Yukawa couplings. The emerging left-right symmetric framework recovers additional appealing features typical of these models, allowing for instance to identify the hypercharges of the involved fermions with their $B-L$ charges and offering a straightforward solution to the strong CP problem. The scheme gives rise to a distinguishing phenomenology that potentially can be tested at the LHC and future colliders through the same interactions that result in the radiative generation of Yukawa couplings, as well as by exploiting the properties of the additional $SU(2{)}_R$ Higgs doublet.

   hep-phPRD(2017)·30 citations
6. 06*

   A framework for second-order parton showers

   Hai Tao Li🇦🇺 · Peter Skands🇦🇺

   A framework is presented for including second-order perturbative corrections to the radiation patterns of parton showers. The formalism allows to combine O(alphaS^2)-corrected iterated 2->3 kernels for "ordered" gluon emissions with tree-level 2->4 kernels for "unordered" ones. The combined Sudakov evolution kernel is thus accurate to O(alphaS^2). As a first step towards a full-fledged implementation of these ideas, we develop an explicit implementation of 2->4 shower branchings in this letter.

   hep-phPLB(2017)·80 citations
7. 07*

   On Lepton-Number-Violating Searches for Muon to Positron Conversion

   Jeffrey M. Berryman🇺🇸 · André de Gouvêa🇺🇸 · Kevin J. Kelly🇺🇸 · Andrew Kobach🇺🇸

   There is no guarantee that the violation of lepton number, assuming it exists, will primarily manifest itself in neutrinoless double beta decay ($0\nu \beta \beta$). Lepton-number violation and lepton-flavor violation may be related, and much-needed information regarding the physics that violates lepton number can be learned by exploring observables that violate lepton flavors other than electron flavor. One of the most promising observables is ${\mu }^{-}\to e^{+}$ conversion, which can be explored by experiments that are specifically designed to search for ${\mu }^{-}\to e^{-}$ conversion. We survey lepton-number-violating dimension-five, -seven, and -nine effective operators in the standard model and discuss the relationships between Majorana neutrino masses and the rates for $0\nu \beta \beta$ and ${\mu }^{-}\to e^{+}$ conversion. While $0\nu \beta \beta$ has the greatest sensitivity to new ultraviolet energy scales, its rate might be suppressed by the new physics relationship to lepton flavor, and ${\mu }^{-}\to e^{+}$ conversion offers a complementary probe of lepton-number-violating physics.

   hep-phPRD(2017)·39 citations
8. 08*

   NNLL resummation for the associated production of a top pair and a Higgs boson at the LHC

   Alessandro Broggio🇩🇪 · Andrea Ferroglia🇺🇸 · Ben D. Pecjak🇬🇧 · Li Lin Yang🇨🇳

   We study the resummation of soft gluon emission corrections to the production of a top-antitop pair in association with a Higgs boson at the Large Hadron Collider. Starting from a soft-gluon resummation formula derived in previous work, we develop a bespoke parton-level Monte Carlo program which can be used to calculate the total cross section along with differential distributions. We use this tool to study the phenomenological impact of the resummation to next-to-next-to-leading logarithmic (NNLL) accuracy, finding that these corrections increase the total cross section and the differential distributions with respect to NLO calculations of the same observables.

   hep-phJHEP(2017)·81 citations
9. 09*

   Where are ${\chi }_{cJ}(3P)$?

   Dian-Yong Chen🇨🇳

   In the present work, we propose $Y(4140)$ as the ${\chi }_{c1}(3P)$ state by studying the ${\chi }_{c1}{\pi }^{+}{\pi }^{-}$ invariant mass spectrum of the $B\to K{\chi }_{c1}{\pi }^{+}{\pi }^{-}$ process. In the $D\bar{D}$ invariant mass spectrum of the $B\to KD\bar{D}$ process, we find a new resonance with the mass and width to be $(4083.0\pm 5.0)$ and $(24.1\pm 15.4)$ MeV, respectively, which could be a good candidate of the ${\chi }_{c0}(3P)$ state. The theoretical investigations on the decay behaviors of the ${\chi }_{cJ}(3P)$ in the present work support the assignments of the $Y(4140)$ and $Y(4080)$ as the ${\chi }_{c1}(3P)$ and ${\chi }_{c0}(3P)$ states, respectively. In addition, the ${\chi }_{c2}(3P)$ state is predicted to be a very narrow state. The results in the present work could be tested by further experiments in the LHCb and forthcoming Belle II.

   hep-phEPJC(2016)·29 citations
10. 10*

    Gluon Sivers function in a light-cone spectator model

    Zhun Lu🇨🇳 · Bo-Qiang Ma🇨🇳

    We calculate the gluon Sivers function of the proton in the valence-$x$ region using a light-cone spectator model with the presence of the gluon degree of freedom. We obtain the values of the parameters by fitting the model resulting gluon density distribution to the known parametrization. We find that our results agree with the recent phenomenological extraction of the gluon Sivers function after considering the evolution effect. We also estimate the mean transverse momentum of the gluon in a transversely polarized proton and find that it is within the range implied by the Burkardt sum rule.

    hep-phhep-exPRD(2016)·44 citations
11. 11*

    Compton scattering in the Endpoint Model

    Sumeet Dagaonkar🇮🇳

    We use the Endpoint model for exclusive hadronic processes to study Compton scattering of the proton. The parameters of the Endpoint model are fixed using the data for $F_1$ and the ratio of Pauli and Dirac form factors ($F_2/F_1$) and then used to get numerical predictions for the differential scattering cross section. We studied the Compton scattering at fixed ${\theta }_{CM}$ in the $s\sim t\gg {\Lambda }_{QCD}$ limit and at fixed $s$ much larger than $t$ limit. We observed that the calculations in the Endpoint Model give a good fit with experimental data in both regions.

    hep-phEPJC(2018)·2 citations
12. 12*

    Exploring detection of nuclearites in a large liquid scintillator neutrino detector

    Wan-Lei Guo🇨🇳 · Cheng-Jun Xia🇨🇳 · Tao Lin🇨🇳 · Zhi-Min Wang🇨🇳

    We take the JUNO experiment as an example to explore nuclearites in the future large liquid scintillator detector. Comparing to the previous calculations, the visible energy of nuclearites across the liquid scintillator will be reestimated for the liquid scintillator based detector. Then the JUNO sensitivities to the nuclearite flux are presented. It is found that the JUNO projected sensitivities can be better than $7.7\times 10^{-17}\mathrm{c}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}\mathrm{s}{\mathrm{r}}^{-1}$ for the nuclearite mass $10^{15}\mathrm{GeV}\le M\le 10^{24}$ GeV and initial velocity $10^{-4}\le {\beta }_0\le 10^{-1}$ with a 20 year running. Note that the JUNO will give the most stringent limits for downgoing nuclearites with $1.6\times 10^{13}\mathrm{GeV}\le M\le 4.0\times 10^{15}$ GeV and a typical galactic velocity ${\beta }_0=10^{-3}$.

    hep-phhep-exnucl-exPRD(2017)·4 citations
13. 13*

    A chiral covariant approach to $\rho \rho$ scattering

    D. Gülmez🇩🇪 · U.-G. Meißner🇩🇪 · J. A. Oller🇪🇸

    We analyze vector meson - vector meson scattering in a unitarized chiral theory based on a chiral covariant framework. We show that a pole assigned to the the scalar meson $f_0(1370)$ can be dynamically generated from the $\rho \rho$ interaction, while this is not the case for the tensor meson $f_2(1270)$ as found in earlier works. We show that the generation of the tensor state is untenable due to an artefact of the extreme non-relativistic kinematics used before. We further consider the effects arising from the coupling of channels with different orbital angular momenta. We suggest to use the formalism outlined here to obtain more reliable results for the dynamical generation of resonances in the vector-vector interaction.

    hep-phhep-latnucl-thEPJC(2017)·64 citations
14. 14*

    Double parton scattering for perturbative transverse momenta

    Maarten G. A. Buffing🇩🇪 · Markus Diehl🇩🇪 · Tomas Kasemets🇳🇱

    The cross section for transverse momentum dependent double parton scattering involves transverse momentum dependent double parton distributions (DTMDs). In the region of perturbative transverse momentum the DTMDs can be matched onto collinear double parton distributions. We present the framework and results for this matching, as well as the evolution equations for DTMDs in the region of large distance between the two partons. We discuss explicit results for one-loop matching coefficients and evolution kernels.

    hep-phPoS(2017)·4 citations
15. 15*

    Inflation from the Finite Scale Gauged Nambu-Jona-Lasinio Model

    Tomohiro Inagaki🇯🇵 · Sergei D. Odintsov🇪🇸 · Hiroki Sakamoto🇯🇵

    The possibility to construct an inflationary universe scenario for the finite-scale gauged Nambu-Jona-Lasinio model is investigated. This model can be described by the Higgs-Yukawa type interaction model with the corresponding compositeness scale. Therefore, the one-loop Higgs-Yukawa effective potential is used with the compositeness condition for the study of inflationary dynamics. We evaluate the fluctuations in the cosmic microwave background for the model with a finite compositeness scale in the slow-roll approximation. We find the remarkable dependence on the gauge group and the number of fermion flavors. It is also proved that the model has similar behavior with the ${\varphi }^{4n}$ chaotic inflation and the Starobinsky model at the flat and steep limits, respectively. It is demonstrated that realistic inflation consistent with Planck data is possible for a range of theory parameters.

    hep-phastro-ph.COgr-qchep-thNPB(2017)·11 citations
16. 16*

    Should T2K run in dominant neutrino mode to detect CP violation ?

    Monojit Ghosh🇯🇵

    The main aim of the T2K experiment in Japan is to discover CP violation in the leptonic sector by measuring the Dirac phase ${\delta }_{CP}$. For that purpose T2K has already started collecting data in both neutrino and antineutrino mode. But in this work we will show that, in T2K the main role of the antineutrinos is to resolve the octant degeneracy. If the octant is known then the pure neutrino run of T2K is capable to give the maximum CP sensitivity. On the other hand in the experiment like NO$\nu$A, antineutrinos are still useful even when octant is known. Thus we propose that let T2K run in the dominant neutrino mode whereas the antineutrino component of the other experiments can resolve the octant degeneracy in T2K. As an example we show that if T2K is combined with the experiments NO$\nu$A and ICAL@INO, then T2K will have the potential to discover CP violation with maximum sensitivity in the dominant neutrino mode.

    hep-ph1 citation
17. 17*

    Model independent analysis of $b\to (c,u)\tau \nu$ leptonic and semileptonic decays

    Rupak Dutta🇮🇳 · Anupama Bhol🇮🇳

    Latest measurement of the ratio of branching ratios $R_D=\mathcal{B}(B\to D\tau \nu )/\mathcal{B}(B\to Dl\nu )$ and $R_{D^{\ast }}=\mathcal{B}(B\to D^{\ast }\tau \nu )/\mathcal{B}(B\to D^{\ast }l\nu )$, where $l$ is either an electron or muon, differs from the standard model expectation by $1.9\sigma$ and $3.3\sigma$, respectively. Similar tension has been observed in purely leptonic $B\to \tau \nu$ decays as well. In this context, we consider the most general effective Lagrangian in the presence of new physics and perform a model independent analysis to explore various new physics couplings. Motivated by the recently proposed new observables $R_D^{\tau }=R_D/\mathcal{B}(B\to \tau \nu )$ and $R_{D^{\ast }}^{\tau }=R_{D^{\ast }}/\mathcal{B}(B\to \tau \nu )$, we impose $2\sigma$ constraints coming from $R_D^{\tau }$ and $R_{D^{\ast }}^{\tau }$ in addition to the constraints coming from $R_D$, $R_{D^{\ast }}$, and $\mathcal{B}(B\to \tau \nu )$ to constrain the new physics parameter space. We study the impact of new physics on various observables related to $B_s\to (D_s,D_s^{\ast })\tau \nu$ and $B\to \pi \tau \nu$ decay processes.

    hep-phPRD(2017)·37 citations
18. 18*

    Open charm-bottom scalar tetraquarks and their strong decays

    S. S. Agaev🇦🇿 · K. Azizi🇹🇷 · H. Sundu🇹🇷

    The mass and meson-current coupling of the diquark-antidiquark states with the quantum numbers $J^P=0^{+}$ and quark contents $Z_q=[cq][\bar{b}\bar{q}]$ and $Z_s=[cs][\bar{b}\bar{s}]$ are calculated using two-point QCD sum rule approach. In calculations the quark, gluon and mixing condensates up to eight dimensions are taken into account. The parameters of the scalar tetraquarks extracted from this analysis are employed to explore the strong vertices $Z_q{B}_c\pi$, $Z_q{B}_c\eta$ and $Z_s{B}_c\eta$ and compute the couplings $g_{Z_q{B}_c\pi }$, $g_{Z_q{B}_c\eta }$ and $g_{Z_s{B}_c\eta }$. The strong couplings are obtained within the soft-meson approximation of QCD light-cone sum rule method: they form, alongside with other parameters, the basis for evaluating the widths of $Z_q\to B_c\pi$, and $Z_s\to B_c\eta$ decays. Obtained in this work results for the mass of the tetraquarks $Z_q$ and $Z_s$ are compared with available predictions presented in the literature.

    hep-phPRD(2017)·29 citations
19. 19*

    Cosmological constraints on exotic injection of electromagnetic energy

    Vivian Poulin🇫🇷 · Julien Lesgourgues🇩🇪 · Pasquale D. Serpico🇫🇷

    We compute cosmic microwave background (CMB) anisotropy constraints on exotic forms of energy injection in electromagnetic (e.m.) channels over a large range of timescales. These constraints are very powerful around or just after recombination, although CMB keeps some sensitivity e.g. to decaying species with lifetimes as long as $10^{25}$s. We review here complementary with CMB spectral distortions and primordial nucleosynthesis bounds, which dominate at earlier timescales. For the first time, we describe the effects of the e.m. energy injection on the CMB power spectra as a function of the injection epoch, using the lifetime of a decaying particle as proxy. We identify a suitable on-the-spot approximation. Our results are of interest not only for early universe relics constituting (a fraction of) the dark matter, but also for other exotic injection of e.m. radiation. For illustration, we apply our formalism to: i) Primordial black holes of mass $\in [10^{13.5},10^{16.8}]$ g, showing that the constraints are comparable to the ones obtained from gamma-ray background studies and even dominate below $\sim 10^{14}$g. ii) To a peculiar mass-mixing range in the sterile neutrino parameter space, complementary to other astrophysical and laboratory probes. iii) Finally, we provide a first estimate of the room for improvement left for forthcoming 21 cm experiments, comparing it with the reach of proposed CMB spectral distortion (PiXiE) and CMB angular power spectrum (CORE) missions. We show that the best and most realistic opportunity to look for this signal (or to improve over current constraints) in the 21 cm probe is to focus on the Cosmic Dawn epoch, $15\lesssim z\lesssim 30$, where the qualitatively unambiguous signature of a spectrum in emission can be expected for models that evade all current constraints.

    ↳ astro-ph.COhep-phJCAP(2017)·306 citations
20. 20*

    Phenomenological predictions of 3+1d anisotropic hydrodynamics

    Mohammad Nopoush🇺🇸 · Michael Strickland🇺🇸 · Radoslaw Ryblewski🇵🇱

    We make phenomenological predictions for particle spectra and elliptic flow in heavy-ion collisions using 3+1d anisotropic hydrodynamics (aHydro) including the effects of both shear and bulk viscosities. The dynamical equations necessary are derived by taking moments of the Boltzmann equation allowing for three distinct (diagonal) momentum-space anisotropy parameters. The formulation is based on relaxation-time approximation for the collisional kernel and a lattice-QCD-based equation of state. Evolving the system to late times, we calculate particle production using THERMINATOR 2, modified to account for an ellipsoidal distribution function. We obtain particle spectra for different particle species such as pions, kaons, and protons, and elliptic flow $v_2$ as a function of centrality, transverse momentum, and rapidity. In our model, we have four free parameters, i.e. freeze-out temperature, initial central energy density, initial momentum-space anisotropies, and shear viscosity to entropy density ratio. Using a multidimensional fit to LHC experimental data, we make a preliminary extraction of these parameters. We find reasonable agreement between 3+1d aHydro and available experimental data for $\eta /s\sim 0.23$.

    ↳ nucl-thhep-phJ.Phys.Conf.Ser.(2017)·12 citations
21. 21*

    Landau gauge gluon vertices from Lattice QCD

    Anthony G. Duarte🇵🇹 · Orlando Oliveira🇵🇹 · Paulo J. Silva🇵🇹

    In lattice QCD the computation of one-particle irreducible (1PI) Green's functions with a large number (> 2) of legs is a challenging task. Besides tuning the lattice spacing and volume to reduce finite size effects, the problems associated with the estimation of higher order moments via Monte Carlo methods and the extraction of 1PI from complete Green's functions are limitations of the method. Herein, we address these problems revisiting the calculation of the three gluon 1PI Green's function.

    ↳ hep-lathep-phhep-thPoS(2016)·3 citations
22. 22*

    Hypercubic Effects in semileptonic $D\to \pi$ decays on the lattice

    V. Lubicz🇮🇹 · L. Riggio🇮🇹 · G. Salerno🇮🇹 · S. Simula🇮🇹 · C. Tarantino🇮🇹

    We present a lattice determination of the vector and scalar form factors of the semileptonic $D\to \pi \ell \nu$ decays, which are relevant for the extraction of the CKM matrix element $|V_{cd}|$ from experimental data. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with $N_f=2+1+1$ flavors of dynamical quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV. Quark momenta are injected on the lattice using non-periodic boundary conditions. The matrix elements of both vector and scalar currents are determined for a plenty of kinematical conditions in which parent and child mesons are either moving or at rest. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data and included in the decomposition of the current matrix elements in terms of additional form factors. Our preliminary estimate for the vector form factor at zero 4-momentum transfer is $f_{+}^{D\to \pi }(0)=0.631(40)$, which can be compared with the latest FLAG average $f_{+}^{D\to \pi }(0)=0.666(29)$ available only at $N_f=2+1$.

    ↳ hep-lathep-phPoS(2016)·10 citations
23. 23*

    Theta dependence in Holographic QCD

    Lorenzo Bartolini🇮🇹 · Francesco Bigazzi🇮🇹 · Stefano Bolognesi🇮🇹 · Aldo L. Cotrone🇮🇹 · Andrea Manenti🇮🇹

    We study the effects of the CP-breaking topological $\theta$-term in the large $N_c$ QCD model by Witten, Sakai and Sugimoto with $N_f$ degenerate light flavors. We first compute the ground state energy density, the topological susceptibility and the masses of the lowest lying mesons, finding agreement with expectations from the QCD chiral effective action. Then, focusing on the $N_f=2$ case, we consider the baryonic sector and determine, to leading order in the small $\theta$ regime, the related holographic instantonic soliton solutions. We find that while the baryon spectrum does not receive $\mathcal{O}(\theta )$ corrections, this is not the case for observables like the electromagnetic form factor of the nucleons. In particular, it exhibits a dipole term, which turns out to be vector-meson dominated. The resulting neutron electric dipole moment, which is exactly the opposite as that of the proton, is of the same order of magnitude of previous estimates in the literature. Finally, we compute the CP-violating pion-nucleon coupling constant ${\bar{g}}_{\pi NN}$, finding that it is zero to leading order in the large $N_c$ limit.

    ↳ hep-thhep-lathep-phJHEP(2017)·46 citations
24. 24*

    On The Existence of a Holographic Description of the LHC Quark-Gluon Plasmas

    Brett McInnes🇸🇬 · Yen Chin Ong🇨🇳

    Peripheral collisions of heavy ions can give rise to extremely intense magnetic fields. It has been suggested that these fields might invalidate the holographic description of the corresponding quark-gluon plasmas, assuming that these can be modelled by strongly coupled field theories. In the case of the plasmas produced in collisions at the RHIC facility (including in the beam energy scans), it is known how to deal with this problem: one has to take into account the large angular momenta generated in these plasmas, and the effects of the baryonic chemical potential. But this does not work for the plasmas produced in peripheral collisions at the LHC. However, these results neglect some (less significant) aspects of bulk physics; could it be that the problem is resolved by taking into account these lower-order effects? Here we use a bulk dilatonic field (fully compatible with boundary data, as well as with the asymptotically AdS character of the bulk geometry) as a model of these effects, and show that this is unlikely to be the solution. Thus, the existence of a consistent holographic description of the most extreme LHC plasmas remains open to question.

    ↳ hep-thgr-qchep-phNPB(2017)·2 citations
25. 25*

    Determination of the number of participating nucleons in p+p interactions at SPS energies

    H. Stroebele🇩🇪

    In the past the analyses of inelastic p+p collision for example in terms of the hadron gas model have assumed that always both protons participate in the interaction. In this article we show that (at sqrt(s) = 17.3 GeV ) on average only 1,89 protons are interacting. Measurements of the mean multiplicities of protons, neutrons, charged pions, charged kaons and {\Lambda} hyperons allow to compute the number of initial state nucleons using conservation of baryon number, strangeness, and isospin. We further argue that once the number of initial state nucleons is given and the mean multiplicities of protons and charged pions are known in p+p interactions at center-of-mass energies below a few tens of GeV, the yields of net neutrons, kaons, and hyperons can be estimated with a precision of a few percent using again baryon and isospin conservation.

    ↳ nucl-thhep-ph1 citation

* 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.