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High Energy Physics - Phenomenology (hep-ph) updates on the e-print archive
  • Boosting the $H\to$ invisibles searches with $Z$ boson polarization. (arXiv:1809.07327v1 [hep-ph])

    Authors: Dorival Goncalves, Junya Nakamura

    It is argued that, in $H \to $ invisibles searches with $Z(\ell\ell)H$ associated production at the LHC, the signal efficiency can be sensibly improved via a detailed study of the $Z$ boson polarization, discriminating between the signal and the dominant-irreducible $Z(\ell\ell)Z(\nu\nu)$ background. We first present a comprehensive polarization study, obtaining the complete set of angular coefficients $A_i$ in the Collins-Soper reference frame and identifying the dominant phenomenological effects. Then, we show the results for a realistic Monte Carlo study to $H\to$ invisibles, taking the polarization analysis into account. We obtain about $20\%$ improvement in the upper bound for the branching ratio of the Higgs boson to invisible particles, assuming $300\ \mathrm{fb}^{-1}$ of data at the 13 TeV LHC.

  • Detecting a Boosted Diboson Resonance. (arXiv:1809.07334v1 [hep-ph])

    Authors: Kaustubh Agashe, Jack H. Collins, Peizhi Du, Sungwoo Hong, Doojin Kim, Rashmish K. Mishra

    New light scalar particles in the mass range of hundreds of GeV, decaying into a pair of $W/Z$ bosons can appear in several extensions of the SM. The focus of collider studies for such a scalar is often on its direct production, where the scalar is typically only mildly boosted. The observed $W/Z$ are therefore well-separated, allowing analyses for the scalar resonance in a standard fashion as a low-mass diboson resonance. In this work we instead focus on the scenario where the direct production of the scalar is suppressed, and it is rather produced via the decay of a significantly heavier (a few TeV mass) new particle, in conjunction with SM particles. Such a process results in the scalar being highly boosted, rendering the $W/Z$'s from its decay merged. The final state in such a decay is a "fat" jet, which can be either four-pronged (for fully hadronic $W/Z$ decays), or may be like a $W/Z$ jet, but with leptons buried inside (if one of the $W/Z$ decays leptonically). In addition, this fat jet has a jet mass that can be quite different from that of the $W/Z$/Higgs/top quark-induced jet, and may be missed by existing searches. In this work, we develop dedicated algorithms for tagging such multi-layered "boosted dibosons" at the LHC. As a concrete application, we discuss an extension of the standard warped extra-dimensional framework where such a light scalar can arise. We demonstrate that the use of these algorithms gives sensitivity in mass ranges that are otherwise poorly constrained.

  • Inflating to the Weak Scale. (arXiv:1809.07338v1 [hep-ph])

    Authors: Michael Geller, Yonit Hochberg, Eric Kuflik

    We present a new solution to the hierarchy problem, where the Higgs mass is at its observed electroweak value because such a patch inflates the most in the early universe. If the Higgs mass depends on a field undergoing quantum fluctuations during inflation, then inflation will fill the universe with the Higgs mass that corresponds to the largest vacuum energy. The hierarchy problem is solved if the maximum vacuum energy occurs for the observed Higgs mass. We demonstrate this notion with a proof-of-principle model containing an axion, a modulus field and the Higgs, and show that inflation can be responsible for the weak scale.

  • Phenomenology of the inflation-inspired NMSSM at the electroweak scale. (arXiv:1809.07371v1 [hep-ph])

    Authors: Wolfgang Gregor Hollik, Stefan Liebler, Gudrid Moortgat-Pick, Sebastian Paßehr, Georg Weiglein

    The concept of Higgs inflation can be elegantly incorporated in the Next-to-Minimal Supersymmetric Standard Model (NMSSM). A linear combination of the two Higgs-doublet fields plays the role of the inflaton which is non-minimally coupled to gravity. This non-minimal coupling appears in the low-energy effective superpotential and changes the phenomenology at the electroweak scale. While the field content of the inflation-inspired model is the same as in the NMSSM, there is another contribution to the $\mu$ term in addition to the vacuum expectation value of the singlet. We explore this extended parameter space and point out scenarios with phenomenological differences compared to the pure NMSSM. A special focus is set on the electroweak vacuum stability and the parameter dependence of the Higgs and neutralino sectors. We highlight regions which yield a SM-like $125\,$GeV Higgs boson compatible with the experimental observations and are in accordance with the limits from searches for additional Higgs bosons. Finally, we study the impact of the non-minimal coupling to gravity on the Higgs mixing and in turn on the decays of the Higgs bosons in this model.

  • Bulk observables in the LHC 5.02 TeV Pb+Pb collisions within the integrated HydroKinetic Model. (arXiv:1809.07400v1 [hep-ph])

    Authors: V. M. Shapoval, Yu. M. Sinyukov

    The paper is devoted to the description and prediction of various bulk observables in the Pb+Pb collisions at the LHC energy $\sqrt{s_{NN}}=5.02$ TeV within the integrated hydrokinetic model (iHKM). Sensitivity of the results to the choice of the appropriate model parameter values is also investigated. It is found that changing of the relaxation time and the rate of thermalization, which characterize the pre-thermal stage of the matter evolution, as well as switching to another equation of state at the hydrodynamic stage and the corresponding hadronization temperature, does not destroy the results, if simultaneously one provides an appropriate adjusting of the initial time for the superdense matter formation and related maximal initial energy density.

  • New Scalar Field Quartessence. (arXiv:1809.07409v1 [gr-qc])

    Authors: Robert Brandenberger, Rodrigo R. Cuzinatto, Jürg Fröhlich, Ryo Namba

    We propose a cosmological scenario involving a single scalar field, $\varphi$, that is a source of Dark Matter as well as Dark Energy. The Lagrangian density of $\varphi$ contains a second field $\chi$, for simplicity assumed to be a scalar. For fixed values of $\chi$, the potential of $\varphi$ decays exponentially at large positive $\varphi$-values. While $\varphi$ is not coupled to Standard Model fields, $\chi$ is assumed to couple to them. Hence, the Green functions of $\chi$ depend on the temperature of the local equilibrium in the expanding universe. We assume that the coupling of $\chi$ to $\varphi$ is such that, at temperatures larger than some critical temperature $T_c$, $\varphi$ is trapped near the origin, and excitations of $\varphi$ about the origin form Dark Matter. After a phase transition at the temperature $T_c$, the trapping force disappears and $\varphi$ rolls towards large field values. A homogenous component of $\varphi$ appears and acts as Dark Energy. Within overdense regions, such as galaxies and galaxy clusters, the kinetic temperature is sufficiently high such that the phase transition does not occur. Thus, at the present time, $\varphi$ can decribe both Dark Energy and Dark Matter.

  • The Role of Mesons in Muon g-2. (arXiv:1809.07413v1 [hep-ph])

    Authors: Fred Jegerlehner

    The muon anomaly $a_\mu=(g_\mu-2)/2$ showing a persisting 3 to 4 $\sigma$ deviation between the SM prediction and the experiment is one of the most promising signals for physics beyond the SM. As is well known, the hadronic uncertainties are limiting the accuracy of the Standard Model prediction. Therefore a big effort is going on to improve the evaluations of hadronic effects in order to keep up with the 4-fold improved precision expected from the new Fermilab measurement in the near future. A novel complementary type experiment planned at J-PARC in Japan, operating with ultra cold muons, is expected to be able to achieve the same accuracy but with completely different systematics. So exciting times in searching for New Physics are under way. I discuss the role of meson physics in calculations of the hadronic part of the muon g-2. The improvement is expected to substantiate the present deviation $\Delta a_\mu^{\rm New \ Physics}=\Delta a_\mu^{\rm Experiment}- \Delta a_\mu^{\rm Standard \ Model}$ to a 6 to 10 standard deviation effect, provided hadronic uncertainties can be reduce by a factor two. This concerns the hadronic vacuum polarization as well as the hadronic light-by-light scattering contributions, both to a large extent determined by the low lying meson spectrum. Better meson production data and progress in modeling meson form factors could greatly help to improve the precision and reliability of the SM prediction of $a_\mu$ and thereby provide more information on what is missing in the SM.

  • Multipartite Dark Matter with Scalars, Fermions and signatures at LHC. (arXiv:1809.07474v1 [hep-ph])

    Authors: Subhaditya Bhattacharya, Purusottam Ghosh, Narendra Sahu

    Basic idea of this analysis is to achieve a two-component dark matter (DM) framework composed of a scalar and a fermion, with non-negligible DM-DM interaction contributing to thermal freeze out (hence relic density), but hiding them from direct detection bounds. We therefore augment the Standard Model (SM) with a scalar singlet ($S$) and three vectorlike fermions: two singlets ($\chi_1,\chi_2$) and a doublet ($N$). Stability of the two DM components is achieved by a discrete $\mathcal{Z}_2 \times {\mathcal{Z}^\prime}_2$ symmetry, under which the additional fields transform suitably. Fermion fields having same $\mathcal{Z}_2 \times {\mathcal{Z}^\prime}_2$ charge ($N,\chi_1$ in the model) mix after electroweak symmetry breaking (EWSB) and the lightest component becomes one of the DM candidates, while scalar singlet $S$ is the other DM component connected to visible sector by Higgs portal coupling. The heavy fermion ($\chi_2$) plays the role of mediator to connect the two DM candidates through Yukawa interaction. This opens up a large parameter space for the heavier DM component through DM-DM conversion. Hadronically quiet dilepton signature, arising from the fermion dark sector, can be observed at Large Hadron Collider (LHC) aided by the presence of a lighter scalar DM component, satisfying relic density and direct search bounds through DM-DM conversion.

  • New narrow nucleon resonances $N^{\ast}(1685)$ and $N^{\ast}(1726)$ within the chiral quark-soliton model. (arXiv:1809.07489v1 [hep-ph])

    Authors: Ghil-Seok Yang, Hyun-Chul Kim

    We investigate the strong and radiative decay widths of the narrow nucleon resonances $N^*(1685)$ and $N^{\ast}(1726)$ within the framework of the SU(3) chiral quark-soliton model. All the relevant parameters are taken from those used to describe the properties of the baryon octet and decuplet in previous works. The masses of the antidecuplet nucleon and the eikosiheptaplet (27-plet) nucleon with spin 3/2 are determined respectively to be $(1690.2\pm 10.5)\, \mathrm{MeV}$ and $(1719.6\pm7.4)\,\mathrm{MeV}$. The decay width for $N^{\ast}(1685)\to \eta + N$ is found to be approximately three times larger than that for $N^{\ast}(1685)\to \pi + N$. The width of the decay $N^{\ast}\left(1726\right)3/2^+\to \eta +N$ is even about 31 times larger than that of $N^{\ast}\left(1726\right)3/2^+\to \pi + N$. The ratio of the radiative decays for $N^*(1685)$ is obtained to be $\Gamma_{nn^*(1685)}/\Gamma_{pp^*(1685)}=8.62\pm3.45$ which explains very well the neutron anomaly. In contrast, we find $\Gamma_{pp^*(1726)}/\Gamma_{nn^*(1726)}=3.72\pm0.64$, which indicates that the production of $N^*(1726)$ is more likely to be observed in the proton channel. We also examined the decay modes of these narrow nucleon resonances with the strangeness hadrons involved.

  • A chiral SU(4) explanation of the $b\to s$ anomalies. (arXiv:1809.07562v1 [hep-ph])

    Authors: Shyam Balaji, Robert Foot, Michael A. Schmidt

    We propose a variant of the Pati-Salam model, with gauge group $SU(4)_C\times SU(2)_L\times U(1)_{Y'}$, in which the chiral left-handed quarks and leptons are unified into a $\underline{4}$ of $SU(4)_C$, while the right-handed quarks and leptons have quite a distinct treatment. The $SU(4)_C$ leptoquark gauge bosons can explain the measured deviation of lepton flavour universality in the rare decays: $\bar B \to \bar K^{(*)}\bar\ell\ell, \ell=\mu,e$ (taken as a hint of new physics). The model satisfies the relevant experimental constraints and makes predictions for the important $B$ and $\tau$ decays. These predictions will be tested at the LHCb and Belle II experiments when increased statistics become available.

  • Transport responses from rate of decay and scattering processes in the Nambu--Jona-Lasinio model. (arXiv:1809.07594v1 [nucl-th])

    Authors: Sabyasachi Ghosh, Fernando E. Serna, Aman Abhishek, Gastao Krein, Hiranmaya Mishra

    We have calculated quark and anti-quark relaxation time by considering different possible elastic and inelastic scatterings in the medium. Comparative role of these elastic and inelastic scatterings on different transport coefficients are explored. The quark-meson effective interaction Lagrangian density in the framework of Nambu--Jona-Lasinio model is used for calculating both type of scatterings. Owing to a kinetic threshold, inelastic scatterings can only exist beyond the Mott line in temperature and chemical potential plane, whereas elastic scatterings occur in the entire plane. Interestingly, the strength of inelastic scatterings near and above Mott line becomes so strong that medium behaves like a perfect fluid, in that all transport coefficients become very small.

  • Pion and constituent quarks strong form factors: a dynamical approach. (arXiv:1809.07608v1 [hep-ph])

    Authors: Fabio L. Braghin

    Form factors for pions interactions with constituent quarks are investigated as the leading effective couplings obtained from a one loop background field method applied to a global color model. Two pion field definitions are considered and the resulting pion and constituent quark form factors are expressed in terms of components of the quark and gluon propagators. Numerical results for different quark effective masses and two different nonperturbative gluon propagators are investigated. The corresponding averaged quadratic radii are also presented as functions of the quark effective mass.

  • Hadron Vacuum Polarization from application of DSEs with intended contours inspired by Gribov-Stingl conjecture of analytical confinement - Part I. (arXiv:1809.07644v1 [hep-ph])

    Authors: Vladimir Sauli

    Within the quark and gluonic degrees of freedom the hadronic vacuum polarization (HVP) is calculated for the spacelike as well as for the timelike momenta. For this purpose an old-fashionable strategy of the Gauge Technique, however within a new integral representations for Green's function is used to find QCD propagators and vertices. The functional method with a small admixture of complex conjugated poles (a Gribov-Stingl interaction) provides confining solution for the propagator of light quarks. The Feynman paramaterization method is extended to nonperturbative QCD via truncated system of Dyson-Schwinger equations (DSEs), which ensures manifestly correct analytical continuation between the Minkowski and the Euclidean space. The later 4d space is used for an analytical momentum integration of DSEs system. While the Gribov-Stingl conjecture offers a tempting explanation of confinement, an unnatural fine tuning is needed to avoid a potential conflict between the Unitarity and the renormalizability of the Standard Model. The paper is divided into two parts, the first part is more introductory and it provides the first result as well. The second part is devoted to technical details, proofs as well as it shows results based on slightly different approximation of DSEs system.

  • Total and differential cross sections for Higgs and top-quark production. (arXiv:1809.07651v1 [hep-ph])

    Authors: Nikolaos Kidonakis

    I present theoretical calculations for Higgs-boson and top-quark production, including high-order soft-gluon corrections. I discuss charged-Higgs production in association with a top quark or a $W$ boson, as well as single-top and top-antitop production. Total cross sections as well as transverse-momentum and rapidity distributions of the top quark or the Higgs boson are presented for various LHC energies.

  • ReSyst: a novel technique to Reduce the Systematic uncertainty for precision measurements. (arXiv:1809.07700v1 [])

    Authors: Petra Van Mulders

    We are in an era of precision measurements at the Large Hadron Collider. The precision that can be achieved on some of the measurements is limited however due to large systematic uncertainties. This paper introduces a new technique to reduce the systematic uncertainty by quantifying the systematic impact of single events and correlating it with event observables to identify parts of the phase space that are more sensitive to systematic effects. A proof of concept is presented by means of a simplified top quark mass estimator applied on simulated events. Even without a thorough optimization, it is shown that the total systematic uncertainty can be reduced by a factor of at least two.

  • Benchmarking the Inert Doublet Model for e+ e- colliders. (arXiv:1809.07712v1 [hep-ph])

    Authors: Jan Kalinowski, Wojciech Kotlarski, Tania Robens, Dorota Sokolowska, Aleksander Filip Zarnecki

    In this short note we present benchmarks for the Inert Doublet Model, a Two Higgs Doublet Model with a dark matter candidate. They are consistent with current constraints on direct detection, including the most recent bounds from the XENON1T experiment and relic density of dark matter, as well as with known collider and low-energy limits. We focus on parameter choices that promise detectable signals at lepton colliders via pair production of H+H- and HA. For these we choose a large variety of benchmark points with different kinematic features, leading to distinctly different final states in order to cover the large variety of collider signatures that can result from the model.

  • Oscillons in Higher-Derivative Effective Field Theories. (arXiv:1809.07724v1 [hep-th])

    Authors: Jeremy Sakstein, Mark Trodden

    We investigate the existence and behavior of oscillons in theories in which higher derivative terms are present in the Lagrangian, such as galileons. Such theories have emerged in a broad range of settings, from higher-dimensional models, to massive gravity, to models for late-time cosmological acceleration. By focusing on the simplest example---massive galileon effective field theories---we demonstrate that higher derivative terms can lead to the existence of completely new oscillons (quasi-breathers). We illustrate our techniques in the artificially simple case of 1 + 1 dimensions, and then present the complete analysis valid in 2 + 1 and 3 + 1 dimensions, exploring precisely how these new solutions are supported entirely by the non-linearities of the quartic galileon. These objects have the novel peculiarity that they are of the differentiability class $C^1$.

  • Glueballs and deconfinement temperature in AdS/QCD. (arXiv:1809.07730v1 [hep-ph])

    Authors: S.S. Afonin, A.D. Katanaeva

    We put forward an alternative way for estimations of the deconfinement temperature in bottom-up holographic models. The deconfinement in AdS/QCD is related to the Hawking-Page phase transition, in which the critical Hawking temperature is identified with the deconfinement one in the gauge theory. The numeric estimation of the latter is only possible when the parameters of a $5D$ dual model are previously determined from a consistency with other physical aspects, standardly, providing description of the QCD resonances. The traditional way of fixation of parameters in simplest AdS/QCD models is to reproduce the mass of the $\rho$ meson or the slope of the approximate radial Regge trajectory of the $\rho$ excitations. Motivated by a general idea that the slope value originates in gluodynamics, we propose to calculate the deconfinement temperature using the trajectory of scalar glueballs. We consider several holographic models and use the recent idea of isospectral potentials to make an additional check of the relevance of our approach. It is demonstrated that different models from an isospectral family (i.e. the models leading to identical predictions for spectrum of hadrons with fixed quantum numbers) result in different predictions for the deconfinement temperature. This difference is found to be quite small in the scalar glueball channel but very large in the vector one. The observed stability in the former case clearly favours the choice of the glueball channel for thermodynamic predictions in AdS/QCD models. As a balanced approach we argue that either assuming $f_0(1500)$ to have a dominating component of $0^{++}$ glueball or accepting the idea of the universality in the radial Regge trajectories of light non-strange vector mesons, one can reproduce the results for the deconfinement temperature obtained before in the lattice simulations in the background of non-dynamical quarks.

  • Recent Improvements for the Lepton Propagator PROPOSAL. (arXiv:1809.07740v1 [hep-ph])

    Authors: Mario Dunsch, Jan Soedingrekso, Alexander Sandrock, Maximilian Meier, Thorben Menne, Wolfgang Rhode

    The lepton propagator PROPOSAL is a Monte-Carlo Simulation library written in C++, propagating high energy muons and other charged particles through large distances of media. In this article, a restructuring of the code is described, which yields a performance improvement of up to $30\,\%$. For an improved accuracy of the propagation processes, more exact calculations of the leptonic and hadronic decay process and more precise parametrizations for the interaction cross sections are now available. The new modular structure allows a more flexible and custom usage, which is further facilitated with a python interface.

  • Interactions of Charmed Mesons with Light Pseudoscalar Mesons from Lattice QCD and Implications on the Nature of the D_{s0}^*(2317). (arXiv:1208.4535v3 [hep-lat] UPDATED)

    Authors: Liuming Liu, Kostas Orginos, Feng-Kun Guo, Christoph Hanhart, Ulf-G. Meißner

    We study the scattering of light pseudoscalar mesons ($\pi$, $K$) off charmed mesons ($D$, $D_s$) in full lattice QCD. The S-wave scattering lengths are calculated using L\"uscher's finite volume technique. We use a relativistic formulation for the charm quark. For the light quark, we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We calculate the scattering lengths of isospin-3/2 $D\pi$, $D_s\pi$, $D_sK$, isospin-0 $D\bar{K}$ and isospin-1 $D\bar{K}$ channels on the lattice. For the chiral extrapolation, we use a chiral unitary approach to next-to-leading order, which at the same time allows us to give predictions for other channels. It turns out that our results support the interpretation of the $D_{s0}^*(2317)$ as a $DK$ molecule. At the same time, we also update a prediction for the isospin breaking hadronic decay width $\Gamma(D_{s0}^*(2317)\to D_s\pi)$ to $(133\pm22)$ keV.

  • What is a parton shower?. (arXiv:1705.08093v3 [hep-ph] UPDATED)

    Authors: Zoltan Nagy, Davison E. Soper

    We consider idealized parton shower event generators that treat parton spin and color exactly, leaving aside the choice of practical approximations for spin and color. We investigate how the structure of such a parton shower generator is related to the structure of QCD. We argue that a parton shower with splitting functions proportional to $\alpha_s$ can be viewed not just as a model, but as the lowest order approximation to a shower that is defined at any perturbative order. To support this argument, we present a formulation for a parton shower at order $\alpha_s ^k$ for any $k$. Since some of the input functions needed are specified by their properties but not calculated, this formulation does not provide a useful recipe for an order $\alpha_s ^k$ parton shower algorithm. However, in this formulation we see how the operators that generate the shower are related to operators that specify the infrared singularities of QCD.

  • Spatially Modulated Vacua in a Lorentz-invariant Scalar Field Theory. (arXiv:1706.02938v3 [hep-th] UPDATED)

    Authors: Muneto Nitta, Shin Sasaki, Ryo Yokokura

    Spatial modulation has been studied for a long time in condensed matter, nuclear matter and quark matter, so far in non-relativistic field theories. In this paper, spatially modulated vacua at zero temperature and zero density are studied in relativistic field theories. We first propose an adaptation of the Nambu-Goldstone theorem to higher derivative theories under the assumption of the absence of ghosts: when a global symmetry is spontaneously broken due to vacuum expectation values of space-time derivatives of fields, a Nambu-Goldstone (NG) boson appears without a canonical kinetic (quadratic derivative) term with a quartic derivative term in the modulated direction while a Higgs boson appears with a canonical kinetic term. We demonstrate this in a simple model allowing (meta)stable modulated vacuum of a phase modulation (Fulde-Ferrell state), where an NG mode associated with spontaneously broken translational and $U(1)$ symmetries appears.

  • The economical 3-3-1 model revisited. (arXiv:1706.06152v3 [hep-ph] UPDATED)

    Authors: P. V. Dong, D. Q. Phong, D. V. Soa, N. C. Thao

    We show that the economical 3-3-1 model poses a very high new physics scale of the order of 1000~TeV due to the constraint on the flavor-changing neutral current. The implications of the model for neutrino masses, inflation, leptogenesis, and superheavy dark matter are newly recognized. Alternatively, we modify the model by rearranging the third quark generation differently from the first two quark generations, as well as changing the scalar sector. The resultant model now predicts a consistent new physics at TeV scale unlike the previous case and may be fully probed at the current colliders. Particularly, due to the minimal particle contents, the models under consideration manifestly accommodate dark matter candidates and neutrino masses, with novel and distinct production mechanisms. The large flavor-changing neutral currents that come from the ordinary and exotic quark mixings can be avoided due to the approximate $B-L$ symmetry.

  • Jets and threshold summation in Deductor. (arXiv:1711.02369v2 [hep-ph] UPDATED)

    Authors: Zoltan Nagy, Davison E. Soper

    We explore jet physics in hadron collisions using the parton shower event generator Deductor. Of particular interest is the one jet inclusive cross section dsigma/dpT for jets of very high pT. Compared to the Born level, the cross section decreases substantially because of pT loss from the jet during showering. We compare to the same effect in Pythia and Dire. The cross section then increases substantially because of the summation of threshold logarithms included in Deductor.

    We also study the cross section to have a gap with no jets between two hard jets that are widely separated in rapidity. Here we compare Deductor with virtuality based ordering with Deductor with kT ordering and we check whether adding an underlying event and hadronization has a significant effect beyond that found with just a parton shower.

  • Dark matter assisted Dirac leptogenesis and neutrino mass. (arXiv:1712.02960v2 [hep-ph] UPDATED)

    Authors: Nimmala Narendra, Nirakar Sahoo, Narendra Sahu

    We propose a minimal extension of the standard model with U(1)_{B-L} \times Z_{2} symmetry. In this model by assuming that the neutrinos are Dirac (i.e. $B-L$ is an exact symmetry), we found a simultaneous solution for non zero neutrino masses and dark matter content of the universe. The observed baryon asymmetry of the universe is also explained using Dirac Leptogenesis, which is assisted by a dark sector, gauged under a U(1)_D symmetry. The latter symmetry of the dark sector is broken at a TeV scale and thereby giving mass to a neutral gauge boson Z_D. The standard model Z-boson mixes with the gauge boson Z_D at one loop level and thus paves a way to detect the dark matter through spin independent elastic scattering at terrestrial laboratories.

  • A Simple Expression for Heavy to Light Meson Semileptonic Decays Form Factors. (arXiv:1801.09534v3 [hep-ph] UPDATED)

    Authors: T. N. Pham

    Like the two-photon and two-gluon decays of the $P$-wave $\chi_{c0,2}$ and $\chi_{b0,2}$ charmonium state for which the Born term produces a very simple decgays amplitude in terms of an effective Lagrangian with two-quark local operator, the Born term for the processes $c\bar{d} \to (\pi,K) \ell \nu $ and $b \bar{d}\to (\pi, K) \ell\nu $, could also produce the $D$ and $B$ meson semileptonic decays with the light meson $\pi, K$ in the final state. In this approach to heavy-light meson form factors with the $\pi$, K meson treated as Goldstone boson, a simple expression is found for the decays form factors, given as~: $ f_{+}(0)/(1 -q^{2}/(m_{H}^{2}+ m_{\pi}^{2}))$, with $H=D,B$ for $D,B \to \pi$ form factors, and $f_{+}(0)/(1 -q^{2}/(m_{H}^{2}+ m_{K}^{2}))$ for $B,D\to K$ form factor. The purpose of this paper is to show that this expression for the form factors could describe rather well the $q^{2}$- behaviour observed in the BaBar, Belle and BESIII measurements and lattice simulation. In particular, the $D\to K$ form factors are in good agreement with the measured values in the whole range of $q^{2}$ showing evidence for $SU(3)$ breaking with the presence of $m_{K}^{2}$ term in the quark propagator, but some corrections to the Born term are needed at large $q^{2}$ for $D,B \to \pi$ form factors.

  • Investigation of Dark Matter in the 3-2-3-1 Model. (arXiv:1802.10402v2 [hep-ph] UPDATED)

    Authors: D. T. Huong, P. V. Dong, N. T. Duy, N. T. Nhuan, L. D. Thien

    We prove that the $SU(3)_C\otimes SU(2)_L \otimes SU(3)_R\otimes U(1)_X$ (3-2-3-1) gauge model always contains a matter parity $W_P=(-1)^{3(B-L)+2s}$ as conserved residual gauge symmetry, where $B-L=2(\beta T_{8R}+X)$ is a $SU(3)_R\otimes U(1)_X$ charge. Due to the non-Abelian nature of $B-L$, the $W$-odd and $W$-even fields are actually unified in gauge multiplets. We investigate two viable versions for dark matter according to $\beta=\pm1/\sqrt{3}$, where the dark matter candidates can be fermion, scalar, or vector fields. We figure out the parameter spaces in the allowed regions of the relic density and direct detection cross-sections. Additionally, we examine the neutrino masses induced by the seesaw mechanism along with associated lepton flavor violation processes. The new gauge boson searches at the LEPII and LHC are discussed.

  • The $H_0$ Tension in Non-flat QCDM Cosmology. (arXiv:1803.07320v2 [astro-ph.CO] UPDATED)

    Authors: Haitao Miao, Zhiqi Huang

    The recent local measurement of Hubble constant leads to a more than $3\sigma$ tension with Planck + $\Lambda$CDM (Riess {\it et al} 2018). In this article we study the $H_0$ tension in non-flat QCDM cosmology, where Q stands for a minimally coupled and slowly-or-moderately rolling quintessence field $\phi$ with a smooth potential $V(\phi)$. By generalizing the QCDM one-parameter and three-parameter parametrizations in Huang {\it et al} 2011 to non-flat universe and using the latest cosmological data, we find that the $H_0$ tension remains above $3.2\sigma$ level for this class of model.

  • A pseudo-conformal equation of state in compact-star matter from topology change and hidden symmetries of QCD. (arXiv:1804.00305v5 [nucl-th] UPDATED)

    Authors: Yong-Liang Ma, Hyun Kyu Lee, Won-Gi Paeng, Mannque Rho

    We construct a new effective field theory approach to the equation of state (EoS), dubbed pseudo-confomal model "PCM," for nuclear and compact star matter entirely in terms of effective hadron degrees of freedom. The possible transition at $n\sim (2-4) n_0$ (where $n_0$ is the normal nuclear matter density) from hadron degrees of freedom to strongly-coupled quark degrees of freedom, giving rise to a soft-to-hard changeover in the EoS that can accommodate the massive stars observed, is effectuated by the topology change at $n_{1/2}\gsim 2n_0$ from skyrmions to half-skyrmions without involving local order-parameter fields. The mechanism exploits possible emergence of hidden scale and local symmetries of QCD at high density, leading to a precocious "pseudo-conformal" sound velocity $v_s^2=1/3$ (in unit of $c=1$) for $n\gsim 3n_0$. The resulting prediction signals a drastic departure from standard nuclear many-body theory in the density regime involved in the massive stars. We suggest that the tidal deformability implemented in gravitational waves coming from coalescing neutron stars in LIGO/Virgo-type observations could pin down the location of the topology change density $n_{1/2}$.

  • Heavy Quark Jet Fragmentation. (arXiv:1805.06014v2 [hep-ph] UPDATED)

    Authors: Lin Dai, Chul Kim, Adam K. Leibovich

    In this paper we study the fragmentation of a parton into a jet containing a heavy quark. When heavy quarks are involved in a jet, the quark mass can lead to a numerically significant correction to the jet cross section and its substructure. With this motivation, we calculated the heavy quark mass effects to next-to-leading order in $\alpha_s$ on the fragmentation functions to a jet (FFJs) and the jet fragmentation functions (JFFs), where the former describes fragmentation of parton into a jet and the latter describes fragmenting processes inside a jet. The finite size of the heavy quark mass does not change the ultraviolet behaviors, but it can give significant corrections to the finite contributions. When we take the zero mass limit, we find that the FFJs and the JFFs reproduce established results for massless partons. If we define the heavy quark jet as one that include at least one heavy (anti-)quark, the tagged heavy quark jet production is sensitive to the heavy quark mass and produces large logarithms of the mass. Taking advantage of the FFJs and JFFs, we formulate a factorization theorem for heavy quark jet production in order to resum these large logarithms systematically. As an application, we study inclusive $b$-jet production and show phenomenological implications due to keeping a non-zero quark mass.

  • Logarithmic accuracy of parton showers: a fixed-order study. (arXiv:1805.09327v3 [hep-ph] UPDATED)

    Authors: Mrinal Dasgupta, Frédéric A. Dreyer, Keith Hamilton, Pier Francesco Monni, Gavin P. Salam

    We formulate some first fundamental elements of an approach for assessing the logarithmic accuracy of parton-shower algorithms based on two broad criteria: their ability to reproduce the singularity structure of multi-parton matrix elements, and their ability to reproduce logarithmic resummation results. We illustrate our approach by considering properties of two transverse momentum ordered final-state showers, examining features up to second order in the strong coupling. In particular we identify regions where they fail to reproduce the known singular limits of matrix elements. The characteristics of the shower that are responsible for this also affect the logarithmic resummation accuracies of the shower, both in terms of leading (double) logarithms at subleading $N_C$ and next-to-leading (single) logarithms at leading $N_C$.

  • Actual Physics behind Mono-X. (arXiv:1805.11637v3 [hep-ph] UPDATED)

    Authors: Elias Bernreuther, Jan Horak, Tilman Plehn, Anja Butter

    Mono-X searches are standard dark matter search strategies at the LHC. First, we show how in the case of initial state radiation they essentially collapse to mono-jet searches. Second, we systematically study mono-X signatures from decays of heavier dark matter states. Direct detection constraints strongly limit our MSSM expectations, but largely vanish for mono-Z and mono-Higgs signals once we include light NMSSM mediators. Finally, the decay topology motivates mono-W-pair and mono-Higgs-pair searches, strengthening and complementing their mono-X counterparts.

  • Probing relic neutrino decays with 21 cm cosmology. (arXiv:1805.11717v2 [hep-ph] UPDATED)

    Authors: Marco Chianese, Pasquale Di Bari, Kareem Farrag, Rome Samanta

    We show how 21 cm cosmology can test relic neutrino radiative decays into sterile neutrinos. Using recent EDGES results, we derive constraints on the lifetime of the decaying neutrinos. If the EDGES anomaly will be confirmed, then there are two solutions, one for much longer and one for much shorter lifetimes than the age of the universe, showing how relic neutrino radiative decays can explain the anomaly in a simple way. We also show how to combine EDGES results with those from radio background observations, showing that potentially the ARCADE 2 excess can be also reproduced together with the EDGES anomaly within the proposed non-standard cosmological scenario. Our calculation of the specific intensity at the redshifts probed by EDGES can be also applied to the case of decaying dark matter and it also corrects a flawed expression appeared in previous literature.

  • Multipartite Dark Matter in $SU(2)_N$ extension of Standard Model and signatures at the LHC. (arXiv:1806.01129v2 [hep-ph] UPDATED)

    Authors: Basabendu Barman, Subhaditya Bhattacharya, Mohammadreza Zakeri

    An $SU(2)_N$ extension ($N$ stands for neutral) of the Standard Model (SM) is proposed with an additional $U(1)=S^{'}$ global symmetry, which stabilizes the lightest of the vector boson ($X,\bar{X}$) as dark matter (DM) through unbroken $S=T_{3N}+S^{'}$. The field content of the model is motivated to address neutrino mass generation, a possible unification to $SU(7)$, along with spontaneous symmetry breaking of $SU(2)_N$ resulting in massive gauge bosons. None of the SM particles are charged under $SU(2)_N$ and therefore $X,\bar{X}$ do not have a direct coupling to the visible sector besides a Higgs portal, which is tiny to avoid any conflict with Higgs data. We show that, a large kinematic region of this model allows the neutral component of $SU(2)_N$ scalar triplet and heavy neutrinos introduced here to become additional DM components. In this paper we explore the viability of such multipartite DM parameter space, including non-zero DM-DM interactions, to comply with relic density and direct search constraints. We also demonstrate that the model may yield hadronically quiet single lepton and two lepton signatures with missing energy at the Large Hadron Collider (LHC) that can be accessed with high luminosity.

  • $K^0\Lambda$ photoproduction off the neutron with nucleon resonances. (arXiv:1806.01992v2 [hep-ph] UPDATED)

    Authors: Sang-Ho Kim, Hyun-Chul Kim

    We investigate kaon photoproduction off the neutron target, i.e., $\gamma n \to K^0 \Lambda$, focusing on the role of nucleon resonances given in the Review of Particle Data Group in the range of $\sqrt{s} \approx 1600 - 2200$ MeV. We employ an effective Lagrangian method and a Regge approach. The strong couplings of nucleon resonances with $K\Lambda$ vertices are constrained by quark model predictions. The numerical results of the total and differential cross sections are found to be in qualitative agreement with the recent CLAS and FOREST experimental data. We discuss the effects of the narrow nucleon resonance $N(1685,1/2^+)$ on both the total and differential cross sections near the threshold energy. In addition, we present the results of the beam asymmetry as a prediction.

  • Long-lived stau, sneutrino dark matter and right-slepton spectrum. (arXiv:1806.04488v2 [hep-ph] UPDATED)

    Authors: Shankha Banerjee, Geneviève Bélanger, Avirup Ghosh, Biswarup Mukhopadhyaya

    The minimal supersymmetric (SUSY) standard model (MSSM) augmented by right chiral sneutrinos may lead to one such sneutrino serving as the lightest supersymmetric particle and a non-thermal dark matter candidate, especially if neutrinos have Dirac masses only. In such cases, if the lightest MSSM particle is a stau, the signal of SUSY at the LHC consists in stable charged tracks which are distinguishable from backgrounds through their time delay between the inner tracker and the muon chamber. We show how to determine in such scenarios the mass hierarchy between the lightest neutralino and right sleptons of the first two families. The techniques of neutralino reconstruction, developed in earlier works, are combined with the endpoint of the variable $M_{T2}$ in smuon (selectron) decays for this purpose. We show that one can thus determine the mass hierarchy for smuons (selectrons) and neutralinos up to 1 TeV, to the level of 5-10\%.

  • The effect of the scalar unparticle on the production of Higgs - radion at high energy colliders. (arXiv:1807.00457v2 [hep-ph] UPDATED)

    Authors: D. V. Soa, B. T. H. Giang

    An attempt is made to present the influence of the scalar unparticle on some scattering processes in the Randall - Sundum model. The contribution of the scalar unparticle on the production of Higgs - radion at high energy colliders is studied in detail. We evaluate the production cross-sections in the electron-positron ($e^{+}e^{-}$), photon-photon ($\gamma\gamma$) and gluon-gluon ($gg$) collisions, which depend strongly on the collision energy $\sqrt{s}$, the scaling dimension $d_{U}$ of the unparticle operator $\mathcal{O}_{U}$ and the energy scale $\Lambda_{U}$. Numerical evaluation shows that the cross - sections for the pair production of scalar particles are much larger than that of the associated production of the scalar particle with unparticle in the same condition

  • Cutoff of IceCube Neutrino Spectrum due to t-channel Resonant Absorption by C$\nu$B. (arXiv:1808.01272v2 [hep-ph] UPDATED)

    Authors: Subhendra Mohanty, Ashish Narang, Soumya Sadhukhan

    The non-observation of neutrinos by the IceCube at the Glashow resonance energy of 6.3 PeV has been a long standing unresolved issue. In this paper we propose a t-channel neutrino absorption by the C$\nu$B, which causes a cutoff at 4.5 PeV neutrino energy, to explain the IceCube observations. We present a neutrinophilic 2HDM where the neutrino masses are generated by a low scale seesaw mechanism. A $\mathcal{O}$(10) MeV scalar mediates the interactions between left and right handed neutrinos and generates the t-channel diagram used for explaining the absence of Glashow resonance. The same scalar mediates the annihilation of the dark matter and generates the correct relic density.

  • Let there be Light Dark Matter: The gauged $U(1)_{L_\mu-L_\tau}$ case. (arXiv:1808.03647v2 [hep-ph] UPDATED)

    Authors: Patrick Foldenauer

    As experimental null results increase the pressure on heavy weakly interacting massive particles (WIMPs) as an explanation of thermal dark matter (DM), it seems timely to explore previously overlooked regions of the WIMP parameter space. In this work we extend the minimal gauged $U(1)_{L_\mu-L_\tau}$ model studied in \cite{Bauer:2018onh} by a light (MeV-scale) vector-like fermion $\chi$. Taking into account constraints from cosmology, direct and indirect detection we find that the standard benchmark of $M_V=3 m_\chi$ for DM coupled to a vector mediator is firmly ruled out for unit DM charges. However, exploring the near-resonance region $M_V\gtrsim 2 m_\chi$ we find that this model can simultaneously explain the DM relic abundance $\Omega h^2 =0.12$ and the $(g-2)_\mu$ anomaly. Allowing for small charge hierarchies of $\lesssim\mathcal{O}(10)$, we identify a second window of parameter space in the few-GeV region, where $\chi$ can account for the full DM relic density.

  • An extension of the SM based on effective Peccei-Quinn Symmetry. (arXiv:1809.06563v2 [hep-ph] UPDATED)

    Authors: Daijiro Suematsu

    Peccei-Quinn (PQ) mechanism based on a chiral global U(1) symmetry is considered to be a simple and elegant solution for strong CP problem. Fact that the mechanism could be experimentally examined through the axion search makes it much more interesting and recently it causes a lot of attention again. However, it is also known that the mechanism is annoyed by two serious problems, that is, a domain wall problem and goodness of global symmetry. Any global symmetry is considered not to be exact due to the quantum effect of gravity. In this paper, we consider a solution to these problems, in which quark mass hierarchy and mixing, neutrino mass generation and existence of dark matter are closely related. In our solution, PQ symmetry is assumed to be induced through symmetry breaking at an intermediate scale of a local U(1) symmetry, and a global U(1) symmetry which plays a role of Froggatt-Nielsen symmetry . In the lepton sector, a remnant of the PQ symmetry controls neutrino mass generation and dark matter existence.

  • Non-linear mixing of Bogoliubov modes in a bosonic Josephson junction. (arXiv:1807.06682v1 [cond-mat.quant-gas] CROSS LISTED)

    Authors: Sofía Martínez-Garaot, Giulio Pettini, Michele Modugno

    We revisit the dynamics of a Bose-Einstein condensate in a double-well potential, from the regime of Josephson plasma oscillations to the self-trapping regime, by means of the Bogoliubov quasiparticle projection method. For very small imbalance between left and right wells only the lowest Bogoliubov mode is significantly occupied. In this regime the system performs plasma oscillations at the corresponding frequency, and the evolution of the condensate is characterized by a periodic transfer of population between the ground and the first excited state. As the initial imbalance is increased, more excited modes -- though initially not macroscopically occupied -- get coupled during the evolution of the system. Since their population also varies with time, the frequency spectrum of the imbalance turns out to be still peaked around a single frequency, which is continuously shifted towards lower values. The nonlinear mixing between Bogoliubov modes eventually drives the system into the the self-trapping regime, when the population of the ground state can be transferred completely to the excited states at some time during the evolution. For simplicity, here we consider a one-dimensional setup, but the results are expected to hold also in higher dimensions.

  • Squeezed vacuum used to accelerate the search for a weak classical signal. (arXiv:1809.06470v1 [quant-ph] CROSS LISTED)

    Authors: M. Malnou, D. A. Palken, B. M. Brubaker, Leila R. Vale, Gene C. Hilton, K. W. Lehnert

    Many experiments that interrogate fundamental theories now use detectors whose sensitivities are limited by the laws of quantum mechanics. For example, in cavity-based searches for axionic dark matter, vacuum fluctuations in the two quadratures of the cavity electromagnetic field limit the sensitivity to an axion-induced field. We demonstrate both theoretically and experimentally that such quantum limits can be overcome through the use of squeezed states in a search for a weak, classical signal of unknown frequency. By preparing a microwave cavity in a squeezed state and measuring just the squeezed quadrature, we find a squeezing-induced enhancement of the spectral scan rate by a factor of $2.12 \pm 0.08$. This enhancement is in quantitative agreement with our calculation which accounts for both imperfect squeezing and measurement.

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