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High Energy Physics - Phenomenology (hep-ph) updates on the e-print archive
  • Neutron Star Stability in Light of the Neutron Decay Anomaly. (arXiv:1811.06546v1 [hep-ph])

    Authors: Benjamin Grinstein, Chris Kouvaris, Niklas Grønlund Nielsen

    A recent proposal suggests that experimental discrepancies on the lifetime of neutrons can be resolved if neutrons decay to dark matter. At the same time it has been demonstrated that such a decay mode would soften the nuclear equation of state resulting in neutron stars with a maximum mass much below currently observed ones. In this paper we demonstrate that appropriate dark matter-baryon interactions can accommodate neutron stars with mass above 2 solar masses. We also show that dark matter self-interactions could also help neutrons stars reach 2 solar masses provided that dark matter is of asymmetric nature.

  • Self-Interacting Dark Matter Through the Majoron Portal. (arXiv:1811.06619v1 [hep-ph])

    Authors: Arvind Rajaraman, Jordan Smolinsky

    We examine the phenomenology of the majoron portal: a simplified model of fermionic dark matter coupled to a light scalar mediator carrying lepton number 2. We find that the mediator can be very light and still consistent with laboratory and cosmological bounds. This model satisfies the thermal relic condition for natural values of dimensionless coupling constants and admits a mediator in the $10 - 100 ~\text{MeV}$ mass range favored by small scale structure observations. As such, this model provides an excellent candidate for self-interacting dark matter.

  • Physics Potentials of the Hyper-Kamiokande Second Detector in Korea. (arXiv:1811.06682v1 [hep-ex])

    Authors: Seon-Hee Seo (for the Hyper-Kamiokande Proto-Collaboration)

    Hyper-Kamiokande (Hyper-K) succeeds the very successful Super-K experiment and will consist of a large detector filled with 260~kton purified water and equipped with 40\% photo-coverage. Physics program of Hyper-K is broad, covering from particle physics to astrophysics and astronomy. The Hyper-K 1$^{st}$ detector will be built in Japan, and the 2$^{nd}$ detector is considered to be built in Korea because locating the 2$^{nd}$ detector in Korea improves physics sensitivities in most cases thanks to the longer baseline ($\sim$1,100~km) and larger overburden ($\sim$1,000~m) for Korean candidate sites. In this talk, we present overview and physics potentials of the Hyper-K 2$^{nd}$ detector in Korea.

  • Confronting hadronic tau decays with non-leptonic kaon decays. (arXiv:1811.06706v1 [hep-ph])

    Authors: Antonio Rodríguez Sánchez, Antonio Pich

    In the chiral limit, the $D=6$ contribution to the Operator Product Expansion (OPE) of the $\mathrm{VV-AA}$ correlator of quark currents only depends on two vacuum condensates, which can be related to hadronic matrix elements associated to CP violation in non-leptonic kaon decays. We use those relations to determine $\langle(\pi\pi)_{I=2}|\mathcal{Q}_{8}|K\rangle$, using the updated ALEPH spectral functions. Alternatively, we use those relations in the opposite direction. Taking the values of the matrix elements from the lattice to obtain the $D=6$ vacuum elements provides a new short-distance constraint which allows for an inclusive determination of $f_{\pi}$ and an updated value for the $D=8$ condensate.

  • Correlation observables in $\Upsilon D$ pair production at the LHC within the parton Reggeization approach. (arXiv:1811.06733v1 [hep-ph])

    Authors: Anton Karpishkov, Maxim Nefedov, Vladimir Saleev

    We study angular correlations in associated hadroproduction of $\Upsilon(1S)$ with the $D^{\pm}$ and $D^0$-mesons at the LHC in the Leading Order of the parton Reggeization approach. Hadronization of $b\bar{b}$-pair to $\Upsilon(1S)$ is described within the NRQCD-factorization framework. Production of $D-$mesons is described in the fragmentation model with scale-dependent fragmentaion functions. We have found good agreement with LHCb data for various differential distributions, except for the case of spectra on azimuthal angle differences at the small $\triangle\varphi$ values. The total cross-section in our Single Parton Scattering model, calculated under conservative assumptions, accounts for almost one half of observed cross-section, thus dramatically shrinking the room for Double Parton Scattering mechanism.

  • Muon-electron scattering at NLO. (arXiv:1811.06743v1 [hep-ph])

    Authors: Massimo Alacevich, Carlo M. Carloni Calame, Mauro Chiesa, Guido Montagna, Oreste Nicrosini, Fulvio Piccinini

    We consider the process of muon-electron elastic scattering, which has been proposed as an ideal framework to measure the running of the electromagnetic coupling constant at space-like momenta and determine the leading-order hadronic contribution to the muon $g-2$ (MUonE experiment). We compute the next-to-leading (NLO) contributions due to QED and purely weak corrections and implement them into a fully differential Monte Carlo event generator, which is available for first experimental studies. We show representative phenomenological results of interest for the MUonE experiment and examine in detail the impact of the various sources of radiative corrections under different selection criteria, in order to study the dependence of the NLO contributions on the applied cuts. The study represents the first step towards the realisation of a high-precision Monte Carlo code necessary for data analysis.

  • Analysis of the duration--hardness ratio plane of gamma-ray bursts using skewed distributions. (arXiv:1811.06745v1 [astro-ph.HE])

    Authors: Mariusz Tarnopolski

    The two widely accepted classes of gamma-ray bursts (GRBs), short and long, are with confidence ascribed to mergers of compact objects and collapse of massive stars, respectively. A third, intermediate/soft class, remains putative. Its existence was claimed based on univariate and bivariate analyses of GRB observables modeled with Gaussian distributions. This, however, may not be the appropriate approach, as it has been already shown that the univariate distributions of durations are better described by mixtures of two skewed components rather than three Gaussian ones.

    This paper investigates whether data in the duration--hardness ratio plane is better modeled by mixtures of skewed bivariate distributions than by normal ones. The archival data set of the Compton Gamma-Ray Observatory/BATSE and Fermi/GBM data from the most recent catalogue release are examined. The preferred model is chosen based on two information criteria, Akaike ($AIC$) and Bayesian ($BIC$). It is found that the best description is given by a two-component mixture of skewed Student-$t$ distributions, which outperforms any other model considered. This implies that the distribution of the studied parameters is intrinsically skewed, introducing spurious Gaussian components, and hence the third class is unlikely to be a real phenomenon. Its existence, based on statistical inference, is therefore rejected as unnecessary to explain the observations.

  • $\pi-N$ Drell-Yan process in TMD factorization. (arXiv:1811.06813v1 [hep-ph])

    Authors: Xiaoyu Wang, Zhun Lu

    This article presents the review of the current understanding on the pion-nucleon Drell-Yan process from the point of view of the TMD factorization. Using the evolution formalism for the unpolarized and polarized TMD distributions developed recently, we provide the theoretical expression of the relevant physical observables, namely, the unpolarized cross section, the Sivers asymmetry, and the $\cos2\phi$ asymmetry contributed by the double Boer-Mulders effect. The corresponding phenomenology, particularly at the kinematical configuration of the COMPASS $\pi N$ Drell-Yan, is displayed numerically.

  • Paleo-detectors: Searching for Dark Matter with Ancient Minerals. (arXiv:1811.06844v1 [astro-ph.CO])

    Authors: Andrzej K. Drukier, Sebastian Baum, Katherine Freese, Maciej Górski, Patrick Stengel

    Recently, we proposed paleo-detectors as a method for the direct detection of Weakly Interacting Massive Particle (WIMP) dark matter. In paleo-detectors, one would search for the persistent traces left by dark matter-nucleon interactions in ancient minerals. Thanks to the large integration time of paleo-detectors, relatively small target masses suffice to obtain exposures, i.e. the product of integration time and target mass, much larger than what is feasible in the conventional direct detection approach. Here, we discuss the paleo-detector proposal in detail, in particular, a range of background sources. For low-mass WIMPs with masses $m_\chi\lesssim10\,$GeV, the largest contribution to the background budget comes from nuclear recoils induced by coherent scattering of solar neutrinos. For heavier WIMPs, the largest background source is nuclear recoils induced by fast neutrons created by heavy radioactive contaminants, particularly $^{238}$U; neutrons can arise in spontaneous fission or from $\alpha$-particles created in $^{238}$U decays. We also discuss the challenges of mineral optimization, specifically the determination of readily available minerals from rocks in deep boreholes which are able to record persistent damage from nuclear recoils. In order to suppress backgrounds induced by radioactive contaminants, we propose to use minerals found in marine evaporites or in ultra-basic rocks. We estimate the sensitivity of paleo-detectors to spin-independent and spin-dependent WIMP-nucleus interactions. In all interaction cases considered here, the sensitivity to low-mass WIMPs with masses $m_\chi\lesssim10\,$GeV extends to WIMP-nucleon cross sections many orders of magnitude smaller than current upper limits. For heavier WIMPs with masses $m_\chi\gtrsim30\,$GeV cross sections a factor of a few to $\sim100$ smaller than current upper limits can be probed by paleo-detectors. [Abridged]

  • Vacuum structure of the left-right symmetric model. (arXiv:1811.06869v1 [hep-ph])

    Authors: P.S. Bhupal Dev, Rabindra N. Mohapatra, Werner Rodejohann, Xun-Jie Xu

    The left-right symmetric model (LRSM), originally proposed to explain parity violation in low energy processes, has since emerged as an attractive framework for light neutrino masses via the seesaw mechanism. The scalar sector of the minimal LRSM consists of an $SU(2)$ bi-doublet, as well as left- and right-handed weak isospin triplets, thus making the corresponding vacuum structure much more complicated than that of the Standard Model. In particular, the desired ground state of the Higgs potential should be a charge conserving, and preferably global, minimum with parity violation at low scales. We show that this is not a generic feature of the LRSM potential and happens only for a small fraction of the parameter space of the potential. We also analytically study the potential for some simplified cases and obtain useful conditions (though not necessary) to achieve successful symmetry breaking. We then carry out a detailed statistical analysis of the minima of the Higgs potential using numerical minimization and find that for a large fraction of the parameter space, the potential does not have a good vacuum. Imposing the analytically obtained conditions, we can readily find a small part of the parameter space with good vacua. Consequences for some scalar masses are also discussed.

  • $\tau$ decay into a pseudoscalar and an axial-vector meson. (arXiv:1811.06875v1 [hep-ph])

    Authors: L. R. Dai, L. Roca, E. Oset

    We study theoretically the decay $\tau^- \to \nu_\tau P^- A$, with $P^-$ a $\pi^-$ or $K^-$ and $A$ an axial-vector resonance $b_1(1235)$, $h_1(1170)$, $h_1(1380)$, $a_1(1260)$, $f_1(1285)$ or any of the two poles of the $K_1(1270)$. The process proceeds through a triangle mechanism where a vector meson pair is first produced from the weak current and then one of the vectors produces two pseudoscalars, one of which reinteracts with the other vector to produce the axial resonance. For the initial weak hadronic production we use a recent formalism to account for the hadronization after the initial quark-antiquark pair produced from the weak current, which explicitly filters G-parity states and obtain easy analytic formulas after working out the angular momentum algebra. The model also takes advantage of the chiral unitary theories to evaluate the vector-pseudoscalar amplitudes, where the axial-vector resonances were obtained as dynamically generated from the VP interaction. We make predictions for invariant mass distribution and branching ratios for the channels considered.

  • Two-photon exchange in nonrelativistic approximation. (arXiv:1811.06928v1 [hep-ph])

    Authors: Dmitry Borisyuk, Alexander Kobushkin

    We calculate two-photon exchange amplitudes for the elastic electron-hadron scattering in the nonrelativistic approximation, and obtain analytical formulae for them. Numerical calculations are performed for proton and $^3$He targets. Comparing our numerical results with relativistic calculations, we find that the real part of the amplitude is described well at moderate $Q^2$, but the imaginary part strongly differs from the relativistic result. Thus the nonrelativistic approximation should not be used for calculation of observables which depend on the imaginary part of the amplitude, such as single-spin asymmetries.

  • Angular decorrelations in $\gamma + 2 jet$ events at high energies in the parton Reggeization approach. (arXiv:1811.06942v1 [hep-ph])

    Authors: Anton Karpishkov, Vladimir Saleev, Alexandra Shipilova

    We discuss associated production of prompt photon plus two jets at high energies in the framework of the parton Reggeization approach, which is based on multi-Regge factorization of hard processes and Lipatov's effective theory of Reggeized gluons and quarks. In this approach, initial-state off-shell effects and transverse momenta of initial partons are included in a gauge-invariant way. We compute transverse momentum spectra of prompt photons in inclusive $\gamma-$production, in $\gamma + jet$ and $\gamma+2jets$ events, and azimuthal angle difference spectrum in $\gamma + 2 jet$ events. We compare our results with the experimental data from D0 Collaboration at Tevatron and with the theoretical predictions obtained in conventional NLO approximation of the collinear parton model. The relation between SPS and DPS production mechanisms is also studied.

  • Exploring Inert Scalars at CLIC. (arXiv:1811.06952v1 [hep-ph])

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

    We investigate the prospect of discovering the Inert Doublet Model scalars at CLIC. As signal processes, we consider the pair-production of inert scalars, namely e+e- -> H+H- and e+e- -> AH, followed by decays of charged scalars H+ and neutral scalars A into leptonic final states and missing transverse energy. We focus on signal signatures with two muons or an electron and a muon pair in the final state. A number of selected benchmark scenarios that cover the range of possible collider signatures of the IDM are considered. For the suppression of SM background with the same visible signature, multivariate analysis methods are employed. For several benchmark points discovery is already possible at low-energy stage of CLIC. Prospects of investigating scenarios that are only accessible at higher collider energies are also discussed.

  • Gluequark Dark Matter. (arXiv:1811.06975v1 [hep-ph])

    Authors: Roberto Contino, Andrea Mitridate, Alessandro Podo, Michele Redi

    We introduce the gluequark Dark Matter candidate, an accidentally stable bound state made of adjoint fermions and gluons from a new confining gauge force. Such scenario displays an unusual cosmological history where perturbative freeze-out is followed by a non-perturbative re-annihilation period with possible entropy injection. When the gluequark has electroweak quantum numbers, the critical density is obtained for masses as large as PeV. Independently of its mass, the size of the gluequark is determined by the confinement scale of the theory, leading at low energies to annihilation rates and elastic cross sections which are large for particle physics standards and potentially observable in indirect detection experiments.

  • Spin-3/2 dark matter in a simple $t$-channel model. (arXiv:1705.05149v3 [hep-ph] UPDATED)

    Authors: Mohammed Omer Khojali, Ashok Goyal, Mukesh Kumar, Alan S. Cornell

    We consider a spin-3/2 fermionic dark matter (DM) particle interacting with the Standard Model quarks through the exchange of a charged and coloured scalar or vector mediator in a simple $t$-channel model. It is found that for the vector mediator case, almost the entire parameter space allowed by the observed relic density is already ruled out by the direct detection LUX data. No such bounds exist on the interaction mediated by scalar particles. Monojet + missing energy searches at the Large Hadron Collider provide the most stringent bounds on the parameters of the model for this case. The collider bounds put a lower limit on the allowed DM masses.

  • Directly Detecting MeV-scale Dark Matter via Solar Reflection. (arXiv:1708.03642v3 [hep-ph] UPDATED)

    Authors: Haipeng An, Maxim Pospelov, Josef Pradler, Adam Ritz

    If dark matter (DM) particles are lighter than a few MeV/$c^2$ and can scatter off electrons, their interaction within the solar interior results in a considerable hardening of the spectrum of galactic dark matter received on Earth. For a large range of the mass vs. cross section parameter space, $\{m_e, \sigma_e\}$, the "reflected" component of the DM flux is far more energetic than the endpoint of the ambient galactic DM energy distribution, making it detectable with existing DM detectors sensitive to an energy deposition of $10-10^3$ eV. After numerically simulating the small reflected component of the DM flux, we calculate its subsequent signal due to scattering on detector electrons, deriving new constraints on $\sigma_e$ in the MeV and sub-MeV range using existing data from the XENON10/100, LUX, PandaX-II, and XENON1T experiments, as well as making projections for future low threshold direct detection experiments.

  • Search for sterile neutrinos in a universe of vacuum energy interacting with cold dark matter. (arXiv:1712.03148v2 [astro-ph.CO] UPDATED)

    Authors: Lu Feng, Jing-Fei Zhang, Xin Zhang

    We investigate the cosmological constraints on sterile neutrinos in a universe in which vacuum energy interacts with cold dark matter by using latest observational data. We focus on two specific interaction models, $Q=\beta H\rho_{\rm v}$ and $Q=\beta H\rho_{\rm c}$. To overcome the problem of large-scale instability in the interacting dark energy scenario, we employ the parametrized post-Friedmann (PPF) approach for interacting dark energy to do the calculation of perturbation evolution. The observational data sets used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation measurements, the type-Ia supernova data, the Hubble constant direct measurement, the galaxy weak lensing data, the redshift space distortion data, and the Planck lensing data. Using the all-data combination, we obtain $N_{\rm eff}<3.522$ and $m_{\nu,{\rm sterile}}^{\rm eff}<0.576$ eV for the $Q=\beta H\rho_{\rm v}$ model, and $N_{\rm eff}=3.204^{+0.049}_{-0.135}$ and $m_{\nu,{\rm sterile}}^{\rm eff}=0.410^{+0.150}_{-0.330}$ eV for the $Q=\beta H\rho_{\rm c}$ model. The latter indicates $\Delta N_{\rm eff}>0$ at the 1.17$\sigma$ level and a nonzero mass of sterile neutrino at the 1.24$\sigma$ level. In addition, for the $Q=\beta H\rho_{\rm v}$ model, we find that $\beta=0$ is consistent with the current data, and for the $Q=\beta H\rho_{\rm c}$ model, we find that $\beta>0$ is obtained at more than 1$\sigma$ level.

  • Statistical approach of pion parton distributions from Drell-Yan process. (arXiv:1802.03153v3 [hep-ph] UPDATED)

    Authors: Claude Bourrely, Jacques Soffer

    The quantum statistical approach proposed more than one decade ago was used to determine the parton distributions for the proton by considering a large set of accurate Deep Inelastic Scattering experimental results. We propose to extend this work to extract the parton distributions for the pion by using data on lepton pair production from various experiments. This global next-to-leading order QCD analysis leads to a good description of several Drell-Yan $\pi^- W$ data. The resulting parton distributions are compared with earlier determinations. We will also discuss the difference between nucleon and pion structure in the same approach.

  • Electroweak interaction beyond the Standard Model and Dark Matter in the Tangent Bundle Quantum Field Theory. (arXiv:1802.03228v2 [hep-ph] UPDATED)

    Authors: Joachim Herrmann

    A generalized theory of electroweak interaction is developed based on the underlying geometrical structure of the tangent bundle with symmetries arising from transformations of tangent vectors along the fiber axis at a fixed space-time point, leaving the scalar product invariant. Transformations with this property are given by the $SO(3,1)$ group with the little groups $SU(2),E^{c}(2)$ and $SU(1,1)$ where the group $E^{c}(2)$ is the central extended group of the Euclidian group $E(2).$ Electroweak interaction beyond the standard model (SM) is described by the transformation group $SU(2)\otimes E^{c}\mathbf{(}2)$ without a priori introduction of a phenomenologically determined gauge group. The Laplacian on this group yields the known internal quantum numbers of isospin and hypercharge, but in addition the extra $E^{c}$-charge $\varkappa $ and the family quantum number $n$ which explains the existence of families in the SM. The connection coefficients deliver the SM gauge potentials but also hypothetical gauge bosons and other hypothetical particles as well as candidate Dark Matter particles are predicted. It is shown that the interpretation of the $SO(3,1)$ connection coefficients as elctroweak gauge potentials is compatible with teleparallel gauge gravity theory based on the translational group.

  • Polarization observables and T-noninvariance in the weak charged current induced electron proton scattering. (arXiv:1802.04469v2 [hep-ph] UPDATED)

    Authors: A. Fatima, M. Sajjad Athar, S. K. Singh

    In this work, we have studied the total scattering cross section ($\sigma$), differential scattering cross section ($d\sigma/dQ^2$) as well as the longitudinal ($P_L(E_e,Q^2)$), perpendicular ($P_P(E_e,Q^2)$), and transverse ($P_T(E_e,Q^2)$) components of the polarization of the final hadron ($n$, $ \Lambda$ and $\Sigma^0$) produced in the electron proton scattering induced by the weak charged current. We have not assumed T-invariance which allows the transverse component of the hadron polarization perpendicular to the production plane to be non-zero. The numerical results are presented for all the above observables and their dependence on the axial vector form factor and the weak electric form factor are discussed. The present study enables the determination of the axial vector nucleon-hyperon transition form factors at high $ Q^2$ in the strangeness sector which can provide test of the symmetries of the weak hadronic currents like T-invariance and SU(3) symmetry while assuming the hypothesis of conserved vector current and partial conservation of axial vector current.

  • Mapping the sensitivity of hadronic experiments to nucleon structure. (arXiv:1803.02777v3 [hep-ph] UPDATED)

    Authors: Bo-Ting Wang, T. J. Hobbs, Sean Doyle, Jun Gao, Tie-Jiun Hou, Pavel M. Nadolsky, Fredrick I. Olness

    Determinations of the proton's collinear parton distribution functions (PDFs) are emerging with growing precision due to increased experimental activity at facilities like the Large Hadron Collider. While this copious information is valuable, the speed at which it is released makes it difficult to quickly assess its impact on the PDFs, short of performing computationally expensive global fits. As an alternative, we explore new methods for quantifying the potential impact of experimental data on the extraction of proton PDFs. Our approach relies crucially on the Hessian correlation between theory-data residuals and the PDFs themselves, as well as on a newly defined quantity --- the sensitivity --- which represents an extension of the correlation and reflects both PDF-driven and experimental uncertainties. This approach is realized in a new, publicly available analysis package PDFSense, which operates with these statistical measures to identify particularly sensitive experiments, weigh their relative or potential impact on PDFs, and visualize their detailed distributions in a space of the parton momentum fraction $x$ and factorization scale $\mu$. This tool offers a new means of understanding the influence of individual measurements in existing fits, as well as a predictive device for directing future fits toward the highest impact data and assumptions. Along the way, many new physics insights can be gained or reinforced. As one of many examples, PDFSense is employed to rank the projected impact of new LHC measurements in jet, vector boson, and $t\bar{t}$ production and leads us to the conclusion that inclusive jet production at the LHC has a potential for playing an indispensable role in future PDF fits. These conclusions are independently verified by preliminarily fitting this experimental information and investigating the constraints they supply using the Lagrange multiplier technique.

  • Nonperturbative Renormalization of Operators in Near-Conformal Systems Using Gradient Flows. (arXiv:1806.01385v3 [hep-lat] UPDATED)

    Authors: Andrea Carosso, Anna Hasenfratz, Ethan T. Neil

    We propose a continuous real space renormalization group transformation based on gradient flow, allowing for a numerical study of renormalization without the need for costly ensemble matching. We apply our technique in a pilot study of SU$(3)$ gauge theory with $N_f = 12$ fermions in the fundamental representation, finding the mass anomalous dimension to be $\gamma_m = 0.23(6)$, consistent with other perturbative and lattice estimates. We also present the first lattice calculation of the nucleon anomalous dimension in this theory, finding $\gamma_N = 0.05(5)$.

  • Natural Inflation with a periodic non-minimal coupling. (arXiv:1806.05511v3 [astro-ph.CO] UPDATED)

    Authors: Ricardo Z.Ferreira, Alessio Notari, Guillem Simeon

    Natural inflation is an attractive model for primordial inflation, since the potential for the inflaton is of the pseudo Nambu-Goldstone form, $V(\phi)=\Lambda^4 [1+\cos (\phi/f)]$, and so is protected against radiative corrections. Successful inflation can be achieved if $f \gtrsim {\rm few}\, M_{P}$ and $\Lambda \sim m_{GUT}$ where $\Lambda$ can be seen as the strong coupling scale of a given non-abelian gauge group. However, the latest observational constraints put natural inflation in some tension with data. We show here that a non-minimal coupling to gravity $\gamma^2(\phi) R$, that respects the symmetry $\phi\rightarrow \phi+2 \pi f$ and has a simple form, proportional to the potential, can improve the agreement with cosmological data. Moreover, in certain cases, satisfactory agreement with the Planck 2018 TT, TE, EE and low P data can be achieved even for a periodicity scale of approximately $M_p$.

  • Consistency of a gauged two-Higgs-doublet model: Scalar sector. (arXiv:1806.05632v2 [hep-ph] UPDATED)

    Authors: Abdesslam Arhrib, Wei-Chih Huang, Raymundo Ramos, Yue-Lin Sming Tsai, Tzu-Chiang Yuan

    We study the theoretical and phenomenological constraints imposed on the scalar sector of the gauged two Higgs doublet model proposed recently as a variant of the popular inert Higgs doublet model of dark matter. The requirements of tree-level vacuum stability and perturbative unitarity in the scalar sector are analyzed in detail. Furthermore, taking into account the constraints from the 125 GeV Higgs boson measurements at the Large Hadron Collider, we map out the allowed ranges for the fundamental parameters of the scalar potential in the model.

  • Second class currents and T violation in quasielastic neutrino and antineutrino scattering from nucleons. (arXiv:1806.08597v2 [hep-ph] UPDATED)

    Authors: A. Fatima, M. Sajjad Athar, S. K. Singh

    The effect of the second class currents with and without time reversal invariance has been studied in the quasielastic production of nucleons and hyperons induced by neutrinos and antineutrinos from the nucleons. The numerical results are presented for the total scattering cross section~($\sigma$) as well as for the longitudinal, perpendicular and transverse components of the polarization of the final baryons ($p$, $n$, $\Lambda$, $\Sigma^-$, $\Sigma^0$) and muon produced in the quasielastic (anti)neutrino-nucleon scattering induced by the weak charged current. In the case of the production of $\Lambda$ hyperon, which is the most suitable candidate for making the polarization measurements, we have also calculated the $Q^2$ dependence of the polarization observables and the differential scattering cross section ($d\sigma/dQ^2$). The measurement of the polarization observables and their $Q^2$ dependence provides an independent way to determine the nucleon-hyperon transition form factors at high $Q^2$ which can provide tests of the symmetries of the weak hadronic currents like G-invariance, T invariance and SU(3) symmetry.

  • Matter parametric neutrino flavor transformation through Rabi resonances. (arXiv:1807.10219v2 [hep-ph] UPDATED)

    Authors: Lei Ma (UNM), Shashank Shalgar (LANL), Huaiyu Duan (UNM)

    We consider the flavor transformation of neutrinos through oscillatory matter profiles. We show that the neutrino oscillation Hamiltonian in this case describes a Rabi system with an infinite number of Rabi modes. We further show that, in a given physics problem, the majority of the Rabi modes have too small amplitudes to be relevant. We also go beyond the rotating wave approximation and derive the relative detuning of the Rabi resonance when multiple Rabi modes with small amplitudes are present. We provide an explicit criterion of whether an off-resonance Rabi mode can affect the parametric flavor transformation of the neutrino.

  • Heavy Higgs boson decays in the alignment limit of the 2HDM. (arXiv:1808.01472v3 [hep-ph] UPDATED)

    Authors: Bohdan Grzadkowski, Howard E. Haber, Odd Magne Ogreid, Per Osland

    The Standard Model (SM)-like couplings of the observed Higgs boson impose strong constraints on the structure of any extended Higgs sector. We consider the theoretical properties and the phenomenological implications of a generic two Higgs doublet model (2HDM). This model constitutes a simple and attractive extension of the SM that is consistent with the observation of the SM-like Higgs boson and precision electroweak observables, while providing a potential new source of CP-violation. In this paper we focus on the so-called Higgs alignment limit of the generic 2HDM, where the neutral scalar field~$H_1$, with the tree-level couplings of the SM Higgs boson, is a mass eigenstate that is aligned in field space with the direction of the Higgs vacuum expectation value. The properties of the two other heavier neutral Higgs scalars, $H_2$ and $H_3$, in the alignment limit of the 2HDM are also elucidated. It is shown that the couplings of $H_2$ and $H_3$ in the alignment limit are tightly constrained and correlated. For example, in the exact alignment limit at tree level, for bosonic final states $\text{BR}(H_{2,3} \to W^+W^-, ZZ, H_1 Z) = 0$ and $\text{BR}(H^\pm \to W^\pm H_1) = 0$, whereas for fermionic final states $\Gamma(H_2 \to f\bar f)/\Gamma(H_3 \to f\bar f) \sim M_2/M_3$ (where $M_\alpha$ is the mass of $H_\alpha$). In some cases, the results of the alignment limit differ depending on whether or not alignment is achieved via the decoupling of heavy scalar states. In particular, in the exact alignment limit without decoupling $\text{BR}(H_{2,3}\to H_1 H_1)=0$, whereas these branching ratios are nonzero in the decoupling regime. Observables that could be used to test the alignment scenario at the LHC are defined and discussed. The couplings of the Higgs bosons away from their exact alignment values are determined to leading order, and some consequences are elucidated.

  • Footprints of New Physics in $b\to c\tau\nu$ Transitions. (arXiv:1808.03565v2 [hep-ph] UPDATED)

    Authors: Zhuo-Ran Huang, Ying Li, Cai-Dian Lu, M. Ali Paracha, Chao Wang

    In this work, we perform a combined analysis of the $R(D)$, $R(D^*)$, and $R(J/\psi)$ anomalies in a model-independent manner based on the general framework of the four-fermion effective field theory, paying special attention to the use of the hadronic form factors. For the $B\to D(D^*)$ transition form factors, we use the HQET parametrization that includes the higher order corrections of $\mathcal{O}(\alpha_s,\Lambda_{\mathrm{QCD}}/m_{b,c})$ and was determined recently from a fit to lattice QCD and light-cone sum rule results in complementary kinematical regions of the momentum transfer. For the $B_c\to J/\psi(\eta_c)$ transitions, we use the form factors calculated in the covariant light-front quark model, which are found to be well consistent with the preliminary lattice results. With this particular treatment of hadronic matrix elements, in our analysis the two classes of vector operators are shown to be the most favored single new physics (NP) operators by the current experimental constraints within $2\sigma$ and the LEP1 data on $Br(B_c\to \tau\nu)$ as well as the minimum $\chi^2$ fit, while the tensor operator is also allowed but severely constrained, and the scalar ones are excluded. Using the favored ranges and fitted values of the Wilson coefficients of the single NP operators, we also give a prognosis for the physical observables such as the ratios of decay rates ($R(D(D^*)), R(J/\psi(\eta_c))$) and other polarized observables as well as the $q^2$ distributions.

  • Symmetries and Mass Degeneracies in the Scalar Sector. (arXiv:1808.08629v2 [hep-ph] UPDATED)

    Authors: Howard E. Haber, O.M. Ogreid, P. Osland, M.N. Rebelo

    We explore some aspects of models with two and three SU(2) scalar doublets that lead to mass degeneracies among some of the physical scalars. In Higgs sectors with two scalar doublets, the exact degeneracy of scalar masses, without an artificial fine-tuning of the scalar potential parameters, is possible only in the case of the inert doublet model (IDM), where the scalar potential respects a global U(1) symmetry that is not broken by the vacuum. In the case of three doublets, we introduce and analyze the replicated inert doublet model, which possesses two inert doublets of scalars. We then generalize this model to obtain a scalar potential, first proposed by Ivanov and Silva, with a CP4 symmetry that guarantees the existence of pairwise degenerate scalar states among two pairs of neutral scalars and two pairs of charged scalars. Here, CP4 is a generalized CP symmetry with the property that (CP4)^n is the identity operator only for integer n values that are multiples of 4. The form of the CP4-symmetric scalar potential is simplest when expressed in the Higgs basis, where the neutral scalar field vacuum expectation value resides entirely in one of the scalar doublet fields. The symmetries of the model permit a term in the scalar potential with a complex coefficient that cannot be removed by any redefinition of the scalar fields within the class of Higgs bases (in which case, we say that no real Higgs basis exists). We demonstrate that it is possible to physically distinguish between the existence or nonexistence of a real Higgs basis in three doublet scalar models governed by a CP4-symmetric scalar potential and vacuum. A striking feature of the CP4-symmetric model is that it preserves CP even in the absence of a real Higgs basis, as illustrated by the cancellation of the contributions to the CP violating form factors of the effective ZZZ and ZWW vertices.

  • New predictions for $\Lambda_b\to\Lambda_c$ semileptonic decays and tests of heavy quark symmetry. (arXiv:1808.09464v2 [hep-ph] UPDATED)

    Authors: Florian U. Bernlochner, Zoltan Ligeti, Dean J. Robinson, William L. Sutcliffe

    The heavy quark effective theory makes model independent predictions for semileptonic $\Lambda_b \to \Lambda_c$ decays in terms of a small set of parameters. No subleading Isgur-Wise function occurs at order $\Lambda_{\rm QCD}/m_{c,b}$, and only two sub-subleading functions enter at order $\Lambda_{\rm QCD}^2/m_c^2$. These features allow us to fit the form factors and decay rates calculated up to order $\Lambda_{\rm QCD}^2/m_c^2$ to LHCb data and lattice QCD calculations. We derive a significantly more precise standard model prediction for the ratio ${\cal B}(\Lambda_b\to \Lambda_c \tau\bar\nu) / {\cal B}(\Lambda_b\to \Lambda_c \mu\bar\nu)$ than prior results, and find the expansion in $\Lambda_{\rm QCD}/m_c$ well-behaved, addressing a long-standing question. Our results allow more precise and reliable calculations of $\Lambda_b\to \Lambda_c\ell\bar\nu$ rates, and are systematically improvable with better data on the $\mu$ (or $e$) modes.

  • A Method to Determine $|V_{cb}|$ at the Weak Scale in Top Decays at the LHC. (arXiv:1810.09424v2 [hep-ph] UPDATED)

    Authors: P. F. Harrison, V. E. Vladimirov

    Until now, the Cabibbo Kobayashi Maskawa matrix element, $|V_{cb}|$, has always been measured in $B$ decays, i.e.~at an energy scale $q_b\sim \frac{m_b}{2}$, far below the weak scale. We consider here the possibility of measuring it close to the weak scale, at $q_W\sim m_W$, in top decays at the Large Hadron Collider (LHC). Our proposed method would use data from the LHC experiments in hadronic top decays $t\rightarrow bW\rightarrow b\overline{b} c$, tagged by the semileptonic decay of the associated top. We estimate the uncertainty of such a measurement, as a function of present and potential future experimental jet flavour-tagging performances, and conclude that first measurements using the data collected during 2016 - 2018 could yield a fractional error on \Vcb\ of order 7\% per experiment. We also give projected performances at higher luminosities, which could yield sensitivity to any Standard Model running of \Vcb\ below the weak scale, if present.

  • Dark Energy and the Refined de Sitter Conjecture. (arXiv:1811.00554v2 [hep-ph] UPDATED)

    Authors: Prateek Agrawal, Georges Obied

    We revisit the phenomenology of quintessence models in light of the recently refined version of the de Sitter Swampland conjecture, which includes the possibility of unstable de Sitter critical points. We show that models of quintessence can evade previously derived lower bounds on $(1+w)$, albeit with very finely-tuned initial conditions. In the absence of such tuning or other rolling quintessence fields, a field with mass close to Hubble is required, which has a generic prediction for $(1+w)$. Slow-roll single field inflation models remain in tension. Other phenomenological constraints arising from the coupling of the quintessence field with the Higgs or the QCD axion are significantly relaxed.

  • Audible Axions. (arXiv:1811.01950v2 [hep-ph] UPDATED)

    Authors: Camila S. Machado, Wolfram Ratzinger, Pedro Schwaller, Ben A. Stefanek

    Conventional approaches to probing axions and axion-like particles (ALPs) typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. Here we show that such invisible axions, which are viable candidates for dark matter, can produce a stochastic gravitational wave background in the early universe. This signal is generated in models where the invisible axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. Incidentally, the same mechanism also widens the viable parameter space for axion dark matter. Quantum fluctuations amplified by the exponentially growing gauge boson modes source chiral gravitational waves. For axion decay constants $f \gtrsim 10^{17}$ GeV, this signal is detectable by either pulsar timing arrays or space/ground-based gravitational wave detectors for a broad range of axion masses, thus providing a new window to probe invisible axion models.

  • Unification of Flavor SU(3) Analyses of Heavy Hadron Weak Decays. (arXiv:1811.03480v2 [hep-ph] UPDATED)

    Authors: Xiao-Gang He, Yu-Ji Shi, Wei Wang

    Flavor SU(3) analyses of heavy mesons and baryons hadronic charmless decays can be formulated in two different forms. One is to construct the SU(3) irreducible representation amplitude (IRA) by decomposing effective Hamiltonian, and the other is to draw the topological diagrams (TDA). We study various $B/D\to PP,VP,VV$, $B_c\to DP/DV$ decays, and two-body nonleptonic decays of beauty/charm baryons, and demonstrate that when all terms are included these two ways of analyzing the decay amplitudes are completely equivalent. We clarify some confusions in drawing topological diagrams using different ways of describing beauty/charm baryon states.

  • Elliptic flow fluctuations in central collisions of spherical and deformed nuclei. (arXiv:1811.03959v2 [nucl-th] UPDATED)

    Authors: Giuliano Giacalone

    Elliptic flow ($v_2$) fluctuations in central heavy-ion collisions are direct probes of the fluctuating geometry of the quark-gluon plasma, and, as such, are strongly sensitive to any deviation from spherical symmetry in the shape of the colliding nuclei. We investigate the consequences of nuclear deformation for $v_2$ fluctuations, and we assess whether current models of medium geometry are able to predict and capture such effects. Assuming linear hydrodynamic response between $v_2$ and the eccentricity of the medium, $\varepsilon_2$, we perform accurate comparisons between model calculations of $\varepsilon_2$ fluctuations and STAR data on cumulants of elliptic flow, in central Au+Au and U+U collisions. From these comparisons, we evince that the most distinct signatures of nuclear deformation appear in the non-Gaussianities of $v_2$ fluctuation, and we show, in particular, that the non-Gaussian $v_2$ fluctuations currently observed in central Au+Au collisions are incompatible with model calculations that implement a quadrupole coefficient of order 12\% in the $^{197}$Au nuclei. Finally, we make robust predictions for the behavior of higher-order cumulants of $v_2$ in collisions of non-spherical nuclei.

  • Dark Matter with Stuckelberg Axions. (arXiv:1811.05792v2 [hep-ph] UPDATED)

    Authors: Claudio Coriano, Paul H. Frampton, Nikos Irges, Alessandro Tatullo

    We review a class of models which generalize the traditional Peccei-Quinn (PQ) axion solution by a St\"uckelberg pseudoscalar. Such axion models represent a significant variant with respect to earlier scenarios where axion fields were associated with global anomalies, because of the St\"uckelberg field, which is essential for the cancellation of gauge anomalies in the presence of extra $U(1)$ symmetries. The extra neutral currents associated to these models have been investigated in the past in orientifold models with intersecting branes, under the assumption that the St\"uckelberg scale was in the multi-TeV region. Such constructions, at the field theory level, are quite general and can be interpreted as the four-dimensional field theory realization of the Green-Schwarz mechanism of anomaly cancellation of string theory. We present an overview of models of this type in the TeV/multi TeV range in their original formulation and their recent embeddings into an ordinary GUT theory, presenting an $E_6\times U(1)_X$ model as an example. In this case the model contains two axions, the first corresponding to a Peccei-Quinn axion, whose misalignment takes place at the QCD phase transition, with a mass in the meV region and which solves the strong CP problem. The second axion is ultralight, in the $10^{-20}-10^{-22}$ eV region, due to a misalignment and a decoupling taking place at the GUT scale. The two scales introduced by the PQ solution, the PQ breaking scale and the misalignment scale at the QCD hadron transition, become the Planck and the GUT scales respectively, with a global anomaly replaced by a gauge anomaly. The periodic potential and the corresponding oscillations are related to a particle whose De Broglie wavelength can reach 10 kpc. Such a sub-galactic scale has been deemed necessary in order to resolve several dark matter issues at the astrophysical level.

  • Baryogenesis with the Berry phase. (arXiv:1811.06197v2 [hep-th] UPDATED)

    Authors: Seishi Enomoto, Tomohiro Matsuda

    The spontaneous baryogenesis scenario explains how a baryon asymmetry can develop while baryon violating interactions are still in thermal equilibrium. However, generation of the chemical potential from the derivative coupling is dubious since the chemical potential may not appear after the Legendre transformation. The geometric phase (Pancharatnam-Berry phase) results from the geometrical properties of the parameter space of the Hamiltonian, which is calculated from the Berry connection. In this paper, using the formalism of the Berry phase, we show that the chemical potential defined by the Berry connection is consistent with the Legendre transformation. The framework of the Berry phase is useful in explaining the mathematical background of the spontaneous baryogenesis, and also is useful for calculating the asymmetry of the non-thermal particle production in time-dependent backgrounds. Using the formalism, we show that the mechanism can be extended to more complex situations.

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