hep-ph updates on
High Energy Physics - Phenomenology (hep-ph) updates on the e-print archive
  • Cosmological constraints with self-interacting sterile neutrinos. (arXiv:1805.08218v1 [astro-ph.CO])

    Authors: Ningqiang Song, M.C. Gonzalez-Garcia, Jordi Salvado

    In this work we revisit the question of whether Cosmology can be made compatible with scenarios with light sterile neutrinos, as invoked to explain the SBL anomalies, in the presence of self-interaction among sterile neutrinos mediated by massive gauge bosons. We examine this proposal by deriving the cosmological predictions of the model in a wide range of the model parameters including the effective interaction strength $G_X$, sterile neutrino mass $m_{\rm st}$ and active-sterile mixings. With those we perform a statistical analysis of the cosmological data from BBN, CMB, and BAO data to infer the posterior probabilities of the sterile self-interaction model parameters. BBN mostly provides information about the effective interaction strength and we find that $\log_{10}(G_X/G_F)\geq 3.6$ can describe the primordial abundances at 95% CL. Our analysis of CMB and BAO data show that when allowing a wide prior for the sterile neutrino mass its posterior is bounded to $m_{\rm st}\leq 0.91~{\rm eV}$ (95% CL) considering CMB data only and $m_{\rm st}\leq 0.37~{\rm eV}$ (95% CL) when adding the BAO information. So the mass bounds are slighly relaxed compared with that of a non-interacting sterile neutrino model but a sterile neutrino mass of 1 eV is still excluded at more than $2\sigma$ CL. Conversely if fixing the sterile neutrino mass and mixing to the values prefered by short baseline data we find that while that CMB data alone favors the self-interacting scenario, including the BAO information severly degrades the agreement with the model. Altogether we conclude then that adding the self-interaction can alleviate the tension between eV sterile neutrinos and CMB data, but when including also the BAO results the self-interacting sterile neutrino model cannot lead to a satisfactory description of the data.

  • $b \to c \tau \nu_{\tau}$ Decays: A Catalogue to Compare, Constrain, and Correlate New Physics Effects. (arXiv:1805.08222v1 [hep-ph])

    Authors: Srimoy Bhattacharya, Soumitra Nandi, Sunando Kumar Patra

    In this article, we have predicted the standard model (SM) values of the asymmetric and angular observables in $B\to D^{(\ast)}\tau\nu_{\tau}$ decays, using the results of the new up-to-date analysis in $B\to D^{(*)}\ell\nu_{\ell}$. We have also revisited the SM prediction of the inclusive ratio $\mathcal{R}_{X_c}$, and our predicted value is $\mathcal{R}_{X_c} = 0.214 \pm 0.004$. In addition, we have analysed the $b\to c\tau\nu_{\tau}$ decay modes in a model-independent framework of effective field theory beyond the standard model. Considering all possible combinations of the effective operators in $b \to c \tau\nu_{\tau}$ decays and using the Akaike Information Criterion, we find out the scenarios which can best explain the available data on these channels. In the selected scenarios, best-fit values and correlations of the new parameters are extracted. Using these results, predictions are made on various observables in the exclusive and inclusive semitaunic $b \to c $ decays. The graphical correlations between these observables are shown, which are found to be useful in discriminating between various new physics scenarios.

  • Supercurrent anomaly and gauge invariance in N=1 supersymmetric Yang-Mills theory. (arXiv:1805.08225v1 [hep-th])

    Authors: Y. R. Batista, Brigitte Hiller, Adriano Cherchiglia, Marcos Sampaio

    We analyse Feynman diagram calculational issues related to the quantum breaking of supercurrent conservation in a supersymmetric non-abelian Yang-Mills theory. For the sake of simplicity, we take a zero mass gauge field multiplet interacting with a massless Majorana spin-$1/2$ field in the adjoint representation of $SU(2)$. We shed light on a long-standing controversy regarding the perturbative evaluation of the supercurrent anomaly in connection with gauge and superconformal symmetry in different frameworks. We find that only superconformal symmetry is unambiguously broken using an invariant four dimensional regularization and compare with the triangle AVV anomaly. Subtleties related to momentum routing invariance in the loops of diagrams and Clifford algebra evaluation inside divergent integrals are also discussed in connection with finite and undetermined quantities in Feynman amplitudes.

  • The stochastic gravitational-wave background in the absence of horizons. (arXiv:1805.08229v1 [gr-qc])

    Authors: Enrico Barausse, Richard Brito, Vitor Cardoso, Irina Dvorkin, Paolo Pani

    Gravitational-wave astronomy has the potential to explore one of the deepest and most puzzling aspects of Einstein's theory: the existence of black holes. A plethora of ultracompact, horizonless objects have been proposed to arise in models inspired by quantum gravity. These objects may solve Hawking's information-loss paradox and the singularity problem associated with black holes, while mimicking almost all of their classical properties. They are, however, generically unstable on relatively short timescales. Here, we show that this "ergoregion instability" leads to a strong stochastic background of gravitational waves, at a level detectable by current and future gravitational-wave detectors. The absence of such background in the first observation run of Advanced LIGO already imposes the most stringent limits to date on black-hole alternatives, showing that certain models of "quantum-dressed" stellar black holes can be at most a small percentage of the total population. The future LISA mission will allow for similar constraints on supermassive black-hole mimickers.

  • Collider Bounds on 2-Higgs Doublet Models with $U(1)_X$ Gauge Symmetries. (arXiv:1805.08231v1 [hep-ph])

    Authors: Daniel A. Camargo, Luigi Delle Rose, Stefano Moretti, Farinaldo S. Queiroz

    2-Higgs Doublet Models (2HDMs) typically need to invoke an ad-hoc discrete symmetry to avoid severe flavor bounds and in addition feature massless neutrinos, thus falling short of naturally complying with existing data. However, when augmented by an Abelian gauge symmetry naturally incorporating neutrino masses via a type-I seesaw mechanism while at the same time escaping flavor changing interactions, such enlarged 2HDMs become very attractive phenomenologically. In such frameworks, the distinctive element is the $Z'$ gauge boson generated by the spontaneous breaking of the Abelian group $U(1)_X$. In this work, we derive updated collider bounds on it. Several theoretical setups are possible, each with different and sometimes suppressed couplings to quarks and leptons. Thus, complementary data from dijet and dilepton resonance searches need to be considered to fully probe these objects. We employ the corresponding datasets as obtained at the Large Hadron Collider (LHC) at the 13 TeV CMs energy for $\mathcal{L}=12,36$ and $300$ fb$^{-1}$ of luminosity. Moreover, we present the potential sensitivity to such $Z'$s of the High Luminosity LHC (HL-LHC) and High Energy LHC (HE-LHC).

  • Baryons under Strong Magnetic Fields or in Theories with Space-dependent $\theta$-term. (arXiv:1805.08245v1 [hep-th])

    Authors: Dimitrios Giataganas

    Baryonic states are sufficiently complex to reveal physics that is hidden in the mesonic bound states. We study analytically and numerically baryons in theories with space-dependent $\theta$-term, or theories under strong magnetic fields. Such studies on baryons are accommodated in a generic analytic framework we develop for anisotropic theories, where their qualitative features are common irrespective of the source that triggers the anisotropy. We find that the distribution of the quarks forming the state, depends on the angle between the baryon and the anisotropic direction. Its shape is increasingly elliptic with respect to the strength of the field sourcing the anisotropy, counterbalancing the broken rotational invariance on the gluonic degrees of freedom. Strikingly, the baryons dissociate in stages with a process that depends on the proximity of the quarks to the anisotropic direction, where certain quark pairs abandon the bound state first, followed by the closest pairs to them as the temperature increases. This observation may also serve as a way to identify the nature of certain exotic states. Finally, we investigate holographic baryons with decreased number of quarks and explain why in theories under consideration the presence of anisotropy does not modify the universal stability condition in contrast to the usual trend.

  • Asymmetric Dark Matter, Inflation and Leptogenesis from B-L Symmetry Breaking. (arXiv:1805.08251v1 [hep-ph])

    Authors: P. V. Dong, D. T. Huong, Daniel A. Camargo, Farinaldo S. Queiroz, José W. F. Valle

    We propose a unified setup for dark matter, inflation and baryon asymmetry generation through the neutrino mass seesaw mechanism. Our scenario emerges naturally from an extended gauge group containing $B-L$ as a non-commutative symmetry, broken by a singlet scalar that also drives inflation. Its decays reheat the universe, producing the lightest right-handed neutrino. Automatic matter parity conservation leads to the stability of an asymmetric dark matter candidate, directly linked to the matter-antimatter asymmetry in the universe.

  • E6 inspired SUSY models with Custodial Symmetry. (arXiv:1805.08260v1 [hep-ph])

    Authors: R. Nevzorov

    The breakdown of E_6 within the supersymmetric (SUSY) Grand Unified Theories (GUTs) can result in SUSY extensions of the standard model (SM) based on the SM gauge group together with extra U(1) gauge symmetry under which right-handed neutrinos have zero charge. In these U(1)_N extensions of the minimal supersymmetric standard model (MSSM) a single discrete \tilde{Z}^H_2 symmetry may be used to suppress the most dangerous operators, that give rise to proton decay as well as non-diagonal flavour transitions at low energies. The SUSY models under consideration involves Z' and extra exotic matter beyond the MSSM. We discuss leptogenesis within this SUSY model and argue that the extra exotic states may lead to the non--standard Higgs decays.

  • $K^*$ mesons with hidden charm arising from $KX(3872)$ and $KZ_c(3900)$ dynamics. (arXiv:1805.08330v1 [hep-ph])

    Authors: Xiu-Lei Ren, Brenda B. Malabarba, Li-Sheng Geng, K. P. Khemchandani, A. Martinez Torres

    Inspired by the recent discovery of the pentaquark states $P_c(4450)$ and $P_c(4380)$, which can be viewed as excited nucleon states with hidden charm, we study the three-body interaction of a kaon and a pair of $D\bar{D}^*+\text{c.c.}$ We show that the two body interactions stringently constrained by the existence of the $D_{s0}^*(2317)$, $D^*_{s1}(2460)$, $X(3872)$, and $Z_c(3900)$, which are widely believed to contain large $DK$, $D^* K$, and $D\bar{D}^*+\text{c.c.}$ components, inevitably lead to the existence of two heavy $K^*$ mesons with hidden charm. Concrete coupled channel three-body calculations yield their masses and widths as $4337.0 - i 3.3$ MeV and $4277.6 - i 14.0$ MeV with $I(J^P)=1/2(1^-)$. These states, if found experimentally, definitely cannot be accommodated in a $q\bar{q}$ picture, and therefore presents a clear case of exotic hadrons.

  • The Effective J-Factor of the Galactic Center for Velocity-Dependent Dark Matter Annihilation. (arXiv:1805.08379v1 [astro-ph.HE])

    Authors: Kimberly K. Boddy, Jason Kumar, Louis E. Strigari

    We present the effective $J$-factors for the Milky Way for scenarios in which dark matter annihilation is p-wave or d-wave suppressed. We find that the velocity suppression of dark matter annihilation can have a sizable effect on the morphology of a potential dark matter annihilation signal in the Galactic Center. The gamma-ray flux from the innermost region of the Galactic Center is in particular suppressed. We find that for dark matter density profiles with steep inner slopes, the morphology of the Inner Galaxy gamma-ray emission in p-wave models can be made similar to the morphology in standard s-wave models. This similarity may suggest that model discrimination between s-wave and p-wave is challenging, for example, when fitting the Galactic Center excess. However, we show that it is difficult to simultaneously match s- and p-wave morphologies at both large and small angular scales. The $J$-factors we calculate may be implemented with astrophysical foreground models to self-consistently determine the morphology of the excess with velocity-suppressed dark matter annihilation.

  • $D \Xi$ and $D^* \Xi$ Molecular States from One Boson Exchange. (arXiv:1805.08384v1 [hep-ph])

    Authors: Ming-Zhu Liu, Tian-Wei Wu, Ju-Jun Xie, Manuel Pavon Valderrama, Li-Sheng Geng

    We explore the existence of $D \Xi$ and $D^* \Xi$ molecular states within the one boson exchange model. We regularize the potential derived in this model with a form factor and a cut-off of the order of $1\,{\rm GeV}$. To determine the cut-off, we use the condition that the $X(3872)$ is reproduced as a pole in the $J^{PC} = 1^{++}$ $D^*\bar{D}$ amplitude. From this we find that the $J^P= {\frac{1}{2}}^{-}$ $D^*\,\Xi$ system is on the verge of binding and has an unnaturally large scattering length. For the $J^P= {\frac{1}{2}}^{-}$ $D\,\Xi$ and the $J^P= {\frac{3}{2}}^{-}$ $D^*\,\Xi$ systems the attraction is not enough to form a bound state. From heavy quark symmetry and the quark model we can extend the previous model to the $P \Xi_{QQ}$ and $P^* \Xi_{QQ}$ systems, with $P = D, \bar{B}$, $P^* = D^*, \bar{B}^*$ and $\Xi_{QQ} = \Xi_{cc}, \Xi_{bb}$. In this case we predict a series of triply heavy pentaquark-like molecules.

  • Testing the universality of free fall towards dark matter with radio pulsars. (arXiv:1805.08408v1 [gr-qc])

    Authors: Lijing Shao, Norbert Wex, Michael Kramer

    The violation of the weak equivalence principle (EP) in the gravitational field of the Earth, described by the E\"otv\"os parameter $\eta_\oplus$, was recently constrained to the level $\left|\eta_\oplus\right| \lesssim 10^{-14}$ by the MICROSCOPE space mission. The E\"otv\"os parameter $\eta_{\rm DM}$, pertaining to the differential couplings of dark matter (DM) and ordinary matter, was only tested to the level $\left| \eta_{\rm DM} \right| \lesssim 10^{-5}$ by the E\"ot-Wash group and lunar laser ranging. This test is limited by the EP-violating driving force in the Solar neighborhood that is determined by the Galactic distribution of DM. Here we propose a novel celestial experiment using the orbital dynamics from radio timing of binary pulsars, and obtain a competing limit on $\eta_{\rm DM}$ from a neutron star (NS) -- white dwarf (WD) system, PSR J1713+0747. The result benefits from the large material difference between the NS and the WD, and the large gravitational binding energy of the NS. If we can discover a binary pulsar within $\sim 10$ parsecs of the Galactic center, where the driving force is much larger in the expected DM spike, precision timing will improve the test of the universality of free fall towards DM and constrain various proposed couplings of DM to the Standard Model by several orders of magnitude. Such a test probes the hypothesis that gravity is the only long-range interaction between DM and ordinary matter.

  • A light singlet at the LHC and DM. (arXiv:1805.08436v1 [hep-ph])

    Authors: Jan Kalinowski

    An interesting scenario of an R-symmetric supersymmetric model with a light singlet is discussed. Since a light scalar in this model necessarily implies a light Dirac neutralino, its viability as a dark matter candidate is addressed.

  • Inflation in gauge theory of gravity with local scaling symmetry and quantum induced symmetry breaking. (arXiv:1805.08507v1 [gr-qc])

    Authors: Yong Tang, Yue-Liang Wu

    Motivated by the gauge theory of gravity with local scaling symmetry proposed recently in 1712.04537 and 1506.01807, we investigate whether the scalar field therein can be responsible for the inflation. We show that the classical theory would suffer from the difficulty that inflation can start but will never stop. We explore possible solutions by invoking the symmetry breaking through quantum effects. The effective potential of the scalar field is shown to have phenomenologically interesting forms to give viable inflation models. The predictions of physical observables agree well with current cosmological measurements and can be further tested in future experiments searching for primordial gravitational waves.

  • Null tests from angular distributions in $D \to P_1 P_2 l^+l^-$, $l=e,\mu$ decays on and off peak. (arXiv:1805.08516v1 [hep-ph])

    Authors: Stefan de Boer, Gudrun Hiller

    We systematically analyze the full angular distribution in $D \to P_1 P_2 l^+ l^-$ decays, where $P_{1,2}=\pi,K$, $l=e,\mu$. We identify several null tests of the standard model (SM). Notably, the angular coefficients $I_{5,6,7}$, driven by the leptons' axial-vector coupling $C_{10}^{(\prime)}$, vanish by means of a superior GIM-cancellation and are protected by parity invariance below the weak scale. CP-odd observables related to the angular coefficients $I_{5,6,8,9}$ allow to measure CP-asymmetries without $D$-tagging. The corresponding observables $A_{5,6,8,9}$ constitute null tests of the SM. Lepton universality in $|\Delta c| =|\Delta u|=1$ transitions can be tested by comparing $D \to P_1 P_2 \mu^+ \mu^-$ to $D \to P_1 P_2 e^+ e^-$ decays. Data for $P_1 P_2=\pi^+ \pi^-$ and $K^+ K^-$ on muon modes are available from LHCb and on electron modes from BESIII. Corresponding ratios of dimuon to dielectron branching fractions are at least about an order of magnitude away from probing the SM. In the future electron and muon measurements should be made available for the same cuts as corresponding ratios $R_{P_1 P_2}^D$ provide null tests of $e$-$\mu$-universality. We work out beyond-SM signals model-independently and in SM extensions with leptoquarks.

  • Dark Matter in Quantum Gravity. (arXiv:1805.08552v1 [hep-th])

    Authors: Xavier Calmet, Boris Latosh

    We show that quantum gravity, whatever its ultra-violet completion might be, could account for dark matter. Indeed, besides the massless gravitational field recently observed in the form of gravitational waves, the spectrum of quantum gravity contains two massive fields respectively of spin 2 and spin 0. If these fields are long-lived, they could easily account for dark matter. In that case, dark matter would be very light and only gravitationally coupled to the standard model particles.

  • MoMEMta, a modular toolkit for the Matrix Element Method at the LHC. (arXiv:1805.08555v1 [hep-ph])

    Authors: Sébastien Brochet (1), Christophe Delaere (1), Brieuc François (1), Vincent Lemaître (1), Alexandre Mertens (1), Alessia Saggio (1), Miguel Vidal Marono (1), Sébastien Wertz (1) ((1) Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université catholique de Louvain)

    The Matrix Element Method has proven to be a powerful method to optimally exploit the information available in detector data. Its widespread use is nevertheless impeded by its complexity and the associated computing time. MoMEMta, a C++ software package to compute the integrals at the core of the method, provides a versatile implementation of the Matrix Element Method to both the theory and experiment communities. Its modular structure covers the needs of experimental analysis workflows at the LHC without compromising ease of use on simpler and smaller simulated samples used for phenomenological studies. In this paper, we present version 1.0 of MoMEMta, together with examples illustrating the wide range of application at the LHC accessible for the first time with a single tool.

  • Phenomenology of GeV-scale Heavy Neutral Leptons. (arXiv:1805.08567v1 [hep-ph])

    Authors: Kyrylo Bondarenko, Alexey Boyarsky, Dmitry Gorbunov, Oleg Ruchayskiy

    We review and revise phenomenology of the GeV-scale heavy neutral leptons (HNLs). We extend the previous analyses by including more channels of HNLs production and decay and provide with more refined treatment, including QCD corrections for the HNLs of masses $\mathcal{O}(1)$ GeV. We summarize the relevance of individual production and decay channels for different masses, resolving a few discrepancies in the literature. Our final results are directly suitable for sensitivity studies of particle physics experiments (ranging from proton beam-dump to the LHC) aiming at searches for heavy neutral leptons.

  • ExDiff Monte Carlo generator for Exclusive Diffraction. Version 2.0. Physics and manual. (arXiv:1805.08591v1 [hep-ph])

    Authors: R.A. Ryutin

    ExDiff2.0 is a Monte Carlo event generator for simulation of Exclusive Diffractive processes in proton-proton collisions. The present version includes reactions: elastic scattering $pp\to pp$ at 7, 8, 13, 14~TeV; $pp\to p+R+p$, $R = f_0(1500)$, $f_0(1710)$, $f_2(1950)$ at 8 and 13~TeV, $f_2(1270)$ at 8~TeV, $f_2(2220)$ at 13~TeV. In the future versions many processes of Central Exclusive Diffractive Production will be added. This version is linked to PYTHIA 8 (to make resonance decays and hadronization) and also to ROOT and HEPMC output via PYTHIA 8 interface. Also some test files of Born distributions for CEDP of two pions are added.

  • Flavour Dynamics and Violations of the CP Symmetry. (arXiv:1805.08597v1 [hep-ph])

    Authors: Antonio Pich

    An overview of flavour physics and CP-violating phenomena is presented. The Standard Model quark-mixing mechanism is discussed in detail and its many successful experimental tests are summarized. Flavour-changing transitions put very stringent constraints on new-physics scenarios beyond the Standard Model framework. Special attention is given to the empirical evidences of CP violation and their important role in our understanding of flavour dynamics. The current status of the so-called flavour anomalies is also reviewed.

  • Pion condensation and phase diagram in the Polyakov-loop quark-meson model. (arXiv:1805.08599v1 [hep-ph])

    Authors: Prabal Adhikari, Jens O. Andersen, Patrick Kneschke

    We use the Polyakov-loop extended two-flavor quark-meson model as a low-energy effective model for QCD to study the phase diagram in the $\mu_I$--$T$ plane where $\mu_I$ is the isospin chemical potential. In particular, we focus on the Bose condensation of charged pions. At $T=0$, the onset of pion condensation is at $\mu_I={1\over2}m_{\pi}$ in accordance with exact results. The phase transition to a Bose-condensed phase is of second order for all values of $\mu_I$ and we find that there is no pion condensation for temperatures larger than approximately 187 MeV. The chiral transition temperature coincides with the critical temperature for Bose condensation for values of the isospin chemical potential larger than $\mu_I\approx110$ MeV. We compare our results with recent lattice simulations and find overall good agreement.

  • Model Selection with Strong-lensing Systems. (arXiv:1805.08640v1 [astro-ph.CO])

    Authors: Kyle Leaf, Fulvio Melia

    In this paper, we use an unprecedentedly large sample (158) of confirmed strong lens systems for model selection, comparing five well studied Friedmann-Robertson-Walker cosmologies: LCDM, wCDM (the standard model with a variable dark-energy equation of state), the R_h=ct universe, the (empty) Milne cosmology, and the classical Einstein-de Sitter (matter dominated) universe. We first use these sources to optimize the parameters in the standard model and show that they are consistent with Planck, though the quality of the best fit is not satisfactory. We demonstrate that this is likely due to under-reported errors, or to errors yet to be included in this kind of analysis. We suggest that the missing dispersion may be due to scatter about a pure single isothermal sphere (SIS) model that is often assumed for the mass distribution in these lenses. We then use the Bayes information criterion, with the inclusion of a suggested SIS dispersion, to calculate the relative likelihoods and ranking of these models, showing that Milne and Einstein-de Sitter are completely ruled out, while R_h=ct is preferred over LCDM/wCDM with a relative probability of ~73% versus ~24%. The recently reported sample of new strong lens candidates by the Dark Energy Survey, if confirmed, may be able to demonstrate which of these two models is favoured over the other at a level exceeding 3 sigma.

  • Flavorful Two Higgs Doublet Models with a Twist. (arXiv:1805.08659v1 [hep-ph])

    Authors: Wolfgang Altmannshofer, Brian Maddock

    We explore Two Higgs Doublet Models with non-standard flavor structures. In analogy to the four, well studied, models with natural flavor conservation (type 1, type 2, lepton-specific, flipped), we identify four models that preserve an approximate $U(2)^5$ flavor symmetry acting on the first two generations. In all four models, the couplings of the 125 GeV Higgs are modified in characteristic flavor non-universal ways. The heavy neutral and charged Higgs bosons show an interesting non-standard phenomenology. We discuss their production and decay modes and identify the most sensitive search channels at the LHC. We study the effects on low energy flavor violating processes finding relevant constraints from $B_d$ and $B_s$ meson oscillations and from the rare decay $B_s \to \mu^+ \mu^-$. We also find that lepton flavor violating $B$ meson decays like $B_s \to \tau \mu$ and $B \to K^{(*)} \tau \mu$ might have branching ratios at an observable level.

  • Axial anomaly and hadronic properties in nuclear medium. (arXiv:1805.08713v1 [nucl-th])

    Authors: G. Fejos, A. Hosaka

    We investigate meson and nucleon dynamics at finite baryon density and temperature by coupling the nucleon field and the omega meson to the three-flavor linear sigma model and calculate hadronic properties around the nuclear liquid-gas transition. We apply the Functional Renormalization Group method, and find that mesonic fluctuations increase the strength of the coefficient of the $U_A(1)$ breaking determinant operator as a function of the chiral condensate. As a consequence, we find that the actual value of the anomaly increases discontinuously at the first order nuclear liquid-gas transition. We calculate how mesonic masses and partial restoration of chiral symmetry are modified due to such an effect.

  • The QCD Axion Window and Low Scale Inflation. (arXiv:1805.08763v1 [hep-ph])

    Authors: Alan H. Guth, Fuminobu Takahashi, Wen Yin

    We show that the upper bound of the classical QCD axion window can be significantly relaxed for low-scale inflation. If the Gibbons-Hawking temperature during inflation is lower than the QCD scale, the initial QCD axion misalignment angle follows the Bunch-Davies distribution. As a result, the axion overproduce problem is significantly relaxed even for the axion decay constant larger than $10^{12}$ GeV. We give concrete hilltop inflation models where the Hubble parameter during inflation is comparable to or much smaller than the QCD scale and the successful reheating takes place via perturbative decays or dissipation processes.

  • Exploring compensated isocurvature perturbations with CMB spectral distortion anisotropies. (arXiv:1805.08773v1 [astro-ph.CO])

    Authors: Taku Haga, Keisuke Inomata, Atsuhisa Ota, Andrea Ravenni

    We develop a linear perturbation theory for the spectral $y$-distortions of the cosmic microwave background~(CMB). The $y$-distortions generated during the recombination epoch are usually negligible because the energy transfer due to the Compton scattering is strongly suppressed at that time, while they can be significant if there is a considerable compensated isocurvature perturbation~(CIP), which is not well constrained from the present CMB observations. The linear $y$-distortions explicitly depend on the baryon density fluctuations, therefore $y$ anisotropies can completely resolve the degeneracy between the baryon isocurvature perturbations and the cold dark matter ones. This novel method is free from lensing contaminations that can affect the previous approach to the CIPs based on the nonlinear modulation of the CMB anisotropies. We compute the cross correlation functions of the $y$-distortions with the CMB temperature and the $E$ mode polarization anisotropies. They are sensitive to the correlated CIPs parameterized by $f'\equiv\mathcal P_{\rm CIP\zeta}/\mathcal P_{\zeta \zeta}$ with $\mathcal P_{\zeta \zeta}$ and $\mathcal P_{\rm CIP\zeta}$ being the auto correlation of the adiabatic perturbations and the cross correlation between them and the CIPs. We investigate how well the $y$ anisotropies will constrain $f'$ in future observations such as those provided by a PIXIE-like and a PRISM-like survey, LiteBIRD and the cosmic variance limited~(CVL) survey, taking into account the degradation in constraining power due to the presence of Sunyaev Zel'dovich effect from galaxy clusters. For example, our optimistic forecast shows that $f'<3\times 10^{3}$ at 68\% C.L. is possible for LiteBIRD, while $f'<5.0\times 10^{2}$ for the CVL observations.

  • Precise prediction for the light MSSM Higgs boson mass combining effective field theory and fixed-order calculations. (arXiv:1608.01880v3 [hep-ph] UPDATED)

    Authors: Henning Bahl, Wolfgang Hollik

    In the Minimal Supersymmetric Standard Model heavy superparticles introduce large logarithms in the calculation of the lightest $\mathcal{CP}$-even Higgs boson mass. These logarithmic contributions can be resummed using effective field theory techniques. For light superparticles, however, fixed-order calculations are expected to be more accurate. To gain a precise prediction also for intermediate mass scales, both approaches have to be combined. Here, we report on an improvement of this method in various steps: the inclusion of electroweak contributions, of separate electroweakino and gluino thresholds, as well as resummation at the NNLL level. These improvements can lead to significant numerical effects. In most cases, the lightest $\mathcal{CP}$-even Higgs boson mass is shifted downwards by about 1 GeV. This is mainly caused by higher order corrections to the $\bar{\text{MS}}$ top-quark mass. We also describe the implementation of the new contributions in the code {\tt FeynHiggs}.

  • Chiral symmetry restoration at finite temperature within the Hamiltonian approach to QCD in Coulomb gauge. (arXiv:1706.06966v2 [hep-ph] UPDATED)

    Authors: Ehsan Ebadati, Hugo Reinhardt, Peter Vastag

    The chiral phase transition of the quark sector of QCD is investigated within the Hamiltonian approach in Coulomb gauge. Finite temperatures $T$ are introduced by compactifying one spatial dimension, which makes all thermodynamical quantities accessible from the ground state on the spatial manifold $\mathbb{R}^2 \times S^1(1/T)$. In the limit of a vanishing quark-gluon coupling, the equations of motion of the quark sector are solved numerically and the chiral quark condensate is evaluated and compared to the results of the usual canonical approach to finite-temperature Hamiltonian QCD based on the density operator of the grand canonical ensemble. For zero bare quark masses, we find a second-order chiral phase transition with a critical temperature of about $107 \, \mathrm{MeV}$.

  • Transverse Momentum Distribution and Elliptic Flow of Charged Hadrons in $U$+$U$ collisions at $\sqrt{s_{NN}}=193$ GeV using HYDJET++. (arXiv:1707.07552v3 [nucl-th] UPDATED)

    Authors: Arpit Singh, P. K. Srivastava, O. S. K. Chaturvedi, S. Ahmad, B. K. Singh

    Recent experimental observations of the charged hadron properties in $U+U$ collisions at $193$ GeV contradict many of the theoretical models of particle production including two-component Monte Carlo Glauber model. The experimental results show a small correlation between the charged hadron properties and the initial geometrical configurations (e.g. body-body, tip-tip etc.) of $U+U$ collisions. In this article, we have modified the Monte Carlo HYDJET++ model to study the charged hadron production in $U+U$ collisions at $193$ GeV center-of-mass energy in tip-tip and body-body initial configurations. We have modified the hard as well as soft production processes to make this model suitable for $U+U$ collisions. We have calculated the pseudorapidity distribution, transverse momentum distribution and elliptic flow distribution of charged hadrons with different control parameters in various geometrical configurations possible for $U+U$ collision. We find that HYDJET++ model supports a small correlation between the various properties of charged hadrons and the initial geometrical configurations of $U+U$ collision. Further, the results obtained in modified HYDJET++ model regarding $dn_{ch}/d\eta$ and elliptic flow ($v_{2}$) suitably matches with the experimental data of $U+U$ collisions in minimum bias configuration.

  • Direct photon spectrum and elliptic flow produced from Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV at the CERN Large Hadron Collider within an integrated hydrokinetic model. (arXiv:1710.07689v2 [hep-ph] UPDATED)

    Authors: V.Yu. Naboka, Yu.M. Sinyukov, G.M. Zinovjev

    The photon transverse momentum spectrum and its anisotropy from Pb+Pb collisions at the CERN Large Hadron Collider energy $\sqrt {s_{NN}}=2.76$ TeV are investigated within the integrated hydrokinetic model (iHKM). Photon production is accumulated from the different processes at the various stages of relativistic heavy ion collisions: from the primary hard photons of very early stage of parton collisions to the thermal photons from equilibrated quark-gluon and hadron gas stages. Along the way a hadronic medium evolution is treated in two distinct, in a sense opposite, approaches: chemically equilibrated and chemically frozen system expansion. Studying the centrality dependence of the results obtained allows us to conclude that a relatively strong transverse momentum anisotropy of thermal radiation is suppressed by prompt photon emission which is an isotropic. We find out that this effect is getting stronger as centrality increases because of the simultaneous increase in the relative contribution of prompt photons in the soft part of the spectra. The substantial results obtained in iHKM with nonzero viscosity ($\eta/s=0.08$) for photon spectra and $v_2$ coefficients are mostly within the error bars of experimental data, but there is some systematic underestimation of both observables for the near central events. We claim that a situation could be significantly improved if an additional photon radiation that accompanies the presence of a deconfined environment is included. Since a matter of a space-time layer where hadronization takes place is actively involved in anisotropic transverse flow, both positive contributions to the spectra and $v_2$ are considerable, albeit such an argument needs further research and elaboration.

  • ${SO(10)}$ inspired $Z'$ models at the LHC. (arXiv:1712.01279v2 [hep-ph] UPDATED)

    Authors: Simon J.D. King, Stephen F. King, Stefano Moretti

    We study and compare various $Z'$ models arising from $SO(10)$, focussing in particular on the Abelian subgroup $U(1)_{R} \times U(1)_{B-L}$, broken at the TeV scale to Standard Model hypercharge $U(1)_{Y}$. The gauge group $U(1)_{R} \times U(1)_{B-L}$, which is equivalent to the $U(1)_{Y}\times U(1)_{\chi}$ in a different basis, is well motivated from $SO(10)$ breaking and allows neutrino mass via the linear seesaw mechanism. Assuming supersymmetry, we consider single step gauge unification to predict the gauge couplings, then consider the detection and characterisation prospects of the resulting $Z'$ at the LHC by studying its possible decay modes into di-leptons as well as into Higgs bosons. The main new result here is to analyse in detail the expected leptonic forward-backward asymmetry at the high luminosity LHC and show that it may be used to discriminate the $U(1)_{R} \times U(1)_{B-L}$ model from the usual $B-L$ model based on $U(1)_{Y}\times U(1)_{B-L}$.

  • Lepton-rich cold QCD matter in protoneutron stars. (arXiv:1712.04773v2 [hep-ph] UPDATED)

    Authors: J. C. Jiménez, E. S. Fraga

    We investigate protoneutron star matter using the state-of-the-art perturbative equation of state for cold and dense QCD in the presence of a fixed lepton fraction in which both electrons and neutrinos are included. Besides computing the modifications in the equation of state due to the presence of trapped neutrinos, we show that stable strange quark matter has a more restricted parameter space. We also study the possibility of nucleation of unpaired quark matter in the core of protoneutron stars by matching the lepton-rich QCD pressure onto a hadronic equation of state, namely TM1 with trapped neutrinos. Using the inherent dependence of perturbative QCD on the renormalization scale parameter, we provide a measure of the uncertainty in the observables we compute.

  • Comprehensive asymmetric dark matter model. (arXiv:1801.05561v3 [hep-ph] UPDATED)

    Authors: Stephen J. Lonsdale, Raymond R. Volkas

    Asymmetric dark matter (ADM) is motivated by the similar cosmological mass densities measured for ordinary and dark matter. We present a comprehensive theory for ADM that addresses the mass density similarity, going beyond the usual ADM explanations of similar number densities. It features an explicit matter-antimatter asymmetry generation mechanism, has one fully worked out thermal history and suggestions for other possibilities, and meets all phenomenological, cosmological and astrophysical constraints. Importantly, it incorporates a deep reason for why the dark matter mass scale is related to the proton mass, a key consideration in ADM models. Our starting point is the idea of mirror matter, which offers an explanation for dark matter by duplicating the standard model with a dark sector related by a $Z_2$ parity symmetry. However, the dark sector need not manifest as a symmetric copy of the standard model in the present day. By utilising the mechanism of "asymmetric symmetry breaking" with two Higgs doublets in each sector, we develop a model of ADM where the mirror symmetry is spontaneously broken, leading to an electroweak scale in the dark sector that is significantly larger than that of the visible sector. The weak sensitivity of the ordinary and dark QCD confinement scales to their respective electroweak scales leads to the necessary connection between the dark matter and proton masses. The dark matter is composed of either dark neutrons or a mixture of dark neutrons and metastable dark hydrogen atoms. Lepton asymmetries are generated by the $CP$-violating decays of heavy Majorana neutrinos in both sectors. These are then converted by sphaleron processes to produce the observed ratio of visible to dark matter in the universe. The dynamics responsible for the kinetic decoupling of the two sectors emerges as an important issue that we only partially solve.

  • A Simple Worldsheet Black Hole. (arXiv:1803.00577v2 [hep-th] UPDATED)

    Authors: Sergei Dubovsky

    We study worldsheet theory of confining strings in two-dimensional massive adjoint QCD. Similarly to confining strings in higher dimensions this theory exhibits a non-trivial $S$-matrix surviving even in the strict planar limit. In the process of two-particle scattering a zigzag is formed on the worldsheet. It leads to an interesting non-locality and exhibits some properties of a quantum black hole. Ordinarily, identical quantum particles do not carry identity. On the worldsheet they acquire off-shell identity due to strings attached. Identity implies complementarity. We discuss similarities and differences of the worldsheet scattering with the $T\bar{T}$ deformation. We also propose a promising candidate for a supersymmetric model with integrable confining strings.

  • Spin polarized phases in strongly interacting matter: interplay between axial-vector and tensor mean fields. (arXiv:1803.08315v2 [hep-ph] UPDATED)

    Authors: Tomoyuki Maruyama, Eiji Nakano, Kota Yanase, Naotaka Yoshinaga

    The spontaneous spin polarization of strongly interacting matter due to axial-vector and tensor type interactions is studied at zero temperature and high baryon-number densities. We start with the mean-field Lagrangian for the axial-vector and tensor interaction channels, and find in the chiral limit that the spin polarization due to the tensor mean field ($U$) takes place first as the density increases for sufficiently strong coupling constants, and then that due to the axial-vector mean field ($A$) emerges in the region of finite tensor mean field. This can be understood that making the axial-vector mean field finite requires a broken chiral symmetry somehow, which is achieved by the finite tensor mean field in the present case. It is also found from symmetry argument that there appear the type I (II) Nambu-Goldstone modes with a linear (quadratic) dispersion in the spin polarized phase with $U\neq0$ and $A=0$ ($U\neq0$ and $A\neq0$), although these two phases exhibit the same symmetry breaking pattern.

  • Zooming in on neutrino oscillations with DUNE. (arXiv:1803.10247v2 [hep-ph] UPDATED)

    Authors: Rahul Srivastava, Christoph A. Ternes, Mariam Tórtola, José W. F. Valle

    We examine the capabilities of the DUNE experiment as a probe of the neutrino mixing paradigm. Taking the current status of neutrino oscillations and the design specifications of DUNE, we determine the experiment's potential to probe the structure of neutrino mixing and CP violation. We focus on the poorly determined parameters $\theta_{23}$ and $\delta_{CP}$ and consider both two and seven years of run. We take various benchmarks as our true values, such as the current preferred values of $\theta_{23}$ and $\delta_{CP}$, as well as several theory-motivated choices. We determine quantitatively DUNE's potential to perform a precision measurement of $\theta_{23}$, as well as to test the CP violation hypothesis in a model-independent way. We find that, after running for seven years, DUNE will make a substantial step in the precise determination of these parameters, bringing to quantitative test the predictions of various theories of neutrino mixing.

  • Exotic triple-charm deuteron-like hexaquarks. (arXiv:1804.02961v3 [hep-ph] UPDATED)

    Authors: Rui Chen, Fu-Lai Wang, Atsushi Hosaka, Xiang Liu

    Adopting the one-boson-exchange model, we perform a systematic investigation of interactions between a doubly charmed baryon $(\Xi_{cc})$ and an $S$-wave charmed baryon ($\Lambda_c$, $\Sigma_c^{(*)}$, and $\Xi_c^{(\prime,*)}$). Both the $S$-$D$ mixing effect and coupled-channel effect are considered in this work. Our results suggest that there may exist several possible triple-charm deuteron-like hexaquarks. Meanwhile, we further study the interactions between a doubly charmed baryon and an $S$-wave anticharmed baryon. We find that a doubly charmed baryon and an $S$-wave anticharmed baryon can be easily bound together to form shallow molecular hexaquarks. These heavy flavor hexaquarks predicted here can be accessible at future experiment like LHCb.

  • Scale independence in an asymptotically free theory at finite temperatures. (arXiv:1804.09531v2 [hep-ph] UPDATED)

    Authors: Gabriel N. Ferrari

    A recently developed variational resummation technique incorporating renormalization group properties has been shown to solve the scale dependence problem that plagues the evaluation of thermodynamical quantities, e.g., within the framework of approximations such as in the hard-thermal-loop resummed perturbation theory. This method is used in the present work to evaluate thermodynamical quantities within the two-dimensional nonlinear sigma model, which shares some common features with Yang-Mills theories, like asymptotic freedom, trace anomaly and the nonperturbative generation of a mass gap. Besides the fact that nonperturbative results can be readily generated solely by considering the lowest-order contribution to the thermodynamic effective potential, we also show that its next-to-leading correction indicates convergence to the sought-after scale invariance.

  • Ruling out Critical Higgs Inflation?. (arXiv:1805.02160v2 [hep-ph] UPDATED)

    Authors: Isabella Masina

    We consider critical Higgs inflation, namely Higgs inflation with a rising inflection point at smaller field values than those of the plateau induced by the non-minimal coupling to gravity. It has been proposed that such configuration is compatible with the present CMB observational constraints on inflation, and also with primordial black hole production accounting for the totality or a fraction of the observed dark matter. We study the model taking into account the NNLO corrections to the Higgs effective potential: such corrections are extremely important to reduce the theoretical error associated to the calculation. We find that, in the 3 sigma window for the relevant low energy parameters, which are the strong coupling and the Higgs mass (the top mass follows by requiring an inflection point), the potential at the inflection point is so large (and so is the Hubble constant during inflation) that the present bound on the tensor-to-scalar ratio is violated. The model is viable only allowing the strong coupling to take its upper 3-4 sigma value. In our opinion, this tension shows that the model of critical Higgs inflation is likely to be not viable: neither inflation nor black holes as dark matter can be originated in this version of the model.

  • Utilising $B \to \pi K$ Decays at the High-Precision Frontier. (arXiv:1805.06705v2 [hep-ph] UPDATED)

    Authors: Robert Fleischer, Ruben Jaarsma, Eleftheria Malami, K. Keri Vos

    For about twenty years, $B\to\pi K$ decays are in the focus of $B$-decay studies. We show that a correlation between the CP asymmetries of $B^0_d\to\pi^0K_{\rm S}$ reveals a tension with the Standard Model. Should it be due to New Physics, a modified electroweak penguin sector provides particularly interesting possibilities. We present a new method to determine the electroweak penguin parameters, which uses an isospin relation and requires only minimal $SU(3)$ input. We apply it to the current data for $B\to\pi K$ decays and discuss the prospects for utilizing CP violation in $B^0_d\to\pi^0K_{\rm S}$. The strategy has the exciting potential to establish New Physics in the electroweak penguin sector in the high-precision era of $B$-physics.

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