Mon·Aug 29, 2016Monday·August 29, 2016

1. 01*

   CP-Conservation in QCD and why only "invisible" Axions work

   Jihn E. Kim🇰🇷

   Among solutions of the strong CP problem, the "invisible" axion in the narrow axion window is argued to be the remaining possibility among natural solutions on the smallness of $\bar{\theta }$. Related to the gravity spoil of global symmetries, some prospective invisible axions from theory point of view are discussed. In all these discussions, including the observational possibility, cosmological constraints must be included.

   hep-phastro-ph.COhep-ex4 citations
2. 02*

   On the impact of kinetic mixing in beta functions at two-loop

   Florian Lyonnet🇺🇸

   Kinetic mixing is a fundamental property of models with a gauge symmetry involving several $\mathrm{U}(1)$ group factors. In this paper, we perform a numerical study of the impact of kinetic mixing on beta functions at two-loop. To do so, we use the recently published PyR@TE 2 software to derive the complete set of RGEs of the SM B-L model at two-loop including kinetic mixing. We show that it is important to properly account for kinetic mixing as the evolution of the parameters with the energy scale can change drastically. In some cases, these modifications can even lead to a different conclusion regarding the stability of the scalar potential.

   hep-phPRD(2016)·5 citations
3. 03*

   PyR@TE 2: A Python tool for computing RGEs at two-loop

   Florian Lyonnet🇺🇸 · Ingo Schienbein🇫🇷

   Renormalization group equations are an essential tool for the description of theories accross different energy scales. Even though their expressions at two-loop for an arbitrary gauge field theory have been known for more than thirty years, deriving the full set of equations for a given model by hand is very challenging and prone to errors. To tackle this issue, we have introduced in [1] a Python tool called PyR@TE; Python Renormalization group equations @ Two-loop for Everyone. With PyR@TE, it is easy to implement a given Lagrangian and derive the complete set of two-loop RGEs for all the parameters of the theory. In this paper, we present the new version of this code, PyR@TE 2, which brings many new features and in particular it incorporates kinetic mixing when several $\mathrm{U}(1)$ gauge groups are involved. In addition, the group theory part has been greatly improved as we introduced a new Python module dubbed PyLie that deals with all the group theoretical aspects required for the calculation of the RGEs as well as providing very useful model building capabilities. This allows the use of any irreducible representation of the $\mathrm{SU}(n)$, $\mathrm{SO}(2n)$ and $\mathrm{SO}(2n+1)$ groups. % Furthermore, it is now possible to implement terms in the Lagrangian involving fields which can be contracted into gauge singlets in more than one way. As a byproduct, results for a popular model (SM+complex triplet) for which, to our knowledge, the complete set of two-loop RGEs has not been calculated before are presented in this paper. Finally, the two-loop RGEs for the anomalous dimension of the scalar and fermion fields have been implemented as well. It is now possible to export the coupled system of beta functions into a numerical C++ function, leading to a consequent speed up in solving them.

   hep-phComput.Phys.Commun.(2017)·55 citations
4. 04*

   Challenges and opportunities for heavy scalar searches in the $t\bar{t}$ channel at the LHC

   Marcela Carena🇺🇸 · Zhen Liu🇺🇸

   Heavy scalar and pseudoscalar resonance searches through the $gg\to S\to t\bar{t}$ process are challenging due to the peculiar behavior of the large interference effects with the standard model $t\bar{t}$ background. Such effects generate non-trivial lineshapes from additional relative phases between the signal and background amplitudes. We provide the analytic expressions for the differential cross sections to understand the interference effects in the heavy scalar signal lineshapes. We extend our study to the case of CP-violation and further consider the effect of bottom quarks in the production and decay processes. We also evaluate the contributions from additional particles to the gluon fusion production process, such as stops and vector-like quarks, that could lead to significant changes in the behavior of the signal lineshapes. Taking into account the large interference effects, we perform lineshape searches at the LHC and discuss the importance of the systematic uncertainties and smearing effects. We present projected sensitivities for two LHC performance scenarios to probe the $gg\to S\to t\bar{t}$ channel in various models.

   hep-phhep-exJHEP(2016)·102 citations
5. 05*

   Probing the hardest branching of jets in heavy ion collisions

   Yang-Ting Chien🇺🇸 · Ivan Vitev🇺🇸

   We present the first calculation of the momentum sharing and angular separation distributions between the leading subjets inside a reconstructed jet in heavy ion collisions. These observables are directly sensitive to the hardest branching in the process of jet formation and are, therefore, ideal for studying the early stage of the in-medium parton shower evolution. The modification of the momentum sharing and angular separation distributions in lead-lead relative to proton-proton collisions is evaluated using the leading-order medium-induced splitting functions obtained in the framework of soft-collinear effective theory with Glauber gluon interactions. Qualitative and in most cases quantitative agreement between theory and preliminary CMS measurements suggests that the parton shower in heavy ion collisions can be dramatically modified early in the branching history. We propose a new measurement which will illuminate the angular distribution of the hardest branching within jets in heavy ion collisions.

   hep-phhep-exnucl-exnucl-thPRL(2017)·129 citations
6. 06*

   Constraining Flavor Changing Interactions from LHC Run-2 Dilepton Bounds with Vector Mediators

   Farinaldo S. Queiroz🇩🇪 · Clarissa Siqueira🇧🇷 · José W. F. Valle🇪🇸

   Within the context of vector mediators, is a new signal observed in flavor changing interactions, particularly in the neutral mesons systems $K^0-{\bar{K}}^0$, $D^0-{\bar{D}}^0$ and $B^0-\overline{B^0}$, consistent with dilepton resonance searches at the LHC? In the attempt to address this very simple question, we discuss the complementarity between flavor changing neutral current (FCNC) and dilepton resonance searches at the LHC run 2 at $13$TeV with $3.2\mathrm{f}{\mathrm{b}}^{-1}$ of integrated luminosity, in the context of vector mediators at tree level. Vector mediators, are often studied in the flavor changing framework, specially in the light of the recent LHCb anomaly observed at the rare B decay. However, the existence of stringent dilepton bound severely constrains flavor changing interactions, due to restrictive limits on the $Z^{\prime }$ mass. We discuss this interplay explicitly in the well motivated framework of a 3-3-1 scheme, where fermions and scalars are arranged in the fundamental representation of the weak SU(3) gauge group. Due to the paucity of relevant parameters, we conclude dilepton data leave little room for a possible new physics signal stemming from these systems, unless a very peculiar texture parametrization is used in the diagonalization of the CKM matrix. In other words, if a signal is observed in such flavor changing interactions, it is unlikely comes from a 3-3-1 model.

   hep-phPLB(2016)·59 citations
7. 07*

   Medium Induced Transverse Momentum Broadening in Hard Processes

   A. H. Mueller🇺🇸 · Bin Wu🇫🇷 · Bo-Wen Xiao🇨🇳 · Feng Yuan🇺🇸

   Using deep inelastic scattering on a large nucleus as an example, we consider the transverse momentum broadening of partons in hard processes in the presence of medium. We find that one can factorize the vacuum radiation contribution and medium related $P_T$ broadening effects into the Sudakov factor and medium dependent distributions, respectively. Our derivations can be generalized to other hard processes, such as dijet productions, which can be used as a probe to measure the medium $P_T$ broadening effects in heavy ion collisions when Sudakov effects are not overwhelming.

   hep-phnucl-thPRD(2017)·54 citations
8. 08*

   A Higgs in the Warped Bulk and LHC signals

   F. Mahmoudi🇫🇷 · U. Maitra🇮🇳 · N. Manglani🇮🇳 · K. Sridhar🇮🇳

   Warped models with the Higgs in the bulk can generate light Kaluza-Klein (KK) Higgs modes consistent with the electroweak precision analysis. The first KK mode of the Higgs (h_{1}) could lie in the 1-2 TeV range in the models with a bulk custodial symmetry. We find that the h_{1} is gaugephobic and decays dominantly into a t\bar{t} pair. We also discuss the search strategy for h_{1} decaying to t\bar{t} at the Large Hadron Collider. We used substructure tools to suppress the large QCD background associated with this channel. We find that h_{1} can be probed at the LHC run-2 with an integrated luminosity of 300 fb^{-1}.

   hep-phJHEP(2016)·8 citations
9. 09*

   Mass Ansatze for the standard model fermions from a composite perspective

   Amir H. Fariborz🇺🇸 · Renata Jora🇷🇴 · Salah Nasri🇦🇪

   We consider a composite model in which the standard model fermions are bound states of elementary spin $\frac{1}{2}$ particles, the preons, situated in the conjugate product representation of the color group. In this framework we propose and analyze two mass Ansatze one for the leptons, the other one for the quarks, based on mass formulae of the Gell-Mann Okubo type. We find that these mass Ansatze can give an adequate description of the known standard model fermion masses.

   hep-phRom.Rep.Phys.(2018)·2 citations
10. 10*

    Directed flow in heavy-ion collisions at NICA: what is interesting to measure?

    L.V. Bravina🇳🇴 · E.E. Zabrodin🇳🇴

    We study the formation of the directed flow of hadrons in nuclear collisions at energies between AGS and SPS in Monte Carlo cascade model. The slope of the proton flow at midrapidity tends to zero (softening) with increasing impact parameter of the collision. For very peripheral topologies this slope becomes negative (antiflow). The effect is caused by rescattering of hadrons in remnants of the colliding nuclei. Since the softening of the proton flow can be misinterpreted as indication of the presence of quark-gluon plasma, we propose several measurements at NICA facility which can help one to distinguish between the cases with and without the plasma formation.

    hep-phnucl-exnucl-thEPJA(2016)·7 citations
11. 11*

    Vacuum alignment with(out) elementary scalars

    Tommi Alanne🇩🇰 · Helene Gertov🇩🇰 · Aurora Meroni🇩🇰 · Francesco Sannino🇩🇰

    We systematically elucidate differences and similarities of the vacuum alignment issue in composite and renormalizable elementary extensions of the Standard Model featuring a pseudo-Goldstone Higgs. We also provide general conditions for the stability of the vacuum in the elementary framework, thereby extending previous studies of the vacuum alignment.

    hep-phPRD(2016)·10 citations
12. 12*

    Naturalness and lepton number/flavor violation in inverse seesaw models

    Naoyuki Haba🇯🇵 · Hiroyuki Ishida🇯🇵 · Yuya Yamaguchi🇯🇵

    We introduce three right-handed neutrinos and three sterile neutrinos, and consider an inverse seesaw mechanism for neutrino mass generation. From naturalness point of view, their Majorana masses should be small, while it induces a large neutrino Yukawa coupling. Then, a neutrinoless double beta decay rate can be enhanced, and a sizable Higgs mass correction is inevitable. We find that the enhancement rate can be more than ten times compared with a standard prediction from light neutrino contribution alone, and an analytic form of heavy neutrino contributions to the Higgs mass correction. In addition, we numerically analyze the model, and find almost all parameter space of the model can be complementarily searched by future experiments of neutrinoless double beta decay and $\mu \to e$ conversion.

    hep-phJHEP(2016)·15 citations
13. 13*

    Search for Mono-Higgs Signals at the LHC in the B-L Supersymmetric Standard Model

    W. Abdallah🇪🇬 · A. Hammad🇪🇬 · S. Khalil🇪🇬 · S. Moretti🇬🇧

    We study mono-Higgs signatures emerging in the $B-L$ supersymmetric standard model induced by new channels not present in the minimal supersymmetric standard model, i.e., via topologies in which the mediator is either a heavy $Z^{\prime }$, with mass of $\mathcal{O}(2\mathrm{TeV})$, or an intermediate $h^{\prime }$ (the lightest CP-even Higgs state of $B-L$ origin), with mass of $\mathcal{O}(0.2\mathrm{TeV})$. The mono-Higgs probe considered is the SM-like Higgs state recently discovered at the large hadron collider, so as to enforce its mass reconstruction for background reduction purposes. With this in mind, its two cleanest signatures are selected: $\gamma \gamma$ and $Z{Z}^{\ast }\to 4l$ ($l=e,\mu$). We show how both of these can be accessed with foreseen energy and luminosity options using a dedicated kinematic analysis performed in presence of partonic, showering, hadronisation and detector effects.

    hep-phPRD(2017)·33 citations
14. 14*

    A hidden classical symmetry of QCD

    L. Ya. Glozman🇦🇹

    The classical part of the QCD partition function (the integrand) has, ignoring irrelevant exact zero modes of the Dirac operator, a local SU(2N_F) \supset SU(N_F)_L \times SU(N_F)_R \times U(1)_A symmetry which is absent at the Lagrangian level. This symmetry is broken anomalously and spontaneously. Effects of spontaneous breaking of chiral symmetry are contained in the near-zero modes of the Dirac operator. If physics of anomaly is also encoded in the same near-zero modes, then their truncation on the lattice should recover a hidden classical SU(2N_F) symmetry in correlators and spectra. This naturally explains observation on the lattice of a large degeneracy of hadrons, that is higher than the SU(N_F)_L \times SU(N_F)_R \times U(1)_A chiral symmetry, upon elimination by hands of the lowest-lying modes of the Dirac operator. We also discuss an implication of this symmetry for the high temperature QCD.

    ↳ hep-lathep-phhep-thEPJ Web Conf.(2017)·7 citations
15. 15*

    The angular power spectrum of the diffuse gamma-ray emission as measured by the Fermi Large Area Telescope and constraints on its Dark Matter interpretation

    Mattia Fornasa🇳🇱 · Alessandro Cuoco🇩🇪 · Jesus Zavala🇩🇰 · Jennifer M. Gaskins🇺🇸 · Miguel A. Sanchez-Conde🇸🇪 · German Gomez-Vargas🇨🇱 · Eiichiro Komatsu🇩🇪 · Tim Linden🇺🇸 · Francisco Prada🇪🇸 · Fabio Zandanel🇳🇱 · Aldo Morselli🇮🇹

    The isotropic gamma-ray background arises from the contribution of unresolved sources, including members of confirmed source classes and proposed gamma-ray emitters such as the radiation induced by dark matter annihilation and decay. Clues about the properties of the contributing sources are imprinted in the anisotropy characteristics of the gamma-ray background. We use 81 months of Pass 7 Reprocessed data from the Fermi Large Area Telescope to perform a measurement of the anisotropy angular power spectrum of the gamma-ray background. We analyze energies between 0.5 and 500 GeV, extending the range considered in the previous measurement based on 22 months of data. We also compute, for the first time, the cross-correlation angular power spectrum between different energy bins. We find that the derived angular spectra are compatible with being Poissonian, i.e. constant in multipole. Moreover, the energy dependence of the anisotropy suggests that the signal is due to two populations of sources, contributing, respectively, below and above 2 GeV. Finally, using data from state-of-the-art numerical simulations to model the dark matter distribution, we constrain the contribution from dark matter annihilation and decay in Galactic and extragalactic structures to the measured anisotropy. These constraints are competitive with those that can be derived from the average intensity of the isotropic gamma-ray background. Data are available at https://www-glast.stanford.edu/pub_data/552.

    ↳ astro-ph.HEastro-ph.COhep-phPRD(2016)·84 citations
16. 16*

    Direct Detection of Dark Matter Bound to the Earth

    Riccardo Catena🇸🇪 · Chris Kouvaris🇩🇰

    We study the properties and direct detection prospects of an as of yet neglected population of dark matter (DM) particles moving in orbits gravitationally bound to the Earth. This DM population is expected to form via scattering by nuclei in the Earth's interior. We compute fluxes and nuclear recoil energy spectra expected at direct detection experiments for the new DM population considering detectors with and without directional sensitivity, and different types of target materials and DM-nucleon interactions. DM particles bound to the Earth manifest as a prominent rise in the low-energy part of the observed nuclear recoil energy spectrum. Ultra-low threshold energies of about 1 eV are needed to resolve this effect. Its shape is independent of the DM-nucleus scattering cross-section normalisation.

    ↳ astro-ph.COhep-phPRD(2017)·5 citations
17. 17*

    Pion transition form factor through Dyson-Schwinger equations

    Khépani Raya🇲🇽

    In the framework of Dyson-Schwinger equations (DSE), we compute the ${\gamma }^{\ast }\gamma \to {\pi }^0$ transition form factor, $G(Q^2)$. For the first time, in a continuum approach to quantun chromodynamics (QCD), it was possible to compute $G(Q^2)$ on the whole domain of space-like momenta. Our result agrees with CELLO, CLEO and Belle collaborations and, with the well-known asymptotic QCD limit, $2f_{\pi }$. Our analysis unifies this prediction with that of the pion's valence-quark parton distribution amplitude (PDA) and elastic electromagnetic form factor.

    ↳ nucl-thhep-phJ.Phys.Conf.Ser.(2016)·0 citations
18. 18*

    A Euclidean bridge to the relativistic constituent quark model

    T. J. Hobbs🇺🇸 · Mary Alberg🇺🇸 · Gerald A. Miller🇺🇸

    $\mathbf{Background}$ Knowledge of nucleon structure is today ever more of a precision science, with heightened theoretical and experimental activity expected in coming years. At the same time, a persistent gap lingers between theoretical approaches grounded in Euclidean methods (e.g., lattice QCD, Dyson-Schwinger Equations [DSEs]) as opposed to traditional Minkowski field theories (such as light-front constituent quark models). $\mathbf{Purpose}$ Seeking to bridge these complementary worldviews, we explore the potential of a Euclidean constituent quark model (ECQM). This formalism enables us to study the gluonic dressing of the quark-level axial-vector vertex, which we undertake as a test of the framework. $\mathbf{Method}$ To access its indispensable elements with a minimum of inessential detail, we develop our ECQM using the simplified quark $+$ scalar diquark picture of the nucleon. We construct a hyperspherical formalism involving polynomial expansions of diquark propagators to marry our ECQM with the results of Bethe-Salpeter Equation (BSE) analyses, and constrain model parameters by fitting electromagnetic form factor data. $\mathbf{Results}$ From this formalism, we define and compute a new quantity --- the Euclidean density function (EDF) --- an object that characterizes the nucleon's various charge distributions as functions of the quark's Euclidean momentum. Applying this technology and incorporating information from BSE analyses, we find the dressing effect on the proton's axial-singlet charge to be small in magnitude and consistent with zero. $\mathbf{Conclusions}$ The scalar quark $+$ diquark ECQM is a step toward a realistic quark model in Euclidean space, and urges additional refinements. The small size we obtain for the impact of the dressed vertex on the axial-singlet charge suggests that models without this effect are on firm ground to neglect it.

    ↳ nucl-thhep-phPRC(2017)·14 citations
19. 19*

    Hadronic weak charges and parity-violating forward Compton scattering

    Mikhail Gorchtein🇩🇪 · Hubert Spiesberger🇩🇪

    Parity-violating elastic electron-nucleon scattering at low momentum transfer allows one to access the nucleon's weak charge, the vector coupling of the $Z$-boson to the nucleon. In the Standard Model and at tree level, the weak charge of the proton is related to the weak mixing angle and accidentally suppressed, $Q_W^{p,\mathrm{tree}}=1-4{\sin }^2{\theta }_W\approx 0.07$. Modern experiments aim at extracting $Q_W^p$ at $\sim 1\%$ accuracy. Similarly, parity non-conservation in atoms allows to access the weak charge of atomic nuclei. We consider a novel class of radiative corrections, an exchange of two photons with parity violation in the hadronic/nuclear system. These corrections may affect the extraction of ${\sin }^2{\theta }_W$ from the experimental data at the relevant level of precision because they are affected by long-range interactions similar to other parity-violating radiative corrections, such as, e.g., the $\gamma Z$-exchange, which has obtained much attention recently. We show that the significance of this new correction increases with the beam energy in parity-violating electron scattering, but the general properties of the parity-violating forward Compton amplitude protect the formal definition of the weak charge as a limit at zero-momentum transfer and zero-energy. We also discuss the relevance of the new correction for upcoming experiments.

    ↳ nucl-thhep-phnucl-exPRC(2016)·6 citations
20. 20*

    Higgs Physics at the CLIC Electron-Positron Linear Collider

    H. Abramowicz🇮🇱 · A. Abusleme🇨🇱 · K. Afanaciev🇧🇾 · N. Alipour Tehrani🇨🇭 · C. Balázs🇦🇺 · Y. Benhammou🇮🇱 · M. Benoit🇨🇭 · B. Bilki🇺🇸 · J.-J. Blaising🇫🇷 · M.J. Boland🇦🇺 · M. Boronat🇪🇸 · O. Borysov🇮🇱 and 112 other authors

    The Compact Linear Collider (CLIC) is an option for a future e+e- collider operating at centre-of-mass energies up to 3 TeV, providing sensitivity to a wide range of new physics phenomena and precision physics measurements at the energy frontier. This paper is the first comprehensive presentation of the Higgs physics reach of CLIC operating at three energy stages: sqrt(s) = 350 GeV, 1.4 TeV and 3 TeV. The initial stage of operation allows the study of Higgs boson production in Higgsstrahlung (e+e- -> ZH) and WW-fusion (e+e- -> Hnunu), resulting in precise measurements of the production cross sections, the Higgs total decay width Gamma_H, and model-independent determinations of the Higgs couplings. Operation at sqrt(s) > 1 TeV provides high-statistics samples of Higgs bosons produced through WW-fusion, enabling tight constraints on the Higgs boson couplings. Studies of the rarer processes e+e- -> ttH and e+e- -> HHnunu allow measurements of the top Yukawa coupling and the Higgs boson self-coupling. This paper presents detailed studies of the precision achievable with Higgs measurements at CLIC and describes the interpretation of these measurements in a global fit.

    ↳ hep-exhep-phEPJC(2017)·277 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.