Thu·Feb 14, 2019Thursday·February 14, 2019

1. 01*

   Effective Theory for a Heavy Scalar Coupled to the SM via Vector-Like Quarks

   Stefan Alte (U. Mainz)🇩🇪 · Matthias Koenig (U. Zurich)🇨🇭 · Matthias Neubert (U. Mainz)🇩🇪

   We illustrate the application of the recently developed SCET${}_{\mathrm{BSM}}$ framework in the context of a specific model, in which the Standard Model (SM) is supplemented by a heavy scalar $S$ and three generations of heavy, vector-like quarks $\Psi$. We construct the appropriate effective field theory for two-body decays of $S$ into SM particles. We explicitly compute the Wilson coefficients of the SCET${}_{\mathrm{BSM}}$ operators appearing at leading and next-to-leading order (NLO) in an expansion in powers of $v/M_S$, as well as for a subset of operators arising at NNLO, retaining the full dependence on the ratio $M_S/M_{\Psi }$. For the phenomenologically most relevant decay channels of the heavy scalar, we study the impact of resummation effects of Sudakov logarithms on the decay rates.

   hep-phEPJC(2019)·15 citations
2. 02*

   The Spin Budget of the Proton at NNLO and Beyond

   Daniel de Florian🇦🇷 · Werner Vogelsang🇩🇪

   We revisit the scale evolution of the quark and gluon spin contributions to the proton spin, $\frac{1}{2}\Delta \Sigma$ and $\Delta G$, using the three-loop results for the spin-dependent evolution kernels available in the literature. We argue that the evolution of the quark spin contribution may actually be extended to four-loop order, and that to all orders a single anomalous dimension governs the evolution of both $\Delta \Sigma$ and $\Delta G$. We present analytical solutions of the evolution equations for $\Delta \Sigma$ and $\Delta G$ and investigate their scale dependence both to large and down to lower "hadronic" scales. We find that the solutions remain perturbatively stable even to low scales, where they come closer to simple quark model expectations. We discuss a curious scenario for the proton spin, in which even the gluon spin contribution is essentially scale independent and has a finite asymptotic value as the scale becomes large. We finally also show that perturbative three-loop evolution leads to a larger spin contribution of strange anti-quarks than of strange quarks.

   hep-phPRD(2019)·17 citations
3. 03*

   Theoretical predictions on polarization asymmetry for Drell-Yan process with spin-one deuteron and tensor-polarized structure function $b_1$

   S. Kumano🇯🇵 · Qin-Tao Song🇯🇵

   We report recent theoretical progress on a polarization asymmetry in the proton-deuteron Drell-Yan process with a polarized-deuteron target and the tensor-polarized structure function $b_1$. Experimental measurements are possible at JLab for $b_1$ and at Fermilab for the Drell-Yan process. First, we show a theoretical estimate for the proton-deuteron Drell-Yan asymmetry in the Fermilab-E1039 experiment. We evolved tensor-polarized parton distribution functions, which explain existing HERMES $b_1$ data, at $Q^2=2.5$ GeV${}^2$ to the $Q^2$ range of the Fermilab Drell-Yan measurements. Then, we predicted that the asymmetry is of the order of a few percent. The Drell-Yan experiment has an advantage to probe the tensor-polarized antiquark distributions, which were suggested by the HERMES experiment as a finite sum for $b_1$ ($\int dx{b}_1(x)\ne 0$). Second, we predicted $b_1$ for the JLab experiment by the standard convolution model of the deuteron. Our theoretical $b_1$ structure function seems to be much different from the HERMES data. Furthermore, a significant distribution exists at very large $x$ ($>1$) beyond the kinematical limit $x_{max}=1$ for the proton. Because the standard deuteron-model estimate is much different from the HERMES data, there could be an interesting development as a new hadron-physics field if future JLab data will be much different from our conventional prediction.

   hep-phhep-exhep-latnucl-thPoS(2019)·0 citations
4. 04*

   Anomalous $H\to ZZ\to 4\ell$ decay and its interference effects at the LHC

   Hua-Rong He🇨🇳 · Xia Wan🇨🇳 · You-Kai Wang🇨🇳

   We calculate the spinor helicity amplitudes of anomalous $H\to ZZ\to 4\ell$ decay. After embedding these analytic formulas into the $\text{MCFM}$ package, we study the interference effects between the anomalous $gg\to H\to ZZ\to 4\ell$ process and the SM processes, which are indispensable in the Higgs off-shell region. Subsequently, the constraints on the anomalous couplings are estimated using LHC experimental data.

   hep-phCPC(2020)·17 citations
5. 05*

   Lepton flavor violation induced by neutral and doubly-charged scalars at future lepton colliders

   P. S. Bhupal Dev🇺🇸 · Rabindra N. Mohapatra🇺🇸 · Yongchao Zhang🇺🇸

   New physics scenarios beyond the Standard Model (SM) for neutrino mass mechanism often necessitate the existence of a neutral scalar $H$ and/or doubly-charged scalar $H^{\pm \pm }$, which couple to the SM charged leptons in a flavor violating way, while evading all existing constraints. Such scalars could be effectively produced at future lepton colliders like CEPC, ILC, FCC-ee and CLIC, either on-shell or off-shell, and induce striking charged lepton flavor violating (LFV) signals. We find that a large parameter space of the scalar masses and the LFV couplings can be probed at lepton colliders, well beyond the current low-energy constraints in the lepton sector. The neutral scalar explanation of the muon $g-2$ anomaly could also be directly tested.

   hep-phhep-ex4 citations
6. 06*

   Low-energy limit of the O(4) quark-meson model

   Jürgen Eser🇩🇪 · Florian Divotgey🇩🇪 · Mario Mitter🇺🇸

   We study the generation of low-energy couplings induced by quantum fluctuations within the O(4)-symmetric quark-meson model. To this end, we compute the functional renormalization group flow of the linearly realized quark-meson model including higher-derivative interactions and subsequently transform the resulting effective action into a nonlinear effective pion action. The latter is referred to as the low-energy limit of the O(4) quark-meson model. The present study may be considered as a preparatory work for the dynamical generation of low-energy couplings from functional QCD fluctuations in order to determine meaningful renormalization scales for purely pionic models.

   hep-phhep-thPoS(2019)·12 citations
7. 07*

   Radiative $b$-baryon decays to measure the photon and $b$-baryon polarization

   Luis Miguel García Martín🇪🇸 · Brij Jashal🇪🇸 · Fernando Martínez Vidal🇪🇸 · Arantza Oyanguren🇪🇸 · Shibasis Roy🇮🇳 · Ria Sain🇮🇳 · Rahul Sinha🇮🇳

   The radiative decays of $b$-baryons facilitate the direct measurement of photon helicity in $b\to s\gamma$ transitions thus serving as an important test of physics beyond the Standard Model. In this paper we analyze the complete angular distribution of ground state $b$-baryon (${\Lambda }_b^0$ and ${\Xi }_b^{-}$) radiative decays to multibody final states assuming an initially polarized $b$-baryon sample. Our sensitivity study suggests that the photon polarization asymmetry can be extracted to a good accuracy along with a simultaneous measurement of the initial $b$-baryon polarization. With higher yields of $b$-baryons, achievable in subsequent runs of the Large Hadron Collider (LHC), we find that the photon polarization measurement can play a pivotal role in constraining different new physics scenarios.

   hep-phhep-exEPJC(2019)·16 citations
8. 08*

   A fresh look at ALP searches in fixed target experiments

   Lucian Harland-Lang🇬🇧 · Joerg Jaeckel🇩🇪 · Michael Spannowsky🇬🇧

   A significant number of high power proton beams are available or will go online in the near future. This provides exciting opportunities for new fixed target experiments and the search for new physics in particular. In this note we will survey these beams and consider their potential to discover new physics in the form of axion-like particles, identifying promising locations and set ups. To achieve this, we present a significantly improved calculation of the production of axion-like particles in the coherent scattering of protons on nuclei, valid for lower ALP masses and/or beam energies. We also provide a new publicly available tool for this process: the Alpaca Monte Carlo generator. This will impact ongoing and planned searches based on this process.

   hep-phhep-exPLB(2019)·61 citations
9. 09*

   What $R_K$ and $Q_5$ can tell us about New Physics in $b\to s\ell \ell$ transitions?

   Marcel Algueró🇪🇸 · Bernat Capdevila🇪🇸 · Sébastien Descotes-Genon🇫🇷 · Pere Masjuan🇪🇸 · Joaquim Matias🇪🇸

   The deviations with respect to the Standard Model that are currently observed in $b\to s\ell \ell$ transitions, or $B$ anomalies, can be interpreted in terms of different New Physics (NP) scenarios within a model-independent effective approach. We identify a set of internal tensions of the fit that require further attention and whose theoretical or experimental nature could be determined with more data. In this landscape of NP, we discuss possible ways to discriminate among favoured NP hypotheses in the short term thanks to current and forthcoming observables. While an update of $R_K$ should help to disentangle the type of NP we may be observing (Lepton-Flavour Universality Violating and/or Lepton Flavour Universal), additional observables, in particular $Q_5$, turn out to be central to determine which NP hypothesis should be preferred. We also analyse the preferences shown by the current global fit concerning various NP hypotheses, using two different tools: the behaviour of the pulls of individual observables under NP scenarios and the directions favoured by approximate quadratic parametrisations of the observables in terms of Wilson coefficients.

   hep-phhep-exJHEP(2019)·39 citations
10. 10*

    Two-mediator dark matter models and cosmic electron excess

    Xuewen Liu🇨🇳 · Zuowei Liu🇨🇳 · Yushan Su🇨🇳

    The cosmic electron energy spectrum recently observed by the DAMPE experiment exhibits two interesting features, including a break around 0.9 TeV and a sharp resonance near 1.4 TeV. In this analysis, we propose a dark matter explanation to both exotic features seen by DAMPE. In our model, dark matter annihilates in the galaxy via two different channels that lead to both a narrow resonance spectrum near 1.4 TeV and electron excess events over an extended energy range thus generating the break structure around TeV. The two annihilation channels are mediated by two gauge bosons that interact both with dark matter and with the standard model fermions. Dark matter annihilations through the s-channel process mediated by the heavier boson produce monoenergetic electron-positron pairs leading to the resonance excess. The lighter boson has a mass smaller than the dark matter such that they can be on-shell produced in dark matter annihilations in the galaxy; the lighter bosons in the final state subsequently decay to generate the extended excess events due to the smeared electron energy spectrum in this process. We further analyze constraints from various experiments, including HESS, Fermi, AMS, and LHC, to the parameter space of the model where both excess events can be accounted for. In order to interpret the two new features in the DAMPE data, dark matter annihilation cross sections in the current galaxy are typically much larger than the canonical thermal cross section needed for the correct dark matter relic abundance. This discrepancy, however, is remedied by the nonperturbative Sommerfeld enhancement because of the existence of a lighter mediator in the model.

    hep-phastro-ph.COastro-ph.HEJHEP(2019)·12 citations
11. 11*

    Triple prompt $J/\psi$ hadroproduction as a hard probe of multiple-parton scatterings

    Hua-Sheng Shao🇫🇷 · Yu-Jie Zhang🇨🇳

    We propose that the process of triple prompt $J/\psi$ hadroproduction is a very clean hard probe of multiple-parton scatterings at high-energy hadron colliders, especially the least known triple-parton scattering. A first complete study is carried out by considering single-, double-, and triple-parton scatterings coherently. Our calculation shows that it is a golden channel to probe double- and triple-parton scatterings, as the single-parton scattering is strongly suppressed. The predictions of the (differential) cross sections in proton-proton collisions at the LHC and the future higher-energy hadron colliders are given. Our study shows that its measurement is already feasible with the existing data collected during the period of the LHC run 2. A method is proposed to extract the triple-parton scattering contribution, and therefore it paves a way to study the possible triple-parton correlations in a proton.

    hep-phhep-exPRL(2019)·31 citations
12. 12*

    Effect of Colorlessness Condition on Phase Transition from Hadronic Gas to Partonic Plasma

    M. A.A. Ahmeda. Cherif · M. Ladreme · H. Zainuddin · N. M. Shah

    One of the most important phase transition in physics is the Deconfinement Phase Transition in thermal Quantum ChromoDynamics. Due to the confinement property, we study the effect of colorlessness condition during the Deconfinement Phase Transition from a Hadronic Gas to a Quark-Gluon Plasma. We investigate the behavior of some thermodynamical quantities of the system such as the energy density and the pressure, the colorlessness condition and without colorlessness.

    hep-phnucl-th0 citations
13. 13*

    Unpolarised TMD PDFs and FFs and the role of transverse momentum dependence in azimuthal spin asymmetries

    M. Anselmino🇮🇹 · M. Boglione🇮🇹 · U. D'Alesio🇮🇹 · F. Murgia🇮🇹 · A. Prokudin🇺🇸

    In the TMD approach, the average transverse momentum of the unpolarised TMD PDFs and FFs is crucial not only to reproduce unpolarised cross sections and hadron multiplicities, but also for the understanding of azimuthal and spin asymmetries. Information on these transverse momenta is nowadays obtained mainly by fitting multiplicities data for SIDIS, where the intrinsic motion in the initial parton distributions and in the hadronisation process are strongly correlated and difficult to estimate separately without ambiguities. In this contribution we discuss the consequences of this correlation effects on the predictions for the Sivers and Collins asymmetries measured in SIDIS and $e^{+}{e}^{-}$ annihilations, and under active investigation for Drell-Yan processes at RHIC and at CERN by the COMPASS experiment. We show that these effects may be relevant and can sensibly modify the size of the predicted asymmetries. Therefore, they must be taken into careful account when investigating other aspects of TMDs, like the evolution properties of the Sivers and Collins functions and the expected process dependence of the Sivers function.

    hep-phPoS(2019)·0 citations
14. 14*

    Quenching of hadron spectra in XeXe and PbPb collisions at the LHC

    François Arleo🇫🇷 · Guillaume Falmagne🇫🇷

    The $p_{\perp }$ dependence of the nuclear modification factor $R_{\text{AA}}$ measured in PbPb collisions at the LHC exhibits a universal shape, which can be very well reproduced in a simple energy loss model based on the BDMPS medium-induced gluon spectrum. We update a former study by including in the analysis the recent CMS measurements on $J/\psi$ production in PbPb collisions at $\sqrt{s}=5.02$ TeV and charged hadron production in XeXe collisions at $\sqrt{s}=5.44$ TeV. The average parton energy loss extracted from minimum bias XeXe collisions is reduced typically by 20% compared to PbPb collisions, consistent with a length dependence $⟨\overline{ϵ}⟩\propto L^{1.3\pm 0.5}$ with $L\propto A^{1/3}$.

    hep-phhep-exnucl-thPoS(2019)·4 citations
15. 15*

    Top-mass observables: all-orders behaviour, renormalons and NLO + Parton Shower effects

    Silvia Ferrario Ravasio🇮🇹

    In this thesis we focus on the theoretical subtleties of the top-quark mass ($m_t$) determination, issue which persists in being highly controversial. In the first part of the thesis, we investigate the presence of linear renormalons in observables that can be employed to determine the top mass. We considered a simplified toy model to describe $W^{\ast }\to t\bar{b}\to Wb\bar{b}$. The computation is carried out in the limit of a large number of flavours ($n_f$), using a new method that allows to easily evaluate any infrared safe observable at order ${\alpha }_s({\alpha }_s{n}_f{)}^n$ for any $n$. The second part of the thesis is devoted to the comparison of several NLO generators for top-pair production, implemented in the POWHEG BOX framework, that differ by the level of accuracy employed to describe the top decay. The impact of the shower Monte Carlo programs, used to complete the NLO events generated by POWHEG BOX, is also studied. In particular, we discuss the two most widely used shower Monte Carlo programs, i.e. Pythia 8.2 and Herwig 7.1, and we present a method to interface them with processes that contain decayed emitting resonances.

    hep-ph4 citations
16. 16*

    Revisiting the Dark Photon Explanation of the Muon Anomalous Magnetic Moment

    Gopolang Mohlabeng🇺🇸

    A massive $U(1{)}^{\prime }$ gauge boson known as a "dark photon" or $A^{\prime }$, has long been proposed as a potential explanation for the discrepancy observed between the experimental measurement and theoretical determination of the anomalous magnetic moment of the muon, ($g_{\mu }-2$) anomaly. Recently, experimental results have excluded this possibility for a dark photon exhibiting exclusively visible or invisible decays. In this work, we revisit this idea and consider a model where $A^{\prime }$ couples inelastically to dark matter and an excited dark sector state, leading to a more exotic decay topology we refer to as a semi-visible decay. We show that for large mass splittings between the dark sector states this decay mode is enhanced, weakening the previous invisibly decaying dark photon bounds. As a consequence, $A^{\prime }$ resolves the $g_{\mu }-2$ anomaly in a region of parameter space the thermal dark matter component of the Universe is readily explained. Interestingly, it is possible that the semi-visible events we discuss may have been vetoed by experiments searching for invisible dark photon decays. A re-analysis of the data and future searches may be crucial in uncovering this exotic decay mode or closing the window on the dark photon explanation of the $g_{\mu }-2$ anomaly.

    hep-phastro-ph.COhep-exPRD(2019)·89 citations
17. 17*

    Matter dependence of the four-loop QCD cusp anomalous dimension: from small angles to all angles

    Robin Brüser🇩🇪 · Andrey Grozin🇷🇺 · Johannes M. Henn🇩🇪 · Maximilian Stahlhofen🇩🇪

    We compute the fermionic contributions to the cusp anomalous dimension in QCD at four loops as an expansion for small cusp angle. As a byproduct we also obtain the respective terms of the four-loop HQET wave function anomalous dimension. Our new results at small angles provide stringent tests of a recent conjecture for the exact angle dependence of the matter terms in the four-loop cusp anomalous dimension. We find that the conjecture does not hold for two of the seven fermionic color structures, but passes all tests for the remaining terms. This provides strong support for the validity of the corresponding conjectured expressions with full angle dependence. Taking the limit of large Minkowskian angle, we extract novel analytic results for certain terms of the light-like cusp anomalous dimension. They agree with the known numerical results. Finally, we study the anti-parallel lines limit of the cusp anomalous dimension. In a conformal theory, the latter is proportional to the static quark-antiquark potential. We use the new four-loop results to determine parts of the conformal anomaly term.

    hep-phhep-thJHEP(2019)·77 citations
18. 18*

    Gravitational Waves from Compact Dark Objects in Neutron Stars

    C. J. Horowitz🇺🇸 · Sanjay Reddy🇺🇸

    Dark matter could be composed of compact dark objects (CDOs). We find that the oscillation of CDOs inside neutron stars can be a detectable source of gravitational waves (GWs). The GW strain amplitude depends on the mass of the CDO, and its frequency is typically in the range 3-5 kHz as determined by the central density of the star. In the best cases, LIGO may be sensitive to CDO masses greater than or of order $10^{-8}$ solar masses.

    ↳ astro-ph.HEgr-qchep-phnucl-thPRL(2019)·52 citations
19. 19*

    Observational constraints on the oscillating dark energy cosmologies

    Mehdi Rezaei🇮🇷

    In this study we combine the background and the growth rate data in order to study the ability of the two oscillating dark energy parameterizations, to fit the observational data. Using the likelihood and MCMC method we try to explore the posterior space and put constraints on the free parameters of the models. Based on the values of the well known Akaike and Bayesian information criteria we find that both of oscillating dark energy models considered in this work are disfavored by the combined (background+growth rate) data. Although using the expansion data we can not reject oscillating dark energy models, the combined analysis provides strong evidences against these models.

    ↳ gr-qcastro-ph.COhep-phMNRAS(2019)·22 citations
20. 20*

    Effective field theory for gravitational radiation in scalar-tensor gravity

    Adrien Kuntz🇫🇷 · Federico Piazza🇫🇷 · Filippo Vernizzi🇫🇷

    A light scalar degree of freedom, as the one possibly responsible for the accelerated expansion of the Universe, could leave observable traces in the inspiral gravitational wave signal of binary systems. In order to study these effects, we extend the effective field theory formalism of Goldberger and Rothstein to minimal scalar-tensor theories of gravity. This class of models is still very broad, because the couplings of the scalar to matter are far less constrained than those a massless spin-2 field. In most of the paper we focus on conformal couplings. Using the effective field theory approach, we discuss the emergence of violations of the strong equivalence principle even in models that exhibit universality of free fall at the microscopic level. Our results on the conservative dynamics of the binary and its power emitted in gravitational and scalar radiation agree with those obtained with the standard post-Newtonian formalism. We also compare them to more recent work. Finally, we discuss the implications of considering a disformal coupling to matter.

    ↳ gr-qcastro-ph.COhep-phhep-thJCAP(2019)·56 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.