Thu·May 16, 2019Thursday·May 16, 2019

1. 01*

   Light Dark Matter from Inelastic Cosmic Ray Collisions

   James Alvey🇬🇧 · Miguel Campos🇬🇧 · Malcolm Fairbairn🇬🇧 · Tevong You🇬🇧

   Direct detection experiments relying on nuclear recoil signatures lose sensitivity to sub-GeV dark matter for typical galactic velocities. This sensitivity is recovered if there exists another source of flux with higher momenta. Such an energetic flux of light dark matter could originate from the decay of mesons produced in inelastic cosmic ray collisions. We compute this novel production mechanism---a cosmic beam dump experiment---and estimate the resulting limits from XENON1T and LZ. We find that the dark matter flux from inelastic cosmic rays colliding with atmospheric nuclei can dominate over the flux from elastic collisions with relic dark matter. The limits that we obtain for hadrophilic scalar mediator models are competitive with those from MiniBoone for light MeV-scale mediator masses.

   hep-phastro-ph.HEPRL(2019)·97 citations
2. 02*

   Study of electromagnetic dipole moment, electric quadrupole moment and weak T-odd (CP-odd) interactions of high energy short-lived particles in straight crystals

   V.G. Baryshevsky🇧🇾

   A particle, which moves in a crystal, experiences weak interactions with electrons and nuclei alongside with electromagnetic interaction. Measuring the polarization vector and the angular distribution of charged and neutral particles scattered by axes (planes) of an unbent (straight) crystal enables to obtain restrictions for the EDM value and for {magnitudes} of constants describing T-odd (CP-odd) interactions Beyond the Standard Model. Spin rotation and polarization conversion from vector to tensor one and vice versa for a channelled in a crystal ${\Omega }^{\pm }$ hyperon enable measuring hyperon's quadrupole moment that is not possible to measure by use of laboratory available noncrystalline electric fields.

   hep-phhep-ex1 citation
3. 03*

   Single Leptoquark Solutions to the $B$-physics Anomalies

   Andrei Angelescu🇺🇸

   We examine various scenarios in which the Standard Model is extended by a light leptoquark state to explain one or both $B$-physics anomalies. Combining low-energy constraints and direct searches at the LHC, we confirm that the only single leptoquark model that can explain both anomalies at the same time is a vector leptoquark, known as $U_1$. Focusing on $U_1$, we highlight the complementarity between LHC and low--energy constraints, and argue that improving the experimental bound on $\mathcal{B}(B\to K\mu \tau )$ by two orders of magnitude could compromise its viability as a solution to the $B$-physics anomalies.

   hep-ph3 citations
4. 04*

   Supervised deep learning in high energy phenomenology: a mini review

   Murat Abdughani🇨🇳 · Jie Ren🇨🇳 · Lei Wu🇨🇳 · Jin Min Yang🇨🇳 · Jun Zhao🇨🇳

   Deep learning, a branch of machine learning, have been recently applied to high energy experimental and phenomenological studies. In this note we give a brief review on those applications using supervised deep learning. We first describe various learning models and then recapitulate their applications to high energy phenomenological studies. Some detailed applications are delineated in details, including the machine learning scan in the analysis of new physics parameter space, the graph neural networks in the search of top-squark production and in the $CP$ measurement of the top-Higgs coupling at the LHC.

   hep-phhep-exCommun.Theor.Phys.(2019)·45 citations
5. 05*

   Connecting neutral current $B$ anomalies with the heaviness of the third family

   Joe Davighi🇬🇧

   It is possible, and for several reasons attractive, to explain a collection of recent anomalies involving $b\to s\mu \mu$ processes with a $Z^{\prime }$ gauge boson coupled only to the third family in the weak eigenbasis. From this premise, requiring cancellation of all gauge anomalies (including mixed and gravitational anomalies) fixes a unique charge assignment for the third family Standard Model fermions, which is simply proportional to hypercharge. After a brief discussion of some general features of anomaly cancellation in $Z^{\prime }$ theories, we discuss the phenomenology of such a `Third Family Hypercharge Model', which is subject to a trio of important constraints: (i) $B_s-{\bar{B}}_s$ mixing, (ii) lepton universality of the $Z$ boson couplings, and (iii) constraints from direct searches for the $Z^{\prime }$ boson at the LHC. Finally, in gauging third family hypercharge, this model forbids all Yukawa couplings (at the renormalisable level) save those of the third family, leading to a possible explanation of the heaviness of the third family.

   hep-phhep-ex12 citations
6. 06*

   Singlet-doublet/triplet dark matter and neutrino masses

   Juri Fiaschi🇩🇪 · Michael Klasen🇩🇪 · Simon May🇩🇪

   In these proceedings, we present a study of a combined singlet--doublet fermion and triplet scalar model for dark matter (DM). Together, these models form a simple extension of the Standard Model (SM) that can account for DM and explain the existence of neutrino masses, which are generated radiatively. However, this also implies the existence of lepton flavour violating (LFV) processes. In addition, this particular model allows for gauge coupling unification. The new fields are odd under a new ${\mathbb{Z}}_2$ symmetry to stabilise the DM candidate. We analyse the DM, neutrino mass and LFV aspects, exploring the viable parameter space of the model. This is done using a numerical random scan imposing successively the neutrino mass and mixing, relic density, Higgs mass, direct detection, collider and LFV constraints. We find that DM in this model is fermionic for masses below about 1 TeV and scalar above. We observe a high degree of complementarity between direct detection and LFV experiments, which should soon allow to fully probe the fermionic DM sector and at least partially the scalar DM sector.

   hep-phastro-ph.CO0 citations
7. 07*

   Novel ideas in nonleptonic decays of double heavy baryons

   Thomas Gutsche🇩🇪 · Mikhail A. Ivanov🇷🇺 · Jürgen G. Körner🇩🇪 · Valery E. Lyubovitskij🇩🇪

   The recent discovery of double charm baryon states by the LHCb Collaborarion and their high precision mass determination calls for a comprehensive analysis of the nonleptonic decays of double and single heavy baryons. Nonleptonic baryon decays play an important role in particle phenomenology since they allow to study the interplay of long and short distance dynamics of the Standard Model (SM). Further, they allow one to search for New Physics effects beyond the SM. We review recent progress in experimental and theoretical studies of the nonleptonic decays of heavy baryons with a focus on double charm baryon states and their decays. In particular, we discuss new ideas proposed by the present authors to calculate the $W$-exchange matrix elements of the nonleptonic decays of double heavy baryons. An important ingredient in our approach is the compositeness condition of Salam and Weinberg, and an effective implementation of infrared confinement both of which allow one to describe the nonperturbative structure of baryons composed of light and heavy quarks. Further we discuss an ab initio calculational method for the treatment of the so-called $W$-exchange diagrams generated by $W^{\pm }$ boson exchange between quarks. We found that the $W^{\pm }$-exchange contributions are not suppressed in comparison with the tree-level (factrorizing) diagrams and must be taken into account in the evaluation of matrix elements. Moreover, there are decay processes such as the doubly Cabibbo-suppressed decay ${\Xi }_c^{+}\to p\varphi$ recently observed by the LHCb Collaboration which is contributed to only by one single $W$-exchange diagram.

   hep-phParticles(2019)·22 citations
8. 08*

   Tau decays into two mesons: an overview

   Sergi Gonzàlez-Solís🇺🇸

   We review the state-of-the-art theoretical analyses of tau decays into a pair of mesons and a neutrino. The participant vector and scalar form factors, $f_{+}(s)$ and $f_0(s)$, are described in the frame of Chiral Perturbation Theory with resonances supplemented by dispersion relations, and the physical parameters of the intermediate resonances produced in the decay are extracted through the pole position of $f_{+,0}(s)$ in the complex plane. As a side result, we also determine the low-energy observables associated to the form factors. We hope our study to be of interest for present and future experimental analyses of these decays.

   hep-phEPJ Web Conf.(2019)·3 citations
9. 09*

   String percolation in AA and p+p collisions

   I.Bautista🇲🇽 · C.Pajares🇪🇸 · J.E.Ramírez🇪🇸

   A brief review of the string percolation model and its results are presented together with the comparison to experimental data. First, it is done an introduction to the quark-gluon phase diagram and the lattice results concerning the confinement and the percolation of center domains. It is studied the interaction of the strings produced in nucleus-nucleus and proton-proton collisions showing how the string percolation arises. The main consequences of the string percolation, concerning the dependence on the energy and centrality, on the multiplicities and the mean transverse momentum are obtained comparing with experimental data. It is emphasized the non-abelian character of the color field of the strings forming the cluster to reproduce the rise of the transverse momentum with multiplicity and the relative suppression of multiplicities. It is also studied different observables like multiplicity and transverse momentum distributions, dependence with multiplicity and transverse momentum correlations, forward-backward correlations, the strength of the Bose-Einstein correlations, dependence on the multiplicity of $J/\Psi$ production and its possible suppression in pp collisions at high multiplicity, strangeness enhancement, elliptic flow, and ridge structure. The comparison with the data shows an overall agreement. The thermodynamical properties of the extended cluster formed in the collision are discussed computing its energy and entropy density, shear viscosity over entropy density ratio, bulk viscosity, sound speed and trace anomaly as a function of temperature, showing a remarkable agreement with lattice QCD evaluations. The string percolation can be regarded as the initial frame able to describe the collective behavior produced in AA and pp collisions.

   hep-phRev.Mex.Fis.(2019)·18 citations
10. 10*

    $R_2$ as a single leptoquark solution to $R_{D^{(\ast )}}$ and $R_{K^{(\ast )}}$

    Oleg Popov🇰🇷 · Michael A. Schmidt🇦🇺 · Graham White🇨🇦

    We show that, up to plausible uncertainties in BR$(B_c\to \tau \nu )$, the $R_2$ leptoquark can simultaneously explain the observation of anomalies in $R_{K^{(\ast )}}$ and $R_{D^{(\ast )}}$ without requiring large couplings. The former is achieved via a small coupling to first generation leptons which boosts the decay rate $\Gamma (\bar{B}\to {\bar{K}}^{(\ast )}{e}^{+}{e}^{-})$. Finally we motivate a neutrino mass model that includes the $S_3$ leptoquark which can alleviate a mild tension with the most conservative limits on BR$(B_c\to \tau \nu )$.

    hep-phPRD(2019)·89 citations
11. 11*

    Neutrino-Dark Matter Connections in Gauge Theories

    Pavel Fileviez Perez🇺🇸 · Clara Murgui🇪🇸 · Alexis D. Plascencia🇺🇸

    We discuss the connection between the origin of neutrino masses and the properties of dark matter candidates in the context of gauge extensions of the Standard Model. We investigate minimal gauge theories for neutrino masses where the neutrinos are predicted to be Dirac or Majorana fermions. We find that the upper bound on the effective number of relativistic species provides a strong constraint in the scenarios with Dirac neutrinos. In the context of theories where the lepton number is a local gauge symmetry spontaneously broken at the low scale, the existence of dark matter is predicted from the condition of anomaly cancellation. Applying the cosmological bound on the dark matter relic density, we find an upper bound on the symmetry breaking scale in the multi-TeV region. These results imply we could hope to test simple gauge theories for neutrino masses at current or future experiments.

    hep-phhep-exPRD(2019)·72 citations
12. 12*

    Direct Detection of Strongly Interacting Sub-GeV Dark Matter via Electron Recoils

    Timon Emken🇩🇰 · Rouven Essig🇺🇸 · Chris Kouvaris🇩🇰 · Mukul Sholapurkar🇺🇸

    We consider direct-detection searches for sub-GeV dark matter via electron scatterings in the presence of large interactions between dark and ordinary matter. Scatterings both on electrons and nuclei in the Earth's crust, atmosphere, and shielding material attenuate the expected local dark matter flux at a terrestrial detector, so that such experiments lose sensitivity to dark matter above some critical cross section. We study various models, including dark matter interacting with a heavy and ultralight dark photon, through an electric dipole moment, and exclusively with electrons. For a dark-photon mediator and an electric dipole interaction, the dark matter-electron scattering cross-section is directly linked to the dark matter-nucleus cross section, and nuclear interactions typically dominate the attenuation process. We determine the exclusion bands for the different dark-matter models from several experiments - SENSEI, CDMS-HVeV, XENON10, XENON100, and DarkSide-50 - using a combination of Monte Carlo simulations and analytic estimates. We also derive projected sensitivities for a detector located at different depths and for a range of exposures, and calculate the projected sensitivity for SENSEI at SNOLAB and DAMIC-M at Modane. Finally, we discuss the reach to high cross sections and the modulation signature of a small balloon- and satellite-borne detector sensitive to electron recoils, such as a Skipper-CCD. Such a detector could potentially probe unconstrained parameter space at high cross sections for a sub-dominant component of dark matter interacting with a massive, but ultralight, dark photon.

    hep-phastro-ph.COJCAP(2019)·212 citations
13. 13*

    Opacity and Effective Field Theory in Anti-de Sitter Backgrounds

    Sylvain Fichet🇧🇷

    We consider quantum field theory in a five-dimensional anti-de Sitter background, possibly truncated by 4d branes. In the Euclidian version of this space, it is known that propagators exponentially decay when they go far enough towards the Poincaré horizon, i.e. deep enough into the IR region of the AdS bulk. In this note we show that an analogous property exists in Lorentzian AdS. The exponential suppression is found to occur in the presence of bulk interactions dressing the AdS propagators. We calculate one-loop gravitational dressing and find that the suppression effect comes from the scalar component of the 5d graviton. We then argue that, at least at strong coupling, this exponential decay censors the region of spacetime where the 5d effective field theory would become invalid. As an application we estimate the rate for the cascade decay of bulk fields---which are known to produce soft spherical events with high multiplicity---and find this rate to be exponentially suppressed.

    ↳ hep-thhep-phPRD(2019)·22 citations
14. 14*

    Bound to unbound states transitions of heavy quarkonia in the cooling phase of QGP

    Nirupam Dutta🇮🇳 · Partha Bagchi🇮🇳 · Jobin Sebastian🇮🇳

    Emphasizing the possibility of moderate suppression of heavy quarkonium states, we invite some attention towards the issue of real time evolution of quarkonia during the cooling phase of quark gluon plasma(QGP). In this context, we have used time dependent perturbation theory to show that ${\rm Y}(1S)$, ${\rm Y}(2S)$, $J/\Psi$ can further be dissociated in the medium at a temperature below their dissociation thresholds even though they survive the Debye screening. We have presented and compared the dissociation probabilities and dissociation rates of these states in real and complex valued potential in this article. We realise that our method is an approximate way to analyse the short time behaviour of quarkonium in real valued potential and for long time behaviour one must adopt a non perturbative technique for solving schrödinger equation of quarkonium bound states in evolving QGP. On the other hand the perturbation technique seems to be valid enough to deal with the same for a complex valued quark anti-quark potential.

    ↳ nucl-thhep-phJ.Subatomic Part.Cosmol.(2025)·4 citations
15. 15*

    Aspects of the QCD $\theta$-vacuum

    Thomas Vonk🇩🇪 · Feng-Kun Guo🇨🇳 · Ulf-G. Meißner🇩🇪

    This paper addresses two aspects concerning the $\theta$-vacuum of Quantum Chromodynamics. First, large-$N_c$ chiral perturbation theory is used to calculate the first two non-trivial cumulants of the distribution of the winding number, i.\,e. the topological susceptibility, ${\chi }_{\mathrm{top}}$, and the fourth cumulant, $c_4$, up to next-to-leading order. Their large-$N_c$ scaling is discussed, and compared to lattice results. It is found that ${\chi }_{\mathrm{top}}=\mathcal{O}(N_c^0)$, as known before, and $c_4=\mathcal{O}(N_c^{-3})$, correcting the assumption of $\mathcal{O}(N_c^{-2})$ in the literature. Second, we discuss the properties of QCD at $\theta \sim \pi$ using chiral perturbation theory for the case of $2+1$ light flavors, i.\,e. by taking the strange quark mass heavier than the degenerate up and down quark masses. It is shown that --- in accordance with previous findings for $N_f=2$ and $N_f=3$ mass-degenerate flavors --- in the region $\theta \sim \pi$ two vacuum states coexist, which become degenerate at $\theta =\pi$. The wall tension of the energy barrier between these degenerate vacua is determined as well as the decay rate of a false vacuum.

    ↳ hep-thhep-lathep-phnucl-thJHEP(2019)·15 citations
16. 16*

    Post-inflationary phases stiffer than radiation and Palatini formulation

    Massimo Giovannini🇨🇭

    If the inflaton and the quintessence fields are identified, the background geometry evolves through a stiff epoch undershooting the expansion rate of a radiation-dominated plasma. For some classes of inflationary potentials this scenario is at odds with the current observational evidence since the corresponding tensor-to-scalar ratio is too large. Quintessential inflation is analyzed when the gravitational action is supplemented by a contribution quadratic in the Einstein-Hilbert term. In the Palatini formulation the addition such a term does not affect the scalar modes during the inflationary phase and throughout the course of the subsequent stiff epoch but it suppresses the tensor power spectrum and the tensor-to-scalar ratio. While in the Palatini formulation the power-law potentials leading to a quintessential inflationary dynamics are again viable, the high-frequency spike of the relic graviton spectrum is squeezed and the whole signal is suppressed at least when the higher-order contributions appearing in the action are explicitly decoupled from the inflaton.

    ↳ gr-qcastro-ph.COhep-phhep-thClass.Quant.Grav.(2019)·29 citations
17. 17*

    Searches for physics beyond the standard model at the LHC

    Jory Sonneveld🇩🇪

    At the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN), protons and heavy ions are accelerated to velocities close to the speed of light and collided in order to study particle interactions and give us an insight to the fundamental laws of nature. The energy and intensity of the particle beams at the LHC are unprecedented, and a tremendous amount of data is collected by three experiments on the circular ring of the LHC that are specialized in proton-proton collisions. The data confirm the most successful theory of particle physics to date known as the standard model of particle physics to very good precision, including the long expected and recently discovered Higgs boson. The standard model cannot, however, accommodate experimentally observed phenomena like gravity, neutrino masses, and dark matter. The theory can also be theoretically unsatisfying as a result of parameters that go unexplained, such as the relatively low value of the Higgs mass despite its large quantum corrections, implying a lack of understanding. For this reason, in addition to precision measurements of standard model observables, experiments search for new physics beyond the standard model that could explain some of the shortcomings of the standard model. A selection of results for searches for new physics beyond the standard model using data recorded by three experiments on the LHC are presented in this talk.

    ↳ hep-exhep-phAfr.Rev.Phys.(2018)·1 citation
18. 18*

    Diffusion-limited Relic Particle Production

    Robert J. Scherrer🇺🇸 · Michael S. Turner🇺🇸

    We examine the thermal evolution of particle number densities in the early universe when the particles have a finite diffusion length. Assuming that annihilations are impossible when the mean separation of the particles is larger than their diffusion length, we derive a version of the Boltzmann equation for freeze out in this scenario and an approximate solution, accurate to better than 2\%. The effect of a finite diffusion length is to increase the final relic freeze-out abundance over its corresponding value when diffusion effects are ignored. When diffusion is limited only by scattering off of the thermal background, and the annihilation cross section is bounded by unitarity, a significant effect on the freeze-out abundance requires a scattering cross section much larger than the annihilation cross section. A similar effect is demonstrated when the relic particles are produced via the freeze-in mechanism, but in this case the finite diffusion length is due to the scattering of particles that annihilate into the relic particle of interest. For freeze in, the effect of a finite diffusion length is to reduce the final relic particle abundance. The effects of a finite diffusion length are most important when the scattering cross section or the relic mass are very large. While we have not found a particularly compelling example where this would affect previous results, with the current interest in new dark matter candidates it could become an important consideration.

    ↳ astro-ph.COhep-phPRD(2019)·1 citation
19. 19*

    Model-independent form-factor constraints for electromagnetic spin-1 currents

    Helmut Haberzettl🇺🇸

    Using local gauge invariance in the form of the Ward-Takahashi identity and the fact that properly constructed current operators must be free of kinematic singularities, it is shown that the magnetic moment $\mu$ and the quadrupole moment $Q$ of an elementary spin-1 particle with mass $m$ and charge $e$ are related by $2m\mu +m^{2}Q=e$, thus constraining the normalizations of the Sachs form factors. This relation holds true as a matter of course at the tree level in the standard model, but we prove it remains true in general for dressed spin-1 states derived from elementary fields. General expressions for spin-1 propagators and currents with arbitrary hadronic dressing are given showing the result to be independent of any dressing effect or model approach.

    ↳ nucl-thhep-phPRD(2019)·11 citations
20. 20*

    Fine Tuning, Sequestering, and the Swampland

    Jonathan J. Heckman🇺🇸 · Cumrun Vafa🇺🇸

    We conjecture and present evidence that any effective field theory coupled to gravity in flat space admits at most a finite number of fine tunings, depending on the amount of supersymmetry and spacetime dimension. In particular, this means that there are infinitely many non-trivial correlations between the allowed deformations of a given effective field theory in the gravitational context. Fine tuning of parameters allows us to obtain some consistent CFTs in the IR limit of gravitational theories. Related to finiteness of fine tunings, we conjecture that except for a finite number of CFTs, the rest cannot be consistently coupled to gravity and belong to the swampland. Moreover, we argue that even though matter sectors coupled to gravity may sometimes be partially sequestered, there is an irreducible level of mixing between them, correlating and coupling infinitely many operators between these sectors.

    ↳ hep-thhep-phPLB(2019)·52 citations
21. 21*

    Valence parton distribution function of pion from fine lattice

    Taku Izubuchi🇺🇸 · Luchang Jin🇺🇸 · Christos Kallidonis🇺🇸 · Nikhil Karthik🇺🇸 · Swagato Mukherjee🇺🇸 · Peter Petreczky🇺🇸 · Charles Shugert🇺🇸 · Sergey Syritsyn🇺🇸

    We present a lattice QCD study of valence parton distribution inside the pion within the framework of Large Momentum Effective Theory. We use a mixed action approach with 1-HYP smeared valence Wilson clover quarks on 2+1 flavor HISQ sea with the valence quark mass tuned to 300 MeV pion mass. We use $48^3\times 64$ lattice at a fine lattice spacing $a=0.06$ fm for this computation. We renormalize the quasi-PDF matrix element in the non-perturbative RI-MOM scheme. As a byproduct, we test the validity of 1-loop matching procedure by comparing the RI-MOM renormalized quasi-PDF matrix element with off-shell quark external states as computed in the continuum 1-loop perturbation theory with the lattice results at $a=0.04$ and 0.06 fm. By applying the RI-MOM to $\overline{\mathrm{MS}}$ one-loop matching, implemented through a fit to phenomenologically motivated PDFs, we obtain the valence PDF of pion.

    ↳ hep-lathep-exhep-phnucl-ex+1PRD(2019)·139 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.