Thu·Jun 28, 2018Thursday·June 28, 2018

1. 01*

   Implications of scalar and tensor explanations of $R_{D^{(\ast )}}$

   Ferruccio Feruglio🇮🇹 · Paride Paradisi🇮🇹 · Olcyr Sumensari🇮🇹

   We investigate the implications of scalar and tensor operators proposed to accommodate the hints of lepton flavor universality violation in charged-current $B$-meson decays. We show that these scenarios unavoidably induce chirality enhanced contributions to charged lepton magnetic moments and Yukawa couplings. By using an effective field theory approach we quantify in a model independent way the connection of the $R_{D^{(\ast )}}$ anomaly with the tau $g-2$ and the Higgs decay $h\to \tau \tau$, which can offer an alternative to test these scenarios. Concrete New Physics models giving rise to our setup will be illustrated.

   hep-phJHEP(2018)·91 citations
2. 02*

   Standard Model Fragmentation Functions at Very High Energies

   Christian W Bauer🇺🇸 · Davide Provasoli🇺🇸 · Bryan R. Webber🇬🇧

   We compute the leading-order evolution of parton fragmentation functions for all the Standard Model fermions and bosons up to energies far above the electroweak scale, where electroweak symmetry is restored. We discuss the difference between double-logarithmic and leading-logarithmic resummation, and show how the latter can be implemented through a scale choice in the SU(2) coupling. We present results for a wide range of partonic center-of-mass energies, including the polarization of fermion and vector boson fragmentation functions induced by electroweak evolution.

   hep-phhep-exJHEP(2018)·42 citations
3. 03*

   A Tale of Two Anomalies

   Hooman Davoudiasl🇺🇸 · William J. Marciano🇺🇸

   A recent improved determination of the fine structure constant, $\alpha =1/137.035999046(27)$, leads to a $\sim 2.4\sigma$ negative discrepancy between the measured electron anomalous magnetic moment and the Standard Model prediction. That situation is to be compared with the muon anomalous magnetic moment where a positive $\sim 3.7\sigma$ discrepancy has existed for some time. A single scalar solution to both anomalies is shown to be possible if the two-loop electron Barr-Zee diagrams dominate the scalar one-loop electron anomaly effect and the scalar couplings to the electron and two photons are relatively large. We also briefly discuss the implications of that scenario.

   hep-phPRD(2018)·160 citations
4. 04*

   Renormalization-scheme variation of a QCD perturbation expansion with tamed large-order behavior

   Irinel Caprini🇷🇴

   The renormalization-scheme and scale dependence of the truncated QCD perturbative expansions is one of the main sources of theoretical error of the standard model predictions, especially at intermediate energies. Recently, a class of renormalization schemes, parametrized by a single real number $C$, has been defined and investigated in the frame of the standard perturbation expansions in powers of the coupling. In the present paper we investigate the $C$-scheme variation of a Borel-improved QCD perturbation series, which implements information about the large-order divergent character of perturbation theory by means of an optimal conformal mapping of the Borel plane. In the new expansions, the powers of the strong coupling are replaced by a set of expansion functions with properties which resemble those of the expanded correlators, having in particular a singular behavior at the origin of the complex coupling plane. On the other hand, the new expansions have a tamed increase at high orders, as demonstrated by previous studies in the $\overline{\text{MS}}$ renormalization scheme. Using as examples the Adler function and the hadronic decay width of the $\tau$ lepton, we investigate the properties of the Borel-improved expansions in the $C$-scheme, in comparison with the standard expansions in the $C$-scheme and the expansions in $\overline{\text{MS}}$. The variation with the renormalization scale and the prescription for the choice of an optimal value of the parameter $C$ are discussed. The good large-order behavior of the Borel-improved expansions is proved also in the $C$-scheme, which is a further argument in favor of using them in applications of perturbative QCD at intermediate energies.

   hep-phPRD(2018)·14 citations
5. 05*

   Analysis of the $\bar{D}{\Sigma }_c$, $\bar{D}{\Sigma }_c^{\ast }$, ${\bar{D}}^{\ast }{\Sigma }_c$ and ${\bar{D}}^{\ast }{\Sigma }_c^{\ast }$ pentaquark molecular states with QCD sum rules

   Zhi-Gang Wang🇨🇳

   In this article, we study the $\bar{D}{\Sigma }_c$, $\bar{D}{\Sigma }_c^{\ast }$, ${\bar{D}}^{\ast }{\Sigma }_c$ and ${\bar{D}}^{\ast }{\Sigma }_c^{\ast }$ pentaquark molecular states with the QCD sum rules by carrying out the operator product expansion up to the vacuum condensates of dimension $13$ in a consistent way. The present calculations support assigning the $P_c(4312)$ to be the $\bar{D}{\Sigma }_c$ pentaquark molecular state with $J^P={\frac{1}{2}}^{-}$, assigning the $P_c(4380)$ to be the $\bar{D}{\Sigma }_c^{\ast }$ pentaquark molecular state with $J^P={\frac{3}{2}}^{-}$, assigning the $P_c(4440/4457)$ to be the ${\bar{D}}^{\ast }{\Sigma }_c$ pentaquark molecular state with $J^P={\frac{3}{2}}^{-}$ or the ${\bar{D}}^{\ast }{\Sigma }_c^{\ast }$ pentaquark molecular state with $J^P={\frac{5}{2}}^{-}$. Special attentions are payed to the operator product expansion.

   hep-phInt.J.Mod.Phys.A(2019)·52 citations
6. 06*

   Are there flux tubes in quark-gluon plasma?

   Edward Shuryak🇺🇸

   We review both lattice evidences and theoretical arguments supporting the existence of electric flux tubes in quark-gluon plasma, above the deconfinement transition temperature $T>T_c$. At the end of this comment, we also point out certain questions which still needs to be answered.

   hep-ph12 citations
7. 07*

   On operator relations for gravitational form factors of a spin-0 hadron

   Kazuhiro Tanaka (Juntendo Univ.)🇯🇵

   The gravitational form factors for a hadron, the form factors for the hadron matrix element of the QCD energy-momentum tensor, not only describe the coupling of the hadron with a graviton, but also serve as unique quantities for describing the shape inside the hadron reflecting dynamics of quarks and gluons, such as the internal shear forces acting on the quarks/gluons and their pressure distributions. We consider the quark contribution to the gravitational form factors for a (pseudo)scalar hadron, and derive and clarify the relations satisfied by them as direct consequences of the symmetries and the equations of motion in QCD, and connections to the generalized parton distributions. Our results reveal the connections between the gravitational form factors and the higher-twist quark-gluon correlation effects inside the hadrons.

   hep-phhep-exnucl-thPRD(2018)·68 citations
8. 08*

   The Dark Side of the Littlest Seesaw: freeze-in, the two right-handed neutrino portal and leptogenesis-friendly fimpzillas

   Marco Chianese🇬🇧 · Stephen F. King🇬🇧

   We propose a minimal model to simultaneously account for a realistic neutrino spectrum through a type-I seesaw mechanism and a viable dark matter relic density. The model is an extension of the Littlest Seesaw model in which the two right-handed neutrinos of the model are coupled to a $Z_2$-odd dark sector via right-handed neutrino portal couplings. In this model, a highly constrained and direct link between dark matter and neutrino physics is achieved by considering the freeze-in production mechanism of dark matter. We show that the neutrino Yukawa couplings which describe neutrino mass and mixing may also play a dominant role in the dark matter production. We investigate the allowed regions in the parameter space of the model that provide the correct neutrino masses and mixing and simultaneously give the correct dark matter relic abundance. In certain cases the right-handed neutrino mass may be arbitrarily large, for example in the range $10^{10}-10^{11}$ GeV required for vanilla leptogenesis, with a successful relic density arising from frozen-in dark matter particles with masses around this scale, which we refer to as "fimpzillas".

   hep-phJCAP(2018)·62 citations
9. 09*

   Joint resummation of two angularities at next-to-next-to-leading logarithmic order

   Massimiliano Procura🇨🇭 · Wouter J. Waalewijn🇳🇱 · Lisa Zeune🇳🇱

   Multivariate analyses are emerging as important tools to understand properties of hadronic jets which play a key role in the LHC experimental program. We take a first step towards precise and differential theory predictions by calculating the cross section for $e^{+}{e}^{-}\to$ 2 jets differential in the angularities $e_{\alpha }$ and $e_{\beta }$. The logarithms of $e_{\alpha }$ and $e_{\beta }$ in the cross section are jointly resummed to next-to-next-to-leading logarithmic accuracy, using the SCET+ framework we developed, and are matched to the next-to-leading order cross section. We perform analytic one-loop calculations that serve as input for our numerical analysis, provide controlled theory uncertainties, and compare our results to Pythia. We also obtain predictions for the cross section differential in the ratio $e_{\alpha }/e_{\beta }$, which cannot be determined from a fixed-order calculation. The effect of nonperturbative corrections is also investigated. Using Event2, we validate the logarithmic structure of the single angularity cross section predicted by factorization theorems at $\mathcal{O}({\alpha }_s^2)$, demonstrating that for specific angularities recoil must be taken into account when using the thrust axis, while it can be ignored if these are measured with respect to the winner-take-all axis.

   hep-phnucl-thJHEP(2018)·57 citations
10. 10*

    Enhancement of strange baryons in high-multiplicity proton-proton and proton-nucleus collisions

    Yuuka Kanakubo🇯🇵 · Michito Okai🇯🇵 · Yasuki Tachibana🇺🇸 · Tetsufumi Hirano🇯🇵

    We investigate the enhancement of yields of strange and multi-strange baryons in proton-proton (p+p), proton-lead (p+Pb) and lead-lead (Pb+Pb) collisions at the Large Hadron Collider (LHC) energies from a dynamical core-corona initialization model. We first generate partons just after the collisions by using event generators. These partons dynamically generate the quark gluon plasma (QGP) fluids through the source terms in the hydrodynamic equations. According to the core-corona picture, this process tends to happen where the density of generated partons is high and their transverse momentum is low. Some partons do not fully participate in this process when they are in dilute regions or their transverse momentum is high and subsequently fragment into hadrons through string fragmentation. In this framework, the final hadrons come from either chemically equilibrated fluids as in the conventional hydrodynamic models or string fragmentation. We calculate the ratio of strange baryons to charged pions as a function of multiplicity and find that it monotonically increases up to $d{N}_{\mathrm{ch}}/d\eta \sim 100$ and then saturates above. This suggests that the QGP fluids are \textit{partly} created and that their fraction increases with multiplicity in p+p and p+Pb collisions at LHC energies.

    ↳ nucl-thhep-phnucl-exPTEP(2018)·16 citations
11. 11*

    Instability of De Sitter Spacetime induced by Quantum Conformal Anomaly

    Hiroki Matsui🇯🇵

    The instability of (quasi) de Sitter spacetime from quantum gravitational effects has been discussed in many works. Especially, the gravitational backreaction from quantum energy momentum tensor is crucial for understanding the low-energy description of quantum gravity and sometimes destabilize the spacetime. In this paper we discuss the (quasi) de Sitter instability from gravitational backreaction involving quantum conformal anomaly. The conformal or trace anomaly corresponds to the quantum gravitational contributions of the massless conformal fields and affects the spacetime homogeneously. First, we derive the conformal anomaly using the adiabatic (WKB) approximation and discuss the renormalization of the quantum energy momentum tensor. Then, we consider the dynamics of the Hubble parameter based on the semiclassical Einstein's equations including the cosmological constant, the conformal anomaly and the higher-derivative terms. We have clearly shown that the classical de Sitter attractor $H_{\mathrm{C}}\simeq \sqrt{\Lambda /3}$ are generally unstable from the viewpoint of the semiclassical gravity and the inflation is destabilized except for the specific conditions. Unless the fine-tuning of the conformal anomaly and the higher derivative terms, the inflation finally becomes the Planckian inflation with the Hubble scale $H\approx M_{\mathrm{P}}\equiv \sqrt{1/8\pi G_N}$ or terminates $H(t)\to 0$. The latter case suggests that the cosmic inflation could not last long and the eternal inflation scenarios are strongly constrained.

    ↳ hep-thgr-qchep-phJCAP(2019)·13 citations
12. 12*

    Effects of localized {\mu}-terms at the fixed points in magnetized orbifold models

    Hiroyuki Abe🇯🇵 · Makoto Ishida🇯🇵 · Yoshiyuki Tatsuta🇩🇪

    We consider magnetized orbifolds, where the supersymmetric mass term for a pair of up- and down-type Higgs (super)fields, called $\mu$-term, is localized at the orbifold fixed points, and study the effects on the zero-mode spectra. The zero-mode degeneracy to be identified as the generation in four-dimensional (4D) effective theories is determined by the magnetic fluxes. It is known that multiple Higgs zero-modes appear in general in magnetized orbifold models. We derive the analytic form of the $\mu$-term matrix in the 4D effective theory generated by the localized sources on $T^2/Z_2$ orbifold fixed points, and find that this matrix can lead to a distinctive pattern of the eigenvalues that yields hierarchical $\mu$-terms for the multiple Higgs fields. The lightest ones can be exponentially suppressed due to the localized wavefunctions of zero-modes determined by the fluxes, while the others are of the order of the compactification scale, which can provide a dynamical origin of the electroweak scale as well as a simultaneous decoupling of extra Higgs fields. We also show that a certain linear combination of the lightest Higgs fields could generate the observed mass ratios of down-type quarks through their Yukawa couplings determined by the wavefunctions.

    ↳ hep-thhep-phNPB(2019)·5 citations
13. 13*

    The Spatial Clustering of Primordial Black Holes

    Vincent Desjacques🇮🇱 · Antonio Riotto🇨🇭

    The possibility that primordial black holes (PBHs) are the dark matter (or a fraction thereof) has attracted much attention recently. Their spatial clustering is a fundamental property which determines, among others, whether current observational constraints are evaded within a given mass range, whether merging is significant and whether primordial black holes could generate cosmological structure. We treat them as discrete objects and clarify the issue of their spatial clustering, with an emphasis on short-range exclusion and its impact on their large scale power spectrum. Even if a Poissonian self-pair term is always present in the zero-lag correlation, this does not necessarily imply that primordial black holes are initially Poisson distributed. However, while the initial PBH clustering depends on the detailed shape of the small-scale power spectrum, we argue that it is not relevant for a narrow spectral feature and primordial black hole masses still allowed by observations.

    ↳ astro-ph.COgr-qchep-phPRD(2018)·143 citations
14. 14*

    The type II Weyl semimetals at low temperatures: chiral anomaly, elastic deformations, zero sound

    M.A. Zubkov🇮🇱 · M. Lewkowicz🇮🇱

    We consider the properties of the type II Weyl semimetals at low temperatures basing on the particular tight - binding model. In the presence of electric field directed along the line connecting the Weyl points of opposite chirality the occupied states flow along this axis giving rise to the creation of electron - hole pairs. The electrons belong to a vicinity of one of the two type II Weyl points while the holes belong to the vicinity of the other. This process may be considered as the manifestation of the chiral anomaly that exists without any external magnetic field. It may be observed experimentally through the measurement of conductivity. Next, we consider the modification of the theory in the presence of elastic deformations. In the domain of the considered model, where it describes the type I Weyl semimetals the elastic deformations lead to the appearance of emergent gravity. In the domain of the type II Weyl semimetals the form of the Fermi surface is changed due to the elastic deformations, and its fluctuations represent the special modes of the zero sound. We find that there is one - to one correspondence between them and the sound waves of the elasticity theory. Next, we discuss the influence of the elastic deformations on the conductivity. The particularly interesting case is when our model describes the intermediate state between the type I and the type II Weyl semimetal. Then without the elastic deformations there are the Fermi lines instead of the Fermi points/Fermi surface, while the DC conductivity vanishes. However, even small elastic deformations may lead to the appearance of large conductivity.

    ↳ cond-mat.mes-hallhep-phAnnals Phys.(2018)·6 citations
15. 15*

    Towards Exotic Matter and Discrete Non-Abelian Symmetries in F-theory

    Mirjam Cvetič🇺🇸 · Jonathan J. Heckman🇺🇸 · Ling Lin🇺🇸

    We present a prescription in F-theory for realizing matter in "exotic" representations of product gauge groups. For 6D vacua, bifundamental hypermultiplets are engineered by starting at a singular point in moduli space which includes 6D superconformal field theories coupled to gravity. A deformation in Higgs branch moduli space takes us to a weakly coupled gauge theory description. In the corresponding elliptically fibered Calabi--Yau threefold, the minimal Weierstrass model parameters $(f,g,\Delta )$ vanish at collisions of the discriminant at least to order $(4,6,12)$, but with sufficiently high order of tangency to ensure the existence of T-brane deformations to a weakly coupled gauge theory with exotic bifundamentals. We present explicit examples including bifundamental hypermultiplets of ${\mathfrak{e}}_7\times {\mathfrak{su}}_2$ and ${\mathfrak{e}}_6\times {\mathfrak{su}}_3$, each of which have dual heterotic orbifold descriptions. Geometrically, these matter fields are delocalized across multiple points of an F-theory geometry. Symmetry breaking with such representations can be used to produce high dimension representations of simple gauge groups such as the four-index symmetric representation of ${\mathfrak{su}}_2$ and the three-index symmetric representation of ${\mathfrak{su}}_3$, and after further higgsing can yield discrete non-abelian symmetries.

    ↳ hep-thhep-phJHEP(2018)·29 citations
16. 16*

    Quark contribution to the proton spin from 2+1+1-flavor lattice QCD

    Huey-Wen Lin🇺🇸 · Rajan Gupta🇺🇸 · Boram Yoon🇺🇸 · Yong-Chull Jang🇺🇸 · Tanmoy Bhattacharya🇺🇸

    We present the first chiral-continuum extrapolated up, down and strange quark spin contribution to the proton spin using lattice QCD. For the connected contributions, we use eleven ensembles of 2+1+1-flavor of Highly Improved Staggered Quarks (HISQ) generated by the MILC Collaboration. They cover four lattice spacings $a\approx \{0.15,0.12,0.09,0.06\}$ fm and three pion masses, $M_{\pi }\approx \{315,220,135\}$ MeV, of which two are at the physical pion mass. The disconnected strange calculations are done on seven of these ensembles, covering the four lattice spacings but only one with the physical pion mass. The disconnected light quark calculation was done on six ensembles at two values of $M_{\pi }\approx \{315,220\}$ MeV. High-statistics estimates on each ensemble for all three quantities allow us to quantify systematic uncertainties and perform a simultaneous chiral-continuum extrapolation in the lattice spacing and the light-quark mass. Our final results are $\Delta u\equiv ⟨1{⟩}_{\Delta u^{+}}=0.777(25)(30)$, $\Delta d\equiv ⟨1{⟩}_{\Delta d^{+}}=-0.438(18)(30)$, and $\Delta s\equiv ⟨1{⟩}_{\Delta s^{+}}=-0.053(8)$, adding up to a total quark contribution to proton spin of ${\sum }_{q=u,d,s}(\frac{1}{2}\Delta q)=0.143(31)(36)$. The second error is the systematic uncertainty associated with the chiral-continuum extrapolation. These results are obtained without model assumptions and are in good agreement with the recent COMPASS analysis $0.13<\frac{1}{2}\Delta \Sigma <0.18$, and with the $\Delta q$ obtained from various global analyses of polarized beam or target data.

    ↳ hep-lathep-phPRD(2018)·71 citations
17. 17*

    Cosmological implications of ultra-light axion-like fields

    Vivian Poulin🇺🇸 · Tristan L. Smith🇺🇸 · Daniel Grin🇺🇸 · Tanvi Karwal🇺🇸 · Marc Kamionkowski🇺🇸

    Cosmological observations are used to test for imprints of an ultra-light axion-like field (ULA), with a range of potentials $V(\varphi )\propto [1-\cos (\varphi /f){]}^n$ set by the axion-field value $\varphi$ and decay constant $f$. Scalar field dynamics dictate that the field is initially frozen and then begins to oscillate around its minimum when the Hubble parameter drops below some critical value. For $n=1$, once dynamical, the axion energy density dilutes as matter; for $n=2$ it dilutes as radiation and for $n=3$ it dilutes faster than radiation. Both the homogeneous evolution of the ULA and the dynamics of its linear perturbations are included, using an effective fluid approximation generalized from the usual $n=1$ case. ULA models are parameterized by the redshift $z_c$ when the field becomes dynamical, the fractional energy density $f_{z_c}\equiv {\Omega }_a(z_c)/{\Omega }_{\mathrm{tot}}(z_c)$ in the axion field at $z_c$, and the effective sound speed $c_s^2$. Using Planck, BAO and JLA data, constraints on $f_{z_c}$ are obtained. ULAs are degenerate with dark energy for all three potentials if $1+z_c\lesssim 10$. When $3\times 10^4\gtrsim 1+z_c\gtrsim 10$, $f_{z_c}$ is constrained to be $\lesssim 0.004$ for $n=1$ and $f_{z_c}\lesssim 0.02$ for the other two potentials. The constraints then relax with increasing $z_c$. These results strongly constrain ULAs as a resolution to cosmological tensions, such as discrepant measurements of the Hubble constant, or the EDGES measurement of the global 21 cm signal.

    ↳ astro-ph.COhep-phPRD(2018)·364 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.