Fri·Oct 25, 2019Friday·October 25, 2019

1. 01*

   Weak decays of magnetized charged pions in the symmetric gauge

   M. Coppola🇦🇷 · D. Gomez Dumm🇦🇷 · S. Noguera🇪🇸 · N.N. Scoccola🇦🇷

   We consider the decay ${\pi }^{-}\to l{\bar{\nu }}_l$ ($l=e^{-},{\mu }^{-}$) in the presence of an arbitrary large uniform magnetic field, using the symmetric gauge. The consequences of the axial symmetry of the problem and the issue of angular momentum conservation are discussed in detail. In particular, we analyze the projection of both the canonical and the mechanical total angular momenta along the direction of the magnetic field. It is found that while the former is conserved in the symmetric gauge, the latter is not conserved in both the symmetric and Landau gauges. We derive an expression for the integrated ${\pi }^{-}\to l{\bar{\nu }}_l$ width that coincides exactly with the one we previously found using the Landau gauge, providing an explicit test of the gauge independence of that result. Such an expression implies that for nonzero magnetic fields the decay width does not vanish in the limit in which the outgoing charged leptons can be considered as massless, i.e. it does not exhibit the helicity suppression found in the case of no external field.

   hep-phhep-latPRD(2020)·10 citations
2. 02*

   Any Room Left for Technicolor? Holographic Studies of NJL Assisted Technicolour

   Alexander Belyaev🇬🇧 · Kazem Bitaghsir Fadafan🇮🇷 · Nick Evans🇬🇧 · Mansoureh Gholamzadeh🇮🇷

   We use a holographic description of technicolor dynamics to study gauge theories that only break chiral symmetry when aided by a strong four fermion interaction. These Nambu-Jona-Lasinio (NJL) assisted technicolor models provide examples of different dynamics from walking technicolor which can, by tuning, generate a light higgs like $\sigma$ meson. We compute the vector meson ($\rho$) and axial vector meson (A) spectrum for a variety of models with techni-quarks in the fundamental representation, enlarging the available parameter space over a previous analysis of walking theories. These predictions determine the parameter space of a low energy effective description where LHC constraints from dilepton channels have already been applied. Many of the models with low numbers of electroweak doublets still lie beyond current constraints and motivate exploration of new signatures beyond dilepton for LHC and a 100 TeV proton collider.

   hep-phhep-thPRD(2020)·10 citations
3. 03*

   Numerical study of a cosmological relaxation model of the Higgs boson mass

   Marco Michel🇩🇪

   In light of no discovered new physics at the LHC, ideas which tackle the Hierarchy Problem without novelties around the TeV scale must be taken seriously. Such is a cosmological relaxation model of the Higgs mass, proposed in the pre-LHC era, which does not rely on new physics below the Planck scale. This scenario introduces a different notion of naturalness according to which the vacuum with a small expectation value of the Higgs field corresponds to an infinitely enhanced entropy point of the vacuum landscape that becomes an attractor of cosmological inflationary evolution. In this framework we study numerically the evolution of the Higgs VEV. We model the inflationary vacuum-to-vacuum transitions that are triggered by nucleation of branes charged under three-form fields as a random walk. In particular, we investigate the impact of the number of coupled three-forms on the convergence rate of the Higgs VEV. We discover an enhanced rate with increasing number of brane charges. Moreover, we show that for late times the inclusion of more charges is equivalent to additional brane nucleations.

   hep-phgr-qchep-thPRD(2020)·2 citations
4. 04*

   The $B\to \pi \ell {\nu }_{\ell }$ semileptonic decay within the LCSR approach under heavy quark effective field theory

   Rui-Yu Zhou🇨🇳 · Lei Guo🇨🇳 · Hai-Bing Fu🇨🇳 · Wei Cheng🇨🇳 · Xing-Gang Wu🇨🇳

   The heavy quark effective field theory (HQEFT) provides an effective way to deal with the heavy meson decays. In the paper, we adopt two different correlators to derive the light-cone sum rules of the $B\to \pi$ transition form factors (TFFs) within the framework of HQEFT. We label those two LCSR results as LCSR-$\mathcal{U}$ and LCSR-$\mathcal{R}$, which are for conventional correlator and right-handed correlator, respectively. We observe that the correlation parameter $|{\rho }_{\mathrm{RU}}|$ for the branching ratio $\mathcal{B}(B\to \pi l{\nu }_l)$ is $\sim 0.85$, implying the consistency of the LCSRs under different correlators. Moreover, we obtain $|V_{\mathrm{ub}}{|}_{\mathrm{LCSR}-\mathcal{U}}=(3.45_{-0.20}^{+0.28}\pm {0.13}_{\exp })\times 10^{-3}$ and $|V_{\mathrm{ub}}{|}_{\mathrm{LCSR}-\mathcal{R}}=(3.38_{-0.16}^{+0.22}\pm {0.12}_{\exp })\times 10^{-3}$. We then obtain ${\mathcal{R}}_{\pi }{|}_{\mathrm{LCSR}-\mathcal{U}}=0.68_{-0.09}^{+0.10}$ and ${\mathcal{R}}_{\pi }{|}_{\mathrm{LCSR}-\mathcal{R}}=0.65_{-0.11}^{+0.13}$, both of them agree with the Lattice QCD predictions. Thus the HQEFT provides a useful framework for studying the $B$ meson decays. Moreover, by using right-handed correlator, the twist-2 terms shall dominant the TFF $f^{+}(q^2)$, which approaches over $\sim 97\%$ contribution in the whole $q^2$-region; and the large twist-3 uncertainty for the conventional correlator is greatly suppressed. One can thus adopt the LCSR-$\mathcal{R}$ prediction to test the properties of the various models for the pion twist-2 distribution amplitudes.

   hep-phCPC(2020)·8 citations
5. 05*

   Computing Tools for the SMEFT

   Editors: Jason Aebischer🇺🇸 · Matteo Fael🇩🇪 · Alexander Lenz🇬🇧 · Michael Spannowsky🇬🇧 · Javier Virto🇪🇸 · Contributors: Ilaria Brivio🇩🇪 · Juan Carlos Criado🇪🇸 · Athanasios Dedes🇬🇷 · Jacky Kumar🇨🇦 · Mikołaj Misiak🇵🇱 · Giampiero Passarino🇮🇹 · Giovanni Marco Pruna🇮🇹 and 10 other authors

   The increasing interest in the phenomenology of the Standard Model Effective Field Theory (SMEFT), has led to the development of a wide spectrum of public codes which implement automatically different aspects of the SMEFT for phenomenological applications. In order to discuss the present and future of such efforts, the "SMEFT-Tools 2019" Workshop was held at the IPPP Durham on the 12th-14th June 2019. Here we collect and summarize the contents of this workshop.

   hep-phhep-exhep-lathep-th31 citations
6. 06*

   Dirac sea and chiral anomaly in the quantum kinetic theory

   Jian-Hua Gao🇨🇳 · Zuo-Tang Liang🇨🇳 · Qun Wang🇨🇳

   We revisit the chiral anomaly in the quantum kinetic theory in the Wigner function formalism under the background field approximation. Our results show that the chiral anomaly is actually from the Dirac sea or the vacuum contribution in the un-normal-ordered Wigner function. We also demonstrate that this contribution modifies the chiral kinetic equation for antiparticles.

   hep-phhep-thnucl-thPRD(2020)·29 citations
7. 07*

   Resummation of large logarithms in the VFN scheme for DIS heavy-quark production

   S. Alekhin🇩🇪 · J. Bluemlein🇩🇪 · S. Moch🇩🇪

   We consider the impact of the resummation of large logarithms, which appear in the QCD evolution of the heavy-quark distributions, on the phenomenology of deep-inelastic heavy-quark production. The heavy-quark PDFs are derived using the fixed-order matching conditions as a boundary for the QCD evolution and the result obtained is compared to the distributions defined by the matching conditions at all scales. With such an approach, the effect of heavy-quark PDF evolution is found to be sizable at LO and dramatically reduces at NLO. The NNLO evolved distributions are not very different from the NLO ones at large scales, however, show substantial differences at low virtualities, i.e. where the additional large logarithms are numerically not important, while a mismatch between the NLO accuracy of the matching conditions and the NNLO accuracy in the evolution kernels causes a substantial excess in the heavy-quark distributions. This excess propagates into the variable flavor number (VFN) scheme predictions for the deep-inelastic structure functions and has to be compensated by a decrease in the small-$x$ gluon distribution determined from PDF fits based on the VFN scheme, which should be considered as a theoretical uncertainty in VFN PDF fits and reaches $\sim 30\%$ for the small-$x$ gluon distribution extracted from the data on deep-inelastic charm-quark production.

   hep-phhep-ex0 citations
8. 08*

   On relation between Parton Branching Approach and CCFM evolution

   A.V. Lipatov🇷🇺 · M.A. Malyshev🇷🇺 · H. Jung🇩🇪

   We consider the associated production of electroweak gauge bosons and charm or beauty quark jets at the LHC using the $k_T$-factorization framework. We apply the transverse momentum dependent (TMD) parton distributions in a proton obtained from the Parton Branching (PB) method as well as from the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation. For the PB approach, our prescription merges the standard leading order $\mathcal{O}(\alpha {\alpha }_s)$ $k_T$-factorization calculations with several tree-level next-to-leading order $\mathcal{O}(\alpha {\alpha }_s^2)$ off-shell production amplitudes. For the CCFM scenario, our consideration is based on the $\mathcal{O}(\alpha {\alpha }_s^2)$ off-shell gluon-gluon fusion subprocess $g^{\ast }{g}^{\ast }\to Z/W+Q\bar{Q}$ and some subleading $\mathcal{O}(\alpha {\alpha }_s^2)$ subprocesses involving quark interactions, taken into account in conventional (collinear) QCD factorization. We find that the $W+c$ and $Z+b$ cross sections, calculated within the PB and CCFM-based schemes with the proper choice of leading and next-to-leading subprocesses, are in good agreement with each other, thus establishing a correspondence between these two scenarios. A comparison with the latest LHC experimental data is given and the necessity for the proper off-shell treatment of the production amplitudes in determination of the parameters of the TMD parton density is demonstrated.

   hep-phPRD(2020)·9 citations
9. 09*

   Magnetic Field Effect in the Fine-Structure Constant and Electron Dynamical Mass

   E. J. Ferrer🇺🇸 · A. Sanchez🇲🇽

   We investigate the effect of an applied constant and uniform magnetic field in the fine-structure constant of massive and massless QED. In massive QED, it is shown that a strong magnetic field removes the so called Landau pole and that the fine-structure constant becomes anisotropic having different values along and transverse to the field direction. Contrary to other results in the literature, we find that the anisotropic fine-structure constant always decreases with the field. We also study the effect of the running of the coupling constant with the magnetic field on the electron mass. We find that in both cases of massive and massless QED, the electron dynamical mass always decreases with the magnetic field, what can be interpreted as an inverse magnetic catalysis effect.

   hep-phPRD(2019)·8 citations
10. 10*

    Rapid bound-state formation of Dark Matter in the Early Universe

    Tobias Binder🇯🇵 · Kyohei Mukaida🇩🇪 · Kalliopi Petraki🇫🇷

    The thermal decoupling description of dark matter (DM) and co-annihilating partners is reconsidered. If DM is realized at around the TeV-mass region or above, even the heaviest electroweak force carriers could act as long-range forces, leading to the existence of meta-stable DM bound states. The formation and subsequent decay of the latter further deplete the relic density during the freeze-out process on top of the Sommerfeld enhancement, allowing for larger DM masses. While so far the bound-state formation was described via the emission of an on-shell mediator ($W^{\pm }$, $Z$, $H$, $g$, photon or exotic), we point out that this particular process does not have to be the dominant scattering-bound state conversion channel in general. If the mediator is coupled in a direct way to any relativistic species present in the Early Universe, the bound-state formation can efficiently occur through particle scattering, where a mediator is exchanged virtually. To demonstrate that such a virtually stimulated conversion process can dominate the on-shell emission even for all temperatures, we analyze a simplified model where DM is coupled to only one relativistic species in the primordial plasma through an electroweak-scale mediator. We find that the bound-state formation cross section via particle scattering can exceed the on-shell emission by up to several orders of magnitude.

    hep-phastro-ph.COhep-thPRL(2020)·34 citations
11. 11*

    A Forest Formula to Subtract Infrared Singularities in Amplitudes for Wide-angle Scattering

    Yao Ma🇺🇸

    For any hard QCD amplitude with massless partons, infrared (IR) singularities arise from pinches in the complex planes of loop momenta, called pinch surfaces. To organize and study their leading behaviors in the neighborhoods of these surfaces, we can construct approximation operators for collinear and soft singularities. A BPHZ-like forest formula can be developed to subtract them systematically. In this paper, we utilize the position-space analysis of Erdogan and Sterman for Green functions, and develop the formalism for momentum space. A related analysis has been carried out by Collins for the Sudakov form factors, and is generalized here to any wide-angle kinematics with an arbitrary number of external momenta. We will first see that the approximations yield much richer IR structures than those of an original amplitude, then construct the forest formula and prove that all the singularities appearing in its subtraction terms cancel pairwise. With the help of the forest formula, the full amplitude can also be reorganized into a factorized expression, which helps to generalize the Sudakov form factor result to arbitrary numbers of external momenta. All our analysis will be on the amplitude level.

    hep-phhep-thJHEP(2020)·45 citations
12. 12*

    Axion Periodicity and Coupling Quantization in the Presence of Mixing

    Katherine Fraser🇺🇸 · Matthew Reece🇺🇸

    Mixing of axion fields is widely used to generate EFTs with phenomenologically advantageous features, such as hierarchies between axion couplings to different gauge fields and/or large effective field ranges. While these features are strongly constrained by periodicity for models with only a single axion, mixing has been used in the literature (sometimes incorrectly) to try to evade some of these constraints. In this paper, we ask whether it is possible to use axion mixing to generate an EFT of axions that evades these constraints by flowing to a theory of a non-compact scalar in the IR. We conclude that as long as the light axion is exactly massless, it will inherit the periodicity and associated constraints of the UV theory. However, by giving the light axion a mass, we can relax these constraints with effects proportional to the axion mass squared, including non-quantized couplings and the realignment of monodromy to a light axion with a larger field range. To show this, we consider various examples of axions mixing with other axions or with non-compact scalar fields, and work in a basis where coupling quantization is manifest. This basis makes it clear that in the case where an axion is eaten through the Higgs or Stuckelberg mechanism, the light axion does not have a large effective field range, in contrast to some recent claims in the literature. Additionally, we relate our results about axion EFTs to a well-known fact about gauge theory: that QFTs with compact gauge groups in the UV flow to QFTs with compact gauge groups in the IR, and make this correspondence precise in the 2+1 dimensional case.

    hep-phhep-thJHEP(2020)·31 citations
13. 13*

    Imaging the nucleus with high-energy photons

    Spencer R. Klein🇺🇸 · Heikki Mantysaari🇫🇮

    In the 1930's, nuclear physicists developed the first realistic atomic models, showing that nuclei were made up of protons and neutrons. In the 1960's, Deep Inelastic Scattering experiments showed that protons and neutrons had internal structure: quarks and gluons (collectively, partons), and later experiments showed that the parton momentum distributions are different in heavy nuclei, compared to those in free nucleons. This difference is not surprising; partons are sensitive to their environment, and two gluons from different nucleons may fuse together, for example. Understanding how quarks and gluons behave in the nuclear environment is a significant focus of modern nuclear physics. Recent measurements have provided us with an improved understanding of how quark and gluon densities are altered in heavy nuclei. We have also begun to make multi-dimensional pictures of the nucleus, exploring how these alterations are distributed within heavy nuclei. We naturally expect these modifications to be largest in the core of a nucleus, and smaller near its periphery; this can change the effective shape of the nucleus. We have also started to explore the transverse momentum distribution of the partons in the nuclei, and, using incoherent photoproduction as a probe, study event-by-event fluctuations in nucleon and nuclei parton densities. This article will explore recent progress in measurements of nuclear structure at high energy, with some emphasis on these multi-dimensional pictures. We will also discuss how a future electron-ion collider (EIC) with high luminosity and center-of-mass energy will make exquisitely detailed images of partons in a nucleus.

    ↳ hep-exhep-phnucl-exNature Rev.Phys.(2019)·159 citations
14. 14*

    Decay constants in AdS/QCD: a different approach

    Miguel Angel Martin Contreras🇨🇱 · Alfredo Vega🇨🇱

    The holographic recipe for the calculation of decay constants is revisited. Starting from the holographic 2-point function and using the fact that normalizable bulk modes scale as $z^{\Delta -S}$, with $S$ the spin, we can obtain a consistent expression that depends on the value of the mode at the boundary, not the derivative. We apply our decay constant expression to other AdS/QCD (static and dynamic) models proving its consistency. We also demonstrated that our approach is equivalent to the usual holographic prescription.

    ↳ hep-thhep-phPRD(2020)·21 citations
15. 15*

    Quantum transport and the phase space structure of the Wightman functions

    Henri Jukkala🇫🇮 · Kimmo Kainulainen🇫🇮 · Olli Koskivaara🇫🇮

    We study the phase space structure of exact quantum Wightman functions in spatially homogeneous, temporally varying systems. In addition to the usual mass shells, the Wightman functions display additional coherence shells around zero frequency $k_0=0$, which carry the information of the local quantum coherence of particle-antiparticle pairs. We find also other structures, which encode non-local correlations in time, and discuss their role and decoherence. We give a simple derivation of the cQPA formalism, a set of quantum transport equations, that can be used to study interacting systems including the local quantum coherence. We compute quantum currents created by a temporal change in a particle's mass, comparing the exact Wightman function approach, the cQPA and the semiclassical methods. We find that the semiclassical approximation, which is fully encompassed by the cQPA, works surprisingly well even for very sharp temporal features. This is encouraging for the application of semiclassical methods in electroweak baryogenesis with strong phase transitions.

    ↳ hep-thastro-ph.COgr-qchep-phJHEP(2020)·16 citations
16. 16*

    Neutrino-electron elastic scattering for flux determination at the DUNE oscillation experiment

    Chris M. Marshall🇺🇸 · Kevin S. McFarland🇺🇸 · Callum Wilkinson🇨🇭

    We study the feasibility of using neutrino-electron elastic scattering to measure the neutrino flux in the DUNE neutrino oscillation experiment. The neutrino-electron scattering cross section is precisely known, and the kinematics of the reaction allow determination of the incoming neutrino energy by precise measurement of the energy and angle of the recoiling electron. For several possible near detectors, we perform an analysis of their ability to measure neutrino flux in the presence of backgrounds and uncertainties. With realistic assumptions about detector masses, we find that a liquid argon detector, even with limitations due to angular resolution, is able to perform better than less dense detectors with more precise event-by-event neutrino energy measurements. We find that the absolute flux normalization uncertainty can be reduced from ~8% to ~2%, and the uncertainty on the flux shape can be reduced by ~20-30%.

    ↳ hep-exhep-phPRD(2020)·46 citations
17. 17*

    Virtual Compton Scattering and Nucleon Generalized Polarizabilities

    H.Fonvieille (1) · B.Pasquini (2)(3) · N.Sparveris (4) · ((1) Université Clermont Auvergne, CNRS/IN2P3, LPC, F-63000 Clermont-Ferrand, France, (2) Dipartimento di Fisica Nucleare e Teorica, Universitá degli Studi di Pavia, (3) Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Italy, (4) Temple University, Philadelphia, PA 19122, USA)

    This review gives an update on virtual Compton scattering (VCS) off the nucleon, ${\gamma }^{\ast }N\to N\gamma$, in the low-energy regime. We recall the theoretical formalism related to the generalized polarizabilities (GPs) and model predictions for these observables. We present the GP extraction methods that are used in the experiments: the approach based on the low-energy theorem for VCS and the formalism of Dispersion Relations. We then review the experimental results, with a focus on the progress brought by recent experimental data on proton generalized polarizabilities, and we conclude by some perspectives in the field of VCS at low energy.

    ↳ nucl-exhep-phnucl-thPPNP(2020)·23 citations
18. 18*

    Global anomalies in the Standard Model(s) and Beyond

    Joe Davighi🇬🇧 · Ben Gripaios🇬🇧 · Nakarin Lohitsiri🇬🇧

    We analyse global anomalies and related constraints in the Standard Model (SM) and various Beyond the Standard Model (BSM) theories. We begin by considering four distinct, but equally valid, versions of the SM, in which the gauge group is taken to be $G=G_{\text{SM}}/{\Gamma }_n$, with $G_{\text{SM}}=SU(3)\times SU(2)\times U(1)$ and ${\Gamma }_n$ isomorphic to $\mathbb{Z}/n$ where $n\in \left\{1,2,3,6\right\}$. In addition to deriving constraints on the hypercharges of fields transforming in arbitrary representations of the $SU(3)\times SU(2)$ factor, we study the possibility of global anomalies in theories with these gauge groups by computing the bordism groups ${\Omega }_5^{\text{Spin}}(BG)$ using the Atiyah-Hirzebruch spectral sequence. In two cases we show that there are no global anomalies beyond the Witten anomaly, while in the other cases we show that there are no global anomalies at all, illustrating the subtle interplay between local and global anomalies. While freedom from global anomalies has been previously shown for the specific fermion content of the SM by embedding the SM in an anomaly-free $SU(5)$ GUT, our results here remain true when the SM fermion content is extended arbitrarily. Going beyond the SM gauge groups, we show that there are no new global anomalies in extensions of the (usual) SM gauge group by $U(1{)}^m$ for any integer $m$, which correspond to phenomenologically well-motivated BSM theories featuring multiple $Z^{\prime }$ bosons. Nor do we find any new global anomalies in various grand unified theories, including Pati-Salam and trinification models. We also consider global anomalies in a family of theories with gauge group $SU(N)\times Sp(M)\times U(1)$, which share the phase structure of the SM for certain $(N,M)$.

    ↳ hep-thhep-phJHEP(2020)·93 citations
19. 19*

    A novel method of searching for an axial-vector mediated force

    Lei Chen🇨🇳 · Jian Liu🇨🇳 · Ka Di Zhu🇨🇳

    We present an atomic, molecular, and optical physics based method for the purpose of search for axial-vector mediated dipole-dipole interaction between electrons. In our scheme, applying a static magnetic field and a pump beam and a probe beam to a hybrid mechanical system composed of a nitrogen-vacancy center and a cantilever resonator, we could obtain a probe absorption spectrum. Based on the study of the relationship between this spectrum and the exotic dipole-dipole interaction, we put forward our detection principle and then provide a prospective constraint most stringent at a rough interaction range from $4\times {10}^{-8}$ to $2\times {10}^{-7}m$ . Our results indicate that this scheme could be put into consideration in relevant experimental searches .

    ↳ quant-phhep-phhep-th0 citations
20. 20*

    Analytical amplitudes from numerical solutions of the scattering equations

    Giuseppe De Laurentis🇬🇧

    The CHY formalism for massless scattering provides a cohesive framework for the computation of scattering amplitudes in a variety of theories. It is especially compelling because it elucidates existing relations among theories which are seemingly unrelated in a standard Lagrangian formulation. However, it entails operations that are highly non-trivial to perform analytically, most notably solving the scattering equations. We present a new Python package ( https://github.com/GDeLaurentis/seampy ) to solve the scattering equations and to compute scattering amplitudes. Both operations are done numerically with high-precision floating-point algebra. Elimination theory is used to obtain solutions to the scattering equations for arbitrary kinematics. These solutions are then applied to a variety of CHY integrands to obtain tree amplitudes for the following theories: Yang-Mills, Einstein gravity, biadjoint scalar, Born-Infeld, non-linear sigma model, Galileon, conformal gravity and $(\text{DF}{)}^2$. Finally, we exploit this high-precision numerical implementation to explore the singularity structure of the amplitudes and to reconstruct analytical expressions which make manifest their pole structure. Some of the expressions for conformal gravity and the $(\text{DF}{)}^2$ gauge theory are new to the best of our knowledge.

    ↳ hep-thhep-phJHEP(2020)·9 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.