Wed·Jul 15, 2020Wednesday·July 15, 2020

1. 01*

   Why is LaMET an effective field theory for partonic structure?

   Xiangdong Ji🇺🇸

   Partons are effective degrees of freedom describing the structure of hadrons involved in high-energy collisions. Familiar theories of partons are QCD light-front quantization and soft-collinear effective theory, both of which are intrinsically Minkowskian and appear unsuitable for classical Monte Carlo simulations. A ``new'' form of the parton theory has been formulated in term of the old-fashioned, Feynman's infinite momentum frame, in which the parton degrees of freedom are filtered through infinite-momentum external states. The partonic structure of hadrons is then related to the matrix elements of static (equal-time) correlators in the state $|P^z=\infty ⟩$. This representation lays the foundation of large-momentum effective theory (LaMET) which approximates parton physics through a systematic $M/P^z$ expansion of the lattice QCD matrix elements at a finite but large momentum $P^z$, and removes the residual logarithmic-$P^z$ dependence by the standard effective-field-theory matching and running.

   hep-phhep-lathep-thnucl-thAAPPS Bull.(2020)·23 citations
2. 02*

   The radiatively corrected Kaluza-Klein masses in aether compactification

   R. J. S. Oliveira🇧🇷 · A. Pinzul🇧🇷 · M. A. Anacleto🇧🇷 · E. Passos🇧🇷 · F. A. Brito🇧🇷 · O. Holanda🇧🇷

   We address the issue of radiative corrections to Kaluza-Klein (KK) masses in five-dimensional QED supplemented by aether Lorentz-violating terms. Specifically, we compute the corrections to the KK photon masses from one fermion loop. In general, the KK masses receive radiative corrections due to breaking the five-dimensional Lorentz invariance by compactification. As we show, the presence of the additional Lorentz violating factor - an aether background, leads to the non-trivial modification of these corrections. This model may be of interest in addressing important phenomenological issues such as the relation between radiative corrected KK mass splitting of a particular mode and uncertainties in the measurements and/or possible spatial variation of the fine-structure constant. For the recent data on the fine-structure constant, we find a KK mass splitting of magnitude $\sim 0.01$ MeV for the first excited Kaluza-Klein gauge boson at TeV scale. On the other hand, the large KK modes limit displays a very interesting phenomenon, showing the very special role of the aether in protecting the higher modes from the quantum corrections.

   hep-phgr-qchep-thPRD(2020)·3 citations
3. 03*

   Dealing with T and CPT violations in mixing as well as direct and indirect CP violations for neutral mesons decaying to two vectors

   Anirban Karan🇮🇳

   A large number of observables can be constructed from differential decay rate based on the polarization of final state while considering decay of a neutral meson $(P^0\text{ or }{\bar{P}}^0)$ to two vector particles. But all of these observables are not independent to each other since there are only a few independent theoretical parameters controlling the whole dynamics and therefore various relations among observables emerge. In this paper, we have studied the behaviour of observables for neutral meson decaying to two vectors in presence of T and CPT violations in mixing accompanied by both direct and indirect CP violations. We have expressed all of the fourteen unknown theoretical parameters for this scenario in terms observables only and constructed the complete set of thirty four relations among observables whose violation would signify the existence of some new Physics involving direct violation of CPT. In addition, using this formalism we have studied three special cases too: a) SM scenario, b) SM plus direct CP violation c) SM plus T and CPT violation in mixing.

   hep-phEPJC(2020)·4 citations
4. 04*

   Impact of quark quasiparticles on transport coefficients in hot QCD

   Valeriya Mykhaylova🇵🇱 · Chihiro Sasaki🇵🇱

   We study the bulk and shear viscosity and the electrical conductivity in a quasiparticle approach to Yang-Mills theory and QCD with light and strange quarks to assess the dynamical role of quarks in transport properties at finite temperature. The interactions with a hot medium are embodied in effective masses of the constituents through a temperature-dependent running coupling extracted from the lattice QCD thermodynamics. In Yang-Mills theory, the bulk viscosity to entropy density ratio exhibits a non-monotonous structure around the phase transition temperature. In QCD, this is totally dissolved because of a substantial contribution from quark quasiparticles. The bulk to shear viscosity ratio near the phase transition behaves consistently to the scaling with the speed of sound derived in the AdS/CFT approach, whereas at high temperature it obeys the same parametric dependence as in perturbation theory. Thus, the employed quasiparticle model is adequate to capture the transport properties in the weak and strong coupling regimes of the theory. This feature is not altered by including dynamical quarks which, however, retards the system from restoring conformal invariance. We also examine the individual flavor contributions to the electrical conductivity and show that the obtained behavior agrees qualitatively well with the recent results of lattice simulations and with a class of phenomenological approaches.

   hep-phPRD(2021)·43 citations
5. 05*

   Hydrodynamization in systems with detailed transverse profiles

   Aleksi Kurkela🇨🇭 · Seyed Farid Taghavi🇩🇪 · Urs Achim Wiedemann🇨🇭 · Bin Wu🇨🇭

   The observation of fluid-like behavior in nucleus-nucleus, proton-nucleus and high-multiplicity proton-proton collisions motivates systematic studies of how different measurements approach their fluid-dynamic limit. We have developed numerical methods to solve the ultra-relativistic Boltzmann equation for systems of arbitrary size and transverse geometry. Here, we apply these techniques for the first time to the study of azimuthal flow coefficients $v_n$ including non-linear mode-mode coupling and to an initial condition with realistic event-by-event fluctuations. We show how both linear and non-linear response coefficients extracted from $v_n$ develop as a function of opacity from free streaming to perfect fluidity. We note in particular that away from the fluid-dynamic limit, the signal strength of linear and non-linear response coefficients does not reduce uniformly, but that their hierarchy and relative size shows characteristic differences.

   hep-phnucl-thPLB(2020)·40 citations
6. 06*

   Shear viscosity of classical Yang-Mills field

   Hidefumi Matsuda🇯🇵 · Teiji Kunihiro🇯🇵 · Berndt Müller🇺🇸 · Akira Ohnishi🇯🇵 · Toru T. Takahashi🇯🇵

   We investigate the shear viscosity $\eta$ of the classical Yang-Mills (CYM) field on a lattice by using the Green-Kubo formula, where the shear viscosity is calculated from the time-correlation function of the energy-momentum tensor in equilibrium. Dependence of the shear viscosity $\eta (g,T)$ on the coupling $g$ and temperature $T$ is represented by a scaling function $f_{\eta }(g^{2}T)$ as $\eta (g,T)=T{f}_{\eta }(g^{2}T)$ due to the scaling-invariant property of the CYM. The explicit functional form of $f_{\eta }(g^{2}T)$ is successfully determined from the calculated shear viscosity: It turns out that $\eta (g,T)$ of the CYM field is proportional to $1/g^{1.10-1.88}$ at weak coupling, which is a weaker dependence on $g$ than that in the leading-order perturbation theory but consistent with that of the "anomalous viscosity" $\eta \propto 1/g^{1.5}$ under the strong disordered field. The obtained shear viscosity is also found to be roughly consistent with that estimated through the analysis of the anisotropy of the pressure of the CYM dynamics in the expanding geometry with recourse to a hydrodynamic equation.

   hep-phhep-latnucl-thPRD(2020)·5 citations
7. 07*

   Analytic Techniques for Solving the Transport Equations in Electroweak Baryogenesis

   Elina Fuchs🇮🇱 · Marta Losada🇦🇪 · Yosef Nir🇮🇱 · Yehonatan Viernik🇮🇱

   We develop an efficient method for solving transport equations, particularly in the context of electroweak baryogenesis. It provides fully-analytical results under mild approximations and can also test semi-analytical results, which are applicable in more general cases. Key elements of our method include the reduction of the second-order differential equations to first order, representing the set of coupled equations as a block matrix of the particle densities and their derivatives, identification of zero modes, and block decomposition of the matrix. We apply our method to calculate the baryon asymmetry of the Universe (BAU) in a Standard Model effective field theory framework of complex Yukawa couplings to determine the sensitivity of the resulting BAU to modifications of various model parameters and rates, and to estimate the effect of the commonly-used thin-wall approximation.

   hep-phastro-ph.COJHEP(2021)·11 citations
8. 08*

   Chaos in a $Q\bar{Q}$ system at finite temperature and baryon density

   P. Colangelo🇮🇹 · F. De Fazio🇮🇹 · N. Losacco🇮🇹

   Onset of chaos for the holographic dual of a $Q\bar{Q}$ system at finite temperature and baryon density is studied. We consider a string in the $AdS$ Reissner-Nordstrom background near the black-hole horizon, and investigate small time-dependent perturbations of the static configurations. The proximity to the horizon induces chaos, which is softened increasing the chemical potential. A background geometry including the effect of a dilaton is also examined. The Maldacena, Shenker and Stanford bound on the Lyapunov exponents characterizing the perturbations is satisfied for finite baryon chemical potential and when the dilaton is included in the metric.

   hep-phPRD(2020)·22 citations
9. 09*

   Different polarization definitions in same-sign $WW$ scattering at the LHC

   Alessandro Ballestrero🇮🇹 · Ezio Maina🇮🇹 · Giovanni Pelliccioli🇩🇪

   We study the polarization of positively charged $W$'s in the scattering of massive electroweak bosons at hadron colliders. We rely on the separation of weak boson polarizations in the gauge-invariant, doubly-resonant part of the amplitude in Monte Carlo simulations. Polarizations depend on the reference frame in which they are defined. We discuss the change in polarization fractions and in kinematic distributions arising from defining polarization vectors in two different reference frames which have been employed in recent experimental analyses.

   hep-phhep-exPLB(2020)·43 citations
10. 10*

    Multi-particle quantum-statistical correlation functions in a Hubble-expanding hadron gas

    Mate Csanad🇭🇺 · Antal Jakovac🇭🇺 · Sandor Lokos🇭🇺 · Ayon Mukherjee🇭🇺 · Srikanta Kumar Tripathy🇭🇺

    Quantum-statistical correlation measurements in high-energy physics represent an important tool to obtain information about the space-time structure of the particle-emitting source. There are several final state effects which may modify the measured femtoscopic correlation functions. One of these may be the interaction of the investigated particles with the expanding hadron gas, consisting of the other final state particles. This may cause the trajectories - and hence the phases - of the quantum-correlated pairs to be modified compared to free streaming. The resulting effect and could be interpreted as an Aharonov-Bohm-like phenomenon, in the sense that the possible paths of a quantum-correlated pair represent a closed loop, with an internally present field caused by the hadron gas. In this paper, the possible role of the effect in heavy-ion experiments is presented with analytical calculations and a simple numerical model. The modification of the strength of multi-particle Bose-Einstein correlation functions is investigated, and the is found that in case of sufficiently large source density, this effect may play a non-negligible role.

    hep-phnucl-thGribov-90 Memorial Volume, pp. 261-273 (2…·4 citations
11. 11*

    Dark Nucleosynthesis: Cross-sections and Astrophysical Signals

    Rakhi Mahbubani🇬🇧 · Michele Redi🇮🇹 · Andrea Tesi🇮🇹

    We investigate dark matter bound-state formation and its implication for indirect-detection experiments. We focus on the case where dark matter is a baryon of a strongly-coupled dark sector and provide generic formulae for the formation of shallow nuclear bound states on emission of photons, and W and Z gauge bosons. These processes can occur via electric and magnetic transitions, and give rise to indirect signals that are testable in monochromatic and diffuse photon measurements by Fermi and HESS. We also study the validity of factorizing the bound-state formation cross section into a short-distance nuclear part multiplied by Sommerfeld-enhancement factors. We find that the short-distance nuclear potential often violates factorization, modifying in particular the location of the peaks associated with zero-energy bound states. Finally we revisit bound-state formation of a (weakly-coupled) Minimal DM quintuplet including isospin-breaking effects, and find it gives rise to indirect-detection signals that are compatible with current bounds.

    hep-phastro-ph.COnucl-thJCAP(2021)·23 citations
12. 12*

    The bottom-charmed meson spectrum from a QCD approach based on Tamm--Dancoff approximation

    L. M. Abreu🇧🇷 · F. M. da Costa Júnior🇧🇷 · A. G. Favero🇨🇦

    The bottom-charmed meson spectrum is studied in this work via an effective version of the Coulomb gauge QCD Hamiltonian. The Tamm-Dancoff approximation is employed to estimate the energies of the low-lying and radial-excited $B_c$ states with quantum numbers $J^P=0^{-},0^{+},1^{-},1^{+},2^{+},2^{-}$. In particular, we analyze the effects of incorporating an effective transverse hyperfine interaction and spin mixing. The Regge trajectories and hyperfine splitting of both $S$- and $P$-wave states are also examined. The numerical results are compared with available experimental data and theoretical predictions of other models.

    hep-phPRD(2020)·12 citations
13. 13*

    Constraints on $N_{\mathrm{eff}}$ of high energy non-thermal neutrino injections upto $z\sim 10^8$ from CMB spectral distortions and abundance of light elements

    Sandeep Kumar Acharya🇮🇳 · Rishi Khatri🇮🇳

    High energy neutrinos and anti-neutrinos ($\gtrsim$ 100 GeV) can inject energetic electromagnetic particles into the baryon-photon plasma in the high redshift universe through electroweak showers from electroweak bremsstrahlung, inelastic scattering with the background electrons and nucleons, and by pair-production of standard model particles on background neutrinos and anti-neutrinos. In this paper, we evolve the particle cascades of high energy non-thermal neutrinos injections, using dark matter decay as a specific example, including relevant collision processes of these neutrinos with the background particles and taking into account the expansion of the universe. We study the effect of these non-thermal neutrino injections on the CMB spectral shape and abundance of light elements produced in the big bang nucleosynthesis. We show that CMB spectral distortions and abundance of light elements can constrain neutrino energy density at the recombination, parameterized as contribution to $N_{\mathrm{eff}}$, from high energy neutrino injection. These constraints are stronger by several orders of magnitudes compared to the CMB anisotropy constraints. We also show that CMB spectral distortions can probe neutrino injections to significantly higher redshifts ($z>2\times 10^6$) as compared to pure electromagnetic energy injection.

    ↳ astro-ph.COastro-ph.HEhep-phJCAP(2020)·9 citations
14. 14*

    QCD Axions and CMB Anisotropy

    Satoshi Iso🇯🇵 · Kiyoharu Kawana🇯🇵 · Kengo Shimada🇯🇵

    In this paper, we consider a possibility that the temperature anisotropy of cosmic microwave background (CMB) is dominantly generated by the primordial fluctuations of QCD-axion like particles under a circumstance that inflaton's perturbation is too small to explain the CMB anisotropy. Since the axion potential is generated by acquiring its energy from radiation, the primordial fluctuations of the axion field generated in the inflation era are correlated with the CMB anisotropies. Consequently, the observations stringently constrain a model of the axion and the early universe scenario. The following conditions must be satisfied: (i) sufficient amplitudes of the CMB anisotropy (ii) consistency with the axion isocurvature constraint and (iii) the non-Gaussianity constraint. To satisfy these conditions, a large energy fraction ${\Omega }_A^{}$ of the axion is necessary at the QCD scale when the axion-potential is generated, but simultaneously, it must become tiny at the present era due to the isocurvature constraint. Thus an additional scenario of the early universe, such as low scale thermal inflation, is inevitable to dilute the axions after the QCD scale. We investigate such a model and obtain its allowed parameter region.

    ↳ astro-ph.COhep-phhep-thPRD(2020)·2 citations
15. 15*

    James Chadwick: ahead of his time

    Gerhard Ecker

    James Chadwick is known for his discovery of the neutron. Many of his earlier findings and ideas in the context of weak and strong nuclear forces are much less known. This biographical sketch attempts to highlight the achievements of a scientist who paved the way for contemporary subatomic physics.

    ↳ physics.hist-phhep-exhep-phnucl-ex+10 citations
16. 16*

    $R(J/\psi )$ and $B_c^{-}\to J/\psi {\ell }^{-}{\bar{\nu }}_{\ell }$ Lepton Flavor Universality Violating Observables from Lattice QCD

    Judd Harrison🇬🇧 · Christine T. H. Davies🇬🇧 · Andrew Lytle🇮🇹

    We use our lattice QCD computation of the $B_c\to J/\psi$ form factors to determine the differential decay rate for the semitauonic decay channel and construct the ratio of branching fractions $R(J/\psi )=\mathcal{B}(B_c^{-}\to J/\psi {\tau }^{-}{\bar{\nu }}_{\tau })/\mathcal{B}(B_c^{-}\to J/\psi {\mu }^{-}{\bar{\nu }}_{\mu })$. We find $R(J/\psi )=0.2582(38)$ and give an error budget. We also extend the relevant angular observables, which were recently suggested for the study of lepton flavor universality violating effects in $B\to D^{\ast }\ell \nu$, to $B_c\to J/\psi \ell \nu$ and make predictions for their values under different new physics scenarios.

    ↳ hep-lathep-phPRL(2020)·106 citations
17. 17*

    $B_c\to J/\psi$ Form Factors for the full $q^2$ range from Lattice QCD

    Judd Harrison🇬🇧 · Christine T. H. Davies🇬🇧 · Andrew Lytle🇮🇹

    We present the first lattice QCD determination of the $B_c\to J/\psi$ vector and axial-vector form factors. These will enable experimental information on the rate for $B_c$ semileptonic decays to $J/\psi$ to be converted into a value for $V_{cb}$. Our calculation covers the full physical $q^2$ range of the decay and uses non-perturbatively renormalised lattice currents. We use the Highly Improved Staggered Quark (HISQ) action for all valence quarks on the second generation MILC ensembles of gluon field configurations including $u$, $d$, $s$ and $c$ HISQ sea quarks. Our HISQ heavy quarks have masses ranging upwards from that of $c$; we are able to reach that of the $b$ on our finest lattices. This enables us to map out the dependence on heavy quark mass and determine results in the continuum limit at the $b$. We use our form factors to construct the differential rates for $B_c^{-}\to J/\psi {\mu }^{-}{\bar{\nu }}_{\mu }$ and obtain a total rate with $7\%$ uncertainty: $\Gamma (B_c^{-}\to J/\psi {\mu }^{-}{\bar{\nu }}_{\mu })/|{\eta }_{\mathrm{EW}}{V}_{cb}{|}^2=1.73(12)\times 10^{13}{\mathrm{s}}^{-1}$. Including values for $V_{cb}$, ${\eta }_{\mathrm{EW}}$ and ${\tau }_{B_c}$ yields a branching fraction for this decay mode of 0.0150(11)(10)(3) ~with uncertainties from lattice QCD, ${\eta }_{\mathrm{EW}}{V}_{cb}$ and ${\tau }_{B_c}$ respectively.

    ↳ hep-lathep-phPRD(2020)·93 citations
18. 18*

    Formation of light nuclei at chemical freezeout: Description within a statistical thermal model

    Deeptak Biswas🇮🇳

    The thermal description of light nuclei at the chemical freeze-out has been investigated. First, I have verified the equilibration of the light nuclei and then introduced a new method to investigate the light nuclei formation. One can study the proximity between the phase space density of light nuclei ratios and their hadronic constituents e.g $\bar{d}/d$ and $(\bar{p}\bar{n}/pn)$. I have found that with the exclusion of the decay feed-down from the hadronic yields in the thermal model, the hadronic representations have good agreement with the light nuclei ratios. I have performed a similar analysis with the ratio of $\Lambda$-hypernuclei and ${}^{3}He$, which is related to the ratio $\Lambda /p$. In this context, the strangeness population factor $S_3$ has been studied also. These results indicate that the nuclei and hypernuclei formation may occur near the standard chemical freeze-out and before the decay of the hadronic resonances. This method will serve as a guideline to discuss the light nuclei formation and the inclusion of decay into their hadronic constituents.

    ↳ nucl-thhep-phPRC(2020)·10 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.