Mon·Jan 13, 2020Monday·January 13, 2020

1. 01*

   Differential comparison of identified-hadron ${\mathbf{p}}_{\mathbf{t}}$ spectra from high-energy A-B nuclear collisions based on a two-component model of hadron production

   Thomas A. Trainor🇺🇸

   Identified-hadron (PID) spectra from 2.76 TeV Pb-Pb and $p$-$p$ collisions are analyzed via a two-component (soft + hard) model (TCM) of hadron production in high-energy nuclear collisions. The PID TCM is adapted with minor changes from a recent analysis of PID hadron spectra from 5 TeV $p$-Pb collisions. Results from LHC data are compared with a PID TCM for 200 GeV Au-Au pion and proton spectra. 2.76 TeV proton spectra exhibit strong inefficiencies above 1 GeV/c estimated by comparing the $p$-$p$ spectrum with the corresponding TCM. After inefficiency correction Pb-Pb proton spectra are very similar to Au-Au proton spectra. PID A-A spectra are generally inconsistent with radial flow. Jet-related Pb-Pb and Au-Au spectrum hard components exhibit strong suppression at higher $p_t$ in more-central collisions corresponding to results from spectrum ratio $R_{AA}$ but also, for pions and kaons, exhibit dramatic enhancements below $p_t=1$ GeV/c that are concealed by $R_{AA}$. In contrast, enhancements of proton hard components appear only above 1 GeV/c suggesting that the baryon/meson "puzzle" is a jet phenomenon. Modification of spectrum hard components in more-central A-A collisions is consistent with increased gluon splitting during jet formation but with approximate conservation of leading-parton energy within a jet via the lower-$p_t$ enhancements.

   hep-phnucl-th5 citations
2. 02*

   Approximate Neutrino Oscillations in the Vacuum

   Emilio Ciuffoli🇨🇳 · Jarah Evslin🇨🇳 · Hosam Mohammed🇨🇳

   It is well known that neutrino oscillations may damp due to decoherence caused by the separation of mass eigenstate wave packets or by a baseline uncertainty of order the oscillation wave length. In this note we show that if the particles created together with the neutrino are not measured and do not interact with the environment, then the first source of decoherence is not present. This demonstration uses the saddle point approximation and also assumes that the experiment lasts longer than a certain threshold. We independently derive this result using the external wave packet model and also using a model in which the fields responsible for neutrino production and detection are treated dynamically. Intuitively this result is a consequence of the fact that the neutrino emission time does not affect the final state and so amplitudes corresponding to distinct emission times must be added coherently. This fact also implies that oscillations resulting from mass eigenstates which are detected simultaneously arise from neutrinos which were not created simultaneously but are nonetheless coherent, realizing the neutrino oscillation paradigm of Kobach, Manohar and McGreevy.

   hep-phEPJC(2021)·7 citations
3. 03*

   Testing the origin of the "$f_1(1420)$" with the $\bar{K}p\to \Lambda (\Sigma )K\bar{K}\pi$ reaction

   Wei-Hong Liang🇨🇳 · E. Oset🇪🇸

   We study the $\bar{K}p\to YK\bar{K}\pi$ reactions with $\bar{K}={\bar{K}}^0,K^{-}$ and $Y={\Sigma }^0,{\Sigma }^{+},\Lambda$, in the region of $K\bar{K}\pi$ invariant masses of $1200-1550$ MeV. The strong coupling of the $f_1(1285)$ resonance to $K^{\ast }\bar{K}$ makes the mechanism based on $K^{\ast }$ exchange very efficient to produce this resonance observed in the $K\bar{K}\pi$ invariant mass distribution. In addition, in all the reactions one observes an associated peak at $1420$ MeV which comes from the $K^{\ast }\bar{K}$ decay mode of the $f_1(1285)$ when the $K^{\ast }$ is placed off shell at higher invariant masses. We claim this to be the reason for the peak of the $K^{\ast }\bar{K}$ distribution seen in the experiments which has been associated to the "$f_1(1420)$" resonance.

   hep-phhep-exnucl-thEPJC(2020)·4 citations
4. 04*

   The semi-classical approximation at high temperature revisited

   Alexander Boccaletti🇭🇺 · Daniel Nogradi🇭🇺

   We revisit the semi-classical calculation of the size distribution of instantons at finite temperature in non-abelian gauge theories in four dimensions. The relevant functional determinants were first calculated in the seminal work of Gross, Pisarski and Yaffe and the results were used for a wide variety of applications including axions most recently. In this work we show that the uncertainty on the numerical evaluations and semi-analytical expressions are two orders of magnitude larger than claimed. As a result various quantities computed from the size distribution need to be reevaluated, for instance the resulting relative error on the topological susceptibility at arbitrarily high temperatures is about 5% for QCD and about 10% for $SU(3)$ Yang-Mills theory. With higher rank gauge groups this discrepancy is even higher. We also provide a simple semi-analytical formula for the size distribution with absolute error $2\cdot 10^{-4}$. In addition we also correct the over-all constant of the instanton size distribution in the MSbar scheme which was widely used incorrectly in the literature if non-trivial fermion content is present.

   hep-phhep-lathep-thJHEP(2020)·27 citations
5. 05*

   Axion detection through resonant photon-photon collisions

   K. A. Beyer🇬🇧 · G. Marocco🇬🇧 · R. Bingham🇬🇧 · G. Gregori🇬🇧

   We investigate the prospect of an alternative laboratory-based search for the coupling of axions and axion-like particles to photons. Here, the collision of two laser beams resonantly produces axions, and a signal photon is detected after magnetic reconversion, as in light-shining-through-walls (LSW) experiments. Conventional searches, such as LSW or anomalous birefrigence measurements, are most sensitive to axion masses for which substantial coherence can be achieved; this is usually well below optical energies. We find that using currently available high-power laser facilities, the bounds that can be achieved by our approach outperform traditional LSW at axion masses between $0.5-6$ eV, set by the optical laser frequencies and collision angle. These bounds can be further improved through coherent scattering off laser substructures, probing axion-photon couplings down to $g_{a\gamma \gamma }\sim 10^{-8}{\text{GeV}}^{-1}$, comparable with existing CAST bounds. Assuming a day long measurement per angular step, the QCD axion band can be reached.

   hep-phhep-exPRD(2020)·17 citations
6. 06*

   An overview of light-front holography

   Ruben Sandapen🇨🇦

   Light-front holography offers a successful first semiclassical approximation to hadronic spectroscopy and dynamics. We review its underlying assumptions, its remarkable predictions as well as attempts to go beyond the semiclassical approximation in order to the describe a wide range of data with a universal AdS/QCD mass scale.

   hep-phPoS(2020)·4 citations
7. 07*

   The generation of matter-antimatter asymmetries and hypermagnetic fields by the chiral vortical effect of transient fluctuations

   S. Abbaslu🇮🇷 · S. Rostam Zadeh🇮🇷 · M. Mehraeen🇮🇷 · S. S. Gousheh🇮🇷

   We study the contribution of temperature-dependent chiral vortical effect to the generation and evolution of the hypermagnetic fields and the matter-antimatter asymmetries, in the symmetric phase of the early Universe, in the temperature range $100\text{mbox}GeV\le T\le 10\text{mbox}TeV$. Our most important result is that, due to the chiral vortical effect, small overlapping transient fluctuations in the vorticity field in the plasma and temperature of matter degrees of freedom can lead to the generation of strong hypermagnetic fields and matter-antimatter asymmetries, all starting from zero initial values. We show that, either an increase in the amplitudes of the fluctuations of vorticity or temperature, or a decrease in their widths, leads to the production of stronger hypermagnetic fields, and therefore, larger matter-antimatter asymmetries. We have the interesting result that fluctuating vorticity fields are more productive, by many orders of magnitude, as compared to vorticities that are constant in time.

   hep-phEPJC(2021)·10 citations
8. 08*

   Open loop amplitudes and causality to all orders and powers from the loop-tree duality

   J. Jesus Aguilera-Verdugo🇪🇸 · Felix Driencourt-Mangin🇪🇸 · Roger J. Hernandez-Pinto🇲🇽 · Judith Plenter🇪🇸 · Selomit Ramirez-Uribe🇪🇸 · Andres E. Renteria-Olivo🇪🇸 · German Rodrigo🇪🇸 · German F. R. Sborlini🇪🇸 · William J. Torres Bobadilla🇪🇸 · Szymon Tracz🇪🇸

   Multiloop scattering amplitudes describing the quantum fluctuations at high-energy scattering processes are the main bottleneck in perturbative quantum field theory. The loop-tree duality is a novel method aimed at overcoming this bottleneck by opening the loop amplitudes into trees and combining them at integrand level with the real-emission matrix elements. In this Letter, we generalize the loop-tree duality to all orders in the perturbative expansion by using the complex Lorentz-covariant prescription of the original one-loop formulation. We introduce a series of mutiloop topologies with arbitrary internal configurations and derive very compact and factorizable expressions of their open-to-trees representation in the loop-tree duality formalism. Furthermore, these expressions are entirely independent at integrand level of the initial assignments of momentum flows in the Feynman representation and remarkably free of noncausal singularities. These properties, that we conjecture to hold to other topologies at all orders, provide integrand representations of scattering amplitudes that exhibit manifest causal singular structures and better numerical stability than in other representations.

   hep-phhep-thPRL(2020)·90 citations
9. 09*

   The rate of photon production in the quark-gluon plasma from lattice QCD

   Marco Cè🇩🇪 · Tim Harris🇮🇹 · Harvey B. Meyer🇩🇪 · Aman Steinberg🇩🇪 · Arianna Toniato🇩🇪

   We calculate the thermal rate of real-photon production in the quark-gluon plasma at a temperature of $T=254$ MeV using lattice QCD. The calculation is based on the difference between the spatially transverse and longitudinal parts of the polarization tensor, which has the advantage of falling off rapidly at large frequencies. We obtain this linear combination in the time-momentum representation from lattice QCD with two flavors of quarks in the continuum limit with a precision of about two parts per mille. Applying a theoretically motivated fit ansatz for the associated spectral function, we obtain values for the photon rate that are in line with QCD weak-coupling calculations; for photon momenta $1.0\le k[\mathrm{GeV}]\le 1.4$, our non-perturbative results constrain the rate to be no larger than twice the weak-coupling prediction. We also provide a physics interpretation of the electromagnetic spectral functions valid for all frequencies and momenta.

   ↳ hep-lathep-phnucl-thPRD(2020)·23 citations
10. 10*

    A Non-Equilibrium Approach to Photon Emission from the Late Stages of Relativistic Heavy-Ion Collisions

    Anna Schäfer🇩🇪 · Juan M. Torres-Rincon🇩🇪 · Charles Gale🇨🇦 · Hannah Elfner🇩🇪

    Cross sections for photon production in hadronic scattering processes have been calculated according to an effective chiral field theory. For $\pi +\rho \to \pi +\gamma$ and $\pi +\pi \to \rho +\gamma$ processes, these cross sections have been implemented into a novel hadronic transport approach (SMASH), which is suitable for collisions at low and intermediate energies. The implementation is verified by systematically comparing the thermal photon rate to theoretical expectations. The photon rates we obtain are compared to previous works, where scattering processes mediated by $\omega$ mesons are found to contribute significantly to the total photon production. Finally, the impact of considering the finite width of the $\rho$ meson is investigated, and a significant enhancement of photon production in the low-energy region is observed. This work is the first step towards a consistent treatment of photon emission in hybrid hydrodynamics+transport approaches. The quantification of the importance of the hadronic stage for the resolution of the direct photon flow puzzle is a next step and can be applied to identify equilibrium and non-equilibrium effects in the hadronic afterburner.

    ↳ nucl-thhep-phnucl-exNPA(2021)·5 citations
11. 11*

    On anomalous conformal Ward identities for Wilson loops on polygon-like contours with circular edges

    Harald Dorn🇩🇪

    We derive the anomalous conformal Ward identities for $\mathcal{N}=4$ SYM Wilson loops on polygon-like contours with edges formed by circular arcs. With a suitable choice of parameterisation they are very similarly to those for local correlation functions. Their solutions have a conformally covariant factor depending on the distances of the corners times a conformally invariant remainder factor depending, besides on cross ratios of the corners, on the cusp angles and angles parameterising the torsion of the contours.

    ↳ hep-thhep-phmath-phmath.MPJHEP(2020)·7 citations
12. 12*

    Neutrino Experiments at J-PARC

    Masahiro Kuze🇯🇵

    Neutrino experiments at J-PARC are reviewed. After an introduction to neutrino physics, with emphasis on neutrino oscillation, the T2K experiment at the Main Ring neutrino beam line and its peripheral experiments are introduced. Also future prospects of the Japanese long-baseline oscillation experiments are given. In addition, a new attempt to search for sterile neutrinos at the J-PARC MLF, JSNS${}^2$ experiment, is introduced.

    ↳ hep-exhep-phphysics.ins-detJPS Conf.Proc.(2021)·0 citations
13. 13*

    Supercritically charged objects and electron-positron pair creation

    Cheng-Jun Xia🇨🇳 · She-Sheng Xue🇮🇹 · Ren-Xin Xu🇨🇳 · Shan-Gui Zhou🇨🇳

    We investigate the stability and $e^{+}{e}^{-}$ pair creation of supercritically charged superheavy nuclei, $ud$QM nuggets, strangelets, and strangeon nuggets based on Thomas-Fermi approximation. The model parameters are fixed by reproducing their masses and charge properties reported in earlier publications. It is found that $ud$QM nuggets, strangelets, and strangeon nuggets may be more stable than ${}^{56}$Fe at $A\gtrsim 315$, $5\times 10^4$, and $1.2\times 10^8$, respectively. For those stable against neutron emission, the most massive superheavy element has a baryon number $\sim$965, while $ud$QM nuggets, strangelets, and strangeon nuggets need to have baryon numbers larger than $39$, 433, and $2.7\times 10^5$. The $e^{+}{e}^{-}$ pair creation will inevitably start for superheavy nuclei with charge numbers $Z\ge 177$, $ud$QM nuggets with $Z\ge 163$, strangelets with $Z\ge 192$, and strangeon nuggets with $Z\ge 212$. A universal relation $Q/R_e=\left(m_e-{\bar{\mu }}_e\right)/\alpha$ is obtained at a given electron chemical potential ${\bar{\mu }}_e$, where $Q$ is the total charge and $R_e$ the radius of electron cloud. This predicts the maximum charge number by taking ${\bar{\mu }}_e=-m_e$. For supercritically charged objects with ${\bar{\mu }}_e<-m_e$, the decay rate for $e^{+}{e}^{-}$ pair production is estimated based on the JWKB approximation. It is found that most positrons are emitted at $t\lesssim 10^{-15}$ s, while a long lasting positron emission is observed for large objects with $R\gtrsim 1000$ fm. The emission and annihilation of positrons from supercritically charged objects may be partially responsible for the short $\gamma$-ray burst during the merger of binary compact stars, the 511 keV continuum emission, as well as the narrow faint emission lines in X-ray spectra from galaxies and galaxy clusters.

    ↳ nucl-thastro-ph.HEhep-phPRD(2020)·19 citations
14. 14*

    Centrifugal acceleration of protons by a supermassive black hole

    Ya. N. Istomin🇷🇺 · A. A. Gunya🇷🇺

    The centrifugal acceleration is due to the rotating poloidal magnetic field in the magnetosphere creates the electric field which is orthogonal to the magnetic field. Charged particles with finite cyclotron radii can move along the electric field and receive energy. Centrifugal acceleration pushes particles to the periphery, where their azimuthal velocity reaches the light speed. We have calculated particle trajectories by numerical and analytical methods. The maximum obtained energies depend on the parameter of the particle magnetization $\kappa$, which is the ratio of rotation frequency of magnetic field lines in the magnetosphere ${\Omega }_F$ to non-relativistic cyclotron frequency of particles ${\omega }_c$, $\kappa ={\Omega }_F/{\omega }_c<<1$, and from the parameter $\alpha$ which is the ratio of toroidal magnetic field $B_T$ to the poloidal one $B_P$, $\alpha =B_T/B_P$. It is shown that for small toroidal fields, $\alpha <{\kappa }^{1/4}$, the maximum Lorentz factor ${\gamma }_m$ is only the square root of magnetization, ${\gamma }_m={\kappa }^{-1/2}$, while for large toroidal fields, $\alpha >{\kappa }^{1/4}$, the energy increases significantly, ${\gamma }_m={\kappa }^{-2/3}$. However, the maximum possible acceleration, ${\gamma }_m={\kappa }^{-1}$, is not achieved in the magnetosphere. For a number of active galactic nuclei, such as M87, maximum values of Lorentz factor for accelerated protons are found. Also for special case of Sgr. A* estimations of the maximum proton energy and its energy flux are obtained. They are in agreement with experimental data obtained by HESS Cherenkov telescope.

    ↳ astro-ph.HEastro-ph.GAhep-phMNRAS(2020)·9 citations
15. 15*

    The Mass of Short-Range Correlated Nucleon

    Rong Wang · Xurong Chen · Taofeng Wang

    The nucleon properties and structure should be modified by short-range correlations (SRC) among nucleons. By analyzing SRC ratio data, we extract the mass of nucleon in the SRC pair and the expected number of pn-SRC pairs in deuterium, under the assumption that the SRC nucleon mass is universal in different nuclei. The nucleon mass of a two-nucleon SRC pair is $m_{\text{SRC}}=852\pm 18$ MeV, and the number of pn-SRC pairs in deuterium is $n_{\text{SRC}}^{\text{d}}=0.021\pm 0.005$. The mass deficit of the strongly overlapping nucleon can be explained by the trace anomaly contribution to the mass in QCD or alternatively by the vacuum energy in the MIT bag model.

    ↳ nucl-thhep-phnucl-exCPC(2021)·6 citations
16. 16*

    Light-front quantization is the same as instant-time quantization

    Philip D. Mannheim🇺🇸

    Commutation or anticommutation relations quantized at equal instant time and commutation or anticommutation relations quantized at equal light-front time cannot be transformed into each other. While they would thus appear to describe different theories, we show that this is not in fact the case. In instant-time quantization unequal instant-time commutation or anticommutation relations for free scalar, fermion, or gauge boson fields are c-numbers. We show that when these unequal instant-time commutation or anticommutation relations are evaluated at equal light-front time they are identical to the equal light-front time commutation or anticommutation relations. Light-front quantization and instant-time quantization are thus the same and thus describe the same physics.

    ↳ hep-thhep-phPoS(2020)·3 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.