Thu·Nov 26, 2020Thursday·November 26, 2020

1. 01*

   $ZH$ production in gluon fusion: two-loop amplitudes with full top quark mass dependence

   Long Chen🇩🇪 · Gudrun Heinrich🇩🇪 · Stephen P. Jones🇨🇭 · Matthias Kerner🇨🇭 · Jonas Klappert🇩🇪 · Johannes Schlenk🇨🇭

   We present results for the two-loop helicity amplitudes entering the NLO QCD corrections to the production of a Higgs boson in association with a $Z$-boson in gluon fusion. The two-loop integrals, involving massive top quarks, are calculated numerically. Results for the interference of the finite part of the two-loop amplitudes with the Born amplitude are shown as a function of the two kinematic invariants on which the amplitudes depend.

   hep-phJHEP(2021)·50 citations
2. 02*

   Recoupling Mechanism for exotic mesons and baryons

   Yu.A.Simonov🇷🇺

   The infinite chain of transitions of one pair of mesons (channel I) into another pair of mesons (channel II) can produce bound states and resonances in both channels even if no interactions inside channels exist. These resonances which can occur also in meson-baryon channels are called channel-coupling (CC) resonances. A new mechanism of CC resonances is proposed where transitions occur due to a rearrangement of confining strings inside each channel -- the recoupling mechanism. The amplitude of this recoupling mechanism is expressed via overlap integrals of the wave functions of participating mesons (baryons). The explicit calculation with the known wave functions yields the peak at $E=4.12$ GeV for the transitions $J/\psi +\varphi \leftrightarrow D_s^{\ast }+{\bar{D}}_s^{\ast }$, which can be associated with ${\chi }_{c1}(4140)$, and a narrow peak at $3.98$ GeV with the width $10$ MeV for the transitions $D_s^{-}+D_0^{\ast }\leftrightarrow J/\psi +K^{\ast -},$ which can be associated with the recently discovered $Z_{cs}(3985)$.

   hep-phhep-exJHEP(2021)·17 citations
3. 03*

   Confinement studies in QCD with Dyson-Schwinger equations

   Marco Frasca🇮🇹

   We provide a study of quantum chromodynamics with the technique of Dyson-Schwinger equations in differential form. In this way, we are able to approach the non-perturbative limit and recover, with some approximations, the 't Hooft limit of the theory. Quark mass in the propagator term goes off-shell at low-energies signaling confinement. A condition for such occurrence in the theory is provided.

   hep-phNucl.Part.Phys.Proc.(2021)·0 citations
4. 04*

   Observability of 2HDM Neutral Higgs Bosons in fully hadronic decay at future linear collider

   Nadia Kausar🇺🇸 · Ijaz Ahmed🇺🇸 · Ather M.W

   The study aims to investigate the observability of pseudoscalar Higgs boson $A$ and neutral heavy CP even Higgs boson $H$, at different benchmark points, in the framework of type-I 2HDM. The study is done for $e^{-}{e}^{+}$ collisions at $\sqrt{s}$ = 1000 GeV centre of mass energy (c.o.m.) a possible scenario in future lepton collider. The associated production of $A$ and $H$ in $e+e-$ collisions are investigated in fully hadronic final state in two different channels. The first one is $AH\to ZHH\to j\bar{j}b\bar{b}b\bar{b}$ while the other one is $AH\to b\bar{b}b\bar{b}$. The observability of neutral heavy Higgs and pseudoscalar Higgs signal is possible within the parameter space $(\tan \beta ,m_A)$ which satisfies all experimental and theoretical constraints. The CP odd and CP even Higgs bosons in all scenarios are observable when signal exceeds $5\sigma$, which is the final extracted value of signal significance. The signal significance is calculated at different integrated luminosities. It is concluded from current analysis that fully hadronic channel is promising for search and measurement of the neutral Higgs Bosons in 2HDM.

   hep-phEur.Phys.J.Plus(2022)·0 citations
5. 05*

   Inclusive diffractive heavy quarkonium photoproduction including quark subprocesses

   Jiayu Wu🇨🇳 · Yanbing Cai🇨🇳 · Wenchang Xiang🇨🇳

   The inclusive $J/\Psi$, $\Psi (2S)$ and ${\rm Y}(1S)$ direct and resolved photoproduction are investigated by including the quark subprocesses in the framework of non-relativistic quantum chromodynamics (NRQCD). We find that the theoretical total cross section of heavy quarkonium productions are in good agreement with the data available at HERA, once the $\gamma q$, $qg$ and $qq$ subprocesses in the heavy quark pair productions are taken into account. The inclusive diffractive rapidity and transverse momentum distributions of $J/\Psi$, $\Psi (2S)$ and ${\rm Y}(1S)$ in $pp$, $pPb$ and $PbPb$ collisions at LHC are also studied by our quark improved NRQCD model combined with the resolved pomeron model. We find that the contributions from the quark involved subprocesses can reach to $8\%$ in the rapidity distribution and $6\%$ in the transverse momentum distribution. The numerical results show that the contributions from quark involved subprocesses are significant in heavy quarkonium photoprodution.

   hep-phPRC(2021)·2 citations
6. 06*

   Mass spectra and decay constants of heavy-light axial quarkonia in the framework of Bethe-Salpeter equation

   Vaishali Guleria🇮🇳 · Shashank Bhatnagar🇮🇳

   In this work we calculate the mass spectrum and decay constants of ground and excited states of heavy-light $P$-wave mesons such as $1^{++}$ and $1^{+-}$, with quark composition, $c\overline{u},c\overline{s},b\overline{u},b\overline{s}$, and $b\overline{c}$ in the framework of a QCD motivated Bethe-Salpeter equation (BSE) by making use of the exact treatment of the spin structure $({\gamma }_{\mu }⨂{\gamma }_{\mu })$ in the interaction kernel, In this $4\times 4$ BSE framework, the coupled Salpeter equations for $Q\overline{q}$ are first solved for the confining part of interaction, and are shown to decouple under heavy-quark approximation. Then the one-gluon-exchange interaction is perturbatively incorporated, leading to their mass spectral equations. The analytic forms of wave functions obtained from these equations are then used for calculation of leptonic decay constants of ground and excited states of $1^{++}$, and $1^{+-}$ as a test of these wave functions and the over all framework.

   hep-phInt.J.Theor.Phys.(2021)·13 citations
7. 07*

   Freeze-in and freeze-out generation of lepton asymmetries after baryogenesis in the $\nu$MSM

   Shintaro Eijima🇯🇵 · Mikhail Shaposhnikov🇨🇭 · Inar Timiryasov🇨🇭

   The $\nu$MSM -- an extension of the Standard Model by three relatively light singlet Majorana fermions $N_{1,2,3}$ -- allows for the generation of lepton asymmetry which is several orders of magnitude larger than the observed baryon asymmetry of the Universe. The lepton asymmetry is produced in interactions of $N_{2,3}$ (with masses in the GeV region) at temperatures below the sphaleron freeze out $T\lesssim 130$ GeV and can enhance the cosmological production of dark matter (DM) sterile neutrinos $N_1$ (with the mass of the keV scale) happening at $T\sim 200$ MeV due to active-sterile neutrino mixing. This asymmetry can be generated in freeze-in, freeze-out, or later in decays of heavy neutral leptons. In this work, we address the question of the magnitude of the late-time asymmetry (LTA) generated by the heavy neutral leptons $N_{2,3}$ during their freeze-in and freeze-out, leaving the decays for later work. We study how much of this asymmetry can survive down to the lower temperatures relevant for the sterile neutrino DM creation. We find that this LTA could result in the production of a sizeable fraction of dark matter. We also examine a role played by magnetic fields and the Abelian chiral anomaly in the generation of LTA, not accounted for in the previous studies. We argue that the production of LTA can be increased significantly and make an estimate of the influence of this effect.

   hep-phJCAP(2022)·19 citations
8. 08*

   Diphoton decay of the higgs from the Epstein--Glaser viewpoint

   Pawel Duch🇩🇪 · Michael Duetsch🇩🇪 · Jose M. Gracia-Bondia🇪🇸

   We revisit a nearly ten-year old controversy on the diphoton decay of the Higgs particle. To a large extent, the controversy turned around the respective merits of the regularization techniques employed. The novel aspect of our approach is that no regularization techniques are brought to bear: we work within the Bogoliubov--Epstein--Glaser scheme of renormalization by extension of distributions. Solving the problem actually required an expansion of this method's toolkit, furnished in the paper.

   hep-phhep-thmath-phmath.MPEPJC(2021)·3 citations
9. 09*

   Evolution of axions in the presence of primordial magnetic fields

   Maxim Dvornikov🇷🇺 · V. B. Semikoz (IZMIRAN)🇷🇺

   We study the evolution of axions interacting with primordial magnetic fields (PMFs) starting just from the QCD phase transition in the expanding universe. This interaction is owing to the Primakoff effect. Adopting the zero mode approximation for axions, we derive the system of equations for axions and magnetic fields, where the expansion of the universe and the spectra of magnetic fields are accounted for exactly. We find that the contribution of the Primakoff effect to the dynamics of axions and magnetic fields is rather weak. It confirms some previous estimates leading to analogous conclusions, when accounting here for the Hubble expansion both for an uniform axion field and non-uniform PMFs using Fourier spectra for their energy and helicity densities. We solve the corresponding system of the evolution equations and find that the axion zero mode, when evolving during radiation era, has its amplitude at the level sufficient for that axion to be a good candidate for the cold dark matter.

   hep-phastro-ph.COgr-qcPRD(2020)·15 citations
10. 10*

    Flavor violation at LHC in events with two opposite sign leptons and a $b$-jet

    Nilanjana Kumar🇮🇳

    Hints of flavor violation at both charged and neutral current decays of mesons have been observed in experiments such as LHCb, Belle, and BaBar. The anomalies in the result can be addressed in the effective field theory (EFT) framework. The effective operators predict different beyond standard model (BSM) signatures and the four point interaction vertices can be probed at Large Hadron Collider (LHC). In this context, the discovery projection of two opposite sign leptons and a $b$-jet signature is studied in this paper at 13 TeV LHC.

    hep-phSpringer Proc.Phys.(2021)·1 citation
11. 11*

    Higgsino Asymmetry and Direct-Detection Constraints of Light Dark Matter in the NMSSM with Non-Universal Higgs Masses

    Kun Wang🇨🇳 · Jingya Zhu🇨🇳 · Quanlin Jie🇨🇳

    In this work, we study the direct-detection constraints of light dark matter in the next-to minimal supersymmetric standard model (NMSSM) with non-universal Higgs masses (NUHM), especially the correlation between higgsino asymmetry and spin-dependent cross section. Finally, we get the following conclusions: (i) The spin-dependent cross section is proportional to the square of higgsino asymmetry in dark matter ${\tilde{\chi }}_1^0$ in the NMSSM-NUHM. (ii) For highly singlino-dominated dark matter ${\tilde{\chi }}_1^0$, the relic density can be sufficient, but the higgsino asymmetry and spin-dependent cross section is always small. (iii) With a sizeable higgsino component in the light dark matter, the higgsino asymmetry and spin-dependent cross section can be sizeable, but dark matter relic density is always small, thus it can escape the direct detections. (iv) Light dark matter in the $h_2$- and $Z$-funnel annihilation channels with sufficient relic density can be covered by future LUX-ZEPLIN (LZ) 7-ton in spin-dependent detections.

    hep-phCPC(2021)·11 citations
12. 12*

    Positivity bounds on Minimal Flavor Violation

    Quentin Bonnefoy🇩🇪 · Emanuele Gendy🇩🇪 · Christophe Grojean🇩🇪

    From general analyticity and unitarity requirements on the UV theory, positivity bounds on the Wilson coefficients of the dimension-8 operators composed of 4 fermions and two derivatives appearing in the Standard Model Effective Field Theory have been derived recently. We explore the fate of these bounds in the context of models endowed with a Minimal Flavor Violation (MFV) structure, models in which the flavor structure of higher dimensional operators is inherited from the one already contained in the Yukawa sector of the Standard Model Lagrangian. Our goal is to check whether the general positivity bounds translate onto bounds on the Yukawa coefficients and/or on elements of the CKM matrix. MFV fixes the coefficients of dimension-8 operators up to some multiplicative flavor-blind factors and we find that, in the most generic setup, the freedom left by those unspecified coefficients is enough as not to constrain the parameters of the renormalizable Yukawa sector. On the contrary, the latter shape the allowed region for the former. Requiring said overall coefficients to take natural $\mathcal{O}(1)$ values could give rise to bounds on the Yukawa couplings. Remarkably, at leading order in an expansion in powers of the Yukawa matrices, no bounds on the CKM entries can be retrieved.

    hep-phhep-thJHEP(2021)·52 citations
13. 13*

    Disentangling QCD and New Physics in $D^{+}\to {\pi }^{+}{\ell }^{+}{\ell }^{-}$

    Aoife Bharucha🇫🇷 · Diogo Boito🇧🇷 · Cédric Méaux🇫🇷

    In this paper we consider the decay $D^{+}\to {\pi }^{+}{\ell }^{+}{\ell }^{-}$, addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low $q^2$ and at high $q^2$, adapting the existing calculation for $B$ decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using $e^{+}{e}^{-}\to (\mathrm{hadrons})$ and $\tau \to (\mathrm{hadrons})+{\nu }_{\tau }$ data as well as the branching ratios for the resonant decays $D^{+}\to {\pi }^{+}R(R\to {\ell }^{+}{\ell }^{-})$, with $R=\rho$, $\omega$, and $\varphi$. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of $q^2$. Focusing then on the observables $F_H$ and $A_{\mathrm{FB}}$, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

    hep-phJHEP(2021)·37 citations
14. 14*

    Examining axion-like particles with superconducting radio-frequency cavity

    Dmitry Salnikov🇷🇺 · Petr Satunin🇷🇺 · D. V. Kirpichnikov🇷🇺 · Maxim Fitkevich🇷🇺

    We address production of massive axion-like particles by two electromagnetic modes inside a superconducting radio-frequency (SRF) cylindrical cavity. We discuss in detail the choice of pump modes and cavity design. We numerically compute time-averaged energy density of produced axion field for various cavity modes and wide range of axion masses. This allows us to estimate optimal conditions for axion production within a cavity. In addition, we consider photon regeneration process initiated by produced axion field in a screened radio-frequency cavity and derive constraints in parameter space $(g_{a\gamma \gamma },m_a)$ for different choice of pump modes.

    hep-phhep-exJHEP(2021)·14 citations
15. 15*

    Halo uncertainties in electron recoil events at direct detection experiments

    Tarak Nath Maity🇮🇳 · Tirtha Sankar Ray🇮🇳 · Sambo Sarkar🇮🇳

    The dark matter direct detection rates are highly correlated with the phase space distribution of dark matter particles in our galactic neighbourhood. In this paper, we make a systematic study of the impact of astrophysical uncertainties on electron recoil events at the direct detection experiments with Xenon and semiconductor detectors. We find that within the standard halo model there can be up to $\sim 50\%$ deviation from the fiducial choice in the exclusion bounds from these observational uncertainties. For non-standard halo models, we report a similar deviation from the fiducial standard halo model when fitted with recent cosmological $N$-body simulations while even larger deviations are obtained in case of the observational uncertainties.

    hep-phastro-ph.GAEPJC(2021)·25 citations
16. 16*

    Bubble wall velocity beyond leading-log approximation in electroweak phase transition

    Xiao Wang🇨🇳 · Fa Peng Huang🇺🇸 · Xinmin Zhang🇨🇳

    The bubble wall velocity is essential for the phase transition dynamics in the early universe and its cosmological implications, such as the energy budget of phase transition gravitational wave and electroweak baryogenesis. One key factor to determine the wall velocity is the collision term that quantifies the interactions between the massive particles in the plasma and the bubble wall. We improve the calculations of the collision term beyond the leading-log approximation, and further obtain more precise bubble wall velocity for a representative effective model.

    hep-ph63 citations
17. 17*

    Simulations of neutrino and gamma-ray production from relativistic black-hole microquasar jets

    Th. V. Papavasileiou🇬🇷 · O. T. Kosmas🇬🇧 · J. Sinatkas🇬🇷

    Recently, microquasar jets have aroused the interest of many researchers focusing on the astrophysical plasma outflows and various jet ejections. In this work, we concentrate on the investigation of electromagnetic radiation and particle emissions from the jets of stellar black hole binary systems characterized by their hadronic content in their jets. Such emissions are reliably described within the context of the relativistic magneto-hydrodynamics. Our model calculations are based on the Fermi acceleration mechanism through which the primary particles (mainly protons) of the jet are accelerated. As a result, a small portion of thermal protons of the jet acquire relativistic energies, through shock-waves generated into the jet plasma. From the inelastic collisions of fast (non-thermal) protons with the thermal (cold) ones, secondary charged and neutral particles (pions, kaons, muons, $\eta$-particles, etc.) are created as well as electromagnetic radiation from the radio wavelength band, to X-rays and even to very high energy $\gamma$-ray emission. One of our main goals is, through the appropriate solution of the transport equation and taking into account the various mechanisms that cause energy losses to the particles, to study the secondary particle distributions within hadronic astrophysical jets. After testing our method on the Galactic MQs SS 433 and Cyg X-1, as a concrete extragalactic binary system, we examine the LMC X-1 located in the Large Magellanic Cloud, a satellite galaxy of our Milky Way Galaxy. It is worth mentioning that, for the companion O star (and its extended nebula structure) of the LMC X-1 system, new observations using spectroscopic data from VLT/UVES have been published few years ago.

    hep-phastro-ph.HEastro-ph.SRphysics.plasm-phGalaxies(2021)·12 citations
18. 18*

    Multi-lepton signatures of vector-like leptons with flavor

    Stefan Bißmann🇩🇪 · Gudrun Hiller🇩🇪 · Clara Hormigos-Feliu🇩🇪 · Daniel F. Litim🇬🇧

    We investigate collider signatures of standard model extensions featuring vector-like leptons and a flavorful scalar sector. Such a framework arises naturally within asymptotically safe model building, which tames the UV behavior of the standard model towards the Planck scale and beyond. We focus on values of Yukawa couplings and masses which allow to explain the present data on the muon and electron anomalous magnetic moments. Using a CMS search based on $77.4{\mathrm{fb}}^{-1}$ at the $\sqrt{s}=13$ TeV LHC we find that flavorful vector-like leptons are excluded for masses below around $300$ GeV if they are singlets under $SU(2{)}_L$, and around $800$ GeV if they are doublets. Exploiting the flavor-violating-like decays of the scalars, we design novel null test observables based on opposite sign opposite flavor invariant masses. These multi-lepton distributions allow to signal new physics and to extract mass hierarchies in reach of near-future searches at the LHC and the HL-LHC.

    hep-phhep-exEPJC(2021)·58 citations
19. 19*

    On the Flavour Structure of Anomaly-free Hidden Photon Models

    Martin Bauer🇬🇧 · Patrick Foldenauer🇬🇧 · Martin Mosny🇬🇧

    Extensions of the Standard Model with an Abelian gauge group are constrained by gauge anomaly cancellation, so that only a limited number of possible charge assignments is allowed without the introduction of new chiral fermions. For flavour universal charges, couplings of the associated hidden photon to Standard Model fermions are flavour conserving at tree-level. We show explicitly that even the flavour specific charge assignments allowed by anomaly cancellation condition lead to flavour conserving tree-level couplings of the hidden photon to quarks and charged leptons \emph{if} the CKM or PMNS matrix can be successfully reconstructed. Further, loop-induced flavour changing couplings are strongly suppressed. As a consequence, the structure of the Majorana mass matrix is constrained and flavour changing tree-level couplings of the hidden photon to neutrino mass eigenstates are identified as a means to distinguish the $U(1{)}_{B-L}$ gauge boson from any other anomaly-free extension of the Standard Model without new chiral fermions. We present a comprehensive analysis of constraints and projections for future searches for a $U(1{)}_{B-3L_i}$ gauge boson, calculate the reach of resonance searches in $B$ meson decays and comment on the implications for non-standard neutrino interactions.

    hep-phPRD(2021)·35 citations
20. 20*

    Challenges and Opportunities of Gravitational Wave Searches at MHz to GHz Frequencies

    N. Aggarwal🇺🇸 · O. D. Aguiar🇧🇷 · A. Bauswein🇩🇪 · G. Cella🇮🇹 · S. Clesse🇧🇪 · A. M. Cruise🇬🇧 · V. Domcke🇩🇪 · D. G. Figueroa🇪🇸 · A. Geraci🇺🇸 · M. Goryachev🇦🇺 · H. Grote🇬🇧 · M. Hindmarsh🇫🇮 and 13 other authors

    The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational wave searches at frequencies above the LIGO/Virgo band, with a particular focus on Ultra High-Frequency Gravitational Waves (UHF-GWs), covering the MHz to GHz range. The absence of known astrophysical sources in this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising gravitational sources. We review several detector concepts which have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of the workshop "Challenges and opportunities of high-frequency gravitational wave detection" held at ICTP Trieste, Italy in October 2019, that set up the stage for the recently launched Ultra-High-Frequency Gravitational Wave (UHF-GW) initiative.

    ↳ gr-qcastro-ph.COastro-ph.IMhep-ex+1Living Rev.Rel.(2021)·472 citations
21. 21*

    The cosmic neutrino background as a collection of fluids in large-scale structure simulations

    Joe Zhiyu Chen🇦🇺 · Amol Upadhye🇦🇺 · Yvonne Y. Y. Wong🇦🇺

    A significant challenge for modelling the massive neutrino as a hot dark matter is its large velocity dispersion. In this work, we investigate and implement a multi-fluid perturbation theory that treats the cosmic neutrino population as a collection of fluids with a broad range of bulk velocities. These fluids respond linearly to the clustering of cold matter, which may be linear and described by standard linear perturbation theory, or non-linear, described using either higher-order perturbation theory or N-body simulations. We verify that such an alternative treatment of neutrino perturbations agrees closely with state-of-the-art neutrino linear response calculations in terms of power spectrum and bispectrum predictions. Combining multi-fluid neutrino linear response with a non-linear calculation for the cold matter clustering, we find for a reference nuLambdaCDM cosmology with neutrino mass sum of 0.93 eV an enhancement of the small-scale neutrino power by an order of magnitude relative to a purely linear calculation. The corresponding clustering enhancement in the cold matter, however, is a modest ~0.05%. Importantly, our multi-fluid approach uniquely enables us to identify that the slowest-moving 25% of the neutrino population clusters strongly enough to warrant a non-linear treatment. Such a precise calculation of neutrino clustering on small scales accompanied by fine-grained velocity information would be invaluable for experiments such as PTOLEMY that probe the local neutrino density and velocity in the solar neighbourhood.

    ↳ astro-ph.COhep-phJCAP(2021)·29 citations
22. 22*

    One line to run them all: SuperEasy massive neutrino linear response in $N$-body simulations

    Joe Zhiyu Chen🇦🇺 · Amol Upadhye🇦🇺 · Yvonne Y. Y. Wong🇦🇺

    We present in this work a novel and yet extremely simple method for incorporating the effects of massive neutrinos in cosmological $N$-body simulations. This so-called "SuperEasy linear response" approach is based upon analytical solutions to the collisionless Boltzmann equation in the clustering and free-streaming limits, which are then connected by a rational function interpolation function with cosmology-dependent coefficients given by simple algebraic expressions of the cosmological model parameters. The outcome is a {\it one-line modification} to the gravitational potential that requires only the cold matter density contrast as a real-time input, and that can be incorporated into any $N$-body code with a Particle--Mesh component with no additional implementation cost. To demonstrate its power, we implement the SuperEasy method in the publicly available \gadgetcode{} code, and show that for neutrino mass sums not exceeding $\sum m_{\nu }\simeq 1$ eV, the total matter and cold matter power spectra are in sub-1\% and sub-0.1\% agreement with those from state-of-the-art linear response simulations in literature. Aside from its minimal implementation cost, compared with existing massive neutrino simulation methods, the SuperEasy approach has better memory efficiency, incurs no runtime overhead relative to a standard $\Lambda$CDM simulation, and requires no post-processing. The minimal nature of the method allows limited computational resources to be diverted to modelling other physical effects of interest, e.g., baryonic physics via hydrodynamics.

    ↳ astro-ph.COhep-phJCAP(2021)·36 citations
23. 23*

    Schwinger Pair Production in SL$(2,\mathbb{C})$ Topologically Non-Trivial Fields via Non-Abelian Worldline Instantons

    Patrick Copinger🇯🇵 · Pablo Morales🇯🇵

    Schwinger pair production is analyzed in a BPST instanton background and in its SL$(2,\mathbb{C})$ complex extension for complex scalar particles. A non-Abelian extension of the worldline instanton method is utilized, wherein Wong's equations in a coherent state picture adopted for SL$(2,\mathbb{C})$ are solved in Euclidean spacetime. While pair production is not predicted in the BPST instanton, a complex extension of the BPST instanton, existing as parallel fields in Minkowski spacetime, is shown to decay via the Schwinger effect.

    ↳ hep-thhep-phPRD(2021)·7 citations
24. 24*

    Cosmology and the massive photon frequency shift in the Standard-Model Extension

    Alessandro D.A.M. Spallicci🇫🇷 · José A. Helayël-Neto🇧🇷 · Martin López-Corredoira🇪🇸 · Salvatore Capozziello🇮🇹

    The total red shift $z$ might be recast as a combination of the expansion red shift and a static shift due to the energy-momentum tensor non-conservation of a photon propagating through Electro-Magnetic (EM) fields. If massive, the photon may be described by the de Broglie-Proca (dBP) theory which satisfies the Lorentz(-Poincaré) Symmetry (LoSy) but not gauge-invariance. The latter is regained in the Standard-Model Extension (SME), associated with LoSy Violation (LSV) that naturally dresses photons of a mass. The non-conservation stems from the vacuum expectation value of the vector and tensor LSV fields. The final colour (red or blue) and size of the static shift depend on the orientations and strength of the LSV and EM multiple fields encountered along the path of the photon. Turning to cosmology, for a zero ${\Omega }_{\Lambda }$ energy density, the discrepancy between luminosity and red shift distances of SNeIa disappears thanks to the recasting of $z$. Massive photons induce an effective dark energy acting `optically' but not dynamically.

    ↳ astro-ph.COgr-qchep-phhep-thEPJC(2021)·39 citations
25. 25*

    Type $\bar{0}$ Heterotic String Orbifolds

    Alon E. Faraggi🇬🇧 · Viktor G. Matyas🇬🇧 · Benjamin Percival🇬🇧

    The $Z_2\times Z_2$ heterotic string orbifold gives rise to a large space of phenomenological three generation models that serves as a testing ground to explore how the Standard Model of particle physics may be incorporated in a theory of quantum gravity. Recently, we demonstrated the existence of type 0 $Z_2\times Z_2$ heterotic string orbifolds in which there are no massless fermionic states. In this paper we demonstrate the existence of non--supersymmetric tachyon--free $Z_2\times Z_2$ heterotic string orbifolds that do not contain any massless bosonic states from the twisted sectors. We dub these configurations type $\bar{0}$ models. They necessarily contain untwisted bosonic states, producing the gravitational, gauge and scalar moduli degrees of freedom, but possess an excess of massless fermionic states over bosonic ones, hence producing a positive cosmological constant. Such configurations may be instrumental when trying to understand the string dynamics in the early universe.

    ↳ hep-thhep-phPLB(2021)·24 citations
26. 26*

    Glueballs in the Klebanov-Strassler Theory: Pseudoscalars vs Scalars

    Cornélio Rodrigues Filho🇧🇷

    We discuss the $0^{+-}$ singlet sector of glueballs in the Klebanov-Strassler theory. We report the results of a numerical study of the linearized equations in the Klebanov-Strasller background and make a comparison with the spectrum of the scalar sector. While for four towers of the total six towers of massive pseudoscalar states our results match the spectrum of the corresponding towers of scalars, the values for the remaining two towers diverge with those of the scalars. We discuss possible interpretations of this divergence.

    ↳ hep-thhep-lathep-phBraz.J.Phys.(2021)·3 citations
27. 27*

    On the energy of the protons producing the very high-energy astrophysical neutrinos

    Esteban Roulet🇦🇷 · Francesco Vissani🇮🇹

    We study the distribution of the energy of the protons that can produce an astrophysical neutrino with a given observed energy, in the TeV--PeV range, both through $pp$ or $p\gamma$ interactions. Due to the increasing multiplicity of the pion production at high center of mass energies, the resulting average proton energies can be much larger than the often used approximate value $E_p\simeq 20E_{\nu }$. Also the threshold of the $p\gamma$ process can lead to a pronounced increase in the values of $⟨E_p⟩/E_{\nu }$ for decreasing neutrino energies. The results depend sensitively on the assumed proton spectrum, since steeper spectra give less weight to the lower energy neutrino tail resulting from the decays of the abundant low-energy pions. In the $p\gamma$ scenarios they also depend sensitively on the spectrum of the target photons. The results are in particular relevant to relate possible characteristics of the neutrino spectrum to those of the corresponding cosmic rays that generated them. We also discuss the associated production of gamma rays at the sources.

    ↳ astro-ph.HEhep-phJCAP(2021)·16 citations
28. 28*

    Gravitational waves from a holographic phase transition

    Fëanor Reuben Ares🇬🇧 · Mark Hindmarsh🇫🇮 · Carlos Hoyos🇪🇸 · Niko Jokela🇫🇮

    We investigate first order phase transitions in a holographic setting of five-dimensional Einstein gravity coupled to a scalar field, constructing phase diagrams of the dual field theory at finite temperature. We scan over the two-dimensional parameter space of a simple bottom-up model and map out important quantities for the phase transition: the region where first order phase transitions take place; the latent heat, the transition strength parameter $\alpha$, and the stiffness. We find that $\alpha$ is generically in the range 0.1 to 0.3, and is strongly correlated with the stiffness (the square of the sound speed in a barotropic fluid). Using the LISA Cosmology Working Group gravitational wave power spectrum model corrected for kinetic energy suppression at large $\alpha$ and non-conformal stiffness, we outline the observational prospects at the future space-based detectors LISA and TianQin. A TeV-scale hidden sector with a phase transition described by the model could be observable at both detectors.

    ↳ hep-thastro-ph.COgr-qchep-phJHEP(2020)·66 citations

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