Thu·Jul 9, 2020Thursday·July 9, 2020

1. 01*

   Soft displaced leptons at the LHC

   Freya Blekman🇧🇪 · Nishita Desai🇮🇳 · Anastasiia Filimonova🇩🇪 · Abanti Ranadhir Sahasransu🇧🇪 · Susanne Westhoff🇩🇪

   Soft displaced leptons are representative collider signatures of compressed dark sectors with feeble couplings to the standard model. Prime targets are dark matter scenarios where co-scattering or co-annihilation sets the relic abundance upon freeze-out. At the LHC, searches for soft displaced leptons are challenged by a large background from hadron or tau lepton decays. In this article, we present an analysis tailored for displaced leptons with a low transverse momentum threshold at 20 GeV. Using a neural network, we perform a comprehensive analysis of the event kinematics, including a study of the expected detection efficiencies and backgrounds at small momenta. Our results show that weak-scale particles decaying into soft leptons with decay lengths between 1mm and 1m can be probed with LHC Run 2 data. This motivates the need for dedicated triggers that maximize the sensitivity to displaced soft leptons.

   hep-phhep-exJHEP(2020)·18 citations
2. 02*

   Two-Loop Rational Terms in Yang-Mills Theories

   Jean-Nicolas Lang🇨🇭 · Stefano Pozzorini🇨🇭 · Hantian Zhang🇨🇭 · Max F. Zoller🇨🇭

   Scattering amplitudes in $D$ dimensions involve particular terms that originate from the interplay of UV poles with the $D-4$ dimensional parts of loop numerators. Such contributions can be controlled through a finite set of process-independent rational counterterms, which make it possible to compute loop amplitudes with numerical tools that construct the loop numerators in four dimensions. Building on a recent study [1] of the general properties of two-loop rational counterterms, in this paper we investigate their dependence on the choice of renormalisation scheme. We identify a nontrivial form of scheme dependence, which originates from the interplay of mass and field renormalisation with the $D-4$ dimensional parts of loop numerators, and we show that it can be controlled through a new kind of one-loop counterterms. This guarantees that the two-loop rational counterterms for a given renormalisable theory can be derived once and for all in terms of generic renormalisation constants, which can be adapted a posteriori to any scheme. Using this approach, we present the first calculation of the full set of two-loop rational counterterms in Yang-Mills theories. The results are applicable to SU(N) and U(1) gauge theories coupled to $n_f$ fermions with arbitrary masses.

   hep-phhep-thJHEP(2020)·34 citations
3. 03*

   Cumulants of multiple conserved charges and global conservation laws

   Volodymyr Vovchenko🇺🇸 · Roman V. Poberezhnyuk🇺🇦 · Volker Koch🇺🇸

   We analyze the behavior of cumulants of conserved charges in a subvolume of a thermal system with exact global conservation laws by extending a recently developed subensemble acceptance method (SAM) [V. Vovchenko et al., arXiv:2003.13905] to multiple conserved charges. Explicit expressions for all diagonal and off-diagonal cumulants up to sixth order that relate them to the grand canonical susceptibilities are obtained. The derivation is presented for an arbitrary equation of state with an arbitrary number of different conserved charges. The global conservation effects cancel out in any ratio of two second order cumulants, in any ratio of two third order cumulants, as well as in a ratio of strongly intensive measures $\Sigma$ and $\Delta$ involving any two conserved charges, making all these quantities particularly suitable for theory-to-experiment comparisons in heavy-ion collisions. We also show that the same cancellation occurs in correlators of a conserved charge, like the electric charge, with any non-conserved quantity such as net proton or net kaon number. The main results of the SAM are illustrated in the framework of the hadron resonance gas model. We also elucidate how net-proton and net-$\Lambda$ fluctuations are affected by conservation of electric charge and strangeness in addition to baryon number.

   hep-phnucl-exnucl-thJHEP(2020)·53 citations
4. 04*

   Apparent modification of the jet-like yield in proton-proton collisions with large underlying event

   Gyula Bencédi🇭🇺 · Antonio Ortiz🇲🇽 · Sushanta Tripathy🇲🇽

   This paper presents the production of charged particles associated with high-$p_{\mathrm{T}}$ trigger particles ($8<p_{\mathrm{T}}^{trig.}<15$ GeV/$c$) in proton-proton collisions at $\sqrt{s}=5.02$ TeV simulated with PYTHIA 8.244. The study is performed as a function of the relative transverse activity classifier, $R_{\mathrm{T}}$, which is the relative charged-particle multiplicity in the transverse region ($\pi /3<|{\varphi }^{trig.}-{\varphi }^{assoc.}|<2\pi /3$) of the di-hadron correlations, and it is sensitive to the Multi-Parton Interactions. The evolution of both the near and the away-side yield of associated particles ($3\le p_{\mathrm{T}}^{assoc.}<8$ GeV/$c$) as a function of $R_{\mathrm{T}}$ is investigated. We propose a strategy which allows for the modelling and subtraction of the underlying event contribution from the near and the away side in challenging environments like those characterised by large $R_{\mathrm{T}}$. We found that the away-side signal becomes broader with increasing $R_{\mathrm{T}}$, while its corresponding yield is independent of $R_{\mathrm{T}}$. Contrarily, the near-side yield increases with $R_{\mathrm{T}}$. This effect is reminiscent of that seen in heavy-ion collisions, where an enhancement in the near-side yield for 0-5% central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV was reported. A discussion on the origin of these effects in PYTHIA, as well as their implications for the interpretation of recent LHC results for pp collisions, is presented.

   hep-phJ.Phys.G(2020)·21 citations
5. 05*

   Asymmetries in Processes of Electron-Positron Annihilation

   Andrej Arbuzov🇷🇺 · Serge Bondarenko🇷🇺 · Lidia Kalinovskaya🇷🇺

   Processes of electron-positron annihilation into a pair of fermions were considered. Forward-backward and left-right asymmetries were studied, taking into account polarization of initial and final particles. Complete 1-loop electroweak radiative corrections were included. A wide energy range including the $Z$ boson peak and higher energies relevant for future $e^{+}{e}^{-}$ colliders was covered. Sensitivity of observable asymmetries to the electroweak mixing angle and fermion weak coupling was discussed.

   hep-phSymmetry(2020)·6 citations
6. 06*

   Fireball tomography from bottomonia elliptic flow in relativistic heavy-ion collisions

   Partha Pratim Bhaduri🇮🇳 · Mubarak Alqahtani🇸🇦 · Nicolas Borghini🇩🇪 · Amaresh Jaiswal🇮🇳 · Michael Strickland🇺🇸

   We calculate the elliptic flow of bottomonia produced in Pb$+$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. We consider temperature-dependent decay widths for the anisotropic escape of various bottomonium states and observe that the transverse momentum dependence of bottomonia elliptic flow provides a tomographic information about the QGP fireball at different stages of its evolution. For the space-time evolution of the fireball, we employ simulation results from the 3+1D quasiparticle anisotropic hydrodynamic model. We find that our results for transverse momentum dependence of bottomonia elliptic flow are in reasonable agreement with experimental results from the ALICE and CMS collaborations.

   hep-phhep-exhep-thnucl-thEPJC(2021)·21 citations
7. 07*

   Exclusive Decays of the Doubly Heavy Baryon ${\Xi }_{bc}$

   A. V. Luchinsky🇷🇺 · A. K. Likhoded🇷🇺

   Exclusive decays of the ${\Xi }_{bc}^{+}$ with light mesons production, ${\Xi }_{bc}^{+}\to {\Xi }_{cc}^{++}\mathcal{R}$ are analyzed. In the framework of the factorization model the matrix elements of the considered reactions are written as a product of ${\Xi }_{bc}\to {\Xi }_{cc}W$ and $W\to \mathcal{R}$ transition amplitudes. As a result theoretical and experimental investigation of these decays allow us to test the physics of heavy and light quarks' sectors. Presented are the branching fractions of these reactions, as well as the distributions over the invariant mass of the light system and some other kinematical variables. Our calculations show that the probabilities of the considered reactions are high enough, so presented results could help with observation of yet unseen ${\Xi }_{bc}$ baryon.

   hep-phPRD(2020)·7 citations
8. 08*

   Axion and neutrino mass from a hidden gauge symmetry model

   Takaaki Nomura🇰🇷 · Hiroshi Okada🇰🇷 · Seokhoon Yun🇰🇷

   We propose a model of dark sector described by gauged hidden $U(1{)}_H$ symmetry in which neutrino masses are generated at one-loop level and axion is induced by assigning Peccei-Quinn charge to fermions in dark sector relevantly. Then our scenario connects exotic fermion mass generation, neutrino mass matrix and axion through scalar fields associated with $U(1{)}_H$ and Peccei-Quinn symmetry breaking. We investigate neutrino mass formula, lepton flavor violation, anomalous magnetic moment of muon, dark matter relic density and axion couplings, which are originated from interactions among our dark sector and the standard model particles.

   hep-ph2 citations
9. 09*

   A new and complete proof of the Landau condition for pinch singularities of Feynman graphs and other integrals

   John Collins🇺🇸

   The Landau equations give a physically useful criterion for how singularities arise in Feynman amplitudes. Furthermore, they are fundamental to the uses of perturbative QCD, by determining the important regions of momentum space in asymptotic problems. Generalizations are also useful. We will show that in existing treatments there are significant gaps in derivations, and in some cases implicit assumptions that will be shown here to be false in important cases like the massless Feynman graphs ubiquitous in QCD applications. In this paper is given a new proof that the Landau condition is both necessary and sufficient for physical-region pinches in the kinds of integral typified by Feynman graphs. The proof's range is broad enough to include the modified Feynman graphs that are used in QCD applications. Unlike many existing derivations, there is no need to use the Feynman parameter method. Some possible further applications of the new proof and its subsidiary results are proposed.

   hep-phhep-th36 citations
10. 10*

    Does Palatini Higgs Inflation Conserve Unitarity?

    J. McDonald🇬🇧

    In the conventional metric formulation of gravity, the Higgs Inflation model violates unitarity in the electroweak vacuum in Higgs scattering at the energy scale $\Lambda \sim M_{Pl}/\xi$, where $\xi \sim 10^4$ is the non-minimal coupling of the Higgs to the Ricci scalar. In the Palatini formulation it is commonly believed that $\Lambda \sim M_{Pl}/\sqrt{\xi }$, where $\xi \sim 10^9$. Here we reconsider unitarity violation in the electroweak vacuum in the Palatini formulation. We argue that there is no unitarity violation in Higgs scattering in the Palatini non-minimally coupled Standard Model in the electroweak vacuum at energies below the Planck scale. In this case Palatini Higgs Inflation completely conserves unitarity and is consistent at all energies up to those at which quantum gravity becomes important. If true, this would imply that Palatini Higgs Inflation has a significant advantage over metric Higgs Inflation.

    hep-phhep-thJCAP(2021)·45 citations
11. 11*

    Exploring CP-violation, via heavy neutrino oscillations, in rare B meson decays at Belle II

    Gorazd Cvetic🇨🇱 · C.S. Kim🇰🇷 · Sebastian Mendizabal🇨🇱 · Jilberto Zamora-Saa🇨🇱

    In this article we study the rare B-meson decay via two on-shell almost-degenerate Majorana Heavy Neutrinos, into two charged leptons and two pseudoscalar mesons ($B^{\pm }\to D^0{\ell }_1^{\pm }{\ell }_2^{\pm }{\pi }^{\mp }$). We consider the scenario where the heavy neutrino masses are $\sim 2$ GeV and the heavy-light mixing coefficients are $|B_{\ell N}{|}^2\sim 10^{-5}$, and evaluate the possibility to measure the CP-asymmetry at Belle II. We present some realistic conditions under which the asymmetry could be detected.

    hep-phEPJC(2020)·22 citations
12. 12*

    Phenomenology of inclusive $\bar{B}\to X_s{\ell }^{+}{\ell }^{-}$ for the Belle II era

    Tobias Huber🇩🇪 · Tobias Hurth🇩🇪 · Jack Jenkins🇺🇸 · Enrico Lunghi🇺🇸 · Qin Qin🇨🇳 · K.Keri Vos🇩🇪

    With the first data being recorded at Belle II, we are at the brink of a new era in quark flavour physics. The many exciting new opportunities for Belle~II include a full angular analysis of inclusive $\bar{B}\to X_s{\ell }^{+}{\ell }^{-}$ which has the potential to reveal new physics, in particular by its interplay with the exclusive $b\to s{\ell }^{+}{\ell }^{-}$ counterparts studied extensively at LHCb. In this paper, we present fully updated Standard Model predictions for all angular observables necessary for this endeavour. These predictions are tailored to Belle II and include an elaborate study of the treatment of collinear photons which become crucial when aiming for the highest precision. In addition, we present a phenomenological study of the potential for Belle II to reveal possible new physics in the inclusive decay channel, both in an independent manner and in combination with exclusive modes.

    hep-phhep-exJHEP(2020)·42 citations
13. 13*

    Deciphering QCD dynamics in small collision systems using event shape and final state multiplicity at the Large Hadron Collider

    Suman Deb🇮🇳 · Sushanta Tripathy🇮🇳 · Golam Sarwar🇮🇳 · Raghunath Sahoo🇮🇳 · Jan-e Alam🇮🇳

    The high-multiplicity pp collisions at the Large Hadron Collider energies with various heavy-ion-like signatures have warranted a deeper understanding of the underlying physics and particle production mechanisms. It is a common practice to use experimental data on the hadronic transverse momentum ($p_T$) spectra to extract thermodynamical properties of the system formed in heavy ion and high multiplicity pp collisions. The non-availability of event topology dependent experimental data for pp collisions at $\sqrt{s}$ = 13 TeV on the spectra of non-strange and strange hadrons constrains us to use the PYTHIA8 simulated numbers to extract temperature-like parameters to study the event shape and multiplicity dependence of specific heat capacity, conformal symmetry breaking measure (CSBM) and speed of sound. The observables show a clear dependence on event multiplicity and event topology. Thermodynamics of the system is largely governed by the light particles because of their relatively larger abundances. In this regards, a threshold in the particle production, ${\mathrm{N}}_{\mathrm{ch}}\simeq$ (10-20) in the final state multiplicity emerges out from the present study, confirming some of the earlier findings in this direction. As for heavier hadrons with relatively small abundances, a similar threshold is observed for $⟨{\mathrm{N}}_{\mathrm{ch}}⟩\simeq$ 40 hinting towards formation of a thermal bath where all the heavier hadrons are in equilibrium.

    hep-phhep-exnucl-exnucl-thEPJA(2020)·12 citations
14. 14*

    One-loop RG improvement of the screened massive expansion in the Landau gauge

    Giorgio Comitini🇮🇹 · Fabio Siringo🇮🇹

    The RG improvement of the screened massive expansion is studied at one loop in two renormalization schemes, the momentum subtraction (MOM) scheme and the screened momentum subtraction (SMOM) scheme. The respective Taylor-scheme running couplings are shown not to develop a Landau pole, provided that the initial value of the coupling is sufficiently small. The improved ghost and gluon propagators are found to behave as expected, displaying dynamical mass generation for the gluons and the standard UV limit of ordinary perturbation theory. In the MOM scheme, when optimized by a matching with the fixed-coupling framework, the approach proves to be a powerful method for obtaining propagators which are in excellent agreement with the lattice data already at one loop. After optimization, the gluon mass parameter is left as the only free parameter of the theory and is shown to play the same role of the ordinary perturbative QCD scale ${\Lambda }_{\text{QCD}}$.

    hep-phhep-lathep-thPRD(2020)·18 citations
15. 15*

    Feebly Interacting $U(1{)}_{\mathrm{B}-\mathrm{L}}$ Gauge Boson Warm Dark Matter and XENON1T Anomaly

    Gongjun Choi🇨🇳 · Tsutomu T. Yanagida🇨🇳 · Norimi Yokozaki🇯🇵

    The recent observation of an excess in the electronic recoil data by the XENON1T detector has drawn many attentions as a potential hint for an extension of the Standard Model (SM). Absorption of a vector boson with the mass of $m_{A^{\prime }}\in (2\mathrm{keV},3\mathrm{keV})$ is one of the feasible explanations to the excess. In the case where the vector boson explains the dark matter (DM) population today, it is highly probable that the vector boson belongs to a class of the warm dark matter (WDM) due to its suspected mass regime. In such a scenario, providing a good fit for the excess, the kinetic mixing $\kappa \sim 10^{-15}$ asks for a non-thermal origin of the vector DM. In this letter, we consider a scenario where the gauge boson is nothing but the $U(1{)}_{\mathrm{B}-\mathrm{L}}$ gauge boson and its non-thermal origin is attributed to the decay of the coherently oscillating scalar of which condensation induces the spontaneous breaking of $U(1{)}_{\mathrm{B}-\mathrm{L}}$. We discuss implications for the early universe physics when the warm nature of the vector DM serves as a resolution to both the small scale problems that $\Lambda$CDM model encounters and the XENON1T anomaly.

    hep-phastro-ph.COPLB(2020)·39 citations
16. 16*

    Large Neutrino Magnetic Moments in the Light of Recent Experiments

    K.S. Babu🇺🇸 · Sudip Jana🇩🇪 · Manfred Lindner🇩🇪

    The excess in electron recoil events reported recently by the XENON1T experiment may be interpreted as evidence for a sizable transition magnetic moment ${\mu }_{{\nu }_e{\nu }_{\mu }}$ of Majorana neutrinos. We show the consistency of this scenario when a single component transition magnetic moment takes values ${\mu }_{{\nu }_e{\nu }_{\mu }}\in (1.65-3.42)\times 10^{-11}{\mu }_B$. Such a large value typically leads to unacceptably large neutrino masses. In this paper we show that new leptonic symmetries can solve this problem and demonstrate this with several examples. We first revive and then propose a simplified model based on $SU(2{)}_H$ horizontal symmetry. Owing to the difference in their Lorentz structures, in the $SU(2{)}_H$ symmetric limit, $m_{\nu }$ vanishes while ${\mu }_{{\nu }_e{\nu }_{\mu }}$ is nonzero. Our simplified model is based on an approximate $SU(2{)}_H$, which we also generalize to a three family $SU(3{)}_H$-symmetry. Collider and low energy tests of these models are analyzed. We have also analyzed implications of the XENON1T data for the Zee model and its extensions which naturally generate a large ${\mu }_{{\nu }_e{\nu }_{\mu }}$ with suppressed $m_{\nu }$ via a spin symmetry mechanism, but found that the induced ${\mu }_{{\nu }_e{\nu }_{\mu }}$ is not large enough to explain recent data. Finally, we suggest a mechanism to evade stringent astrophysical limits on neutrino magnetic moments arising from stellar evolution by inducing a medium-dependent mass for the neutrino.

    hep-phastro-ph.SRhep-exJHEP(2020)·112 citations
17. 17*

    Towards Machine Learning Analytics for Jet Substructure

    Gregor Kasieczka🇩🇪 · Simone Marzani🇮🇹 · Gregory Soyez🇫🇷 · Giovanni Stagnitto🇫🇷

    The past few years have seen a rapid development of machine-learning algorithms. While surely augmenting performance, these complex tools are often treated as black-boxes and may impair our understanding of the physical processes under study. The aim of this paper is to move a first step into the direction of applying expert-knowledge in particle physics to calculate the optimal decision function and test whether it is achieved by standard training, thus making the aforementioned black-box more transparent. In particular, we consider the binary classification problem of discriminating quark-initiated jets from gluon-initiated ones. We construct a new version of the widely used N-subjettiness, which features a simpler theoretical behaviour than the original one, while maintaining, if not exceeding, the discrimination power. We input these new observables to the simplest possible neural network, i.e. the one made by a single neuron, or perceptron, and we analytically study the network behaviour at leading logarithmic accuracy. We are able to determine under which circumstances the perceptron achieves optimal performance. We also compare our analytic findings to an actual implementation of a perceptron and to a more realistic neural network and find very good agreement.

    hep-phJHEP(2020)·49 citations
18. 18*

    Precision Global Determination of the $B\to X_s\gamma$ Decay Rate

    SIMBA collaboration: Florian U. Bernlochner🇩🇪 · Heiko Lacker🇩🇪 · Zoltan Ligeti🇺🇸 · Iain W. Stewart🇺🇸 · Frank J. Tackmann🇩🇪 · Kerstin Tackmann🇩🇪

    We perform the first global fit to inclusive $B\to X_s\gamma$ measurements using a model-independent treatment of the nonperturbative $b$-quark distribution function, with next-to-next-to-leading logarithmic resummation and $\mathcal{O}({\alpha }_s^2)$ fixed-order contributions. The normalization of the $B\to X_s\gamma$ decay rate, given by $|C_7^{\mathrm{incl}}{V}_{tb}{V}_{ts}^{\ast }{|}^2$, is sensitive to physics beyond the Standard Model (SM). We determine $|C_7^{\mathrm{incl}}{V}_{tb}{V}_{ts}^{\ast }|=(14.77\pm 0.51_{\mathrm{fit}}\pm 0.59_{\mathrm{theory}}\pm 0.08_{\mathrm{param}})\times 10^{-3}$, in good agreement with the SM prediction, and the $b$-quark mass $m_b^{1S}=(4.750\pm 0.027_{\mathrm{fit}}\pm 0.033_{\mathrm{theory}}\pm 0.003_{\mathrm{param}})\mathrm{GeV}$. Our results suggest that the uncertainties in the extracted $B\to X_s\gamma$ rate have been underestimated by up to a factor of two, leaving more room for beyond-SM contributions.

    hep-phhep-exnucl-thPRL(2021)·59 citations
19. 19*

    A Singlet Dark Matter in the SU(6)/SO(6) Composite Higgs Model

    Haiying Cai🇰🇷 · Giacomo Cacciapaglia🇫🇷

    Singlet scalar Dark Matter can naturally arise in composite Higgs models as an additional stable pseudo-Nambu-Goldstone boson. We study the properties of such a candidate in a model based on $SU(6)/SO(6)$, with the light quark masses generated by 4-fermion interactions. The presence of non-linearities in the couplings allows to saturate the relic density for masses $400<m_{\mathrm{DM}}<1000$ GeV, and survive the bound from Direct Detection and Indirect Detection. The viable parameter regions are in reach of the sensitivities of future upgrades, like XENONnT and LZ.

    hep-phPRD(2021)·25 citations
20. 20*

    A linear seesaw model with $A_4$-modular flavor and local $U(1{)}_{B-L}$ symmetries

    Takaaki Nomura🇰🇷 · Hiroshi Okada🇰🇷

    We discuss a linear seesaw model with local $U(1{)}_{B-L}$ and modular $A_4$ symmetries. The neutrino mass matrix for linear seesaw mechanism is realized by $U(1{)}_{B-L}$ charge assignment and the nature of modular $A_4$ symmetry. We formulate neutrino mass and carry our numerical analysis showing some predictions for observables in neutrino sector. Remarkably, the case of inverted neutrino mass ordering (IO) is realized by a specific region around $\tau =\omega =e^{2\pi i/3}$, which is favored by a string theory. Thus, our prediction would be very strong in case of IO.

    hep-phJCAP(2022)·64 citations
21. 21*

    Three dimensional Yukawa models and CFTs at strong and weak couplings

    Marcus Benghi Pinto🇧🇷

    The massless three dimensional Gross-Neveu-Yukawa (GNY) and Nambu--Jona-Lasinio--Yukawa (NJLY) models at finite temperatures are analyzed within the mean field framework considering all coupling values. When the number of Dirac fermions is taken to be $N_f=1/4$ (GNY) and $N_f=1/2$ (NJLY) these models relate to the supersymmetric Wess-Zumino (WZ) theory with cubic superpotential and one superfield. In this case the results show that the strong-weak entropy density ratio decreases from the Stefan-Boltzmann value, in the weak limit, to $s/s_{free}=31/35$ at strong couplings. This value agrees with the one recently obtained by applying the large-$N$ approximation to the supersymmetric $O(N)$ WZ model with quartic superpotential and $N$ superfields. When $N_f=0$ one obtains $s/s_{free}=4/5$ recovering, as expected, the ratio predicted in the context of the $O(N)$ scalar model. However, contrary to the $O(N)$ WZ model the simple Yukawa models analyzed here do not behave as CFTs for all couplings since the conformal measure exactly vanishes only at the extreme weak and strong limits although the speed of sound indicates that the deviation, at intermediate couplings, appears to be rather small. By comparing the thermal masses behavior in each case one can trace this difference as being a consequence that in the GNY/NJLY case the fermionic mass vanishes for all couplings while within the $O(N)$ WZ it only vanishes at the weak and strong limits. On the other hand, the Yukawa bosonic dimensionless masses display a more universal behavior decreasing from $2\ln [(1+\sqrt{5})/2]$, at infinite coupling, to zero (at vanishing coupling).

    ↳ hep-thhep-phPRD(2020)·10 citations
22. 22*

    Eternal inflation in light of Wheeler-DeWitt equation

    Min-Seok Seo🇰🇷

    The Wheeler-DeWitt equation provides the probability distribution for the curvature perturbation, the gauge invariant quantum fluctuation of the inflaton. From this, we can find a tower of power spectra which is not found in a perturbative approach. Since the power spectrum for the modes that cross the horizon contributes to the uncertainty in the classical inflaton displacement, we obtain new conditions for eternal inflation. In the presence of the patch in the higher excitations, the bound on the slow-roll parameter allowing eternal inflation is given by at most $ϵ\lesssim (2n+1)(H/m_{\mathrm{Pl}}{)}^2$ with $n$ integer indicating the quantum number labelling the excitation. For large $n$, the bound on $ϵ$ is relaxed such that eternal inflation can take place with even larger value of $ϵ$. While the second law of thermodynamics implies that $n=0$ state is preferred, we cannot ignore such large $n$ effect since the nonlinear interaction inducing transitions to the $n=0$ state is suppressed.

    ↳ hep-thastro-ph.COgr-qchep-phJCAP(2020)·11 citations
23. 23*

    Properties of the QCD thermal transition with $N_f=2+1$ flavours of Wilson quark

    G. Aarts🇬🇧 · C. Allton🇬🇧 · J. Glesaaen🇬🇧 · S. Hands🇬🇧 · B. Jäger🇩🇰 · S. Kim🇰🇷 · M. P. Lombardo🇮🇹 · A. A. Nikolaev🇬🇧 · S. M. Ryan🇮🇪 · J.-I. Skullerud🇮🇪 · L.-K. Wu🇨🇳

    We study properties of the thermal transition in QCD, using anisotropic, fixed-scale lattice simulations with $N_f=2+1$ flavours of Wilson fermion. Observables are compared for two values of the pion mass, focusing on chiral properties. Results are presented for the Polyakov loop, various susceptibilities, the chiral condensate and its susceptibility, and the onset of parity doubling in the light and strange baryonic sector.

    ↳ hep-lathep-phnucl-thPRD(2022)·55 citations
24. 24*

    Pion interferometry at 200 GeV using anisotropic hydrodynamics

    Mubarak Alqahtani🇸🇦 · Michael Strickland🇺🇸

    In this paper, we continue our phenomenological studies of heavy-ion collisions using 3+1d anisotropic hydrodynamics (aHydro). In previous works, we compared quasiparticle aHydro (aHydroQP) with ALICE 2.76 TeV Pb-Pb and RHIC 200 GeV Au-Au collision results. At both energies, the agreement was quite good between aHydroQP and the experimental data for many observables. In this work, we present comparisons of the Hanbury Brown--Twiss (HBT) radii and their ratios determined using pi+ pi+ pairs produced in 200 GeV Au-Au collisions. We first present comparisons with STAR results for the HBT radii and their ratios. We then present comparisons with PHENIX results for the HBT radii and their ratios. In both cases, we find reasonable agreement between aHydroQP predictions and available experimental results for the ratios of HBT radii. At the level of the radii themselves, in some cases quantitative differences on the order of 10-20% remain, which deserve further study.

    ↳ nucl-thhep-phPRC(2020)·15 citations
25. 25*

    Comment on "Braneworld Effective Field Theories -- Holography, Consistency and Conformal Effects"

    Florian Nortier🇫🇷

    Several arguments given in arXiv:1912.12316 suggest that braneworld effective models with fields strictly localized on $\delta$-like branes cannot be UV-completed by a fundamental theory including gravity, i.e. they belong to the Swampland. It is concluded that one should instead only consider models with quasilocalized zero-modes of higher-dimensional fields. In this comment, the arguments are critically reviewed, and various loopholes are proposed. Beyond that, the main point that is discussed is the notion of effective brane form factors, which are required when the singular behavior of the branes is softened in the UV-completion.

    ↳ hep-thhep-ph3 citations
26. 26*

    Radial oscillations and stability of multiple-fluid compact stars

    Ben Kain🇺🇸

    I derive a system of pulsation equations for compact stars made up of an arbitrary number of perfect fluids that can be used to study radial oscillations and stability with respect to small perturbations. I assume spherical symmetry and that the only inter-fluid interactions are gravitational. My derivation is in line with Chandrasekhar's original derivation for the pulsation equation of a single-fluid compact star and keeps the contributions from the individual fluids manifest. I illustrate solutions to the system of pulsations equations with one-, two-, and three-fluid examples.

    ↳ gr-qcastro-ph.HEhep-phPRD(2020)·38 citations
27. 27*

    Harmonic Hybrid Inflation

    Federico Carta🇩🇪 · Nicole Righi🇩🇪 · Yvette Welling🇩🇪 · Alexander Westphal🇩🇪

    We present a mechanism for realizing hybrid inflation using two axion fields with a purely non-perturbatively generated scalar potential. The structure of scalar potential is highly constrained by the discrete shift symmetries of the axions. We show that harmonic hybrid inflation generates observationally viable slow-roll inflation for a wide range of initial conditions. This is possible while accommodating certain UV arguments favoring constraints $f\lesssim M_{\mathrm{P}}$ and $\Delta {\varphi }_{60}\lesssim M_{\mathrm{P}}$ on the axion periodicity and slow-roll field range, respectively. We discuss controlled ${\mathbb{Z}}_2$-symmetry breaking of the adjacent axion vacua as a means of avoiding cosmological domain wall problems. Including a minimal form of ${\mathbb{Z}}_2$-symmetry breaking into the minimally tuned setup leads to a prediction of primordial tensor modes with the tensor-to-scalar ratio in the range $10^{-4}\lesssim r\lesssim 0.01$, directly accessible to upcoming CMB observations. Finally, we outline several avenues towards realizing harmonic hybrid inflation in type IIB string theory.

    ↳ hep-thastro-ph.COhep-phJHEP(2020)·17 citations
28. 28*

    Moduli Stabilisation and the Statistics of SUSY Breaking in the Landscape

    Igor Broeckel🇮🇹 · Michele Cicoli🇮🇹 · Anshuman Maharana🇮🇳 · Kajal Singh🇮🇳 · Kuver Sinha🇺🇸

    The statistics of the supersymmetry breaking scale in the string landscape has been extensively studied in the past finding either a power-law behaviour induced by uniform distributions of F-terms or a logarithmic distribution motivated by dynamical supersymmetry breaking. These studies focused mainly on type IIB flux compactifications but did not systematically incorporate the Kähler moduli. In this paper we point out that the inclusion of the Kähler moduli is crucial to understand the distribution of the supersymmetry breaking scale in the landscape since in general one obtains unstable vacua when the F-terms of the dilaton and the complex structure moduli are larger than the F-terms of the Kähler moduli. After taking Kähler moduli stabilisation into account, we find that the distribution of the gravitino mass and the soft terms is power-law only in KKLT and perturbatively stabilised vacua which therefore favour high scale supersymmetry. On the other hand, LVS vacua feature a logarithmic distribution of soft terms and thus a preference for lower scales of supersymmetry breaking. Whether the landscape of type IIB flux vacua predicts a logarithmic or power-law distribution of the supersymmetry breaking scale thus depends on the relative preponderance of LVS and KKLT vacua.

    ↳ hep-thhep-phJHEP(2021)·37 citations
29. 29*

    Increasing Temperature toward the Completion of Reheating

    Raymond T. Co🇺🇸 · Eric Gonzalez🇺🇸 · Keisuke Harigaya🇺🇸

    Reheating is a process where the energy density of a dominant component of the universe other than radiation, such as a matter component, is transferred into radiation. It is usually assumed that the temperature of the universe decreases due to cosmic expansion even during the reheating process, in which case the maximal temperature of the universe is much higher than the reheat temperature. We point out that the temperature of the universe during reheating may in fact increase in well-motivated scenarios. We derive the necessary conditions for the temperature to increase during reheating and discuss concrete examples involving a scalar field. We comment on implications for particle physics and cosmology due to an increasing temperature during reheating.

    ↳ astro-ph.COhep-phJCAP(2020)·58 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.