Tue·Sep 8, 2020Tuesday·September 8, 2020

1. 01*

   Quarkonium Semiclassical Transport in Quark-Gluon Plasma: Factorization and Quantum Correction

   Xiaojun Yao🇺🇸 · Thomas Mehen🇺🇸

   We study quarkonium transport in the quark-gluon plasma by using the potential nonrelativistic QCD (pNRQCD) effective field theory and the framework of open quantum systems. We argue that the coupling between quarkonium and the thermal bath is weak using separation of scales, so the initial density matrix of the total system factorizes and the time evolution of the subsystem is Markovian. We derive the semiclassical Boltzmann equation for quarkonium by applying a Wigner transform to the Lindblad equation and carrying out a semiclassical expansion. We resum relevant interactions to all orders in the coupling constant at leading power of the nonrelativistic and multipole expansions. The derivation is valid for both weakly coupled and strongly coupled quark-gluon plasmas. We find reaction rates in the transport equation factorize into a quarkonium dipole transition function and a chromoelectric gluon distribution function. For the differential reaction rate, the definition of the momentum dependent chromoelectric gluon distribution function involves staple-shaped Wilson lines. For the inclusive reaction rate, the Wilson lines collapse into a straight line along the real time axis and the distribution becomes momentum independent. The relation between the two Wilson lines is analogous to the relation between the Wilson lines appearing in the gluon parton distribution function (PDF) and the gluon transverse momentum dependent parton distribution function (TMDPDF). The centrality dependence of the quarkonium nuclear modification factor measured by experiments probes the momentum independent distribution while the transverse momentum dependence and measurements of the azimuthal angular anisotropy may be able to probe the momentum dependent one. We discuss one way to indirectly constrain the quarkonium in-medium real potential by using the factorization formula and lattice calculations. The leading quantum correction to the semiclassical transport equation of quarkonium is also worked out. The study can be easily generalized to quarkonium transport in cold nuclear matter, which is relevant for quarkonium production in eA collisions in the future Electron-Ion Collider.

   hep-phnucl-thJHEP(2021)·74 citations
2. 02*

   The Effects of Primordial Black Holes on Dark Matter Models

   Paolo Gondolo🇺🇸 · Pearl Sandick🇺🇸 · Barmak Shams Es Haghi🇺🇸

   We investigate the effects of producing dark matter by Hawking evaporation of primordial black holes (PBHs) in scenarios that may have a second well-motivated dark matter production mechanism, such as freeze-out, freeze-in, or gravitational production. We show that the interplay between PBHs and the alternative sources of dark matter can give rise to model-independent modifications to the required dark matter abundance from each production mechanism, which in turn affect the prospects for dark matter detection. In particular, we demonstrate that for the freeze-out mechanism, accounting for evaporation of PBHs after freeze-out demands a larger annihilation cross section of dark matter particles than its canonical value for a thermal dark matter. For mechanisms lacking thermalization due to a feeble coupling to the thermal bath, we show that the PBH contribution to the dark matter abundance leads to the requirement of an even feebler coupling. Moreover, we show that when a large initial abundance of PBHs causes an early matter-dominated epoch, PBH evaporation alone cannot explain the whole abundance of dark matter today. In this case, an additional production mechanism is required, in contrast to the case when PBHs are formed and evaporate during a radiation-dominated epoch.

   hep-phastro-ph.COgr-qcPRD(2020)·152 citations
3. 03*

   Monte-Carlo Based QCD Sum Rules Analysis of $X_0(2900)$ and $X_1(2900)$

   Halil Mutuk🇹🇷

   Motivated by the very recent discovery of fully open-flavor exotic states $X_0(2900)$ and $X_1(2900)$ by the LHCb Collaboration, we study possible interpretations of these exotic states by QCD Sum Rules method. We have calculated mass and decay constant by traditional QCD Sum Rules analysis and Monte-Carlo based analysis. $X_0(2900)$ and $X_1(2900)$ are studied in molecular and diquark-antidiquark tetraquark pictures, respectively. Obtained mass results agree well with the masses observed in the experiment. We also made a Monte-Carlo based analysis within QCD Sum Rules for the mass and decay constant distributions to investigate the possible assignments for the structures of $X_0(2900)$ and $X_1(2900)$.

   hep-phhep-exJ.Phys.G(2021)·37 citations
4. 04*

   Scotogenic neutrino masses and dark matter stability from residual gauge symmetry

   Julio Leite🇧🇷 · Oleg Popov🇰🇷 · Rahul Srivastava🇮🇳 · José W. F. Valle🇪🇸

   In the context of the $\mathrm{SU}(3{)}_{\mathrm{c}}\otimes \mathrm{SU}(3{)}_{\mathrm{L}}\otimes \mathrm{U}(1{)}_{\mathrm{X}}\otimes \mathrm{U}(1{)}_{\mathrm{N}}$ (3-3-1-1) extension of the standard model, we show how the spontaneous breaking of the gauge symmetry gives rise to a residual symmetry which accounts for dark matter stability and small neutrino masses in a scotogenic fashion. As a special feature, the gauge structure implies that one of the light neutrinos is massless and, as a result, there is a lower bound for the $0\nu \beta \beta$ decay rate.

   hep-ph0 citations
5. 05*

   Precision calculations of the double radiative bottom-meson decays in soft-collinear effective theory

   Yue-Long Shen🇨🇳 · Yu-Ming Wang🇨🇳 · Yan-Bing Wei🇨🇳

   Employing the systematic framework of soft-collinear effective theory (SCET) we perform an improved calculation of the leading-power contributions to the double radiative $B_{d,s}$-meson decay amplitudes in the heavy quark expansion. We then construct the QCD factorization formulae for the subleading power contributions arising from the energetic photon radiation off the constituent light-flavour quark of the bottom meson at tree level. Furthermore, we explore the factorization properties of the subleading power correction from the effective SCET current $J^{(A2)}$ at $\mathcal{O}({\alpha }_s^0)$. The higher-twist contributions to the $B_{d,s}\to \gamma \gamma$ helicity form factors from the two-particle and three-particle bottom-meson distribution amplitudes are evaluated up to the twist-six accuracy. In addition, the subleading power weak-annihilation contributions from both the current-current and QCD penguin operators are taken into account at the one-loop accuracy. We proceed to apply the operator-production-expansion-controlled dispersion relation for estimating the power-suppressed soft contributions to the double radiative $B_{d,s}$-meson decay form factors. Phenomenological explorations of the radiative $B_{d,s}\to \gamma \gamma$ decay observables in the presence of the neutral-meson mixing, including the CP-averaged branching fractions, the polarization fractions and the time-dependent CP asymmetries, are carried out subsequently with an emphasis on the numerical impacts of the newly computed ingredients together with the theory uncertainties from the shape parameters of the HQET bottom-meson distribution amplitudes.

   hep-phhep-exhep-latJHEP(2020)·31 citations
6. 06*

   QCD vacuum and baryon masses

   Youngman Kim🇰🇷 · Igor A. Mazur🇰🇷 · Masayasu Harada🇯🇵 · Hyun Kyu Lee🇰🇷

   To study a possible role of the quantum chromodynamics (QCD) vacuum in nuclear and hadron physics, we evaluate a physical quantity in a candidate of the QCD vacuum. In this study we adopt the Copenhagen (spaghetti) picture of the QCD vacuum and calculate the ground-state baryon masses in a constituent quark model. We find that the calculated baryon mass does depend on a parameter that characterizes the Copenhagen picture of the QCD vacuum and satisfies the Gell-Mann-Okubo mass relation for the baryon octet. We also observe that the effective constituent quark mass defined in this study contains a contribution attributed to the Copenhagen vacuum, that is the gluon background field. We then estimate the value of the background gluon field as a function of the up (down) constituent quark mass by using the baryon masses as inputs.

   hep-phnucl-thIJMPE(2023)·1 citation
7. 07*

   The PQCD approach towards to next-to-leading order: a short review

   Shan Cheng🇨🇳 · Zhen-jun Xiao🇨🇳

   In this short review we elaborate the significance of resummation in $k_T$ factorization theorem, and summarize the recent progresses in the calculations of the next-to-leading order contributions to B meson decays from the perturbative QCD (PQCD) approach. We also comment on the current status of the PQCD approach and highlight some key issues to develop it in the near future for more phenomenological applications.

   hep-phFront.Phys.(Beijing)(2021)·11 citations
8. 08*

   Resolving the spacetime structure of jets with medium

   Adam Takacs🇳🇴 · Daniel Pablos🇳🇴 · Konrad Tywoniuk🇳🇴

   Away from the strictly soft and collinear limit of QCD radiation the choice of evolution scale in a parton shower algorithm is ambiguous and several options have been implemented in existing Monte Carlo event generators for proton-proton collisions. However, the resulting space-time evolution could result in subtle differences depending on the particular choice. In this work we quantify measurable consequences of the choice of the evolution variable and show how the implications of such a choice propagates into jet quenching observables. We develop a parton shower algorithm for a general evolution variable, that includes as special cases the virtuality, angle, transverse momentum and formation time. We study the interplay between the shower history for different evolution variables and the phase space affected by parton energy loss. In particular, we implement effects of jet quenching in the dense limit and highlight the role of color coherence effects. We compare the results of the different ordering variables to existing Monte Carlo shower implementations on the parton level by analyzing primary Lund planes. Finally, we study the sensitivity of quenched jets to the choice of evolution variable by confronting our results for a certain key observable, such as the jet mass.

   hep-phhep-exnucl-thPoS(2021)·1 citation
9. 09*

   Energy loss and equilibration of jets in a QCD plasma

   Soeren Schlichting🇩🇪 · Ismail Soudi🇩🇪

   We investigate the medium induced fragmentation of jets in a high-temperature QCD plasma. Based on an effective kinetic theory of QCD, we study the non-equilibrium evolution of the jet shower and the chemical equilibration of jet fragments in the medium. By including radiative emissions as well as elastic interactions, our approach extends all the way from the jet energy scale to the temperature of the medium and includes important effects such as the recoil of the medium. We present results for the in-medium fragmentation, including chemical and kinetic equilibration of the soft fragments and discuss implications of our result to jet quenching physics and the problem of thermalization of the quark-gluon plasma in heavy ion collisions.

   hep-phnucl-thPoS(2021)·1 citation
10. 10*

    Little-Bang and Femto-Nova in Nucleus-Nucleus Collisions

    Kenji Fukushima🇯🇵 · Bedangadas Mohanty🇮🇳 · Nu Xu🇺🇸

    We make a theoretical and experimental summary of the state-of-the-art status of hot and dense QCD matter studies on selected topics. We review the Beam Energy Scan program for the QCD phase diagram and present the current status of search for QCD Critical Point, particle production in high baryon density region, hypernuclei production, and global polarization effects in nucleus-nucleus collisions. The available experimental data in the strangeness sector suggests that a grand canonical approach in thermal model at high collision energy makes a transition to the canonical ensemble behavior at low energy. We further discuss future prospects of nuclear collisions to probe properties of baryon-rich matter. Creation of a quark-gluon plasma at high temperature and low baryon density has been called the "Little-Bang" and, analogously, a femtometer-scale explosion of baryon-rich matter at lower collision energy could be called the "Femto-Nova", which may possibly sustain substantial vorticity and magnetic field for non-head-on collisions.

    hep-phhep-exnucl-thAAPPS Bull.(2021)·52 citations
11. 11*

    The complete study on polarization of ${\rm Y}(nS)$ hadroproduction at QCD next-to-leading order

    Yu Feng🇨🇳 · Bin Gong🇨🇳 · Chao-Hsi Chang🇨🇳 · Jian-Xiong Wang🇨🇳

    Applying the nonrelativistic quantum chromodynamics factorization formalism to the ${\rm Y}(1S,2S,3S)$ hadroproduction, a complete analysis on the polarization parameters ${\lambda }_{\theta }$, ${\lambda }_{\theta \varphi }$, ${\lambda }_{\varphi }$ for the production are presented at QCD next-to-leading order. With the long-distance matrix elements extracted from experimental data for the production rate and polarization parameter ${\lambda }_{\theta }$ of ${\rm Y}$ hadroproduction, our results provide a good description for the measured parameters ${\lambda }_{\theta \varphi }$ and ${\lambda }_{\varphi }$ in both the helicity and the Collins-Soper frames. In our calculations the frame invariant parameter $\tilde{\lambda }$ is consistent in the two frames. Finally, it is pointed out that there are discrepancies for $\tilde{\lambda }$ between available experimental data and corresponding theoretical predictions.

    hep-phCPC(2021)·15 citations
12. 12*

    Stealth decaying spin-1 dark matter

    Cédric Delaunay🇫🇷 · Teng Ma🇮🇱 · Yotam Soreq🇮🇱

    We consider models of decaying spin-1 dark matter whose dominant coupling to the standard model sector is through a dark-Higgs Yukawa portal connecting a TeV-scale vector-like lepton to the standard model (right-handed) electron. Below the electron-positron threshold, dark matter has very slow, loop-suppressed decays to photons and (electron) neutrinos, and is stable on cosmological time-scale for sufficiently small gauge coupling values. Its relic abundance is set by in-equilibrium dark lepton decays, through the freeze-in mechanism. We show that this model accommodates the observed dark matter abundance for natural values of its parameters and a dark matter mass in the ~5keV to 1MeV range, while evading constraints from direct detection, indirect detection, stellar cooling and cosmology. We also consider the possibility of a nonzero gauge kinetic mixing with the standard model hypercharge field, which is found to yield a mild impact on the model's phenomenology.

    hep-phJHEP(2021)·19 citations
13. 13*

    Heavy quark radiative energy loss in nuclei within the improved high-twist approach

    Yi-Lun Du🇳🇴

    In this proceedings, we review our recent work on the heavy quark radiative energy loss in nuclei due to multiple parton scattering within the recently improved high-twist approach, where gauge invariance can be ensured by a delicate setup of the initial partons' transverse momenta. Our new result is consistent with the previous calculations of light quark energy loss in the massless limit and heavy quark energy loss in the soft gluon radiation limit, respectively. We show numerically the correction to the heavy quark energy loss as compared with previous result and with soft gluon radiation approximation. The necessity to go beyond soft gluon radiation limit is demonstrated for a global description of light and heavy flavor data in heavy-ion collisions.

    hep-phPoS(2021)·0 citations
14. 14*

    Jet quenching and scaling properties of medium-evolved gluon cascade in expanding media

    Souvik Priyam Adhya🇨🇿 · Carlos A. Salgado🇪🇸 · Martin Spousta🇨🇿 · Konrad Tywoniuk🇳🇴

    We present a study of the impact of the expansion of deconfined medium on single-gluon emission spectra and the jet suppression factor ($Q_{AA}$) within the BDMPS-Z formalism. These quantities are calculated for three types of media (static medium, exponentially decaying medium and Bjorken expanding medium). The distribution of medium-induced gluons and the jet $Q_{AA}$ are calculated using the evaluation of in-medium evolution with splitting kernels derived from the gluon emission spectra. Scaling behavior of splitting kernels is derived for low-x and high-x regimes in the asymptote of large times and its impact on the resulting jet $Q_{AA}$ is discussed. For the full phase space of the radiation, the scaling of jet $Q_{AA}$ with an effective quenching parameter is presented.

    hep-phPoS(2021)·2 citations
15. 15*

    Planck-scale deformation of CPT and particle lifetimes

    Michele Arzano🇮🇹 · Jerzy Kowalski-Glikman🇵🇱 · Wojciech Wislicki🇵🇱

    We carry out a systematic study of the bounds that can be set on Planck-scale deformations of relativistic symmetries and CPT from precision measurements of particle and antiparticle lifetimes. Elaborating on our earlier work [1] we discuss a new form of departure from CPT invariance linked to the possibility of a non-trivial geometry of four-momentum and its consequences for the particle and antiparticle mass-shells and decay probabilities. Our main result is a collection of experimental bounds that can be obtained for the deformation parameter of the theoretical model under consideration based on current data and sensitivities of planned experiments at high energies.

    hep-phgr-qchep-th13 citations
16. 16*

    On the extraction of the valence transversity distributions from SIDIS data

    M. Anselmino🇮🇹 · R. Kishore🇮🇳 · A. Mukherjee🇮🇳

    The transversity distribution for $u$ and $d$ quarks is usually extracted from data on spin asymmetries in Semi Inclusive Deep Inelastic Scattering (SIDIS): however, due to its chiral odd nature, it has to be coupled to another chiral odd function, typically the Collins or the di-hadron fragmentation function. A recent suggestion of considering SIDIS data involving ratios of spin asymmetries and avoiding a knowledge of the Collins function, is briefly discussed. New measurements, involving ratios of cross sections, are suggested. They would allow a direct extraction of the transversity ratio, $h_1^{d_V}/h_1^{u_V}$. Numerical estimates are given.

    hep-phPRD(2020)·5 citations
17. 17*

    Flavoured Resonant Leptogenesis at Sub-TeV Scales

    A. Granelli🇮🇹 · K. Moffat🇬🇧 · S. T. Petcov🇮🇹

    We consider sub-TeV scale flavoured resonant leptogenesis within the minimal type-I seesaw scenario with two right-handed singlet neutrinos $N_{1,2}$ forming a pseudo-Dirac pair, concentrating on the case of masses of the pseudo-Dirac pair having values $M_{1,2}\lesssim 100$ GeV. The case when the CP violating asymmetries in the individual lepton charges $L_l$, $l=e,\mu ,\tau$, and in the total lepton charge $L$ of the Universe are generated in $1\leftrightarrow 2$ decay processes is investigated. We show that successful leptogenesis is possible for $M_{1,2}$ lying in the interval $M_{1,2}=(0.3-100)$ GeV. Our results show also, in particular, that for vanishing initial $N_{1,2}$ abundance, flavour effects can play an important role in the generation of the baryon asymmetry, leading to an enhancement of the asymmetry by a factor up to $\sim 300$ with respect to the "unflavoured" leptogenesis scenario.

    hep-phNPB(2021)·43 citations
18. 18*

    Exploring the role of new physics in $b\to u\tau \bar{\nu }$ decays

    Aishwarya Bhatta🇮🇳 · Atasi Ray🇮🇳 · Rukmani Mohanta🇮🇳

    The recent measurements on $R_D$, $R_{D^{\ast }}$ and $R_{J/\psi }$ by three pioneering experiments, BaBar, Belle and LHCb, indicate that the notion of lepton flavour universality is violated in the weak charged-current processes, mediated through $b\to c\ell {\bar{\nu }}_{\ell }$ transitions. These intriguing results, which delineate a tension with their standard model predictions at the level of $(2-3)\sigma$ have triggered many new physics propositions in recent times, and are generally attributed to the possible implication of new physics in $b\to c\tau \bar{\nu }$ transition. This, in turn, opens up another avenue, i.e., $b\to u\tau \bar{\nu }$ processes, to look for new physics. Since these processes are doubly Cabibbo suppressed, the impact of new physics could be significant enough, leading to sizeable effects in some of the observables. In this work, we investigate in detail the role of new physics in $B\to (\pi ,\rho ,\omega )\tau \bar{\nu }$ and $B_s\to (K,K^{\ast })\tau \bar{\nu }$ processes considering a model independent approach. In particular, we focus on the standard observables like branching fraction, lepton flavour non-universality (LNU) parameter, forward-backward asymmetry and polarization asymmetries. We find significant deviations in some of these observables, which can be explored by the currently running experiments LHCb and Belle-II. We also briefly comment on the impact of scalar leptoquark $R_2(3,2,7/6)$ and vector leptoquark $U_1(3,1,2/3)$ on these decay modes.

    hep-phPTEP(2021)·3 citations
19. 19*

    Impact of LHCb 13 TeV $W$ and $Z$ pseudo-data on the Parton Distribution Functions

    Qilin Deng🇨🇳 · Qundong Han🇨🇳 · Hang Yin🇨🇳 · Sayipjamal Dulat🇨🇳 · Tie-Jiun Hou🇨🇳 · C.-P. Yuan🇺🇸

    We study the potential of the LHCb 13 TeV single $W^{\pm }$ and $Z$ boson pseudo-data for constraining the parton distribution functions (PDFs) of the proton. As an example, we demonstrate the sensitivity of the LHCb 13 TeV data, collected with integrated luminosities of 5 fb${}^{-1}$ and 300 fb${}^{-1}$, to reducing the PDF uncertainty bands of the CT14HERA2 PDFs, using the error PDF updating package {\sc ePump}. The sensitivities of various experimental observables are compared. Generally, sizable reductions in PDF uncertainties can be observed in the 300 fb${}^{-1}$ data sample, particularly in the small-$x$ region. The double-differential cross section measurement of $Z$ boson $p_T$ and rapidity can greatly reduce the uncertainty bands of $u$ and $d$ quarks in almost the whole $x$ range, as compared to various single observable measurements.

    hep-phCPC(2021)·9 citations
20. 20*

    One-loop radiative corrections to $e^{+}{e}^{-}\to Z{h}^0/H^0{A}^0$ in the Inert Higgs Doublet Model

    Hamza Abouabid🇲🇦 · Abdesslam Arhrib🇲🇦 · Rachid Benbrik🇲🇦 · Jaouad El Falaki🇲🇦 · Bin Gong🇨🇳 · Wenhai Xie🇨🇳 · Qi-Shu Yan🇨🇳

    We compute the full one-loop radiative corrections (including both weak and QED corrections) for two processes $e^{+}{e}^{-}\to Z{h}^0,H^0{A}^0$ in the Inert Higgs Doublet model (IHDM). Up to $O({\alpha }_w)$ and $O({\alpha }_{em})$ order, we use FeynArts/FormCalc to compute the one-loop virtual corrections and Feynman Diagram Calculation (FDC) to evaluate the real emission, respectively. Being equipped with these computing tools, we investigate radiative corrections of new physics for both the degenerate and non-degenerate scenarios with three typical collision energies of future electron-positron colliders: 250 GeV, 500 GeV, and 1000GeV. By scanning the parameter space of IHDM, we identify the allowed regions which are consistent with constraints and bounds, from both theoretical and experimental sides. We find that the radiative corrections of the IHDM to $e^{+}{e}^{-}\to Z{h}^0$ can be sizeable and are within the detection potentials of future Higgs factories. We also find that the new physics of IHDM could also be directly detected by observing the process $e^{+}{e}^{-}\to H^0{A}^0$ which could have large enough production rate. We propose five benchmark points and examine their salient features which can serve as physics targets for future electron-positron colliders, such as CEPC/CLIC/FCC-ee/ILC as well as for LHC.

    hep-phJHEP(2021)·28 citations
21. 21*

    Chiral phase transition and kaon-to-pion ratios in the entanglement SU(3) PNJL model

    D. Blaschke🇵🇱 · A.V. Friesen🇷🇺 · Yu.L. Kalinovsky🇷🇺 · A. Radzhabov🇷🇺

    Within the three-flavor PNJL and EPNJL chiral quark models we have obtained pseudoscalar meson properties in quark matter at finite temperature $T$ and baryochemical potential ${\mu }_B$. We compare the meson pole (Breit-Wigner) approximation with the Beth-Uhlenbeck (BU) approach that takes into account the continuum of quark-antiquark scattering states when determining the partial densities of pions and kaons. We evaluate the kaon-to-pion ratios along the (pseudo-)critical line in the $T-{\mu }_B$ plane as a proxy for the chemical freezeout line, whereby the variable $x=T/{\mu }_B$ is introduced that corresponds to the conserved entropy per baryon as initial condition for the heavy-ion collision experiments. We present a comparison with the experimental pattern of kaon-to-pion ratios within the BU approach and using $x$-dependent pion and strange quark potentials. A sharp "horn" effect in the energy dependence $K^{+}/{\pi }^{+}$ ratio is explained by the enhanced pion production at energies above $\sqrt{s_{NN}}=8$ GeV, when the system enters the regime of meson dominance. This effect is in line with the enhancement of low-momentum pion spectra that is discussed as a precursor of the pion Bose condensation and entails the occurrence of a nonequilibrium pion chemical potential of the order of the pion mass. We elucidate that the horn effect is not related to the existence of a critical endpoint in the QCD phase diagram.

    hep-phhep-exnucl-thEur.Phys.J.ST(2020)·5 citations
22. 22*

    $CP$ asymmetries in the rare top decays $t\to c\gamma$ and $t\to cg$

    Shyam Balaji🇦🇺

    The rare radiative flavour changing top decays $t\to c\gamma$ and $t\to cg$ (and the even rarer $t\to u\gamma$ and $t\to ug$) have been processes of interest for decades as they offer a key probe for studying top quark properties. However an explicit analytical study of the branching ratios and $CP$ asymmetries resulting from these loop level processes has thus far evaded attention. In this work, we provide the formulation for the $CP$ asymmetry resulting from the total kinetic contribution of the loop integrals and their imaginary parts, as well as an updated numerical computation of the predicted Standard Model (SM) branching fractions. These rare processes are suppressed in the SM by the Glashow-Iliopoulos-Maiani (GIM) mechanism. However, the results presented here can easily be exported for use in minimal extensions of the SM including vector-like quarks or in Two-Higgs-Doublet models where radiative fermionic decay processes can be enhanced relative to the SM by several orders of magnitude. Such processes provide an experimentally clean signature for new fundamental physics and can potentially be tested by current collider experiments. These topical beyond the SM theories are an elegant means to provide improved global fits to the latest results emerging from flavour physics, CKM and precision electroweak measurements.

    hep-phPRD(2020)·24 citations
23. 23*

    Disentangling Jet Modification

    Jasmine Brewer🇺🇸 · Quinn Brodsky🇺🇸 · Krishna Rajagopal🇺🇸

    Jet modification in heavy-ion collisions is an important probe of the nature and structure of the quark-gluon plasma (QGP) produced in these collisions and also encodes information about how the wakes that jets excite in a droplet of QGP form and relax. However, in experiment, one cannot know what a particular jet in a heavy ion collision would have looked like without quenching, making it difficult to interpret measurements in terms of individual jet modification. The goal of this Monte Carlo study is to gain insight into the modification of jet observables using the hybrid strong/weak coupling model of jet quenching as a test bed. In this Monte Carlo study (but not in experiment) it is possible to watch $\text{the same jet}$ as it evolves in vacuum or in QGP. We use this ability to disentangle the effects of modification of individual jets in heavy ion collisions vs. the effects of differing selection bias on the distribution of two observables: fractional energy loss and groomed $\Delta R$. We find that in the hybrid model the distribution of groomed $\Delta R$ appears to be unmodified in a sample of jets selected after quenching, as in heavy ion collisions, and confirm that this lack of modification arises because of a selection bias toward jets that lose only a small fraction of their energy. If instead we select jets in a way that avoids this bias, and then follow these selected jets as they are quenched, we show that there is, in fact, a substantial modification of the $\Delta R$ of individual jets. We show that this jet modification is principally due to the incorporation of particles coming from the wake that the parton shower excites in the plasma as a component of what an experimentalist reconstructs as a jet. The effects we discuss are substantial in magnitude, suggesting that our qualitative conclusions are more general than the Monte Carlo study in which we obtain them.

    hep-phnucl-thPoS(2021)·7 citations
24. 24*

    Fast Flavor Depolarization of Supernova Neutrinos

    Soumya Bhattacharyya (Tata Inst.)🇮🇳 · Basudeb Dasgupta (Tata Inst.)🇮🇳

    Flavor-dependent neutrino emission is critical to the evolution of a supernova and its neutrino signal. In the dense anisotropic interior of the star, neutrino-neutrino forward-scattering can lead to fast collective neutrino oscillations, which has striking consequences. We present a theory of fast flavor depolarization, explaining how neutrino flavor differences become smaller, i.e., depolarize, due to diffusion to smaller angular scales. We show that transverse relaxation determines the epoch of this irreversible depolarization. We give a method to compute the depolarized fluxes, presenting an explicit formula for simple initial conditions, which can be a crucial input for supernova theory and neutrino phenomenology.

    hep-phastro-ph.HEastro-ph.SRhep-exPRL(2021)·115 citations
25. 25*

    A tale of three diagonalizations

    Howard E. Haber🇺🇸

    In addition to the diagonalization of a normal matrix by a unitary similarity transformation, there are two other types of diagonalization procedures that sometimes arise in quantum theory applications -- the singular value decomposition and the Autonne-Takagi factorization. In these pedagogical notes, we carry out each of these diagonalization procedures for the most general $2\times 2$ matrices for which the corresponding diagonalization is possible and provide explicit analytical results in each of the three cases.

    hep-phquant-phInt.J.Mod.Phys.A(2021)·13 citations
26. 26*

    Constraints on jet quenching from a multi-stage energy-loss approach

    C. Park🇨🇦 · A. Angerami🇺🇸 · S. A. Bass🇺🇸 · S. Cao🇺🇸 · Y. Chen🇺🇸 · J. Coleman🇺🇸 · L. Cunqueiro🇺🇸 · T. Dai🇺🇸 · L. Du🇺🇸 · R. Ehlers🇺🇸 · H. Elfner🇩🇪 · D. Everett🇺🇸 and 38 other authors

    We present a multi-stage model for jet evolution through a quark-gluon plasma within the JETSCAPE framework. The multi-stage approach in JETSCAPE provides a unified description of distinct phases in jet shower contingent on the virtuality. We demonstrate a simultaneous description of leading hadron and integrated jet observables as well as jet $v_n$ using tuned parameters. Medium response to the jet quenching is implemented based on a weakly-coupled recoil prescription. We also explore the cone-size dependence of jet energy loss inside the plasma.

    ↳ nucl-thhep-exhep-phPoS(2021)·3 citations
27. 27*

    A closed-formula solution to the color-trace decomposition problem

    Ruggero Bandiera · Carlos R. Mafra

    In these notes we present a closed-formula solution to the problem of decomposing traces of Lie algebra generators into symmetrized traces and structure constants. The solution is written in terms of Solomon idempotents and exploits a projection derived by Solomon in his work on the Poincare-Birkhoff-Witt theorem.

    ↳ math.COhep-phhep-th5 citations
28. 28*

    Directed flow induced by electromagnetic fields in heavy ion collisions

    Yifeng Sun🇮🇹 · Salvatore Plumari🇮🇹 · Vincenzo Greco🇮🇹

    Strong electromagnetic fields are expected to be generated in off-central relativistic heavy ion collisions, which can induce a splitting of the directed flow of charged particles and anti-particles ($\Delta v_1$). Such a splitting manifests even for neutral charmed mesons pairs ($D^0,{\bar{D}}^0$), hence being a direct probe of the formation of deconfined phase with charm quarks as degree of freedom. In the limit of large $p_T$ and weak interaction with the QGP, a formula of $\Delta v_1(p_T,y_z)$ of charged particles and anti-particles as a function of $p_T$ and rapidity $y_z$ can be obtained, which is found to be related to the spectra of charged particles and the integrated effect of the Lorentz force. This formula is expected to be valid to heavy quarks and leptons at high $p_T$, where the modification to their equations of motion due to the interaction with both QGP and electromagnetic fields is small, and should have a general application. We also proposed a measurement of $\Delta v_1(p_T,y_z)$ of leptons from $Z^0$ decay and its correlation to that of $D$ mesons, which would be a strong probe determining whether the large splitting measured in experiments has the electromagnetic origin.

    ↳ nucl-thhep-exhep-phPoS(2021)·2 citations
29. 29*

    Measurements of heavy-flavor jets with ALICE at the LHC

    Ashik Ikbal Sheikh (for the ALICE Collaboration)🇮🇳

    Heavy quarks created in ultra-relativistic heavy-ion collisions are mostly produced in hard QCD processes during the early stages of the reaction. They interact with the hot and cold nuclear matter throughout the evolution of the medium via semi-hard and soft processes such as energy loss via gluon radiations and collisions. Nuclear modification of heavy flavors in p-A systems provides insight into cold nuclear matter effects such as (anti)shadowing and $k_T$-broadening, and serves as a baseline for A-A studies. In addition to that the fully reconstructed heavy-flavor jets provide additional information on the flavor (or mass) dependence of fragmentation, color charge effects as well as insight into the contribution of late gluon splitting. In this contribution, we present the measurements of $b$-jet production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and $c$-jet production in pp, p-Pb and Pb-Pb collisions measured by the ALICE experiment at the LHC. The measurements of the nuclear modification factors for $c$-jet in p-Pb and Pb-Pb collisions are also presented. The experimental measurements are compared with the results from Monte Carlo event generators (PYTHIA 6, PYTHIA 8 and Herwig 7) and the NLO pQCD calculations (POWHEG+PYTHIA6). We find good agreement of the measurements with the results from Monte Carlo event generators and from NLO pQCD calculations.

    ↳ nucl-exhep-phnucl-thNucl.Part.Phys.Proc.(2020)·3 citations
30. 30*

    Two phase reheating: CMB constraints on inflaton and dark matter phenomenology

    Md Riajul Haque🇮🇳 · Debaprasad Maity🇮🇳 · Pankaj Saha🇮🇳

    We propose a two-phase reheating scenario where the initial preheating dynamics is described by an effective dynamics followed by the standard perturbative reheating. Some of the important universal results of lattice simulation during preheating have been considered as crucial inputs in our two-phase dynamics. In this framework, detailed phenomenological constraints have been obtained on the inflaton couplings with reheating fields, and dark matter parameters in terms of CMB constrained inflationary scalar spectral index. It is observed that the conventional reheating scenario generically predicts the maximum reheating temperature $T_{re}^{max}\simeq 10^{15}$ GeV, corresponding to an almost instantaneous transition from the end of inflation to radiation domination. This fact will naturally lead to the problem of non-perturbative inflaton decay, which is in direct conflict with the perturbative reheating itself. Taking into account this by incorporating effective non-perturbative dynamics as the initial phase, our model of two-phase reheating scenarios also predicts model-independent maximum reheating temperature, which does not correspond to the instantaneous process. Further, $T_{re}^{max}$ is predicted to lie within $(10^{13},10^{10})$ GeV if CMB constraints on inflaton couplings with different reheating field are taken into account. We have further studied in detail the dark matter phenomenology in a model-independent manner and show how dark matter parameter space can be constrained through CMB parameters via the inflaton spectral index. Considering dark matter production during reheating via the Freeze-in mechanism, its parameter space has been observed to be highly constrained by our two-phase reheating than the constraints predicted by the conventional reheating scenarios, which are believed to theoretically incomplete.

    ↳ hep-thhep-phPRD(2020)·34 citations
31. 31*

    Three problems of superfluid dark matter and their solution

    Tobias Mistele🇩🇪

    In superfluid dark matter (SFDM), the phonon field plays a double role: It carries the superfluid's energy density and it mediates the MOND-like phonon force. We show that these two roles are in tension with each other on galactic scales: A MOND-like phonon force is in tension with a superfluid in equilibrium and with a significant superfluid energy density. To avoid these tensions, we propose a model where the two roles are split between two different fields. This also allows us to solve a stability problem in a more elegant way than standard SFDM. We argue that the standard estimates for the size of a galaxy's superfluid core need to be revisited.

    ↳ gr-qchep-phhep-thJCAP(2021)·10 citations
32. 32*

    Identifying the nature of the QCD transition in heavy-ion collisions with deep learning

    Yi-Lun Du🇳🇴 · Kai Zhou🇩🇪 · Jan Steinheimer🇩🇪 · Long-Gang Pang🇨🇳 · Anton Motornenko🇩🇪 · Hong-Shi Zong🇨🇳 · Xin-Nian Wang🇨🇳 · Horst Stoecker🇩🇪

    In this proceeding, we review our recent work using deep convolutional neural network (CNN) to identify the nature of the QCD transition in a hybrid modeling of heavy-ion collisions. Within this hybrid model, a viscous hydrodynamic model is coupled with a hadronic cascade "after-burner". As a binary classification setup, we employ two different types of equations of state (EoS) of the hot medium in the hydrodynamic evolution. The resulting final-state pion spectra in the transverse momentum and azimuthal angle plane are fed to the neural network as the input data in order to distinguish different EoS. To probe the effects of the fluctuations in the event-by-event spectra, we explore different scenarios for the input data and make a comparison in a systematic way. We observe a clear hierarchy in the predictive power when the network is fed with the event-by-event, cascade-coarse-grained and event-fine-averaged spectra. The carefully-trained neural network can extract high-level features from pion spectra to identify the nature of the QCD transition in a realistic simulation scenario.

    ↳ nucl-thhep-phNPA(2021)·5 citations
33. 33*

    Dielectric Skyrmions

    Sven Bjarke Gudnason🇨🇳

    We consider the dielectric Skyrme model proposed recently, with and without the addition of the standard pion mass term. Then we write down Bogomol'nyi-type energy bounds for both the massless and massive cases. We further show that, except for when taking the strict BPS limit, the Skyrmions are made of 3 orthogonal dipoles that can always be placed in their attractive channel and form bound states. Finally, we study the model numerically and discover that, long before realistic binding energies are reached, the Skyrmions become bound states of well-separated point-particle-like Skyrmions. By going sufficiently close to the BPS limit, we are able to obtain classical binding energies of realistic values compared with experiments.

    ↳ hep-thhep-phnucl-thPRD(2020)·10 citations
34. 34*

    Non-linear quantum effects in electromagnetic radiation of a vortex electron

    D.V. Karlovets🇷🇺 · A.M. Pupasov-Maksimov🇧🇷

    There is a controversy of how to interpret interactions of electrons with a large spatial coherence with light and matter. When such an electron emits a photon, it can do so either as if its charge were confined to a point within a coherence length, the region where a square modulus of a wave function $|\psi {|}^2$ is localized, or as a continuous cloud of space charge spread over it. This problem was addressed in a recent study R.~Remez, et al., Phys. Rev. Lett. {\bf 123}, 060401 (2019) where a conclusion was drawn in favor of the first (point) interpretation. Here we argue that there is an alternative explanation for the measurements reported in that paper, which relies on purely classical arguments and does not allow one to refute the second interpretation. We propose an experiment of Smith-Purcell radiation from a non-relativistic vortex electron carrying orbital angular momentum, which can unambiguously lead to the opposite conclusion. Beyond the paraxial approximation, the vortex packet has a non-point electric quadrupole moment, which grows as the packet spreads and results in a non-linear $L^3$-growth of the radiation intensity with the length $L$ of the grating when $L$ is much larger than the packet's Rayleigh length. Such a non-linear effect has never been observed for single electrons and, if detected, it would be a hallmark of the non-point nature of charge in a wave packet. Thus, two views on $|\psi {|}^2$ are complementary to each other and an electron radiates either as a point charge or as a continuous charge flow depending on the experimental conditions and on its quantum state. Our conclusions hold for a large class of non-Gaussian packets and emission processes for which the radiation formation length can exceed the Rayleigh length, such as Cherenkov radiation, transition radiation, diffraction radiation, and so forth.

    ↳ quant-phhep-phPRA(2021)·12 citations
35. 35*

    Novel formulation of Hamilton-Jacobi equation for higher derivative theory and quantum mechanical correspondence

    Zhi-Qiang Guo🇨🇳

    For higher derivative theories, using the approach of Caratheodory's equivalent Lagrangian, we show that there exist novel formulations of Hamilton-Jacobi equations, which are different from the formulations derived from Hamilton's canonical approach. The quantum mechanical correspondences of these novel Hamilton-Jacobi equations lead to nonlinear quantum mechanics, which seem being able to avoid the unbounded negative energy problem in the quantum mechanics of higher derivative theories.

    ↳ hep-thgr-qchep-phphysics.class-ph+10 citations
36. 36*

    CosmoBit: A GAMBIT module for computing cosmological observables and likelihoods

    The GAMBIT Cosmology Workgroup: Janina J. Renk🇬🇧 · Patrick Stöcker🇩🇪 · Sanjay Bloor🇬🇧 · Selim Hotinli🇬🇧 · Csaba Balázs🇦🇺 · Torsten Bringmann🇳🇴 · Tomás E. Gonzalo🇦🇺 · Will Handley🇬🇧 · Sebastian Hoof🇩🇪 · Cullan Howlett🇦🇺 · Felix Kahlhoefer🇩🇪 · Pat Scott🇬🇧 · Aaron C. Vincent🇨🇦 · Martin White🇦🇺

    We introduce $\mathsf{CosmoBit}$, a module within the open-source $\mathsf{GAMBIT}$ software framework for exploring connections between cosmology and particle physics with joint global fits. $\mathsf{CosmoBit}$ provides a flexible framework for studying various scenarios beyond $\Lambda$CDM, such as models of inflation, modifications of the effective number of relativistic degrees of freedom, exotic energy injection from annihilating or decaying dark matter, and variations of the properties of elementary particles such as neutrino masses and the lifetime of the neutron. Many observables and likelihoods in $\mathsf{CosmoBit}$ are computed via interfaces to $\mathsf{AlterBBN}$, $\mathsf{CLASS}$, $\mathsf{DarkAges}$, $\mathsf{MontePython}$, $\mathsf{MultiModeCode}$, and $\mathsf{plc}$. This makes it possible to apply a wide range of constraints from large-scale structure, Type Ia supernovae, Big Bang Nucleosynthesis and the cosmic microwave background. Parameter scans can be performed using the many different statistical sampling algorithms available within the $\mathsf{GAMBIT}$ framework, and results can be combined with calculations from other $\mathsf{GAMBIT}$ modules focused on particle physics and dark matter. We include extensive validation plots and a first application to scenarios with non-standard relativistic degrees of freedom and neutrino temperature, showing that the corresponding constraint on the sum of neutrino masses is much weaker than in the standard scenario.

    ↳ astro-ph.COhep-phJCAP(2021)·38 citations
37. 37*

    Strengthening the bound on the mass of the lightest neutrino with terrestrial and cosmological experiments

    The GAMBIT Cosmology Workgroup: Patrick Stöcker🇩🇪 · Csaba Balázs🇦🇺 · Sanjay Bloor🇬🇧 · Torsten Bringmann🇳🇴 · Tomás E. Gonzalo🇦🇺 · Will Handley🇬🇧 · Selim Hotinli🇬🇧 · Cullan Howlett🇦🇺 · Felix Kahlhoefer🇩🇪 · Janina J. Renk🇬🇧 · Pat Scott🇬🇧 · Aaron C. Vincent🇨🇦 · Martin White🇦🇺

    We determine the upper limit on the mass of the lightest neutrino from the most robust recent cosmological and terrestrial data. Marginalizing over possible effective relativistic degrees of freedom at early times ($N_{\mathrm{eff}}$) and assuming normal mass ordering, the mass of the lightest neutrino is less than 0.037 eV at 95% confidence; with inverted ordering, the bound is 0.042 eV. These results improve upon the strength and robustness of other recent limits and constrain the mass of the lightest neutrino to be barely larger than the largest mass splitting. We show the impacts of realistic mass models, and different sources of $N_{\mathrm{eff}}$.

    ↳ astro-ph.COhep-phPRD(2021)·53 citations
38. 38*

    Conifold Vacua with Small Flux Superpotential

    Mehmet Demirtas🇺🇸 · Manki Kim🇺🇸 · Liam McAllister🇺🇸 · Jakob Moritz🇺🇸

    We introduce a method for finding flux vacua of type IIB string theory in which the flux superpotential is exponentially small and at the same time one or more complex structure moduli are stabilized exponentially near to conifold points.

    ↳ hep-thhep-phFortsch.Phys.(2020)·90 citations
39. 39*

    de Sitter decay through goldstino evaporation

    Fotis Farakos🇮🇹 · Alex Kehagias🇬🇷 · Nikolaos Liatsos🇬🇷

    We study supergravity theories with supersymmetry intrinsically non-linearly realized supported only by four-form flux. We demonstrate that supersymmetry can be restored by the evaporation of the goldstino multiplet. Such procedure requires the existence of a super-extremal 2-brane, in accordance with the WGC, and suggests an imminent decay in de Sitter supergravity, leaving the system to relax in supersymmetric AdS after the transition. In particular, the same decay mechanism also implies that the KKLT de Sitter vacua are short-lived. Our findings thus provide an effective realization of KPV-type of decays within 4D supergravity and in this way may reconcile the nilpotent superfield constructions of de Sitter with some aspects of the swampland program.

    ↳ hep-thgr-qchep-phJHEP(2021)·14 citations
40. 40*

    Completely Dark Photons from Gravitational Particle Production During Inflation

    Edward W. Kolb🇺🇸 · Andrew J. Long🇺🇸

    Starting with the de Broglie--Proca Lagrangian for a massive vector field, we calculate the number density of particles resulting from gravitational particle production (GPP) during inflation, with detailed consideration to the evolution of the number density through the reheating. We find plausible scenarios for the production of dark-photon dark matter of mass in a wide range, as low as a micro-electron volt to $10^{14}$ GeV. Gravitational particle production does not depend on any coupling of the dark photon to standard-model particles.

    ↳ astro-ph.COgr-qchep-phhep-thJHEP(2021)·169 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.