Wed·Mar 24, 2021Wednesday·March 24, 2021

1. 01*

   Detecting the radiative decay of the cosmic neutrino background with line-intensity mapping

   José Luis Bernal🇺🇸 · Andrea Caputo🇮🇱 · Francisco Villaescusa-Navarro🇺🇸 · Marc Kamionkowski🇺🇸

   We study the possibility to use line-intensity mapping (LIM) to seek photons from the radiative decay of neutrinos in the cosmic neutrino background. The Standard Model prediction for the rate for these decays is extremely small, but it can be enhanced if new physics increases the neutrino electromagnetic moments. The decay photons will appear as an interloper of astrophysical spectral lines. We propose that the neutrino-decay line can be identified with anisotropies in LIM clustering and also with the voxel intensity distribution. Ongoing and future LIM experiments will have -- depending on the neutrino hierarchy, transition and experiment considered -- a sensitivity to an effective electromagnetic transition moment $\sim 10^{-12}-10^{-8}(m_i{c}^2/0.1\mathrm{eV}{)}^{3/2}{\mu }_{\mathrm{B}}$, where $m_i$ is the mass of the decaying neutrino and ${\mu }_{\mathrm{B}}$ is the Bohr magneton. This will be significantly more sensitive than cosmic microwave background spectral distortions, and it will be competitive with stellar cooling studies. As a byproduct, we also report an analytic form of the one-point probability distribution function for neutrino-density fluctuations, obtained from the Quijote simulations using symbolic regression.

   hep-phastro-ph.COPRL(2021)·35 citations
2. 02*

   QCD factorization for twist-three axial-vector parton quasidistributions

   Vladimir M. Braun🇩🇪 · Yao Ji🇩🇪 · Alexey Vladimirov🇩🇪

   The transverse component of the axial-vector correlation function of quark fields is a natural starting object for lattice calculations of twist-3 nucleon parton distribution functions. In this work we derive the corresponding factorization expression in terms of twist-2 and twist-3 collinear distributions to one-loop accuracy. The results are presented both in position space, as the factorization theorem for Ioffe-time distributions, and in momentum space, for the axial-vector quasi- and pseudodistributions.

   hep-phJHEP(2021)·30 citations
3. 03*

   Sparticle and Higgs boson masses from the landscape: dynamical versus spontaneous supersymmetry breaking

   Howard Baer🇺🇸 · Vernon Barger🇺🇸 · Shadman Salam🇺🇸 · Hasan Serce🇺🇸

   Perturbative supersymmetry breaking on the landscape of string vacua is expected to favor large soft terms as a power-law or log distribution, but tempered by an anthropic veto of inappropriate vacua or vacua leading to too large a value for the derived weak scale -- a violation of the atomic principle. Indeed, scans of such vacua yield a statistical prediction for light Higgs boson mass m_h~ 125 GeV with sparticles (save possibly light higgsinos) typically beyond LHC reach. In contrast, models of dynamical SUSY breaking (DSB) -- with a hidden sector gauge coupling g^2 scanned uniformly -- lead to gaugino condensation and a uniform distribution of soft parameters on a log scale. Then soft terms are expected to be distributed as $m_{\mathrm{soft}}^{-1}$ favoring small values. A scan of DSB soft terms generally leads to $m_h\ll 125$ GeV and sparticle masses usually below LHC limits. Thus, the DSB landscape scenario seems excluded from LHC search results. An alternative is that the exponential suppression of the weak scale is set anthropically on the landscape via the atomic principle.

   hep-phhep-thPRD(2021)·7 citations
4. 04*

   Dark photon dark matter from a rolling inflaton

   Mar Bastero-Gil🇪🇸 · Jose Santiago🇪🇸 · Lorenzo Ubaldi🇮🇹 · Roberto Vega-Morales🇪🇸

   We study in detail a recently proposed mechanism for producing non-thermal dark photon dark matter at the end of inflation in the mass range $\mu \mathrm{eV}\lesssim m\lesssim 10\mathrm{TeV}$. A tachyonic instability induced by a rolling inflaton leads to the coherent production of dark (abelian) gauge bosons with a peak in the power spectrum corresponding to the Hubble scale at the end of inflation. As the Universe expands after inflation the dark photons redshift and, at some point in their cosmic evolution, they obtain a mass. We focus in particular on the case where the dark photons are relativistic at the time their mass is generated and examine the associated cosmic evolution to compute the relic abundance today. We also examine the late time power spectrum demonstrating explicitly that it preserves the peak generated at the end of inflation. We show that the peak corresponds to small physical scales today, ${\ell }_{\mathrm{today}}\sim \mathrm{cm}-100\mathrm{km}$, with large density fluctuations at ${\ell }_{\mathrm{today}}$ leading to a clumpy nature for the dark photon dark matter. We also discuss potential phenomenology and future directions, briefly commenting on the non-relativistic case.

   hep-phJCAP(2022)·38 citations
5. 05*

   Modern Machine Learning and Particle Physics

   Matthew D. Schwartz🇺🇸

   Over the past five years, modern machine learning has been quietly revolutionizing particle physics. Old methodology is being outdated and entirely new ways of thinking about data are becoming commonplace. This article will review some aspects of the natural synergy between modern machine learning and particle physics, focusing on applications at the Large Hadron Collider. A sampling of examples is given, from signal/background discrimination tasks using supervised learning to direct data-driven approaches. Some comments on persistent challenges and possible future directions for the field are included at the end.

   hep-phHarvard Data Science Review, 2021 May 13;…·80 citations
6. 06*

   Vacuum angle theta in a strongly interacting hidden sector and its effect

   Shinji Maedan🇯🇵

   Introducing a vacuum angle ${\theta }_h$ in a strongly interacting hidden sector like QCD, we study how ${\theta }_h$ affects physical quantities in a scale invariant extension of the standard model with that hidden sector. In this model the dynamical chiral symmetry breaking occurs in the hidden sector and generates a scale $|⟨\bar{q}q⟩|$ which triggers electroweak symmetry breaking. We find that the expression for a vacuum expectation value of the Higgs field depends on ${\theta }_h$, while the condition which determines the Higgs particle mass does not. This model contains the hidden-sector pions ${\pi }^0$ and ${\pi }^{\pm }$ which are candidates for cold dark matter, and we find the mass difference between the hidden-sector ${\pi }^0$ and ${\pi }^{\pm }$ will not be negligible for ${\theta }_h\approx \pi$.

   hep-ph0 citations
7. 07*

   Almost exact diagonal reflection symmetries and three-zero texture

   Masaki J. S. Yang🇯🇵

   In this paper, we consider a three-zero texture with diagonal reflection symmetries in the SM. The three-zero texture has two less assumptions ($(M_u{)}_{11},(M_{\nu }{)}_{11}\ne 0$) than the universal four-zero texture of mass matrices $(M_f{)}_{11}=(M_f{)}_{13,31}=0$ for $f=u,d,\nu ,e$. The texture allows diagonal reflection symmetries to be almost exact and $d$\,-\,$e$ unification. They reproduce the CKM and MNS matrices with accuracies of $O(10^{-4})$ and $O(10^{-3})$. Some perturbative diagonalizations yield two relations with good accuracy for quark mass and mixing. Although this calculation is done in a special basis, it is a general result in a sense, because other textures and generalized $CP$ symmetries exist by some weak basis transformation. By assuming a $d$\,-\,$e$ unified relation ($M_d\sim M_e$), we obtain the lightest neutrino mass $m_1\simeq 2.12-5.64$[meV] and the effective mass of the double beta decay $|m_{ee}|\simeq 1.23-2.15$[meV].

   hep-phNPB(2021)·13 citations
8. 08*

   Influence of intense laser fields on measurable quantities in $W^{-}$-boson decay

   M. Jakha🇲🇦 · S. Mouslih🇲🇦 · S. Taj🇲🇦 · B. Manaut🇲🇦

   In principle, this paper suggests powerful laser technology as a promising instrument that can be experimentally useful to control the lifetime and branching ratio for an unstable particle decay. In a recent paper [arXiv:2101.00224], we calculated theoretically the $W^{-}$-boson leptonic decay $(W^{-}\to {\ell }^{-}{\bar{\nu }}_{\ell })$ in the presence of a circularly polarized laser and we showed that the laser significantly contributed to the diminution of the leptonic decay rate. In this paper, as a continuation of the previous one, we mainly deal with the theoretical calculation of the $W^{-}$-boson hadronic decay $(W^{-}\to q{\bar{q}}^{\prime })$ and we combine the analytical results obtained in both papers to examine the effect of an intense laser, in terms of its field strength and frequency, on the three measurable quantities in $W^{-}$-boson decay (total decay rate, lifetime and branching ratios). It was found that the laser has notably contributed to the reduction of the total decay rate leading to a longer lifetime. Most importantly, the two branching ratios (one for leptons and the other for hadrons) are affected (increased or decreased) by the presence of a strong external electromagnetic field. Combined together, these two complementary works may provide an in-depth and comprehensive study that would be useful for any experimental investigation in the future.

   hep-phChin.J.Phys.(2022)·17 citations
9. 09*

   The explanation of some exotic states in the $cs\bar{c}\bar{s}$ tetraquark system

   Xuejie Liu🇨🇳 · Hongxia Huang🇨🇳 · Jialun Ping🇨🇳 · Dianyong Chen🇨🇳 · Xinmei Zhu🇨🇳

   Inspired by the recent observation of ${\chi }_{c0}(3930)$, $X(4685)$ and $X(4630)$ by the LHCb Collaboration and some exotic resonances such as $X(4350)$, $X(4500)$, etc. by several experiment collaborations, the $cs\bar{c}\bar{s}$ tetraquark systems with $I{J}^P=00^{+}$, $01^{+}$ and $02^{+}$ are systematically investigated in the framework of the quark delocalization color screening model(QDCSM). Two structures, the meson-meson and diquark-antidiquark structures, as well as the channel-coupling of all channels of these two configurations are considered in this work. The numerical results indicate that the molecular bound state ${\bar{D}}_s{D}_s$ with $I{J}^P=00^{+}$ can be supposed to explain the ${\chi }_{c0}(3930)$. Besides, by using the stabilization method, several resonant states are obtained. There are four $I{J}^P=00^{+}$ states around the resonance mass 4035 MeV, 4385 MeV, 4524 MeV, and 4632 MeV, respectively; one $I{J}^P=01^{+}$ state around the resonance mass 4327 MeV; and two $I{J}^P=02^{+}$ states around the resonance mass 4419 MeV and 4526 MeV, respectively. All of them are compact tetraquarks. Among these states, $X(4350)$, $X(4500)$ and $X(4700)$ can be explained as the compact tetraquark state with $I{J}^P=00^{+}$, and the $X(4274)$ is possible to be a candidate of the compact tetraquark state with $I{J}^P=01^{+}$. More experimental tests are expected to check the existence of all these possible resonance states.

   hep-phhep-exhep-thEPJC(2021)·34 citations
10. 10*

    On the single leptoquark solutions to the $B$-physics anomalies

    Andrei Angelescu🇩🇪 · Damir Bečirević🇫🇷 · Darius A. Faroughy🇨🇭 · Florentin Jaffredo🇫🇷 · Olcyr Sumensari🇫🇷

    We revisit the possibilities of accommodating the experimental indications of the lepton flavor universality violation in $b$-hadron decays in the minimal scenarios in which the Standard Model is extended by the presence of a single $\mathcal{O}(1\mathrm{TeV})$ leptoquark state. To do so we combine the most recent low energy flavor physics constraints, including $R_{K^{(\ast )}}^{\exp }$ and $R_{D^{(\ast )}}^{\exp }$, and combine them with the bounds on the leptoquark masses and their couplings to quarks and leptons as inferred from the direct searches at the LHC and the studies of the large $p_T$ tails of the $pp\to \ell \ell$ differential cross section. We find that none of the scalar leptoquarks of $m_{\mathrm{LQ}}\simeq 1÷2$ TeV can accommodate the $B$-anomalies alone. Only the vector leptoquark, known as $U_1$, can provide a viable solution which, in the minimal setup, provides an interesting prediction, i.e. a lower bound to the lepton flavor violating $b\to s{\mu }^{\pm }{\tau }^{\mp }$ decay modes, such as $\mathcal{B}(B\to K\mu \tau )\gtrsim 0.7\times 10^{-7}$.

    hep-phhep-exhep-latPRD(2021)·228 citations
11. 11*

    Near threshold heavy vector meson photoproduction at LHC and EicC

    Ya-Ping Xie🇨🇳 · Victor P. Goncalves🇧🇷

    The exclusive $J/\Psi$ and ${\rm Y}$ photoproduction in fixed - target collisions at the LHC and $ep(A)$ collisions at the Electron ion collider in China (EicC) is investigated considering different models for the treatment of the vector meson production at low energies, close to the threshold. Results for the total cross sections and associated distributions are presented. We predict a large number of $J/\Psi$ events at the LHC in the rapidity range covered by the LHCb detector. For the EicC, our predictions point out that a detailed analysis of the near threshold $J/\Psi$ and ${\rm Y}$ photoproduction is feasible. Moreover, our results indicate that the modeling of the near threshold vector meson production can be constrained by future experimental analyzes at the LHC and EicC.

    hep-phhep-exEPJC(2021)·11 citations
12. 12*

    Fate of electroweak symmetry in the early Universe: Non-restoration and trapped vacua in the N2HDM

    Thomas Biekötter🇩🇪 · Sven Heinemeyer🇪🇸 · José Miguel No🇪🇸 · María Olalla Olea🇩🇪 · Georg Weiglein🇩🇪

    Extensions of the Higgs sector of the Standard Model allow for a rich cosmological history around the electroweak scale. We show that besides the possibility of strong first-order phase transitions, which have been thoroughly studied in the literature, also other important phenomena can occur, like the non-restoration of the electroweak symmetry or the existence of vacua in which the Universe becomes trapped, preventing a transition to the electroweak minimum. Focusing on the next-to-minimal two-Higgs-doublet model (N2HDM) of type II and taking into account the existing theoretical and experimental constraints, we identify the scenarios of electroweak symmetry non-restoration, vacuum trapping and first-order phase transition in the thermal history of the Universe. We analyze these phenomena and in particular their relation to each other, and discuss their connection to the predicted phenomenology of the N2HDM at the LHC. Our analysis demonstrates that the presence of a global electroweak minimum of the scalar potential at zero temperature does not guarantee that the corresponding N2HDM parameter space will be physically viable: the existence of a critical temperature at which the electroweak phase becomes the deepest minimum is not sufficient for a transition to take place, necessitating an analysis of the tunnelling probability to the electroweak minimum for a reliable prediction of the thermal history of the Universe.

    hep-phJCAP(2021)·72 citations
13. 13*

    Higgs flavor phenomenology in a supersymmetric left-right model with parity

    Syuhei Iguro🇯🇵 · Junichiro Kawamura🇰🇷 · Yuji Omura🇯🇵 · Yoshihiro Shigekami🇨🇳

    In this paper, we focus on the supersymmetric model with left-right (LR) symmetry, that is especially proposed in our previous work [1]. In this model, there are four Higgs doublets in order to realize the Standard Model (SM) fermion masses and the Cabibbo-Kobayashi-Maskawa matrix. The heavy Higgs doublets unavoidably have flavor changing couplings to the SM fermions and induce flavor-changing neutral currents at tree level. We study broader parameter space than the previous work with including the renormalization group corrections to the Yukawa couplings between the LR breaking scale, $\mathcal{O}(10^{13})$ GeV, and the supersymmetry breaking scales, $\mathcal{O}(100)$ TeV. The CP violating observable in $K$-$\overline{K}$ mixing, ${ϵ}_K$, strongly constrains the model, so that heavy Higgs mass should be heavier than $\mathcal{O}(100)$ TeV. We study the lepton flavor violating (LFV) processes setting heavy Higgs masses to be 170 TeV. The branching ratios of $\mu \to 3e$ and the $\mu$-$e$ conversion can be larger than $10^{-16}$ that could be covered by the future experiments. We also study the degree of fine-tuning in the parameter region that predicts testable LFV processes.

    hep-phhep-exJHEP(2021)·3 citations
14. 14*

    Flavorful leptoquarks at the LHC and beyond: Spin 1

    Gudrun Hiller🇩🇪 · Dennis Loose🇩🇪 · Ivan Nišandžić🇭🇷

    Evidence for electron-muon universality violation that has been revealed in $b\to s\ell \ell$ transitions in the observables $R_{K,K^{\ast }}$ by the LHCb Collaboration can be explained with spin-1 leptoquarks in $SU(2{)}_L$ singlet $V_1$ or triplet $V_3$ representations in the $\mathcal{O}(1-10)$ TeV range. We explore the sensitivity of the high luminosity LHC (HL-LHC) and future proton-proton colliders to $V_1$ and $V_3$ in the parameter space connected to $R_{K,K^{\ast }}$-data. We consider pair production and single production in association with muons in different flavor benchmarks. Reinterpreting a recent ATLAS search for scalar leptoquarks decaying to $b\mu$ and $j\mu$, we extract improved limits for the leptoquark masses: For gauge boson-type leptoquarks ($\kappa =1$) we obtain $M_{V_1}>1.9$ TeV, $M_{V_1}>1.9$ TeV, and $M_{V_1}>1.7$ TeV for leptoquarks decaying predominantly according to hierarchical, flipped and democratic quark flavor structure, respectively. Future sensitivity projections based on extrapolations of existing ATLAS and CMS searches are worked out. We find that for $\kappa =1$ the mass reach for pair (single) production of $V_1$ can be up to 3 TeV (2.1 TeV) at the HL-LHC and up to 15 TeV (19.9 TeV) at the FCC-hh with $\sqrt{s}=100$ TeV and $20\text{mbox}{ab}^{-1}$. The mass limits and reach for the triplet $V_3$ are similar or higher, depending on flavor. While there is the exciting possibility that leptoquarks addressing the $R_{K,K^{\ast }}$-anomalies are observed at the LHC, to fully cover the parameter space $pp$-collisions beyond the LHC-energies are needed.

    hep-phhep-exJHEP(2021)·40 citations
15. 15*

    Implications of new evidence for lepton-universality violation in $b\to s{\ell }^{+}{\ell }^{-}$ decays

    Li-Sheng Geng🇨🇳 · Benjamín Grinstein🇺🇸 · Sebastian Jäger🇬🇧 · Shuang-Yi Li🇨🇳 · Jorge Martin Camalich🇪🇸 · Rui-Xiang Shi🇨🇳

    Motivated by renewed evidence for new physics in $b\to s\ell \ell$ transitions in the form of LHCb's new measurements of theoretically clean lepton-universality ratios and the purely leptonic $B_s\to {\mu }^{+}{\mu }^{-}$ decay, we quantify the combined level of discrepancy with the Standard Model and fit values of short-distance Wilson coefficients. A combination of the clean observables $R_K$, $R_{K^{\ast }}$, and $B_s\to \mu \mu$ alone results in a discrepancy with the Standard Model at $4.0\sigma$, up from $3.5\sigma$ in 2017. One-parameter scenarios with purely left-handed or with purely axial coupling to muons fit the data well and result in a $\sim 5\sigma$ pull from the Standard Model. In a two-parameter fit of %$C_9$ and $C_{10}$, new-physics contributions with both vector and axial-vector couplings to muons the allowed region is much more restricted than in 2017, principally due to the much more precise result on $B_s\to {\mu }^{+}{\mu }^{-}$, which probes the axial coupling to muons.Including angular observables data restricts the allowed region further.A by-product of our analysis is an updated average of $\text{BR}(B_s\to {\mu }^{+}{\mu }^{-})=(2.8\pm 0.3)\times 10^{-9}$.

    hep-phhep-exPRD(2021)·153 citations
16. 16*

    The three flavor revolution in fast pairwise neutrino conversion

    Shashank Shalgar🇩🇰 · Irene Tamborra🇩🇰

    The modeling of fast flavor evolution of neutrinos in dense environments has been traditionally carried out by relying on a two flavor approximation for simplicity. In addition, vacuum mixing has been deemed negligible. For the first time, we highlight that the fast flavor evolution in three flavors is intrinsically different from the one obtained in the two flavor approximation. This is due to the exponential growth of flavor mixing in the $e$--$\mu$ and $e$--$\tau$ sectors generated by the vacuum term in the Hamiltonian. As a result, substantially larger flavor mixing is found in three flavors. Our findings highlight that the two flavor approximation is not justified for fast pairwise conversion, even if the angular distributions of non-electron type neutrinos are initially identical.

    hep-phastro-ph.HEPRD(2021)·44 citations
17. 17*

    Tensor-Train Numerical Integration of Multivariate Functions with Singularities

    Lev I. Vysotsky (1,2 and 3)🇷🇺 · Alexander V. Smirnov (4 and 3)🇷🇺 · Eugene E. Tyrtyshnikov (5 and 4) ((1) HSE University, (2) Faculty of Computational Mathematics and Cybernetics of Moscow State University, (3) Moscow Center for Fundamental and Applied Mathematics, (4) Research Computing Center of Moscow State University, (5) Marchuk Institute of Numerical Mathematics of Russian Academy of Sciences)🇷🇺

    Numerical integration is a classical problem emerging in many fields of science. Multivariate integration cannot be approached with classical methods due to the exponential growth of the number of quadrature nodes. We propose a method to overcome this problem. Tensor-train decomposition of a tensor approximating the integrand is constructed and used to evaluate a multivariate quadrature formula. We show how to deal with singularities in the integration domain and conduct theoretical analysis of the integration accuracy. The reference open-source implementation is provided.

    ↳ math.NAcs.NAhep-phLobachevskii J.Math.(2021)·6 citations
18. 18*

    Cosmological perturbations for ultra-light axion-like particles in a state of Bose-Einstein condensate

    Shinji Tsujikawa🇯🇵

    For ultra-light scalar particles like axions, dark matter can form a state of the Bose-Einstein condensate (BEC) with a coherent classical wave whose wavelength is of order galactic scales. In the context of an oscillating scalar field with mass $m$, this BEC description amounts to integrating out the field oscillations over the Hubble time scale $H^{-1}$ in the regime $m\gg H$. We provide a gauge-invariant general relativistic framework for studying cosmological perturbations in the presence of a self-interacting BEC associated with a complex scalar field. In particular, we explicitly show the difference of BECs from perfect fluids by taking into account cold dark matter, baryons, and radiation as a Schutz-Sorkin description of perfect fluids. We also scrutinize the accuracy of commonly used Newtonian treatment based on a quasi-static approximation for perturbations deep inside the Hubble radius. For a scalar field which starts to oscillate after matter-radiation equality, we show that, after the BEC formation, a negative self-coupling hardly leads to a Laplacian instability of the BEC density contrast. This is attributed to the fact that the Laplacian instability does not overwhelm the gravitational instability for self-interactions within the validity of the nonrelativistic BEC description. Our analysis does not accommodate the regime of parametric resonance which can potentially occur for a large field alignment during the transient epoch prior to the BEC formation.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2021)·3 citations
19. 19*

    4D Gauss-Bonnet gravity: cosmological constraints, $H_0$ tension and large scale structure

    Deng Wang🇨🇳 · David Mota🇳🇴

    We perform correct and reasonable cosmological constraints on the newly proposed 4D Gauss-Bonnet gravity. Using the joint constraint from cosmic microwave background, baryon acoustic oscillations, Type Ia supernovae, cosmic chronometers and redshift space distortions, we obtain, so far, the strongest constraint $\tilde{\alpha }=(1.2\pm 5.2)\times 10^{-17}$, namely $\alpha =(2.69\pm 11.67)\times 10^{48}$ eV${}^{-2}$, among various observational limitations from different information channels, which is tighter than previous bound from the speed of gravitational wave by at least one order of magnitude. We find that our bound is well supported by the observations of temperature and lensing potential power spectra of cosmic microwave background from the Planck-2018 final release. Very interestingly, the large $H_0$ tension between the local measurement from the Hubble Space Telescope and global derivation from the Planck-2018 final data under the assumption of $\Lambda$CDM can be greatly resolved from $4.4\sigma$ to $1.94\sigma$ level in the 4D Gauss-Bonnet gravity. In theory, we find that this model can partly relieve the coincidence problem and the rescaling Gauss-Bonnet term, which needs the help of the cosmological constant to explain current cosmic acceleration, is unable to serve as dark energy alone.

    ↳ astro-ph.COgr-qchep-phPhys.Dark Univ.(2021)·34 citations
20. 20*

    Estimation of initial state structures in high energy heavy-ion collisions using Principal Component Analysis (PCA)

    Shreyasi Acharya🇮🇳 · Subhasis Chattopadhyay🇮🇳

    In high-energy heavy-ion collisions, structures in the initial collision zone are a matter of intense investigation, both from theory and experimental points of view. A large number of models have been developed to represent the initial state of the collision including Glauber model, Colour Glass Condensate (CGC) among others. Another important aspect of the study is to investigate proper observables that will be sensitive to the initial collision zone. In this work, we have discussed a formalism to implement the spatial clusters at the partonic level in the string melting version of the AMPT model for PbPb collisions at $\sqrt{s_{NN}}$ = 200 GeV. These clusters are then propagated through the AMPT hadronization scheme. The Principal Component Analysis (PCA) has been used on the $\eta$, $\varphi$ and $p_T$ distributions of the produced charged particles and the eigenvalues have been compared before and after the implementation of the clustering. It is found that for all these three different distributions, all the prominent PCA modes have shown sensitivity to the clustering. A centrality dependent study has also been performed on those eigenvalues.

    ↳ nucl-thhep-phPRC(2021)·8 citations
21. 21*

    Thermoelectric response of a weakly magnetized thermal QCD medium

    Debarshi Dey🇮🇳 · Binoy Krishna Patra🇮🇳

    We estimate the thermoelectric response, namely, the Seebeck and Nernst coefficients of a hot and deconfined plasma of quarks and gluons, created post ultrarelativistic heavy ion collisions in the presence of a weak, homogeneous background magnetic field. We employ the kinetic theory framework, wherein we use the relativistic Boltzmann transport equation in the relaxation time approximation. In-medium interactions are taken into account via the quasiparticle masses of the partons extracted from one loop perturbative thermal QCD. We calculate the individual and total Seebeck coefficients in 2 different approaches (1-D and 2-D formulations). In the 1-D analysis, we find that a larger current quark mass has an amplifying effect on the individual Seebeck coefficient in the presence of a weak magnetic field. The temperature sensitivities of the individual Seebeck coefficients increase with increase in the current mass of the quark species in the case of a weak magnetic field whereas the same records a decreasing trend in the presence of a strong magnetic field. The variation of individual and total Seebeck coefficients with temperature, chemical potential and background magnetic field are found to follow similar trends in both the approaches, viz. decrease in magnitude with increasing temperature and increase in magnitude with increase in chemical potential and magnetic field. We also calculate the individual and total Nernst coefficients (in 2-D formulation) which are found to decrease with both temperature and chemical potential and increase with the magnetic field. Further, we find that the sign of the Nernst coefficient is independent of the electric charge of the charge carrier of the medium.

    ↳ nucl-thhep-phPRD(2021)·12 citations
22. 22*

    Accessing weak neutral-current coupling $g_{AA}^{eq}$ using positron and electron beams at Jefferson Lab

    Xiaochao Zheng🇺🇸 · Jens Erler🇩🇪 · Qishan Liu🇩🇪 · Huber Spiesberger🇩🇪

    Low-energy neutral-current couplings arising in the Standard Model of electroweak interactions can be constrained in lepton scattering off hydrogen or a nuclear fixed target. Recent polarized electron scattering experiments at Jefferson Lab (JLab) have improved the precision in the parity-violating types of effective couplings. On the other hand, the only known way to access the parity-conserving counterparts is to compare scattering cross sections between a lepton and an anti-lepton beam. We review the current knowledge of both types of couplings and how to constrain them. We also present exploratory calculations for a possible measurement of $g_{AA}^{eq}$ using the planned SoLID spectrometer combined with a possible positron beam at JLab.

    ↳ nucl-exhep-phEPJA(2021)·18 citations
23. 23*

    Unnuclear physics

    Hans-Werner Hammer🇩🇪 · Dam Thanh Son🇺🇸

    We investigate a nonrelativistic version of Georgi's "unparticle physics." We define the unnucleus as a field in a nonrelativistic conformal field theory. Such a field is characterized by a mass and a conformal dimension. We then consider the formal problem of scatterings to a final state consisting of a particle and an unnucleus and show that the differential cross section, as a function of the recoil energy received by the particle, has a power-law singularity near the maximal recoil energy, where the power is determined by the conformal dimension of the unnucleus. We argue that unlike the relativistic unparticle, which remains a hypothetical object, the unnucleus is realized, to a good approximation, in nuclear reactions involving emission of a few neutrons, when the energy of the final-state neutrons in their center-of-mass frame lies in the range between about 0.1 MeV and 5 MeV. Combining this observation with the known universal properties of fermions at unitarity in a harmonic trap, we predict a power-law behavior of an inclusive cross section in this kinematic regime. We compare our predictions with previous effective field theory and model calculations of the ${}^6$He$(p,p\alpha )2n$, ${}^3$H$({\pi }^{-},\gamma )3n$, and ${}^3$H$({\mu }^{-},{\nu }_{\mu })3n$ reactions and find excellent agreement.

    ↳ nucl-thcond-mat.quant-gashep-phhep-thProc.Nat.Acad.Sci.(2021)·35 citations
24. 24*

    Gravitational Effective Field Theory Islands, Low-Spin Dominance, and the Four-Graviton Amplitude

    Zvi Bern🇺🇸 · Dimitrios Kosmopoulos🇺🇸 · Alexander Zhiboedov🇨🇭

    We analyze constraints from perturbative unitarity and crossing on the leading contributions of higher-dimension operators to the four-graviton amplitude in four spacetime dimensions, including constraints that follow from distinct helicity configurations. We focus on the leading-order effect due to exchange by massive degrees of freedom which makes the amplitudes of interest infrared finite. In particular, we place a bound on the coefficient of the $R^3$ operator that corrects the graviton three-point amplitude in terms of the $R^4$ coefficient. To test the constraints we obtain nontrivial effective field-theory data by computing and taking the large-mass expansion of the one-loop minimally-coupled four-graviton amplitude with massive particles up to spin 2 circulating in the loop. Remarkably, we observe that the leading EFT coefficients obtained from both string and one-loop field-theory amplitudes lie in small islands. The shape and location of the islands can be derived from the dispersive representation for the Wilson coefficients using crossing and assuming that the lowest-spin spectral densities are the largest. Our analysis suggests that the Wilson coefficients of weakly-coupled gravitational physical theories are much more constrained than indicated by bounds arising from dispersive considerations of $2\to 2$ scattering. The one-loop four-graviton amplitudes used to obtain the EFT data are computed using modern amplitude methods, including generalized unitarity, supersymmetric decompositions and the double copy.

    ↳ hep-thgr-qchep-phJ.Phys.A(2021)·197 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.