Fri·Dec 4, 2020Friday·December 4, 2020

1. 01*

   Jet radiation in a longitudinally expanding medium

   Paul Caucal🇫🇷 · Edmond Iancu🇫🇷 · Gregory Soyez🇫🇷

   In a series of previous papers, we have presented a new approach, based on perturbative QCD, for the evolution of a jet in a dense quark-gluon plasma. In the original formulation, the plasma was assumed to be homogeneous and static. In this work, we extend our description and its Monte Carlo implementation to a plasma obeying Bjorken longitudinal expansion. Our key observation is that the factorisation between vacuum-like and medium-induced emissions, derived in the static case, still holds for an expanding medium, albeit with modified rates for medium-induced emissions and transverse momentum broadening, and with a modified phase-space for vacuum-like emissions. We highlight a scaling relation valid for the energy spectrum of medium-induced emissions, through which the case of an expanding medium is mapped onto an effective static medium. We find that scaling violations due to vacuum-like emissions and transverse momentum broadening are numerically small. Our new predictions for the nuclear modification factor for jets $R_{AA}$, the in-medium fragmentation functions, and substructure distributions are very similar to our previous estimates for a static medium, maintaining the overall good qualitative agreement with existing LHC measurements. In the case of $R_{AA}$, we find that the agreement with the data is significantly improved at large transverse momenta $p_T\gtrsim 500$ GeV after including the effects of the nuclear parton distribution functions.

   hep-phnucl-thJHEP(2021)·37 citations
2. 02*

   Gluon distributions and their applications to Ioffe-time distributions

   Raza Sabbir Sufian🇺🇸 · Tianbo Liu🇺🇸 · Arpon Paul🇮🇹

   We investigate unpolarized and polarized gluon distributions and their applications to the Ioffe-time distributions, which are related to lattice QCD calculations of parton distribution functions. Guided by the counting rules based on the perturbative QCD at large momentum fraction $x$ and the color coherence of gluon couplings at small $x$, we parametrize gluon distributions in the helicity basis. By fitting the unpolarized gluon distribution, the inferred polarized gluon distribution from our parametrization agrees with the one from global analysis. A simultaneous fit to both unpolarized and polarized gluon distributions is also performed to explore the model uncertainty. The agreement with the global analysis supports the $(1-x)$ power suppression of the helicity-antialigned distribution relative to the helicity-aligned distribution. The corresponding Ioffe-time distributions and their asymptotic expansions are calculated from the gluon distributions. Our results of the Ioffe-time distributions can provide guidance to the extrapolation of lattice QCD data to the region lacking precise gluonic matrix elements. Therefore, they can help regulate the ill-posed inverse problem associated with extracting the gluon distributions from discrete data from first-principle calculations, which are available in a limited range of the nucleon momentum and the spatial separation between the gluonic currents. Given various limitations in obtaining lattice QCD data at large Ioffe time, phenomenological approaches can provide important complementary information to extract the gluon distributions in the entire $x$ region. The possibility of investigating higher-twist effects and other systematic uncertainties in the contemporary first-principle calculations of parton distributions from phenomenologically well-determined Ioffe-time distributions in the large Ioffe-time region is also discussed.

   hep-phhep-latnucl-thPRD(2021)·25 citations
3. 03*

   Magnetized vector boson gas at any temperature

   G. Quintero Angulo🇨🇺 · L. C. Suárez González🇨🇺 · A. Pérez Martínez🇨🇺 · H. Pérez Rojas🇨🇺

   We study the thermodynamic properties of a relativistic magnetized neutral vector boson gas at any temperature. By comparing the results with the low temperature and the non relativistic descriptions of this gas, we found that the fully relativistic case can be separated in two regimes according to temperature. For low temperatures, magnetic field effects dominate and the system shows a spontaneous magnetization, its pressure splits in two components and, eventually, a transversal magnetic collapse might occur. In the high temperature region, the gas behavior is led by pair production. The presence of antiparticles preserves the isotropy in the pressure, and increases the magnetization and the total pressure of the system by several orders. Astrophysical implications of those behaviors are discussed.

   hep-phastro-ph.HEcond-mat.quant-gasPRC(2021)·3 citations
4. 04*

   Single-top-quark production in the $t$-channel at NNLO

   John Campbell🇺🇸 · Tobias Neumann🇺🇸 · Zack Sullivan🇺🇸

   We present a calculation of t-channel single-top-quark production and decay in the five-flavor scheme at NNLO. Our results resolve a disagreement between two previous calculations of this process that found a difference in the inclusive cross section at the level of the NNLO coefficient itself. We compare in detail with the previous calculations at the inclusive, differential and fiducial level including b-quark tagging at a fixed scale $\mu =m_t$. In addition, we advocate the use of double deep inelastic scattering (DDIS) scales (${\mu }^2=Q^2$ for the light-quark line and ${\mu }^2=Q^2+m_t^2$ for the heavy-quark line) that maximize perturbative stability and allow for robust scale uncertainties. All NNLO and NLO$\otimes$NLO contributions for production and decay are included in the on-shell and vertex-function approximation. We present fiducial and differential results for a variety of observables used in Standard Model and Beyond Standard Model analyses, and find an important difference between the NLO and NNLO predictions of exclusive $t+n$-jet cross sections. Overall we find that NNLO corrections are crucial for a precise identification of the t-channel process.

   hep-phhep-exJHEP(2021)·144 citations
5. 05*

   Electroweak axial structure functions and improved extraction of the $V_{ud}$ CKM matrix element

   K. Shiells🇨🇦 · P.G. Blunden🇨🇦 · W. Melnitchouk🇺🇸

   We present a comprehensive analysis of the $\gamma W$ interference radiative correction to the neutron $\beta$-decay matrix element. Within a dispersion relations approach, we compute the axial-vector part of the $\gamma W$ box amplitude ${\square }_A^{\gamma W}$ in terms of the isoscalar part of the $F_3^{\gamma W}$ interference structure function. Using the latest available phenomenology for $F_3^{\gamma W}$ from the nucleon elastic, resonance, deep-inelastic, and Regge regions, we find the real part of the box correction to be ${\square }_A^{\gamma W}=3.90(9)\times 10^{-3}$. This improved correction gives a theoretical estimate of the CKM matrix element $|V_{ud}{|}^2=0.94805(26)$, which represents a 4$\sigma$ violation of unitarity.

   hep-phhep-exnucl-thPRD(2021)·99 citations
6. 06*

   Lepton-pair production in di-pion $\tau$ lepton decays

   J. L. Gutiérrez Santiago🇲🇽 · G. López Castro🇲🇽 · P. Roig🇲🇽

   We study the ${\tau }^{-}\to {\nu }_{\tau }{\pi }^{-}{\pi }^0{\ell }^{+}{\ell }^{-}$ ($\ell =e,\mu$) decays, which are $O({\alpha }^2)$-suppressed with respect to the dominant di-pion tau decay channel. Both the inner-bremsstrahlung and the structure- (and model-)dependent contributions are considered. In the $\ell =e$ case, structure-dependent effects are $\mathcal{O}(1\%)$ in the decay rate, yielding a clean prediction of its branching ratio, $2.3\times 10^{-5}$, measurable with BaBar or Belle(-II) data. For $\ell =\mu$, both contributions have similar magnitude and we get a branching fraction of $(1.6\pm 0.3)\times 10^{-7}$, reachable by the end of Belle-II operation. These decays allow to study the dynamics of strong interactions with simultaneous weak and electromagnetic probes; their knowledge will contribute to reducing backgrounds in lepton flavor/number violating searches.

   hep-phhep-exPRD(2021)·13 citations
7. 07*

   Gauge-invariant TMD factorization for Drell-Yan hadronic tensor at small x

   Ian Balitsky🇺🇸

   The Drell-Yan hadronic tensor for electromagnetic (EM) current is calculated in the Sudakov region $s\gg Q^2\gg q_{\perp }^2$ with $\frac{1}{Q^2}$ accuracy, first at the tree level and then with the double-log accuracy. It is demonstrated that in the leading order in $N_c$ the higher-twist quark-quark-gluon TMDs reduce to leading-twist TMDs due to QCD equation of motion. The resulting tensor for unpolarized hadrons is EM gauge-invariant and depends on two leading-twist TMDs: $f_1$ responsible for total DY cross section, and Boer-Mulders function $h_1^{\perp }$. The order-of-magnitude estimates of angular distributions for DY process seem to agree with LHC results at corresponding kinematics.

   hep-phJHEP(2021)·25 citations
8. 08*

   LHC as a photon-photon collider: bounds on ${\Gamma }_{X\to \gamma \gamma }$

   S. I. Godunov🇷🇺 · E. K. Karkaryan🇷🇺 · V. A. Novikov🇷🇺 · A. N. Rozanov🇷🇺 · M. I. Vysotsky🇷🇺 · E. V. Zhemchugov🇷🇺

   In the relatively recent CMS data, there is a hint on the existence of a resonance with the mass 28 GeV coupling to muons. Such a resonance should also couple to photons through the fermion loop, therefore it can be searched for in ultraperipheral collisions (UPC) of protons. We set an upper bound on the $X\gamma \gamma$ coupling constant from the data on ${\mu }^{+}{\mu }^{-}$ pair production in UPC at the LHC. Our approach can be used for similar resonances should they appear in the future.

   hep-phhep-exPRD(2021)·6 citations
9. 09*

   Spontaneous CP violation by modulus $\tau$ in $A_4$ model of lepton flavors

   Hiroshi Okada🇰🇷 · Morimitsu Tanimoto🇯🇵

   We discuss the modular $A_4$ invariant model of leptons combining with the generalized CP symmetry. In our model, both CP and modular symmetries are broken spontaneously by the vacuum expectation value of the modulus $\tau$. The source of the CP violation is a non-trivial value of $\mathrm{Re}[\tau ]$ while other parameters of the model are real. The allowed region of $\tau$ is in very narrow one close to the fixed point $\tau =i$ for both normal hierarchy (NH) and inverted ones (IH) of neutrino masses. The CP violating Dirac phase ${\delta }_{CP}$ is predicted clearly in $[98^{\circ },110^{\circ }]$ and $[250^{\circ },262^{\circ }]$ for NH at $3\sigma$ confidence level. On the other hand, ${\delta }_{CP}$ is in $[95^{\circ },100^{\circ }]$ and $[260^{\circ },265^{\circ }]$ for IH at $5\sigma$ confidence level. The predicted $\sum m_i$ is in $[82,102]$ meV for NH and $\sum m_i=[134,180]$ meV for IH. The effective mass $⟨m_{ee}⟩$ for the $0\nu \beta \beta$ decay is predicted in $[12.5,20.5]$ meV and $[54,67]$ meV for NH and IH, respectively.

   hep-phJHEP(2021)·96 citations
10. 10*

    Multiscalar $B-L$ extension based on $S_4$ flavor symmetry for neutrino mass and mixing

    V. V. Vien🇻🇳 · H. N. Long🇻🇳

    A multiscalar and nonrenormalizable $B-L$ extension of the standard model (SM) with $S_4$ symmetry which successfully explains the recent observed neutrino oscillation data is proposed. The tiny neutrino masses and their hierarchies are generated via the type-I seesaw mechanism. The model reproduces the recent experiments of neutrino mixing angles and Dirac CP violating phase in which the atmospheric angle $({\theta }_{23})$ and the reactor angle $({\theta }_{13})$ get the best-fit values while the solar angle $({\theta }_{12})$ and Dirac CP violating phase ($\delta$) belong to $3\text{si}$ range of the best-fit value for normal hierarchy (NH). For inverted hierarchy (IH), ${\theta }_{13}$ gets the best-fit value and ${\theta }_{23}$ together with $\text{de}$ belongs to $1\text{si}$ range while ${\theta }_{12}$ belongs to $3\text{si}$ range of the best-fit value. The effective neutrino masses are predicted to be $⟨m_{ee}⟩=6.81\text{mbox}meV$ for NH and $⟨m_{ee}⟩=48.48\text{mbox}meV$ for IH being in good agreement with the most recent experimental data.

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

    QCD evolution of the gluon Sivers function in heavy flavor dijet production at the Electron-Ion Collider

    Zhong-Bo Kang🇺🇸 · Jared Reiten🇺🇸 · Ding Yu Shao🇺🇸 · John Terry🇺🇸

    Using Soft-Collinear Effective Theory, we develop the transverse-momentum-dependent factorization formalism for heavy flavor dijet production in polarized-proton-electron collisions. We consider heavy flavor mass corrections in the collinear-soft and jet functions, as well as the associated evolution equations. Using this formalism, we generate a prediction for the gluon Sivers asymmetry for charm and bottom dijet production at the future Electron-Ion Collider. Furthermore, we compare theoretical predictions with and without the inclusion of finite quark masses. We find that the heavy flavor mass effects can give sizable corrections to the predicted asymmetry.

    hep-phhep-exnucl-thJHEP(2021)·25 citations
12. 12*

    The resonances $X(4140)$, $X(4160)$, and $P_{cs}(4459)$ in the decay of ${\Lambda }_b\to J/\psi \Lambda \varphi$

    Wen-Ying Liu🇨🇳 · Wei Hao🇨🇳 · Guan-Ying Wang🇨🇳 · Yan-Yan Wang🇨🇳 · En Wang🇨🇳 · De-Min Li🇨🇳

    We study the decay of ${\Lambda }_b\to J/\psi \Lambda \varphi$ by taking into account the intermediate resonances $X(4140)$, $X(4160)$, and $P_{cs}(4459)$. In addition to the peak of the $X(4140)$, we also find a bump structure around 4160 MeV followed by a cusp structure around $D_s^{\ast }{\bar{D}}_s^{\ast }$ threshold in the $J/\psi \varphi$ invariant mass distribution of the ${\Lambda }_b\to J/\psi \Lambda \varphi$ process, which can be associated to the $D_s^{\ast }{\bar{D}}_s^{\ast }$ molecular state $X(4160)$. We also show that this reaction can also be used to confirm the existence of the hidden-charm pentaquark $P_{cs}(4459)$ with strangeness. We predict an enhancement structure close to the threshold in the $D_s^{\ast }{\bar{D}}_s^{\ast }$ invariant mass distribution of the ${\Lambda }_b\to D_s^{\ast }{\bar{D}}_s^{\ast }\Lambda$ process, which is the reflection of the $X(4160)$ and should not be misidentified with a new resonance. We strongly suggest experimentalists to further measure these processes, which can be useful to clarify the nature of $X(4140)$ and $X(4160)$ resonances, and to confirm the existence of the $P_{cs}(4459)$.

    hep-phPRD(2021)·25 citations
13. 13*

    Angular correlations in pA collisions from CGC: multiplicity and mean transverse momentum dependence of $v_2$

    Tolga Altinoluk🇵🇱 · Néstor Armesto🇪🇸 · Alex Kovner🇺🇸 · Michael Lublinsky🇮🇱 · Vladimir V. Skokov🇺🇸

    Within the dense-dilute Color Glass Condensate approach, and using the Golec-Biernat-Wuesthoff model for the dipole scattering amplitude, we calculate $v_2^2$ as well as the correlations between $v_2^2$ and both the total multiplicity and the mean transverse momentum of produced particles. We find that the correlations are generally very small consistent with the observations. We note an interesting sharp change in the value of $v_2^2$ as well as of its correlations as a function of the width of the transverse momentum bin. This crossover is associated with the change from Bose enhancement dominance of the correlation for narrow bin to HBT dominated correlations for larger bin width.

    hep-phEPJC(2021)·12 citations
14. 14*

    Nucleon electric dipole moment from polarized deep inelastic scattering

    Yoshitaka Hatta🇺🇸

    In a previous paper \cite{Hatta:2020ltd}, we have pointed out the connection between the $CP$-odd three-gluon (Weinberg) operator and certain twist-four corrections in polarized deep inelastic scattering. Based on this observation, we give a numerical estimate of the electric dipole moment of the proton and neutron induced by the Weinberg operator. Our result is smaller than the previous estimates based on QCD sum rules by a factor of about 3 or more.

    hep-phPLB(2021)·11 citations
15. 15*

    Light dark matter from dark sector decay

    Yu Cheng🇨🇳 · Wei Liao🇨🇳

    We study the possibility that light dark matter can be produced with right relic density by the decay of other dark sector particles. We study this possibility in a model with right-handed neutrinos, a dark sector singlet scalar and a dark sector singlet fermion. The decay of the heavier dark sector singlet scalar gives rise to the lighter dark sector singlet fermion which serves as the dark matter candidate. We show that the right dark matter relic density can be produced by the decay of the dark sector singlet scalar. We find that the mass of the dark sector singlet fermion can be GeV scale or MeV scale and the interaction of the dark sector singlet fermion is very weak. The dark sector singlet scalar can have a mass of GeV-TeV scale and can have weak scale interactions with the Standard Model(SM) particles. So, in this scenario, dark matter has an interaction with the SM much weaker than the weak interaction, but the dark sector still has weak scale interaction with the SM.

    hep-phPLB(2021)·14 citations
16. 16*

    Masses and decay constants of (axial-)vector mesons at finite chemical potential

    Pascal J. Gunkel🇩🇪 · Christian S. Fischer🇩🇪

    We update our previous results for (pseudo-)scalar mesons at zero temperature and finite quark chemical potential and generalize the investigation to include (axial-)vector mesons. We determine bound-state properties such as meson masses and decay constants up to chemical potentials far in the first-order coexistence region. To extract the bound-states properties, we solve the Bethe-Salpeter equation and utilize Landau-gauge quark and gluon propagators obtained from a coupled set of (truncated) Dyson-Schwinger equations with N${}_{\text{f}}=2+1$ dynamical quark flavors at finite chemical potential and vanishing temperature. For multiple (pseudo-)scalar and (axial-)vector mesons, we observe constant masses and decay constants for chemical potentials up to the coexistence region of the first-order phase transition thus verifying explicitly the Silver-Blaze property of QCD. Inside the coexistence region the pion becomes more massive and its decay constants decrease, whereas corresponding quantities for the (axial-)vector mesons remain (almost) constant.

    hep-phEPJA(2021)·16 citations
17. 17*

    Quark mixing with soft breaking of the parity in the minimal Left-Right model

    Alessio Maiezza🇭🇷

    We study the possibility of soft breaking effects of the generalized parity within the minimal Left-Right model. One aim of the paper is to elaborate on the potentiality, the limit, and the predictivity of a restored parity at high scale. While revisiting the issue of strong CP in the Left-Right theories, we motivate the possibility of explicit-parity-breaking, that we then parameterize in the right-handed quark mixing matrix. The strong CP parameter $\bar{\theta }$ is also parameterized in terms of the breaking. We discuss some possible phenomenological consequences in this scenario. In particular, the constraint provided by $\bar{\theta }$ enables us to quantify the maximal deviation of the right-handed quark mixings from the standard case with exact parity in term of a single parameter. This deviation has a direct impact on flavor physics.

    hep-ph3 citations
18. 18*

    Study of $qqq\bar{q}Q$ pentaquark system in the Chiral Quark Model

    Qi Zhang🇨🇳 · Xiao-Huang Hu🇨🇳 · Bing-Ran He🇨🇳 · Jia-Lun Ping🇨🇳

    With the discovery of some hidden-charm pentaquark resonances by the LHCb Collaboration, investigations of pentaquark states containing heavy quarks have aroused the interest of theorists. We study herein $qqq\bar{q}Q$ ($q=u$ or $d$, $Q=c$ or $b$) pentaquark system, in the framework of the chiral quark model. In consequence, some charmed and bottomed pentaquarks are considered to exist by five-body dynamical calculations. In the charm sector, ${\Sigma }_c\pi (I{J}^P=0{\frac{1}{2}}^{-})$ and ${\Sigma }_c^{\ast }\pi (I{J}^P=0{\frac{3}{2}}^{-})$ are possible candidates of ${\Lambda }_c(2595)$ and ${\Lambda }_c(2625)$, respectively. Besides, two high-spin states, ${\Sigma }_c^{\ast }\rho (I{J}^P=0{\frac{5}{2}}^{-})$ and $\Delta D^{\ast }(I{J}^P=1{\frac{5}{2}}^{-})$, are also found in the energy region of $3.2\sim 3.3$ GeV. In the bottom sector, ${\Sigma }_b\pi (I{J}^P=0{\frac{1}{2}}^{-})$, ${\Sigma }_b^{\ast }\pi (I{J}^P=0{\frac{3}{2}}^{-})$ could be candidates of ${\Lambda }_b(5912)$ and ${\Lambda }_b(5920)$, respectively. And ${\Sigma }_b^{\ast }\rho (I{J}^P=0{\frac{5}{2}}^{-})$ and $\Delta B^{\ast }(I{J}^P=1{\frac{5}{2}}^{-})$ are found in the energy region of $6.5\sim 6.6$ GeV. ${\Sigma }_c^{(\ast )}\pi$ and ${\Sigma }_b^{(\ast )}\pi$ are expected as compact states, while ${\Sigma }_c^{\ast }\rho$, ${\Sigma }_b^{\ast }\rho$, $\Delta D^{\ast }$ and $\Delta B^{\ast }$ are expected as molecular states.

    hep-phhep-exhep-latEPJC(2021)·6 citations
19. 19*

    Parton color reconnection in Herwig 7 using a spacetime event topology

    Johannes Bellm🇸🇪 · Cody B. Duncan🇦🇺 · Stefan Gieseke🇩🇪 · Miroslav Myska🇨🇿 · Andrzej Siodmok🇵🇱

    Herwig 7 is a general-purpose Monte Carlo generator of particle collisions comprising both hard perturbative as well as soft phenomenological physics. Herwig is therefore capable to describe the entire final state of hadronized particles in a collision event. A spacetime topology of a parton system entering hadronization is fully described and tested for the first time. A combination of information from particles momenta and spacetime positions is utilized to minimize a boost-invariant distance measure of the parton system. We present a reasonable agreement of the model with a selection of experimental data and conclude that spacetime event topology can be meaningfully used in the further development.

    hep-phPoS(2021)·1 citation
20. 20*

    Lepton-Quark Fusion at Hadron Colliders, precisely

    Admir Greljo🇨🇭 · Nudzeim Selimovic🇨🇭

    When a TeV-scale leptoquark has a sizeable Yukawa coupling, its dominant production mechanism at hadron colliders is the partonic-level lepton-quark fusion. Even though the parton distribution functions for leptons inside the proton are minuscule, they get compensated by the resonant enhancement. We present the first computation of higher order radiative corrections to the resonant leptoquark production cross section at the Large Hadron Collider (LHC). Next-to-leading (NLO) QCD and QED corrections are similar in size but come with the opposite sign. We compute NLO $K$-factors for a wide range of scalar leptoquark masses, as well as, all possible combinations of quark and lepton flavors and leptoquark charges. Theoretical uncertainties due to the renormalisation and factorisation scale variations and the limited knowledge of parton distribution functions are quantified. We finally discuss how to disentangle the flavor structure of leptoquark interactions by exploiting the interplay between different production channels.

    hep-phhep-exJHEP(2021)·49 citations
21. 21*

    Comparison of lattice QCD+QED predictions for radiative leptonic decays of light mesons with experimental data

    R. Frezzotti🇮🇹 · M. Garofalo🇩🇪 · V. Lubicz🇮🇹 · G. Martinelli🇮🇹 · C.T. Sachrajda🇬🇧 · F. Sanfilippo🇮🇹 · S. Simula🇮🇹 · N. Tantalo🇮🇹

    We present a comparison of existing experimental data for the radiative leptonic decays $P\to \ell {\nu }_{\ell }\gamma$, where $P=K$ or $\pi$ and $\ell =e$ or $\mu$, from the KLOE, PIBETA, E787, ISTRA+ and OKA collaborations with theoretical predictions based on the recent non-perturbative determinations of the structure-dependent vector and axial-vector form factors, $F_V$ and $F_A$ respectively. These were obtained using lattice QCD+QED simulations at order $O({\alpha }_{\mathrm{em}})$ in the electromagnetic coupling. We find good agreement with the KLOE data on $K\to e{\nu }_e\gamma$ decays from which the form factor $F^{+}=F_V+F_A$ can be determined. For $K\to \mu {\nu }_{\mu }\gamma$ decays we observe differences of up to 3\,-\,4 standard deviations at large photon energies between the theoretical predictions and the data from the E787, ISTRA+ and OKA experiments and similar discrepancies in some kinematical regions with the PIBETA experiment on radiative pion decays. A global study of all the kaon-decay data within the Standard Model results in a poor fit, largely because at large photon energies the KLOE and E787 data cannot be reproduced simultaneously in terms of the same form factor $F^{+}$. The discrepancy between the theoretical and experimental values of the form factor $F^{-}=F_V-F_A$ is even more pronounced. These observations motivate future improvements of both the theoretical and experimental determinations of the structure-dependent form factors $F^{+}$ and $F^{-}$, as well as further theoretical investigations of models of "new physics" which might for example, include possible flavor changing interactions beyond $V-A$ and/or non-universal corrections to the lepton couplings.

    hep-phhep-exhep-latPRD(2021)·35 citations
22. 22*

    Novel multi-lepton signatures of dark sectors in light meson decays

    Matheus Hostert🇺🇸 · Maxim Pospelov🇺🇸

    We point out kaon decays to multiple charged leptons as a novel probe of light dark particles $X$. Previously neglected channels, such as $K^{+}\to {\pi }^{+}\left(XX\to 2(e^{+}{e}^{-})\right)$, $K_L\to {\pi }^0\left(XX\to 2(e^{+}{e}^{-})\right)$, and $K_S\to \left(XX\to 2(e^{+}{e}^{-})\right)$ may have very large rates, exceeding not only the Standard Model expectations but also possible backgrounds, such as Dalitz decays of neutral pions. We apply this idea to dark sector models where the production of dark Higgses or heavy neutral leptons leads to final states with several visible dark photons. We also investigate a recently proposed model of an MeV-scale QCD axion, where the rates for kaon decays to multiple axion states are large due to the non-linear interactions of the axion with the light mesons. In addition, we point out new probes of this axion in pion decays, such as the single production of $a$ in ${\pi }^{+}\to \nu \left((e^{+}{)}^{\ast }\to e^{+}a\to e^{+}{e}^{+}{e}^{-}\right)$, double production in pion capture ${\pi }^{-}+(p\text{ or D})\to aa+(n\text{ or }nn)\to 2(e^{+}{e}^{-})+(n\text{ or }nn)$, as well as ${\pi }^0\to aaa\to 3(e^{+}{e}^{-})$. The latter decay is fixed at $\mathcal{B}({\pi }^0\to aaa)=1.0\times 10^{-3}$ for a $17$ MeV axion.

    hep-phhep-exPRD(2022)·49 citations
23. 23*

    Large-$N_c$ and renormalization group constraints on parity-violating low-energy coefficients for three-derivative operators in pionless effective field theory

    Son T. Nguyen🇺🇸 · Matthias R. Schindler🇺🇸 · Roxanne P. Springer🇺🇸 · Jared Vanasse🇺🇸

    We extend from operators with one derivative to operators with three derivatives the analysis of two-body hadronic parity violation in a combined pionless effective field theory (EFT${}_{\pi /}$) and large-$N_c$ expansion, where $N_c$ is the number of colors in quantum chromodynamics (QCD). In elastic scattering, these operators contribute to $S$-$P$ and $P$-$D$ wave transitions, with five operators and their accompanying low energy coefficients (LECs) characterizing the $S$-$P$ transitions and six operators and LECs those in $P$-$D$ transitions. We show that the large-$N_c$ analysis separates them into leading order in $N_c$, next-to-leading order in $N_c$, etc. Relationships among EFT${}_{\pi /}$ LECs emerge in the large-$N_c$ expansion. We also discuss the renormalization scale dependence of these LECs. Our analysis can complement lattice QCD calculations and help prioritize future parity-violating experiments.

    hep-phnucl-thPRC(2021)·6 citations
24. 24*

    Effective Field Theory for Leptoquarks

    Bianka Mecaj🇩🇪 · Matthias Neubert🇩🇪

    Leptoquarks enter in several extensions of the Standard Model as possible solutions to a number of observed anomalies. We work within the soft-collinear effective theory framework to present a detailed analysis of the decay rates of the three leptoquarks that appear the most in literature, the scalars $S_1$ and $S_3$ and the vector $U_1^{\mu }$. Using renormalization group methods we resum the large logarithms arising from the evolution of the Wilson coefficients between the New Physics scale and the electroweak scale. We also derive the tree-level matching relations for the Wilson coefficients in the effective theory for some specific leptoquark models.

    hep-phJHEP(2023)·9 citations
25. 25*

    Time reclustering for jet quenching studies

    Liliana Apolinário🇵🇹 · André Cordeiro🇵🇹 · Korinna Zapp🇸🇪

    The physics program of ultra-relativistic heavy-ion collisions at the Large Hadron Collider (LHC) and Relativistic Heavy-Ion Collider (RHIC) has brought a unique insight into the hot and dense QCD matter created in such collisions, the Quark-Gluon Plasma (QGP). Jet quenching, a collection of medium-induced modifications of the jets' internal structure that occur through their development in dense QCD matter, has a unique potential to assess the time structure of the produced medium. In this work, we perform an exploratory study to identify jet reclustering tools that can potentiate future QGP tomographic measurements with jets at current energies. Our results show that by using the inverse of formation time to obtain the jet clustering history, one can identify more accurately the time structure of QCD emissions inside jets, even in the presence of jet quenching.

    hep-phEPJC(2021)·36 citations
26. 26*

    Assessment of systematic theory uncertainties in IAM unitarization

    Juan Escudero-Pedrosa🇪🇸 · Felipe J. Llanes-Estrada🇪🇸 · José Antonio Oller🇪🇸 · Alexandre Salas-Bernárdez🇪🇸

    Effective Field Theories (EFTs) for Goldstone Boson scattering at a low order allow the computation of near--threshold observables in terms of a few coefficients arranged by a counting. As a matter of principle they should make sense up to an energy scale $E\sim 4\pi F$ but the expansion in powers of momentum violates exact elastic unitarity and renders the derivative expansion unreliable at much lower energies. If new--physics deviations from the Standard Model are found and encoded in low-energy coefficients, perhaps at the LHC, it will be profitable to extend the reach of the EFT to regimes where partial waves are saturating unitarity. The methods known in hadron physics as "Unitarized Chiral Perturbation Theory" extend the EFT up to its nominal reach or up to the first new physics resonance or structure (if found below that energy reach) in the partial wave amplitude, but they usually have unknown uncertainties. We recapitulate our analysis of the systematic theory uncertainties of the well known Inverse Amplitude Method (IAM).

    hep-phNucl.Part.Phys.Proc.(2021)·3 citations
27. 27*

    On the observability of field-assisted birefringent Delbrück scattering

    N. Ahmadiniaz🇩🇪 · M. Bussmann🇩🇪 · T. E. Cowan🇩🇪 · A. Debus🇩🇪 · T. Kluge🇩🇪 · R. Schützhold🇩🇪

    We consider the scattering of an x-ray free-electron laser (XFEL) beam on the superposition of a strong magnetic field ${\mathbf{B}}_{\mathrm{ext}}$ with the Coulomb field ${\mathbf{E}}_{\mathrm{ext}}$ of a nucleus with charge number $Z$. In contrast to pure Delbrück scattering (Coulomb field only), the magnetic field ${\mathbf{B}}_{\mathrm{ext}}$ introduces an asymmetry (i.e., polarization dependence) and renders the effective interaction volume quite large, while the nuclear Coulomb field facilitates a significant momentum transfer $\Delta \mathbf{k}$. For a field strength of $B_{\mathrm{ext}}=10^6\mathrm{T}$ (corresponding to an intensity of order $10^{22}W/c{\mathrm{m}}^2$) and an XFEL frequency of 24 keV, we find a differential cross section $d\sigma /d\Omega \sim 10^{-25}{Z}^2/(\Delta \mathbf{k}{)}^2$ in forward direction for one nucleus. Thus, this effect might be observable in the near future at facilities such as the Helmholtz International Beamline for Extreme Fields (HIBEF) at the European XFEL.

    hep-phPRD(2021)·16 citations
28. 28*

    A search for a cosmologically-relevant boson in muon decay

    J.I. Collar🇺🇸

    Experiments looking for a lepton flavor-violating decay ${\mu }^{+}\to e^{+}{X}^0$ are reviewed in light of present-day germanium detector technology, with an eye on scenarios where a long-lived, slow-moving massive boson $X^0$ might have a cosmological impact. A broad swath of interesting, unexplored parameter space very close to the kinematic limit of the decay is found to be within the reach of a new proposed search. A number of possible roles for $X^0$ in past and present epochs can be investigated.

    ↳ nucl-exastro-ph.COhep-exhep-phPRD(2021)·4 citations
29. 29*

    Probing fast oscillating scalar dark matter with atoms and molecules

    Dionysios Antypas🇩🇪 · Oleg Tretiak🇩🇪 · Ke Zhang🇩🇪 · Antoine Garcon🇩🇪 · Gilad Perez🇮🇱 · Mikhail G. Kozlov🇷🇺 · Stephan Schiller🇩🇪 · Dmitry Budker🇩🇪

    Light scalar Dark Matter with scalar couplings to matter is expected within several scenarios to induce variations in the fundamental constants of nature. Such variations can be searched for, among other ways, via atomic spectroscopy. Sensitive atomic observables arise primarily due to possible changes in the fine-structure constant or the electron mass. Most of the searches to date have focused on slow variations of the constants (i.e. modulation frequencies $<$ 1 Hz). In a recent experiment \mbox{[Phys. Rev. Lett. 123, 141102 (2019)]} called WReSL (Weekend Relaxion-Search Laboratory), we reported on a direct search for rapid variations in the radio-frequency band. Such a search is particularly motivated within a class of relaxion Dark Matter models. We discuss the WReSL experiment, report on progress towards improved measurements of rapid fundamental constant variations, and discuss the planned extension of the work to molecules, in which rapid variations of the nuclear mass can be sensitively searched for.

    ↳ physics.atom-phhep-phQuantum Sci.Technol.(2021)·27 citations
30. 30*

    Phenomenological QCD equations of state for neutron star dynamics: Nuclear-2SC continuity and evolving effective couplings

    Toru Kojo🇨🇳 · Defu Hou🇨🇳 · Jude Okafor🇨🇳 · Hajime Togashi🇯🇵

    We delineate the quark-hadron continuity by constructing QCD equations of state for neutron star dynamics, covering the wide range of charge chemical potential (${\mu }_Q$) and temperatures ($T$). Based on the nuclear-2SC continuity scenario, we match equations of state for nuclear and two-flavor color-superconducting (2SC) quark matter, where the matching baryon density is $n_B\simeq 1.5n_0$ ($n_0\simeq 0.16\mathrm{f}{\mathrm{m}}^{-3}$: nuclear saturation density). The effective vector and diquark couplings in a quark matter model evolve as functions of $n_B,{\mu }_Q,T$, whose low density values are constrained by the nuclear matter properties and neutron star radii, with the high density behavior by the two-solar mass ($2M_{\odot }$) constraint. With couplings dependent on $n_B$, we examined how smooth the nuclear-2SC continuity can be, and found problems in matching nuclear and 2SC entropies at low temperatures. To proceed with the continuity scenario, we enforce smooth matching by making the couplings ($n_B,{\mu }_Q,T$)-dependent. In effect, this adds phenomenological contributions which we call "X". After the phenomenological matching, we take the rest as our predictions. The 2SC and color-flavor-locked (CFL) phases computed with these evolving couplings are called 2SCX and CFLX. The CFLX appears around $n_B\simeq 2$-$4n_0$ and, in contrast to the conventional CFL, has non-negligible dependence on $({\mu }_Q,T)$. To examine the astrophysical consequences of our modeling, we add charged leptons and neutrinos, and study the composition of matter for lepton fractions relevant for protoneutron stars and neutron star mergers. The abundance of neutrinos and thermal effects reduce the strangeness fraction and stiffen equations of state. For a neutrino trapped neutron star at $T\simeq 30$ MeV with a lepton fraction $Y_L\simeq 0.05$, the mass is larger than its cold static counterpart by $\sim 0.1M_{\odot }$.

    ↳ astro-ph.HEhep-phhep-thnucl-thPRD(2021)·33 citations
31. 31*

    Latest D0 results on exotic hadrons produced in $p\bar{p}$ collisions

    A. Drutskoy (on behalf of the D0 collaboration)🇷🇺

    Prompt and nonprompt productions of exotic multiquark states are studied using the $\sim$10.4 fb${}^{-1}$ data sample collected by the D0 experiment in Tevatron $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV. The recent D0 results on the prompt and nonprompt production of the $X(3872)$ and $Z_c^{+}(3900)$ states and the $P_c$ pentaquarks at the 4450 MeV region are reported. Signals corresponding to these states are found in the nonprompt production, whereas only the $X(3872)$ state is seen in the prompt production. The ratio of prompt to nonprompt $X(3872)$ production is about three times larger in the D0 measurement than that obtained by the ATLAS experiment at 8 TeV. Theoretically, the production, formation, coalescence, and disassociation processes are expected to be quite different for conventional mesons with a spatial size of (0.4-0.8) fm, compact multiquark states such as tetraquarks with a size of a few fm, and spatially extended molecular states with a size of (4-10) fm. They can be differently affected in prompt hadron-hadron collisions where there are many additional particles emitted from the interaction point. Consequently, the prompt to nonprompt production ratio of spatially extended exotic states can be suppressed at LHC comparing with the Tevatron conditions, because of large difference in the hadron-hadron collisions particle multiplicity. The prompt production studies provide an opportunity to better understand the nature of exotic states.

    ↳ hep-exhep-phPoS(2021)·0 citations
32. 32*

    The path from lattice QCD to the short-distance contribution to $0\nu \beta \beta$ decay with a light Majorana neutrino

    Zohreh Davoudi🇺🇸 · Saurabh V. Kadam🇺🇸

    Neutrinoless double-$\beta$ ($0\nu \beta \beta$) decay of certain atomic isotopes, if observed, will have significant implications for physics of neutrinos and models of physics beyond the Standard Model. In the simplest scenario, if the mass of the light neutrino of the Standard Model has a Majorana component, it can mediate the decay. Systematic theoretical studies of the decay rate in this scenario, through effective field theories matched to \emph{ab initio} nuclear many-body calculations, are needed to draw conclusions about the hierarchy of neutrino masses, and to plan the design of future experiments. However, a recently identified short-distance contribution at leading order in the effective field theory amplitude of the subprocess $nn\to pp(ee)$ remains unknown, and only lattice quantum chromodynamics (QCD) can directly and reliably determine the associated low-energy constant. While the numerical computations of the correlation function for this process are underway with lattice QCD, the connection to the physical amplitude, and hence this short-distance contribution, is missing. A complete framework that enables this complex matching is developed in this paper. The complications arising from Euclidean and finite-volume nature of the corresponding correlation function are fully resolved, and the value of the formalism is demonstrated through a simple example. The result of this work, therefore, fills the gap between first-principle studies of the $nn\to pp(ee)$ amplitude from lattice QCD and those from effective field theory, and can be readily employed in the ongoing lattice-QCD studies of this process.

    ↳ hep-lathep-phnucl-thPRL(2021)·51 citations
33. 33*

    $S$-Matrix and Anomaly of de Sitter

    Gia Dvali🇩🇪

    $S$-matrix formulation of gravity excludes de Sitter vacua. In particular, this is organic to string theory. The $S$-matrix constraint is enforced by an anomalous quantum break-time proportional to the inverse values of gravitational and/or string couplings. Due to this, de Sitter can satisfy the conditions for a valid vacuum only at the expense of trivializing the graviton and closed-string $S$-matrixes. At non-zero gravitational and string couplings, de Sitter is deformed by corpuscular $1/N$ effects, similarly to Witten-Veneziano mechanism in QCD with $N$ colors. In this picture, an $S$-matrix formulation of Einstein gravity, such as string theory, nullifies an outstanding cosmological puzzle. We discuss possible observational signatures which are especially interesting in theories with large number of particle species. Species can enhance the primordial quantum imprints to potentially observable level even if the standard inflaton fluctuations are negligible.

    ↳ hep-thastro-ph.COgr-qchep-phSymmetry(2020)·65 citations
34. 34*

    Fluctuations of anisotropic flow from the finite number of rescatterings in a two-dimensional massless transport model

    Hendrik Roch🇩🇪 · Nicolas Borghini🇩🇪

    We investigate the fluctuations of anisotropic transverse flow due to the finite number of scatterings in a two-dimensional system of massless particles. Using a set of initial geometries from a Monte Carlo Glauber model, we study how flow coefficients fluctuate about their mean value at the corresponding eccentricity, for several values of the scattering cross section. We also show how the distributions of the second and third event planes of anisotropic flow about the corresponding participant plane in the initial geometry evolve as a function of the mean number of scatterings in the system.

    ↳ nucl-thhep-phEPJC(2021)·18 citations
35. 35*

    Constraining the initial stages of ultrarelativistic nuclear collisions

    Jakub Jankowski🇵🇱 · Syo Kamata🇵🇱 · Mauricio Martinez🇺🇸 · Michał Spaliński🇵🇱

    It is frequently supposed that quark-gluon plasma created in heavy-ion collisions undergoes free streaming at early times. We examine this issue based on the assumption that a universal attractor dominates the dynamics already at the earliest stages, which offers a way to connect the initial state with the start of the hydrodynamic expansion in an approximate but conceptually transparent fashion. We demonstrate that the centrality dependence of the measured particle multiplicities can be used to quantitatively constrain the pressure anisotropy and find that it strongly depends on the model of the initial energy deposition. As an illustration, we compare three initial state models and show that they predict rather different early-time values of the pressure anisotropy. This strongly suggests that assuming free streaming prior to hydrodynamization is not necessarily compatible with a generic initial state model and that features of the pre-hydrodynamic flow need to be matched with the model of the initial state.

    ↳ nucl-thhep-phnucl-exPRD(2021)·15 citations
36. 36*

    Finite Quantum Field Theory and Renormalization Group

    M. A. Green🇨🇦 · J. W. Moffat🇨🇦

    Renormalization group methods are applied to a scalar field within a finite, nonlocal quantum field theory formulated perturbatively in Euclidean momentum space. It is demonstrated that the triviality problem in scalar field theory, the Higgs boson mass hierarchy problem and the stability of the vacuum do not arise as issues in the theory. The scalar Higgs field has no Landau pole.

    ↳ physics.gen-phhep-phhep-thEur.Phys.J.Plus(2021)·12 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.