Quark Transition Research Articles

Imprints of new physics operators in the semileptonic [formula omitted] process in SMEFT approach

At present, there are several measurements of B decays that exhibit discrepancies with the predictions of the Standard Model, and suggest the presence of new physics in b→s and b→c(u) quark level transitions. Motivated by the prospects of the ongoing high-luminosity B factories, we study the exclusive B→a1(1260)ℓ−ν¯ℓ process within the Standard Model Effective Field Theory (SMEFT) formalism, to understand the sensitivity of various new physics operators. The new physics parameters are constrained by using the experimental branching fractions of the (semi)leptonic B→ℓν¯ and B→(π,ρ,ω)ℓν¯ processes (where ℓ=e,μ,τ) which undergo b→uℓν¯ quark level transitions. We then perform a comprehensive angular analysis of the exclusive B→a1(1260)ℓ−ν¯ℓ process in the Standard Model and in the presence of various new physics operators. We also provide the predictions and comment on various observables, such as branching ratio, forward-backward asymmetry, and the test of lepton flavor non universality of the B→a1(1260)ℓ−ν¯ℓ channel.

Constraining the Onset Density for the QCD Phase Transition with the Neutrino Signal from Core-collapse Supernovae

The occurrence of a first-order hadron–quark matter phase transition at high baryon densities is investigated in astrophysical simulations of core-collapse supernovae, to decipher yet incompletely understood properties of the dense matter equation of state (EOS) using neutrinos from such cosmic events. It is found that the emission of a nonstandard second neutrino burst, dominated by electron antineutrinos, is not only a measurable signal for the appearance of deconfined quark matter but also reveals information about the state of matter at extreme conditions encountered at the supernova (SN) interior. To this end, a large set of spherically symmetric SN models is investigated, studying the dependence on the EOS and the stellar progenitor. General relativistic neutrino-radiation hydrodynamics is employed featuring three-flavor Boltzmann neutrino transport and a microscopic hadron-quark hybrid matter EOS class. Therefore, the DD2 relativistic mean-field hadronic model is employed, and several variations of it, and the string-flip model for the description of deconfined quark matter. The resulting hybrid model covers a representative range of onset densities for the phase transition and latent heats. This facilitates the direct connection between intrinsic signatures of the neutrino signal and properties of the EOS. In particular, a set of linear relations has been found empirically. These potentially provide a constraint for the onset density of a possible QCD phase transition from the future neutrino observation of the next galactic core-collapse SN, if a millisecond electron anti-neutrino burst is present around or less than 1 s.

FCNC charmed-hadron decays with invisible singlet particles in light of recent data

The flavor-changing neutral current (FCNC) decays of charmed hadrons with missing energy (Ɇ) can serve as potentially promising hunting grounds for hints of new physics, as the standard-model backgrounds are very suppressed. A few of such processes have been searched for in recent experiments, specifically D0→ Ɇ by Belle and D0→ π0Ɇ and Λc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Lambda}_c^{+} $$\\end{document}→ pɆ by BESIII, resulting in upper bounds on their branching fractions. We consider them to illuminate the possible contributions of the quark transition c → uɆ with a couple of invisible spinless bosons carrying away the missing energy, assuming that they are not charge conjugates of each other and hence can have unequal masses. We find that these data are complementary in that they constrain different sets of the underlying operators and do not cover the same ranges of the bosons’ masses, but there are regions not yet accessible. From the allowed parameter space, we show that other D-meson decays, such as D → ρɆ, and the charmed-baryon ones Ξc → (Σ, Λ)Ɇ can have sizable branching fractions and therefore may offer further probes of the new-physics interactions. We point out the importance of D0 → γɆ which are not yet searched for but could access parts of the parameter space beyond the reach of the other modes. In addition, we look at a scenario where the invisibles are instead fermionic, namely sterile neutrinos, and a scalar leptoquark mediates c → uɆ. We discuss the implications of the aforesaid bounds for this model. The predictions we make for the various charmed-hadron decays in the different scenarios may be testable in the near future by BESIII and Belle II.

Impact of b → c measurements on [formula omitted] decay in U1 leptoquark model

The measurements of several lepton flavor universality (LFU) violating observables in the decays induced by the quark level transition b→cτν¯ provide an inkling of plausible physics beyond the standard model of electroweak interactions. Such new physics would also impact other sectors. In this work, we estimate the leverage of new physics in b→cτν¯ on Λb→pτν¯ decay in the context of U1 leptoquark model. In this model, the new physics couplings in b→uτν¯ transition can be written in terms of b→cτν¯ couplings and hence the extent of allowed new physics in Λb→pτν¯ would be determined by b→cτν¯ transition. Using the new physics parameter space obtained by performing a fit to all b→cτν¯ data, we obtain predictions of several Λb→pτν¯ observables. We find that the current b→cτν¯ data allows two times of magnitude enhancement in the branching ratio as well as in the LFU ratio. The other observables such as convexity parameter, lepton forward-backward asymmetry, longitudinal polarization of final state baryon and tau lepton are consistent with the SM value.

Testing the phase transition parameters inside neutron stars with the production of protons and lambdas in relativistic heavy-ion collisions

We demonstrate the consistency of the quark deconfinement phase transition parameters in the beta-stable neutron star matter and in the nearly symmetric nuclear matter formed in heavy-ion collisions (HICs). We investigate the proton and $\mathrm{\ensuremath{\Lambda}}$ flow in $\mathrm{Au}+\mathrm{Au}$ collisions at 3 and $4.5\text{ }\text{ }\mathrm{GeV}/\mathrm{nucleon}$ incident beam energies with the pure hadron cascade version of a multiphase transport model. The phase transition in HICs and neutron stars is described based on a class of hybrid equations of state from the quark mean-field model for the hadronic phase and a constant-speed-of-sound parametrization for the high-density quark phase. The measurements of the anisotropic proton flow at $3\text{ }\text{ }\mathrm{GeV}/\mathrm{nucleon}$ by the STAR Collaboration favor a relatively low phase transition density lower than $\ensuremath{\sim}2.5$ times saturation density indicated by the gravitational wave and electromagnetic observations of neutron stars. And the proton flow data at the higher energy of $4.5\text{ }\text{ }\mathrm{GeV}/\mathrm{nucleon}$ can be used to effectively constrain the softness of high-density quark matter equations of state. Finally, compared to the proton flow, the $\mathrm{\ensuremath{\Lambda}}$ flow is found to be less sensitive and not constraining to the equations of state.

B→K and D→K form factors from fully relativistic lattice QCD

We present the result of lattice QCD calculation of the scalar, vector and tensor form factors for the $B\to K\ell^+\ell^-$ decay, across the full physical range of momentum transfer. We use the highly improved staggered quark (HISQ) formalism for all valence quarks on eight ensembles of gluon field configurations generated by the MILC collaboration. These include four flavours of HISQ quarks in the sea, with three ensembles having the light $u/d$ quarks at physical masses. In the first fully relativistic calculation of these form factors, we use the heavy-HISQ method. This allows us to determine the form factors as a function of heavy quark mass from the $c$ to the $b$, and so we also obtain new results for the $D\to K$ tensor form factor. The advantage of the relativistic formalism is that we can match the lattice weak currents to their continuum counterparts much more accurately than in previous calculations; our scalar and vector currents are renormalised fully nonperturbatively and we use a well-matched intermediate momentum-subtraction scheme for our tensor current. Our scalar and vector $B\to K$ form factors have uncertainties of less than 4% across the entire physical $q^2$ range and the uncertainty in our tensor form factor is less than 7%. Our heavy-HISQ method allows us to map out the dependence on heavy-quark mass of the form factors and we can also see the impact of changing spectator quark mass by comparing to earlier HPQCD results for the same quark weak transition but for heavier mesons.

On the moment of inertia of PSR J0737-3039 A from LIGO/Virgo and NICER

ABSTRACT We perform a Bayesian analysis of neutrons star moment of inertia by utilizing the available gravitational-wave data from LIGO/Virgo (GW170817 and GW190425) and mass-radius measurements from the Neutron Star Interior Composition Explorer (PSR J0030+0415 and PSR J0740 + 6620), incorporating the possible phase transition in the pulsar inner core. We find that the moment of inertia of pulsar A in the double pulsar binary J0737-3039 is $\sim 1.30\times 10^{45}\, {\rm g\, cm^2}$, which only slightly depends on the employed hadronic equation of states. We also demonstrate how a moment of inertia measurement would improve our knowledge of the equation of state and the mass–radius relation for neutron stars and discuss whether a quark deconfinement phase transition is supported by the available data and forthcoming data that could be consistent with this hypothesis. We find that if pulsar A is a quark star, its moment of inertia is a large value of $\sim 1.55\times 10^{45}\, {\rm g\, cm^2}$ suggesting the possibility of distinguishing it from (hybrid-)neutron stars with measurements of PSR J0737-3039A moment of inertia. We finally demonstrate the moment-of-inertia-compactness universal relations and provide analytical fits for both (hybrid-)neutron star and quark star results based on our analysis.

Gravitational wave signal from primordial magnetic fields in the Pulsar Timing Array frequency band

The NANOGrav, Parkes, European, and International Pulsar Timing Array (PTA) Collaborations have reported evidence for a common-spectrum process that can potentially correspond to a stochastic gravitational wave background (SGWB) in the 1--100 nHz frequency range. We consider the scenario in which this signal is produced by magnetohydrodynamic (MHD) turbulence in the early Universe, induced by a nonhelical primordial magnetic field at the energy scale corresponding to the quark confinement phase transition. We perform MHD simulations to study the dynamical evolution of the magnetic field and compute the resulting SGWB. We show that the SGWB output from the simulations can be very well approximated by assuming that the magnetic anisotropic stress is constant in time, over a time interval related to the eddy turnover time. The analytical spectrum that we derive under this assumption features a change of slope at a frequency corresponding to the GW source duration that we confirm with the numerical simulations. We compare the SGWB signal with the PTA data to constrain the temperature scale at which the SGWB is sourced, as well as the amplitude and characteristic scale of the initial magnetic field. We find that the generation temperature is constrained to be in the 1--200 MeV range, the magnetic field amplitude must be $>1$\% of the radiation energy density at that time, and the magnetic field characteristic scale is constrained to be $>10$\% of the horizon scale. We show that the turbulent decay of this magnetic field will lead to a field at recombination that can help to alleviate the Hubble tension and can be tested by measurements in the voids of the Large Scale Structure with gamma-ray telescopes like the Cherenkov Telescope Array.

Lepton Polarization Asymmetry in B*s,d → μ+ μ− with new Z′ Couplings

We study the effect of non-universal Z′ boson on the rare leponic decay modes of \( {B}_s^{\ast } \) mesons, mediated by b → sll quark transition. Rare B decays are sensitive to various new physics operators. As B mesons are composite particles, such decay modes of the excited states are ideal for probing new physics beyond the standard model. We have constrained our model parameters from \( {B}_{s,d}-{\overline{B}}_{s,d} \) mixing data to predict the lepton polarization asymmetry of \( {B}_{s,d}^{\ast}\to {\mu}^{+}{\mu}^{-} \) channel. It is found that this asymmetry deviates from its SM prediction along with the Z′ effect.

Isoentropic equations of state of beta -stable hadronic matter with a quark phase transition

We construct isoentropic equations of state (EOSs) of beta -stable dense hadronic matter considering the possibility that a quark deconfinement phase transition can take place. These conditions can be actually realized in different astrophysical contexts like core-collapse supernovae (CCSNe), during the early stages of the evolution of a newly formed neutron star (protoneutron star, PNS) or in the postmerger compact object formed in binary neutron star (BNS) mergers. We consider four different EOSs to describe the hadronic phase: three EOSs from relativistic mean field theory and one EOS recently derived from microscopic calculations in the framework of the Brueckner–Hartree–Fock approach. We combine these hadronic EOSs with a quark matter EOS obtained from a modified MIT-Bag model which takes into account some perturbative corrections in the grand canonical potential due to the quark–quark interaction. The two phases are then joined up through a Gibbs construction. For each model we study thermal and neutrino trapping effects on the matter composition and consequently on the EOS. We finally determine the PNS static structure integrating the Tolman–Oppenheimer–Volkoff equations. We find that the thermal contribution and particularly the effect of neutrino trapping play an important role on the full EOS. The latter can get softer or stiffer according to the strangeness content in the hadronic phase. These effects are thus crucial to provide a proper description of the dynamical evolution of both the postmerger compact object formed in a BNS merger or the PNS formed in a CCSN.

Lepton universality and lepton flavor conservation tests with dineutrino modes

SU(2)_L-invariance links charged dilepton and dineutrino couplings. Phenomenological implications are worked out for flavor changing neutral currents involving strange, charm, beauty and top quark transitions in a model-independent way. We put forward novel tests of lepton universality and lepton flavor conservation in |varDelta c|= |varDelta u|=1 and |varDelta b|= |varDelta q|=1, q=d,s, transitions suitable for the experiments Belle II and BES III. Single top production plus dileptons uniquely probes semileptonic four-fermion |varDelta t|= |varDelta q'|=1, q'=u,c, couplings and further study at the LHC is encouraged. Tests with single top production associated with dileptons and missing energy are suitable for study at future e^+ e^- or muon colliders.

Quark-quark interaction and quark matter in neutron stars

Hyperon ($Y$) mixing in neutron-star matter brings about a remarkable softening of the equation of state (EoS) and the maximum mass is reduced to a value far less than $2M_{\odot}$. One idea to avoid this "hyperon puzzle in neutron stars" is to assume that the many-body repulsions work universally for every kind of baryons. The other is to take into account the quark deconfinement phase transitions from a hadronic EoS to a sufficiently stiff quark-matter EoS. In the present approach, both effects are handled in a common framework. As well as the hadronic matter, the quark matter with the two-body quark-quark interactions are treated within the Brueckner-Bethe-Goldstone theory beyond the mean field frameworks, where interaction parameters are based on the terrestrial data. The derived mass-radius relations of neutron stars show that maximum masses reach over $2M_{\odot}$ even in the cases of including hadron-quark phase transitions, being consistent with the recent observations for maximum masses and radii of neutron stars by the NICER measurements and the other multimessenger data.

Impact of b rightarrow s ell ell anomalies on rare charm decays in non-universal Z' models

In this work, we study the impact of b rightarrow s ell ell , B_s - bar{B_s} mixing and neutrino trident measurements on observables in decays induced by c rightarrow u transition in the context of a non-universal Z' model which generates C^{mathrm{NP}}_{9} <0 and C^{mathrm{NP}}_9 = - ,C^{mathrm{NP}}_{10} new physics scenarios at the tree level. We inspect the effects on D^0 rightarrow pi ^0 nu {bar{nu }}, D^+ rightarrow pi ^+ nu {bar{nu }} and B_c rightarrow B^+ nu {bar{nu }} decays which are induced by the quark level transition c rightarrow u nu {bar{nu }}. The fact that the branching ratios of these decays are negligible in the standard model (SM) and the long distance effects are relatively smaller in comparison to their charged dileptons counterparts, they are considered to provide genuine null-tests of SM. Therefore the observation of these modes at the level of current as well as planned experimental sensitivities would imply unambiguous signature of new physics. Using the constraints on Z' couplings coming from a combined fit to b rightarrow s ell ell , varDelta M_s and neutrino trident data, we find that any meaningful enhancement over the SM value is ruled out in the considered framework. The same is true for D - {bar{D}} mixing observable varDelta M_D along with D^0 rightarrow mu ^+ mu ^- and D^+ rightarrow pi ^+ mu ^+ mu ^- decay modes which are induced through c rightarrow u mu ^+ mu ^- transition.

Exotic bottomonium hadronic transitions

We report on a recent computation of the transitions of exotic bottomonium to standard bottomonium and light quark hadrons. We work under the assumption that the ϓ(10753) and ϓ(11020) can be described as the lowest laying and first excitation 1− − hybrid bottomonium states, respectively. The computation has two distinct parts: the heavy quark transition matrix elements, which are obtained in a nonrelativistic EFT incorporating the heavy quark, multipole and adiabatic expansions; and the hadronization of the gluonic operators into the light-meson final states. The single mesons production is obtained through the axial anomaly and a standard π0 - η - ηʹ mixing scheme. Two pion and kaon production is obtained by solving the coupled Omnès problem. We also present result for semi-inclusive transitions.

Signatures of deconfined quark phases in binary neutron star mergers

We investigate the quark deconfinement phase transition in the context of binary neutron star (BNS) mergers. We treat hadronic matter using a Brueckner-Hartree-Fock quantum many-body approach and modern two-body and three-body nuclear interactions derived within chiral effective field theory. Quark matter is modeled using an extended version of the bag model. We combine these approaches to construct a new finite-temperature composition-dependent equation of state (EOS) with a first-order phase transition between hadrons and deconfined quarks. We perform numerical relativity simulations of BNS mergers with this new EOS and compare results obtained with or without the deconfinment phase transition. We find that deconfined quark production in a neutron star merger results from matter crossing the phase boundary over a wide range of temperatures and densities. The softening of the EOS due to the phase transition causes the merger remnants to be more compact and to collapse to a black hole at earlier times. The phase transition is imprinted on the postmerger gravitational wave (GW) signal duration, amplitude, and peak frequency. However, this imprint is only detectable for binaries with sufficiently long-lived remnants. Moreover, the phase transition does not result in significant deviations from quasiuniversal relations for the postmerger GW peak frequency. Consequently, the postmerger GW peak frequency alone is not sufficient to conclusively exclude or confirm the presence of a phase transition in a BNS merger. We also study the impact of the phase transition on dynamical ejecta, remnant accretion disk masses, $r$-process nucleosynthetic yields and associated electromagnetic counterparts. While there are differences in the electromagnetic counterparts and nucleosynthesis yields between the purely hadronic models and the models with phase transitions, these can be primarily ascribed to the difference in remnant collapse time between the two, so they are degenerate with other effects. An exception is the nonthermal afterglow caused by the interaction of the fastest component of the dynamical ejecta and the interstellar medium, which is systematically boosted in the binaries with phase transition as a consequence of the more violent merger they experience.

Probing new physics effects in Λ b → Λ(→pπ −)ℓ + ℓ − decay via model-independent approach

In the last few decades, the FCNC transitions played a pivotal role in the ongoing efforts to test the Standard Model (SM) parameters. These transitions are also in the limelight to constrain the various New Physics (NP) scenarios. Regarding this, both the rare meson and baryon decays are pertinent as they occur through FCNC transitions and contain information about the heavy to light quark transition sector, where the SM has not yet examined totally. Therefore, it is interesting to analyze a phenomenological rich four-body decay channel . Here, we incorporate the NP through a model-independent approach, which modifies both the SM Wilson coefficients (WCs), and introduces the new vector, axial-vector, scalar, pseudo-scalar, and tensor operators. To check the SM and to explore the possibilities of the NP, several physical observables such as the branching ratio , forward-backward asymmetries , and , longitudinal (transverse) polarization fractions , asymmetry parameters , the angular moments, and some other angular observables, extracted from certain foldings, have been examined to compare our results with LHCb. To see which new coupling among VA, SP, and T can accommodate the available experimental data, we have examined the influence of these couplings separately to the values of these observables. For the angular moments, most of the LHCb observations lie close to the SM, and the current constraints on new VA couplings do not change the SM results significantly. For angular coefficients, , and the agreement with the experimental measurement gets improved if we invoke the tensor couplings along with SM WCs. We hope that when experimental measurements become more accurate, together with B meson decays, the will help us to put constraints on the parametric space of these WCs.

Study of the semileptonic Bc → ηcτ−v̄τ decay in W′ model

Recently, many discrepancies between the Standard Model (SM) predictions and experimental results have been found in [Formula: see text] quark transitions. Motivated by these discrepancies, we investigated the semileptonic [Formula: see text] decay in [Formula: see text] model. In this paper, we have estimated different decay observables such as branching ratio, lepton flavor universality (LFU) ratio [Formula: see text] and forward–backward asymmetry in the SM as well as in the [Formula: see text] model. In [Formula: see text] model, we find significant deviations from the SM for the observables except for the forward–backward asymmetry. This deviation gives us a possible indication of new physics (NP).

Lepton flavour violation in rare Lambda _b decays

Lepton flavour violation (LFV) naturally occurs in many new physics models, specifically in those explaining the B anomalies. While LFV has already been studied for mesonic decays, it is important to consider also baryonic decays mediated by the same quark transition. In this paper, we study LFV in the baryonic Lambda _b rightarrow Lambda ell _1 ell _2 using for the first time a full basis of New Physics operators. We present expected bounds on the branching ratio in a model-independent framework and using two specific new physics models. Finally, we point out the interplay and orthogonality between the baryonic and mesonic LFV searches.

Studying radiative baryon decays with the SU(3) flavor symmetry

The weak and electromagnetic radiative baryon decays of octet T 8, decuplet T 10, single charmed antitriplet T c3 and sextet T c6, and single heavy bottomed antitriplet T b3 and sextet T b6 are investigated by using the SU(3) flavor symmetry irreducible representation approach. We analyze the contributions from a single quark transition q 1 → q 2 γ and the W exchange transitions and find that the amplitudes could be easily related by the SU(3) flavor symmetry in the T b3,b6, T c3,c6, and T 10 weak radiative decays as well as T 10 → T 8 γ electromagnetic decays. Nevertheless, the amplitude relations are a little complex in the and T 8 → T 10 γ weak decays due to the quark antisymmetry in the octet T 8 and the W exchange contributions. The predictions for the branching ratios of , , , , , , Ξ* → Ξγ, Σ∗0 → Σ0 γ, Δ0 → nγ and Δ+ → pγ are given by the relevant experimental data. The seven predictions of are obtained by using previous other theoretical predictions of . The results in this work can be used to test the SU(3) flavor symmetry approach in the radiative baryon decays by the future experiments at BESIII, LHCb and Belle-II.

Isospin Effect on Baryon and Charge Fluctuations from the pNJL Model

We have studied the possible isospin corrections on the skewness and kurtosis of net-baryon and net-charge fluctuations in the isospin asymmetric matter formed in relativistic heavy-ion collisions at RHIC-BES energies, based on a 3-flavor Polyakov-looped Nambu–Jona–Lasinio model. With typical scalar–isovector and vector–isovector couplings leading to the splitting of u and d quark chiral phase transition boundaries and critical points, we have observed considerable isospin effects on the susceptibilities, especially those of net-charge fluctuations. Reliable experimental measurements at even lower collision energies are encouraged to confirm the observed isospin effects.