Search

We present a detailed study concerning a new physics scenario involving four fermion operators of the Nambu-Jona-Lasinio type characterized by a strong-coupling ultraviolet fixed point where composite particles are formed as bound states of elementary fermions at the scale Λ = O TeV . After implementing the model in the Universal FeynRules Output format, we focus on the phenomenology of the scalar leptoquarks at the LHC and the High-Luminosity option. Leptoquark particles have undergone extensive scrutiny in the literature and experimental searches, primarily relying on pair production and, more recently, incorporating single, Drell-Yan t-channel, and lepton-induced processes. This study marks, for the first time, the examination of these production modes at varying jet multiplicities. Novel mechanisms emerge, enhancing the total production cross section. A global strategy is devised to capture all final state particles produced in association with leptoquarks or originating from their decay, which we termed "exclusive", in an analogy to the nomenclature used in nuclear reactions. The assessment of the significance in current and future LHC runs, focusing on the case of a leptoquark coupling to a muon–c quark pair, reveals greater sensitivity compared to ongoing searches. Given this heightened discovery potential, we advocate the incorporation of exclusive leptoquark searches in future investigations at the LHC. [ABSTRACT FROM AUTHOR]

We have investigated the structural properties of strange quark stars (SQSs) in a modified theory of gravity known as massive gravity. In order to obtain the equation of state (EOS) of strange quark matter, we have employed a modified version of the Nambu–Jona-Lasinio model (MNJL) which includes a combination of NJL Lagrangian and its Fierz transformation by using weighting factors (1 - α) and α. Additionally, we have also calculated dimensionless tidal deformability (Λ) in massive gravity. To constrain the allowed values of the parameters appearing in massive gravity, we have imposed the condition Λ 1.4 M ⊙ ≲ 580. Notably, in the MNJL model, the value of α varies between zero and one. As α increases, the EOS becomes stiffer, and the value of Λ increases accordingly. We have demonstrated that by softening the EOS with increasing the bag constant, one can obtain objects in massive gravity that not only satisfy the constraint Λ 1.4 M ⊙ ≲ 580 , but they also fall within the unknown mass gap region (2.5 M ⊙ - 5 M ⊙). To establish that the obtained objects in this region are not black holes, we have calculated Schwarzschild radius, compactness, and Λ M TOV in massive gravity. [ABSTRACT FROM AUTHOR]

We study the possibly-existing molecular pentaquark states with open charm and bottom flavors, i.e., the states with the quark contents c b ¯ q q q and b c ¯ q q q ( q = u , d , s ). We investigate the meson-baryon interactions through the coupled-channel unitary approach within the local hidden-gauge formalism, and extract the poles by solving the Bethe-Salpeter equation in coupled channels. These poles qualify as molecular pentaquark states, which are dynamically generated from the meson-baryon interactions through the exchange of vector mesons. Our results suggest the existence of the Σ c (∗) B (∗) and Σ b (∗) D ¯ (∗) molecular states with isospin I = 1 / 2 , the Ξ c (′ , ∗) B (∗) and Ξ b (′ , ∗) D ¯ (∗) molecular states with isospin I = 0 and I = 1 , as well as the Ω c (∗) B (∗) and Ω b (∗) D ¯ (∗) molecular states with isospin I = 1 / 2 . [ABSTRACT FROM AUTHOR]

In this paper, we employ gauge/gravity duality to investigate the string breaking and melting of doubly-heavy tetraquark that includes two heavy quarks and two light antiquarks in a holographic model at finite temperature. Firstly, four different configurations of QQ q ¯ q ¯ are studied at different separation distances of the heavy quarks at finite temperatures. At high temperature, QQ q ¯ q ¯ will melt at certain distances and the screening distance has been given for different temperatures. As the temperature continues to increase, some configurations of doubly-heavy tetraquark can not exist. Furthermore, we investigate three decay modes of QQ q ¯ q ¯ and compare the potential energy of QQ q ¯ q ¯ with that of QQq at finite temperature. [ABSTRACT FROM AUTHOR]

We have studied the strong decay properties of the recently observed T c s ¯ 0 a (2900) + + / 0 by considering it as a c u d ¯ s ¯ / c d u ¯ s ¯ fully open-flavor tetraquark state with I (J P) = 1 (0 +) . In the framework of QCD sum rules, we have calculated the three-point correlation functions of the two-body strong decay processes T c s ¯ 0 a (2900) + + → D s + π + , D + K + , D s ∗ + ρ + and D s 1 + π + . The full width of T c s ¯ 0 a (2900) + + / 0 is obtained as 161.7 ± 94.8 MeV, which is consistent with the experimental observation. We predict the relative branching ratios as Γ (T → D s π) : Γ (T → D K) : Γ (T → D s ∗ ρ) : Γ (T → D s 1 π) ≈ 1.00 : 1.10 : 0.04 : 0.43 , implying that the main decay modes of T c s ¯ 0 a (2900) + + / 0 state are D s π and DK channels in our calculations. However, the P-wave decay mode D s 1 π is also comparable and important by including the uncertainties. To further identify the nature of T c s ¯ 0 a (2900) + + / 0 , we suggest confirming them in the DK and D s π final states, and measuring the above ratios in future experiments. [ABSTRACT FROM AUTHOR]

We study a lattice Nambu–Jona-Lasinio model with interacting staggered fermions in the Kogut–Susskind Hamiltonian formalism. The model has a discrete chiral symmetry but not the usual continuous chiral symmetry. In a strong coupling regime for the four-fermion interaction, we prove that the mass of the fermions is spontaneously generated at sufficiently low non-zero temperatures in the dimensions ν ≥ 3 of the model and zero temperature in ν ≥ 2 . Due to the phase transition, the discrete chiral symmetry of the model is broken. Our analysis is based on the reflection positivity for fermions and the method of the infrared bound. [ABSTRACT FROM AUTHOR]

Corrections to the Wess–Zumino–Witten anomaly caused by the explicit breaking of the chiral symmetry are studied using the effective meson Lagrangian based on the Nambu–Jona-Lasinio model with the simultaneous expansion in derivatives, current quark masses, and 1/Nc powers. The leading contribution and the first correction for the amplitudes of the π0, η, η' → γγ decays and the contact term in the amplitudes have been calculated. The results are compared with similar 1/Nc chiral perturbation calculations and existing experimental data. [ABSTRACT FROM AUTHOR]

We investigate the combined finite-size and thermo-magnetic effects on the properties of the quark matter, in the context of the two-flavored Nambu–Jona-Lasinio model. In particular, by using the mean-field approximation and the Schwinger proper time method in a toroidal topology with periodic or antiperiodic conditions, we evaluate the chiral phase transition, the constituent quark mass and the thermal and spatial susceptibilities under the change of the size, temperature and strength of external magnetic field. To take into account the inverse magnetic catalysis phenomenon, we make use of a recently proposed magnetized coupling constant. The findings suggest that the observables are strongly affected by the variation of the variables and also by the periodicity of the boundary conditions, with the final outcomes depending on the balance of these competing phenomena. [ABSTRACT FROM AUTHOR]

It is well known that the gluon anomaly is responsible for the mass of the U(1) Goldstone boson. It is also manifested in the properties of pseudo-Goldstone states: the gluon anomaly in the next order of the 1/Nc expansion induces interactions violating the Zweig rule. A necessary condition for this is the explicit breaking of the chiral symmetry by the masses of light quarks. One of the physical consequences is that the η–η' mixing does not affect the amplitude. Another consequence is the suppression of the first 1/Nc correction to the η–η' mixing angle. The mechanism of such suppression is discussed in detail. The conclusions are based on the 1/Nc expansion and the effective meson Lagrangian of the Nambu–Jona-Lasinio model and are compared with the results of the 1/Nc chiral perturbation theory. [ABSTRACT FROM AUTHOR]

We have estimated parallel and perpendicular components of electrical conductivity and shear viscosity of quark matter at finite magnetic field and temperature by using their one-loop Kubo expressions in the framework of Nambu–Jona-Lasinio (NJL) model. At finite magnetic field, a non-trivial medium dependence of those quantities can be found. Previously these NJL-profiles have been addressed in relaxation time approximation, where cyclotron motion of quarks with medium dependent mass plays the key role. With respect to the earlier estimations, the present work provides further enriched profiles via Kubo framework, where field theoretical descriptions of quark transport with medium dependent mass and (Landau) quantized energy have been identified as the key ingredients. Hence the present study can be considered as the complete quantum field theoretical description of the transport coefficients in the framework of NJL model at finite temperature and magnetic field. [ABSTRACT FROM AUTHOR]

The branching fractions of τ lepton decays with the production of strange scalar mesons both in the ground and first radially excited states and are calculated in the extended chiral quark Nambu–Jona-Lasinio model. All mesons are considered as systems. The obtained results should be considered as predictions for future experiments. [ABSTRACT FROM AUTHOR]

The effect of neutrino oscillations on the thermodynamic characteristics of three-flavor hot quark matter in β-equilibrium that is opaque for neutrinos is examined in terms of the local SU(3) Nambu-Jona-Lasinio (NJL) model which also accounts for the 't Hooft interaction that leads to quark flavor mixing. The thermodynamic characteristics of quark matter are determined for two temperatures, T = 60 and 100 MeV, with neutrino oscillations taken into account. These results are compared with those obtained without taking neutrino oscillations into account. The calculations show that during cooling of quark matter that is opaque to neutrinos, the energy released per unit of baryon charge is 150 ÷ 350 MeV. [ABSTRACT FROM AUTHOR]

The total cross sections for the e+e– → a1π, e+e– → K1(1270)K, and e+e– → K1(1400)K processes have been calculated within the U(3) × U(3) chiral Nambu–Jona-Lasinio model. Since experimental data on these processes are absent, the reported theoretical results can be treated as predictions. [ABSTRACT FROM AUTHOR]

In this work, we consider the effect of a constant anomalous magnetic moment (AMM) of quarks in the SU(2) Nambu–Jona-Lasinio model in the mean field approximation. To this end, we use the Schwinger ansatz, which represents a linear magnetic field term in the Lagrangian. A regularization method inspired in the vacuum magnetic regularization (VMR) is adopted to avoid ultraviolet divergences. Our results indicate a smooth decrease of the pseudocritical temperature and quark condensates for magnetic fields B ≤ 0.1 GeV 2 when a sizable AMM is considered. We found only a small window for Inverse Magnetic Catalysis (IMC), in contradiction with NJL predictions made in the literature. For a low value of AMM, we observe for all ranges of magnetic fields considered that the pseudocritical temperature increases with the magnetic field, indicating only Magnetic Catalysis (MC). In our approach, for nonvanishing quark AMM, the chiral symmetry restoration happens always as a smooth crossover and never turns into a first order phase transition. [ABSTRACT FROM AUTHOR]

Mass formulas, mixing angles, and decay constants of the pseudoscalar π0, η, and η' mesons have been obtained in the theory with four-quark interactions with an accuracy to terms inclusively. Unlike the standard Nambu–Jona-Lasinio model, the meson Lagrangian has been obtained using the Volterra series, which allows a more detailed description of effects caused by the inequality of quark masses. The results have been compared to similar calculations in the 1/Nc chiral perturbation theory. The first corrections to the interaction violating the Zweig formulas have been calculated, and it has been shown that they are important for the description of the mass spectrum of the η–η' mesons. [ABSTRACT FROM AUTHOR]

More evolved models, however, continue to play a very relevant role in our understanding of effects from strong magnetic fields on compact star structure (magnetars) and on heavy ion collision phenomenology (including the chiral magnetic effect) that may help to uncover the response of the QCD phase diagram to strong magnetic fields. An important achievement was the investigation of inverse magnetic catalysis, which has been established by lattice QCD calculations and may rule out too simplistic mean field models of the QCD phase diagram. In recent years, the impact of strong magnetic fields on the strongly interacting matter phase diagram has been a very active field of research with important developments. [Extracted from the article]

The partial width of the decay has been calculated within the extended Nambu–Jona-Lasinio model including the contact and vector channels. The contributions from the ρ meson in the ground and first radially excited states have been taken into account in the vector channel. The results are in satisfactory agreement with experimental data. The inclusion of the final-state interaction of kaons results only in insignificant corrections within the accuracy of the model. [ABSTRACT FROM AUTHOR]

We use a three-flavor Nambu–Jona-Lasinio model to study the thermodynamics of strange quark matter under a strong magnetic field. The model Lagrangian features flavor SU(3) four-quark interactions and six-quark interactions that break the U A (1) symmetry. We incorporate thermomagnetic effects in the four-quark coupling by fitting lattice results for the average of u and d quark condensates close to the pseudocritical temperature. We compute the pressure at the mean field level and obtain the magnetization of quark matter. We adopt the recently proposed vacuum magnetic regularization (VMR) scheme, in that divergent quark mass independent contributions are not subtracted, thereby avoiding unphysical results for the magnetization. We devote special attention to the renormalized magnetization, a projected quantity that allows for direct comparisons with lattice QCD simulations. Our results are in very good agreement with lattice data indicating a paramagnetic behavior for quark matter. [ABSTRACT FROM AUTHOR]

In this review, we summarize recent progress on the possible phases of quantum chromodynamics (QCD) in the presence of a strong magnetic field, mainly from the views of the chiral effective Nambu–Jona-Lasinio model. Four kinds of phase transitions are explored in detail: chiral symmetry breaking and restoration, neutral pseudoscalar superfluidity, charged pion superfluidity and charged rho superconductivity. In particular, we revisit the unsolved problems of inverse magnetic catalysis effect and competition between the chiral density wave and solitonic modulation phases. It is shown that useful results can be obtained by adopting self-consistent schemes. [ABSTRACT FROM AUTHOR]

The width of the decay has been calculated within the extended Nambu–Jona-Lasinio model including the final-state interaction of mesons. Both the contact term and the channel with the intermediate ground state and its first radial excitation have been taken into account. To describe the final-state interaction, a triangle diagram with three mesons has been considered. The cutoff parameter in the diverging integrals over the meson loop has been taken the same as in our preceding work to describe the decay, so no additional parameters are introduced. Satisfactory agreement with experimental data has been obtained. [ABSTRACT FROM AUTHOR]

We review the main features of the QCD phase diagram description, at finite temperature, baryon density and in the presence of a magnetic field, from the point of view of effective models, whose main ingredient is chiral symmetry. We concentrate our attention on two of these models: The linear sigma model with quarks and the Nambu–Jona-Lasinio model. We show that a main ingredient to understand the characteristics of the phase transitions is the inclusion of plasma screening effects that capture the physics of collective, long-wave modes, and thus describe a prime property of plasmas near transition lines, namely, long distance correlations. Inclusion of plasma screening makes possible to understand the inverse magnetic catalysis phenomenon even without the need to consider magnetic field-dependent coupling constants. Screening is also responsible for the emergence of a critical end point in the phase diagram even for small magnetic field strengths. Although versatile, the NJL model is also a more limited approach since, being a non-renormalizable model, a clear separation between pure vacuum and medium effects is not always possible. The model cannot describe inverse magnetic catalysis unless a magnetic field dependent coupling is included. The location of the critical end point strongly depends on the choice of the type of interaction and on the magnetic field dependence of the corresponding coupling. Overall, both models provide sensible tools to explore the properties of magnetized, strongly interacting matter. However, a cross talk among them as well as a consistent physical approach to determine the model parameters is much needed. [ABSTRACT FROM AUTHOR]

The decay has been described within the Nambu–Jona-Lasinio model including the contact term and the contribution from an intermediate vector meson. The final-state interaction of mesons has been taken into account by the inclusion of diverging meson loops. The additional ultraviolet cutoff parameter in these loops is fixed using the experimental width of the process under consideration. [ABSTRACT FROM AUTHOR]

We study strongly-coupled, approximately scale-invariant gauge theories, which develop a mass gap in the infrared. We argue that a large number of fermion flavours is most suitable to provide an ultraviolet completion for the composite Higgs scenario. The holographic approach allows to describe the qualitative features of the non-perturbative dynamics in the Veneziano limit. We introduce new bottom-up holographic models, which incorporate the backreaction of flavour on the geometry, and show that this can correlate the mass gap to the scale of flavour-symmetry breaking. We compute the mass spectrum for the various composite bosonic states, and study its dependence on the scaling dimension of the symmetry-breaking operators, as well as on the number of flavours. The different regions with a light dilaton are critically surveyed. We carefully assess the domain of validity of the holographic approach, and compare it with lattice simulations and the Nambu-Jona-Lasinio model. [ABSTRACT FROM AUTHOR]

Nonperturbative equations of state (EoSs) for two and three quark flavors are constructed with the functional renormalization group (FRG) within a quark-meson model truncation augmented by vector mesons for low temperature and high density. Based on previous FRG studies without repulsive vector meson interactions the influence of isoscalar vector ω- and ϕ-mesons on the dynamical fluctuations of quarks and (pseudo)scalar mesons is investigated. The grand potential as well as vector meson condensates are evaluated as a function of quark chemical potential and the quark matter EoS in β-equilibrium is applied to neutron star (NS) physics. The tidal deformability and mass-radius relations for hybrid stars from combined hadronic and quark matter EoSs are compared for different vector couplings. We observe a significant impact of the vector mesons on the quark matter EoS such that the resulting EoS is sufficiently stiff to support two-solar-mass neutron stars. [ABSTRACT FROM AUTHOR]

We present a brief review of results of chiral quark models for soft matrix elements in the pion state, appearing in high-energy processes as well as accessible in present and future lattice studies. A particular attention is paid to the recently explored double parton distribution functions of the pion. [ABSTRACT FROM AUTHOR]

In this paper the phase structure of dense baryon matter composed of u and d quarks with two colors has been investigated in the presence of baryon μB , isospin μI and chiral isospin μI5 chemical potentials in the framework of Nambu-Jona-Lasinio model with quark-antiquark and quark-quark interaction channels. In the chiral limit, it has been shown in the mean-field approximation that the duality between phases with spontaneous chiral symmetry breaking and condensation of charged pions, found in the three color case, remains valid in the two color case. In addition, it has been shown that there are two more dualities in the phase diagram in two color case, namely (as in the case with μI5 = 0), at μI5 ≠ 0 the general (μ, μI, μI5)-phase portrait of the model has dual symmetry between the phase with condensation of charged pions and the phase with diquark condensation. This duality stays exact even in the physical point, m0 ≠ 0. And at m0 = 0 the (μ, μI, μI5)- phase portrait becomes even more symmetrical, since dual symmetry between phases with spontaneous chiral symmetry breaking and diquark condensation appears. It is shown that due to the dualities the phase diagram is extremely symmetric and has interlacing structure. One can show that the phase portrait of two-color NJL model can be obtained just by duality properties from the results of investigations of three-color NJL model (it was noticed only after the numerical calculations have been performed). Three-color case shares only one duality of the two color one, and one can only see a facet of this enormously symmetric picture in the case of three colors. Using dualities only, it is possible to show that there are no mixed phases (phases with two non-zero condensates). This prediction of dualities is of great use, because for sure it can be shown by the direct calculations but it would be enormously more complicated and time-consuming numerically. [ABSTRACT FROM AUTHOR]

The stringent experimental bound on μ → eγ is compatible with a simultaneous and sizable new physics contribution to the electron and muon anomalous magnetic moments (g − 2)ℓ (ℓ = e, μ), only if we assume a non-trivial flavor structure of the dipole operator coefficients. We propose a mechanism in which the realization of the (g − 2)ℓ correction is manifestly related to the mass generation through a flavor symmetry. A radiative flavon correction to the fermion mass gives a contribution to the anomalous magnetic moment. In this framework, we introduce a chiral enhancement from a non-trivial O (1) quartic coupling of the scalar potential. We show that the muon and electron anomalies can be simultaneously explained in a vast region of the parameter space with predicted vector-like mediators of masses as large as Mχ ∈ [0.6, 2.5] TeV. [ABSTRACT FROM AUTHOR]

We investigate the charmless decays of excited P-wave charmonia χ c 1 ′ → V V and χ c 2 ′ → V P via intermediate charmed meson loops, where V and P denote the light vector and pseudoscalar mesons, respectively. Within the model parameters, the charmed meson loop contributions are evaluated by using the effective Lagrangian approach. For χ c 1 ′ → V V , the partial widths of the ρ ρ , ω ω , and K ∗ K ¯ ∗ channels can reach to the order of MeV, while the partial width of the ϕ ϕ channel is very small and in the order of keV. For χ c 2 ′ → V P , the partial widths of χ c 2 ′ → K ∗ K ¯ + c. c turns out to be sizeable, while the partial widths of χ c 2 ′ → ρ + π - + c. c is found to be much smaller than the K ∗ K ¯ + c. c channel. Our calculations may be examined by the future BESIII experiments. [ABSTRACT FROM AUTHOR]

We have studied the masses for fully open-flavor tetraquark states b c q ¯ s ¯ and s c q ¯ b ¯ ( q = u , d ) with quantum numbers J P = 0 + , 1 + . We systematically construct all diquark–antiquark interpolating currents and calculate the two-point correlation functions and spectral densities in the framework of QCD sum rule method. Our calculations show that the masses are about 7.1 - 7.2 GeV for the b c q ¯ s ¯ tetraquark states and 7.0 - 7.1 GeV for the s c q ¯ b ¯ tetraquarks. The masses of b c q ¯ s ¯ tetraquarks are below the thresholds of B ¯ s D and B ¯ s ∗ D final states for the scalar and axial-vector channels respectively. The s c q ¯ b ¯ tetraquark states with J P = 1 + lie below the B c + K ∗ and B s ∗ D thresholds. Such low masses for these possible tetraquark states indicate that they can only decay via weak interaction and thus are very narrow and stable. [ABSTRACT FROM AUTHOR]

A sharp peak in the K+/π+ ratio in relativistic heavy-ion collision is discussed in the framework of the SU(3) Polyakov-loop extended Nambu-Jona-Lasinio model with vector interaction. In the model, the K+/π+ ratio has been calculated along the chiral phase transition line for different values of the vector coupling gV. It has been shown that the value of the vector coupling hardly affects the behavior of the K+/π+ ratio. [ABSTRACT FROM AUTHOR]

We analyse the validity of a commonly used identification between structures of the virtual photon γ ∗ → Q Q ¯ and vector meson V → Q Q ¯ transitions. In the existing studies of S-wave vector-meson photoproduction in the literature, such an identification is typically performed in the light-front (LF) frame while the radial component of the meson wave function is rather postulated than computed from the first principles. The massive photon-like V → Q Q ¯ vertex, besides the S-wave component, also contains an extra D-wave admixture in the Q Q ¯ rest frame. However, the relative weight of these contributions cannot be justified by any reasonable nonrelativistic Q Q ¯ potential model. In this work, we investigate the relative role of the D-wave contribution starting from the photon-like quarkonium V → Q Q ¯ transition in both frames: in the Q Q ¯ rest frame (with subsequent Melosh spin transform to the LF frame) and in the LF frame (without Melosh transform). In both cases, we employ the same radial wave functions found in the potential approach. We show that the photon-like transition imposed in the Q Q ¯ rest frame, with subsequent boosting to the LF frame, leads to significant discrepancies with the experimental data. In the second case, i.e. imposing the photon-like transition straight in the LF frame, we find that the corresponding total J / ψ (1 S) photoproduction cross sections are very close to those obtained with the "S-wave only" V → Q Q ¯ transition, both leading to a good description of the data. However, we find that the "S-wave only" transition leads to a better description of photoproduction data for excited (e.g. ψ ′ (2 S) ) heavy quarkonium states, which represent a more effective tool for study of D-wave effects. Consequently, the predictions for production of excited states based on the photon-like structure of V → Q Q ¯ transition should be treated with a great care due to a much stronger sensitivity of the D-wave contribution to the nodal structure of quarkonium wave functions. [ABSTRACT FROM AUTHOR]

A standing problem in neutrino physics is the consistent and universal definition of oscillating neutrino states as coherent superpositions of massive neutrino states. This problem is solved in a quantum field theoretical framework of neutrino mixing developed in analogy with the Nambu–Jona–Lasinio model for the dynamical generation of nucleon masses. The massive neutrino states are Bogoliubov quasiparticles and their vacuum is a condensate of "Cooper pairs" of massless flavour neutrinos. Their superpositions as oscillating neutrino states have intrinsic quantum coherence by construction. In this quantization framework, the standard phenomenological flavour neutrino states and oscillation probability formula are validated in the ultrarelativistic approximation. [ABSTRACT FROM AUTHOR]

We study the thermodynamics and the susceptibilities of quark matter in the framework of two-flavor Nambu–Jona–Lasinio model at finite isospin chemical potential and temperature. Isospin number density, normalized energy density and trace anomaly are shown to be in good agreement with the available lattice data as well as with the results from chiral perturbation theory at zero temperature. We also study how susceptibilities depend on the isospin chemical potential and on temperature. We find a peak for the chiral, pion, and isospin susceptibilities at the critical isospin chemical potential, μ I c (T) , at the boundary of the phase transition between the normal and pion superfluid phase. Moreover, temperature makes the transition from normal to pion condensed phase smoother. We also note that the pion susceptibility always remains zero in the normal phase while it is finite in the superfluid phase. [ABSTRACT FROM AUTHOR]

Two-parton correlations in the pion, a non perturbative information encoded in double parton distribution functions, are investigated in the Nambu–Jona-Lasinio model. It is found that double parton distribution functions expose novel dynamical information on the structure of the pion, not accessible through one-body parton distributions, as it happens in several estimates for the proton target and in a previous evaluation for the pion, in a light-cone framework. Expressions and predictions are given for double parton distributions corresponding to leading-twist Dirac operators in the quark vertices, and to different regularization methods for the Nambu–Jona-Lasinio model. These results are particularly relevant in view of forthcoming lattice data. [ABSTRACT FROM AUTHOR]

In this work, we propose minimal realizations for generating Dirac neutrino masses in the context of a right-handed abelian gauge extension of the Standard Model. Utilizing only U (1) R symmetry, we address and analyze the possibilities of Dirac neutrino mass generation via (a) tree-level seesaw and (b) radiative correction at the one-loop level. One of the presented radiative models implements the attractive scotogenic model that links neutrino mass with Dark Matter (DM), where the stability of the DM is guaranteed from a residual discrete symmetry emerging from U (1) R . Since only the right-handed fermions carry non-zero charges under the U (1) R , this framework leads to sizable and distinctive Left–Right asymmetry as well as Forward–Backward asymmetry discriminating from U (1) B - L models and can be tested at the colliders. We analyze the current experimental bounds and present the discovery reach limits for the new heavy gauge boson Z ′ at the LHC and ILC. Furthermore, we also study the associated charged lepton flavor violating processes, dark matter phenomenology and cosmological constraints of these models. [ABSTRACT FROM AUTHOR]

The width of the τ → K ¯ 0 * (892) π − ν τ decay has been calculated within the extended Nambu-Jona-Lasinio model taking into account intermediate axial-vector, vector, and pseudoscalar mesons in the ground and first radially excited states. The splitting of the axial-vector intermediate state K1A into two physical mesons K1(1270) and K1(1400) caused by the mixing of axial-vector strange mesons from the 3P1 and 1P1 nonets has also been taken into account. The results are in satisfactory agreement with experimental data. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the thermodynamic properties of strange quark matter using the Nambu-Jona-Lasinio (NJL) model at finite temperatures where we considered the dynamical mass as the effective interaction between quarks. By considering the pressure of strange quark matter (SQM) at finite temperatures, we showed that the equation of state of this system gets stiffer with increasing temperature. In addition, we investigated the energy conditions and stability of the equation of state and showed that the equation of state of SQM satisfies the conditions of stability. Finally, we computed the structure properties of hot strange quark stars (SQS) including the gravitational mass, radius, Schwarzschild radius, average density, compactness, and gravitational redshift. Our calculations showed that in this model, the maximum mass and radius of SQS increase with increasing temperature. Furthermore it was shown that the average density of SQS is greater than the normal nuclear density, and it is an increasing function of temperature. We also discussed the temperature dependence of the maximum gravitational mass calculated by different methods. [ABSTRACT FROM AUTHOR]

The integral parameters of neutron stars are studied taking into account the hadron-quark phase transition, which leads to the formation of a core of quark matter in the central part of a star. The quark matter is described using the local Nambu-Jona-Lasinio (NJL) model. The thermodynamic characteristics of the hadron matter are calculated in the framework of an extended version of the relativistic mean field (RMF) model that includes the contribution of the scalar-isovector δ -meson effective field. A Maxwell construction is used to determine the parameters of the phase transition. It is shown that for the equation of state examined here, stable hybrid stars correspond to a narrow range of values for the central density ρc ∈ (1.71÷1.73]·1015 g/cm3. In our model hybrid stars lie on the same branch as neutron stars, so that a branch with a third family is not formed. The maximum mass of a stable hybrid star is found to be _ Mmax = 2.05M⨀. The configuration with the maximum mass has a quark core with mass Mcore ≈ 10-3 M⨀ and radius Rcore ≈ 0.6 km. [ABSTRACT FROM AUTHOR]

In this paper, we firstly combine the 2 + 1 flavors Nambu-Jona-Lasinio (NJL) model with propertime regularization (PTR) to study the equation of state (EOS) and fix the corresponding parameters in 2 + 1 flavors system. Based on this model, we calculate chiral susceptibility and quark number susceptibility and we find a crossover with chemical potential from 220 to 400 MeV. Then we consider the chemical equilibrium and electric charge neutrality conditions in electroweak reactions, which give some constrains of chemical potentials of different quark flavors. At last, we find that the 2 + 1 flavors system is more stable than 2 flavors system after a comparison and discussion of these two cases. [ABSTRACT FROM AUTHOR]

The phenomenon of inverse magnetic catalysis of chiral symmetry in QCD predicted by lattice simulations can be reproduced within the Nambu-Jona-Lasinio model if the coupling G of the model decreases with the strength B of the magnetic field and temperature T. The thermo-magnetic dependence of G( B, T) is obtained by fitting recent lattice QCD predictions for the chiral transition order parameter. Different thermodynamic quantities of magnetized quark matter evaluated with G( B, T) are compared with the ones obtained at constant coupling, G. The model with G( B, T) predicts a more dramatic chiral transition as the field intensity increases. In addition, the pressure and magnetization always increase with B for a given temperature. Being parametrized by four magnetic-field-dependent coefficients and having a rather simple exponential thermal dependence our accurate ansatz for the coupling constant can be easily implemented to improve typical model applications to magnetized quark matter. [ABSTRACT FROM AUTHOR]

Using a three- and four-dimensional Pauli-Villars regularization scheme, we investigate quark-antiquark and diquark condensation in the framework of the Nambu-Jona-Lasinio model. Using the particle Fermi momentum as a cutoff parameter, we study the energy gap width and coherence length for the meson condensate 〈 $$q\bar q$$ 〉. We also study the energy gap width and critical coherence length ( the distance over which there would be no diquark condensation) for the diquark 〈 qq〉 and the dependence on the Fermi momentum. We obtain an estimate of the Fermi momentum value for meson and diquark condensates with an energy gap width of the order of 100 MeV. [ABSTRACT FROM AUTHOR]

The well-known [ρ(770), ω(782)] → γ[π, η] electromagnetic decays have been considered within the Nambu-Jona-Lasinio model taking into account contributions from intermediate transitions between axial-vector and pseudoscalar vertices using the [f1(1285), a1(1260)] → γ[ρ(770), ω(782)] vertices recently obtained within this model. The results are in satisfactory agreement with experimental data. [ABSTRACT FROM AUTHOR]

By extending the $$\Phi $$ -derivable approach in the Nambu-Jona-Lasinio model to a finite magnetic field we calculate the properties of pion, $$\sigma $$ , and $$\rho $$ mesons in a magnetic field at finite temperature not only in the quark-antiquark bound state scheme but also in the pion-pion scattering resonant state scenario. Our calculation as a result makes manifest that the masses of $$\pi ^{0}$$ and $$\sigma $$ meson can be nearly degenerate at the pseudo-critical temperature which increases with increasing magnetic field strength, and the $$\pi ^{\pm }$$ mass ascends suddenly at almost the same critical temperature. Meanwhile the $$\rho $$ mesons' masses decrease with the temperature but increase with the magnetic field strength. We also check the Gell-Mann-Oakes-Renner relation and find that the relation can be violated clearly with increasing temperature, and the effect of the magnetic field becomes pronounced around the critical temperature. With different criteria, we analyze the effect of the magnetic field on the chiral phase transition and find that the pseudo-critical temperature of the chiral phase cross, $$T_\mathrm{c}^{\chi }$$ , is always enhanced by the magnetic field. Moreover, our calculations indicate that the $$\rho $$ mesons will get melted as the chiral symmetry has not yet been restored, but the $$\sigma $$ meson does not disassociate even at very high temperature. Particularly, it is the first to show that there does not exist a vector meson condensate in the QCD vacuum in the pion-pion scattering scheme. [ABSTRACT FROM AUTHOR]

The decays τ → (η, η') K-ν are described in the framework of the extended Nambu-Jona-Lasinio model. Both full and differential widths of these decays are calculated. The vector and scalar channels are considered. In the vector channel, the subprocesses with the intermediate K*(892) and K*(1410) mesons play the main role. In the scalar channel, the subprocesses with the intermediate and K(800) and K(1430) mesons are taken into account. The scalar channel gives an insignificant contribution to the full width of the decay τ → η K-ν. The obtained results are in satisfactory agreement with the experimental data. The prediction for the width of the process τ → η′ K-ν is made. [ABSTRACT FROM AUTHOR]

We revisit three of the mathematical formalisms used to describe magnetized quark matter in compact objects within the MIT and the Nambu-Jona-Lasinio models and then compare their results. The tree formalisms are based on 1) isotropic equations of state, 2) anisotropic equations of state with different parallel and perpendicular pressures and 3) the assumption of a chaotic field approximation that results in a truly isotropic equation of state. We have seen that the magnetization obtained with both models is very different: while the MIT model produces well-behaved curves that are always positive for large magnetic fields, the NJL model yields a magnetization with lots of spikes and negative values. This fact has strong consequences on the results based on the existence of anisotropic equations of state. We have also seen that, while the isotropic formalism results in maximum stellar masses that increase considerably when the magnetic fields increase, maximum masses obtained with the chaotic field approximation never vary more than 5.5%. The effect of the magnetic field on the radii is opposed in the MIT and NJL models: with both formalisms, isotropic and chaotic field approximation, for a fixed mass, the radii increase with the increase of the magnetic field in the MIT bag model and decrease in the NJL, the radii of quark stars described by the NJL model being smaller than the ones described by the MIT model. [ABSTRACT FROM AUTHOR]

In the extended NJL model the radiative decay widths of the radially excited states of the pseudo-scalar π, η, and η′ mesons are calculated. The predictions for the decay widths of the processes π(1300) → (ρ, ω)γ, η(1295) → (ρ, ω, φ)γ, and η(1475) → (ρ, ω, φ)γ are given. Nowadays, there are no solid experimental data for these processes. The comparison of the results obtained in the framework of the standard and the extended NJL models for decays of the ground states of mesons is given. It is shown that these calculations correspond to each other and are also in satisfactory agreement with experimental data. This allows one to expect that the extended NJL can give reliable predictions for the excited states of mesons. [ABSTRACT FROM AUTHOR]

We consider the 'two flavour' Nambu-Jona-Lasinio model in the presence of a vector and an axial external chemical potential and study the phase structure of the model at zero temperature. The Nambu-Jona-Lasinio model is often used as a toy replica of QCD and it is therefore interesting to explore the consequences of adding external vector and axial chemical potentials in this model, mostly motivated by claims that such external drivers could trigger a phase where parity could be broken in QCD. We are also motivated by some lattice analysis that attempt to understand the nature of the so-called Aoki phase using this simplified model. Analogies and differences with the expected behaviour in QCD are discussed and the limitations of the model are pointed out. [ABSTRACT FROM AUTHOR]

The (1 + 1)-dimensional Nambu-Jona-Lasinio model describing the system of two-flavor quarks is studied in the limit of a large number of colors in the presence of a baryon chemical potential µ and an isospin chemical potential µ I. The possible formation of a nonuniform pion condensate in dense quark matter is considered for the cases of both the massive and the massless model. [ABSTRACT FROM AUTHOR]

We investigate the existence of possible stable strange matter and related stability windows at finite temperature for different models that are generally applied to describe quark stars, namely, the quark-mass density dependent model, the MIT bag model and the Nambu-Jona-Lasinio model. We emphasize that, although the limits for stable strange matter depend on a comparison with the ground state of Fe, which is a zero temperature state, the quantity that has to be used in the search for strange matter in proto-quark stars is the free energy and we analyze stability windows up to temperatures of the order of 40 MeV. The effects of strong magnetic fields on stability windows are computed and the resulting mass-radius relations for different stages of the proto-quark star are analyzed. [ABSTRACT FROM AUTHOR]

We consider the Cartan extension of Riemann geometry as the basis upon which to build the Sciama-Kibble completion of Einstein gravity, developing the most general theory in which torsion and metric have two independent coupling constants: the main problem of the ESK theory was that torsion, having the Newton constant, was negligible beyond the Planck scale, but in this $$\mathrm {ESK}^{2}$$ theory torsion, with its own coupling constant, may be relevant much further Planck scales; further consequences of these torsionally-induced interactions will eventually be discussed. [ABSTRACT FROM AUTHOR]