We investigate the pion electromagnetic charge radii and mass dropping of the rho meson at finite density. We first calculate the pion charge radii within the framework of the nonlocal chiral quark model from the instanton vacuum both at zero and finite densities. In order to relate the change of the pion charge radius to that of the rho-meson mass at finite density, we employ the vector-meson dominance for the pion electromagnetic form factor. It turns out that the pion charge radius is getting larger as the quark chemical potential increases. As a result, the rho-meson mass falls off as the quark chemical potential grows and is found to be dropped by about 10% at normal nuclear matter density: m*_rho/m_rho ~ 1 - 0.12 mu_B/mu_0, which is compatible to the results of the measurement at the KEK recently.
The Kroll-Lee-Zumino renormalizable Abelian quantum field theory of pionic strong interactions is used to compute the rho-meson propagator at the two-loop level.
Considering analyticity, unitarity and an influence of coupled channels, experimental data on the isovector P-wave of pion-pion scattering was analyzed to study rho-like mesons below 1900 MeV. The analysis indicates evidently that in the energy range 1200--1800 MeV, there are three rho-like mesons: rho(1250), rho(1450) and rho(1600), unlike the PDG tables. The obtained P-wave pion-pion scattering length (a_1^1=33.9+- 2.02 [10^{-3}m_{pi^+}^{-3}]) most matches to the one calculated in the local Nambu--Jona-Lasinio model.
In the approach, based on analyticity and unitarity and assuming an influence of coupled channels, experimental data on the isovector P-wave of pion-pion scattering have been analyzed to study rho-like mesons below 1.9 GeV.
The electromagnetic pion form-factor is calculated in a Bethe-Salpeter approach which accounts for pion rescattering. In the scattering kernel the pion-pion contact interaction from lowest-order chiral perturbation theory is considered together with an optional vector meson in the s-channel. Correspondingly the virtual photon couples to a two-pion state and optionally to the vector meson. It is shown that for reasonable ranges of input parameters the experimentally observed pion form-factor cannot be described by the iterated pion-pion contact interaction alone, i.e. without an elementary vect…
A chiral SU(2) x SU(2) Lagrangian containing, besides the usual meson fields, their first radial excitations is considered. The Lagrangian is derived by bosonization of the Nambu-Jona-Lasinio quark model with separable non-local interactions, with form factors corresponding to 3-dimensional ground and excited state wave functions. The spontaneous breaking of chiral symmetry is governed by the NJL gap equation. The first radial excitations of the pions, rho-and omega-mesons are described with the help of two form factors. The weak decay constant F_pi' is calculated. The values for the decay wid…
The excitation curve of e+e- annihilation into four charged pions in the rho(770) region is calculated using three existing models with rho mesons and pions in intermediate states supplemented by Feynman diagrams with the a_1(1260)pi intermediate states. A two-term phenomenological Lagrangian of the a_1-rho-pi interaction is used. The mixing angle is determined by fitting the e+e- --> pi+pi-pi+pi- cross section data of the Novosibirsk CMD-2 collaboration and also its combination with the low-energy part of the BaBar collaboration data. It is shown that the inclusion of the a_1-pi intermediate …
Valence quark distributions in transversally and longitudinally polarizied rho mesons in the region of intermediate x are obtained by generalizied QCD sum rules. Power corrections up to d=6 are taken into account. Comparison of the results for pi and rho mesons shows, that polarization effects are very significant and SU(6) symmetry of distribution functions is absent. The strong suppression of quark and gluon sea distributions in longitudinally polarizied rho mesons is found.
In this paper we improve and extend a recent analysis which showed that the rho-omega mixing amplitude cannot be unambiguously extracted from the pion electromagnetic form-factor in a model independent way. In particular, we focus on the argument that the extraction is sensitive to the presence of any intrinsic omega_I -> pi pi coupling. Our extended analysis confirms the original conclusion, with only minor, quantitative differences. The extracted mixing amplitude is shown to be sensitive to both the intrinsic coupling omega_I -> pi pi and to the value assumed for the mass of the rho^0-meson.
Using a holographic dual model of QCD, we compute the pion electromagnetic form factor F_pi(Q^2) in the spacelike momentum transfer region, as well as pion couplings to vector mesons g_rho^(n) pi pi. Spontaneous and explicit chiral symmetry breaking are intrinsic features of this particular holographic model. We consider variants with both ``hard-wall'' and ``soft-wall'' infrared cutoffs, and find that the F_pi(Q^2) data tend to lie closer to the hard-wall model predictions, although both are too shallow for large Q^2. By allowing the parameters of the soft-wall model (originally fixed by obse…
We study the p(e,e' pi+)n reaction in the framework of an effective Lagrangian approach including nucleon, pi and rho meson degrees of freedom and show the importance of the rho-meson t-pole contribution to sigmaT, the transverse part of cross section. We test two different field representations of the rho meson, vector and tensor, and find that the tensor representation of the rho meson is more reliable in the description of the existing data. In particular, we show that the rho-meson t-pole contribution, including the interference with an effective non-local contact term, sufficiently improv…
We study inelastic meson-meson scattering that is governed by quark-antiquark annihilation and creation involving a quark and an antiquark annihilating into a gluon, and subsequently the gluon creating another quark-antiquark pair. The resultant hadronic reactions include for I=1: pion + pion to rho + rho, kaon + antikaon to kaon* + antikaon*, kaon + antikaon* to kaon* + antikaon*, kaon* + antikaon to kaon* + antikaon*, as well as pion + pion to kaon + antikaon, pion + rho to kaon + antikaon*, pion + rho to kaon* + antikaon, and kaon + antikaon to rho + rho. In each reaction, one or two Feynma…
In this talk, we introduce an effective chiral action, derived from the instanton QCD vacuum configuration, in order to study the modification of mesonic properties in medium. We present our recent theoretical results on the electromagnetic from factor and rho-meson mass shift at finite density. We observe that the rho-meson mass is dropped by about 10%: m*_rho/m_rho ~ 1-0.12 mu_B/mu_0, which is compatible with that estimated by the QCD sum rule as well as by Brown and Rho.
The couplings and decay widths of the proceses (1^+,2^+)->(0^-,1^-)+rho are studied with ligh-cone QCD sum rules in the leading order of heavy quark effective theory. These processes are employed to estimate the two pion transition widths of the (1^+,2^+) doublet through the low mass tail of the rho resonance. Our calculation shows that the two pion decay widths are much smaller than the single pion decay widths. However, B_1 and B_2^* mesons should also have significant two pion decay widths around 1.5 MeV.
We study the temperature dependence of the pion decay constant and rho-meson mass in the hidden local symmetry model at one loop. Using the standard imaginary time formalism, we include the thermal effect of rho meson as well as that of pion. We show that the pion gives a dominant contribution to the pion decay constant and rho-meson contribution slightly decreases the critical temperature. The rho-meson pole mass increases as T^4/m_ρ^2 at low temperature dominated by the pion-loop effect. At high temperature, although the pion-loop effect decreases the rho-meson mass, the rho-loop contributio…
In order to reveal possible mass shifts of the vector mesons in a dense strongly interacting medium presumably created in high energy heavy ion collisions it is necessary to know their free masses reliably. The rho(770) mass quoted in the last two editions of the Review of Particle Physics is significantly larger than the values quoted in previous editions. The new value is mostly influenced by the results of recent experiments CMD-2 and SND at the VEPP-2M e+e- collider at Novosibirsk. We show that the values of the mass and width of the rho(770) meson measured in the e+e- -> pi+pi- annihilati…
We study the implications of several recent high-precision measurements of the pion form factor in the region of the rho-omega interference "shoulder" for (i) the extraction of the rho-omega mixing matrix element, Pi_{ρω}(m_rho^2), and (ii) the evaluation of the isospin-breaking (IB) correction needed to incorporate hadronic tau decay data into the determination of the Standard Model expectation for the leading order hadronic contribution, [a_mu]_{had}^{LO}, to the anomalous magnetic moment of the muon, focussing, in the latter case, on the model-dependence of the rho-omega mixing component of…
We review our recent study of the pion mass dependence of the rho and sigma resonances, generated from one-loop SU(2) Chiral Perturbation Theory (ChPT) with the Inverse Amplitude Method (IAM). In order to properly account for the Adler zero region, we also review the recently obtained modified version of the IAM; which is based on analyticity, elastic unitarity and ChPT at low energies, thus yielding the correct pion mass dependence of the resonance pole positions up to next-to-leading order in ChPT. As main results we find that the rho-pi-pi coupling constant is almost pion mass independent a…
A realistic model for the free rho meson with coupling to two-pion states is employed to calculate the rho propagator in a hot and dense hadron gas. The medium modifications are based on hadronic rescattering processes: intermediate two-pion states are renormalized through interactions with surrounding nucleons and deltas, and rho meson scattering is considered off nucleons, deltas, pions and kaons. Constraints from gauge invariance as well as the full off-shell dynamics of the interactions are accounted for. Within the vector dominance model we apply the resulting in-medium rho spectral funct…
We carry out a theoretical and Monte Carlo study on the $J/ψ$ decays into $ωππ$ and $K\bar{K}π$ through intermediate subthreshold $ρ$ meson by using SU(3)-symmetric Lagrangian approach. It is found that the subthreshold $ρ$ contribution is not negligible and may have significant influence on partial wave analysis of resonances in these channels, especially near the $ωπ$ and $K \bar{K}$ thresholds.
Medium modifications of the pion-omega-rho vertex are analyzed in context of the omega -> pi gamma* and rho -> pi gamma* decays in nuclear matter. A relativistic hadronic model with mesons, nucleons, and Delta(1232)isobars is applied. A substantial increase of the widths for the decays omega -> pi gamma* and rho -> pi gamma* is found for photon virtualities in the range 0.3-0.6 GeV. This enhancement has a direct importance for the description of dilepton yields obtained in relativistic heavy-ion collisions.
The suggestion of momentum dependence in the amplitude for rho-omega mixing has generated concern over related implications for vector meson dominance and the photon-rho coupling. We discuss two established representations of vector meson dominance and show that one of these is completely consistent with such a coupling. We then apply it to a calculation of the pion electromagnetic form-factor. Our analysis leads to a new value for the on-shell rho-omega mixing amplitude of (-3800 +/- 370) MeV^2.
We extend hadronic models for rho-meson propagation in cold nuclear matter via coupling to in-medium pions to include finite three-momentum. Special care is taken to preserve gauge invariance. Consequences for photoabsorption on the proton and on nuclei as well as for the dilepton production in relativistic heavy-ion collisions are discussed.
A systematic study of low mass dilepton production from $π-ρ$ interactions in a hot medium is presented. Applying finite temperature perturbation theory the dilepton rate, respectively the virtual photon rate, is computed up to order $g_ρ^2$. For dilepton masses below the $ρ$ the two-body reactions $ππ\to ργ^*$, $πρ\to πγ^*$, and the decay process $ρ\to ππγ^*$ give significant contributions. Non-equilibrium contributions to the thermal rate are estimated, including the modification of the particle distribution function with non-zero pion chemical potential. The comparison of the dilepton rate …
We show that the a_1-rho-pi Lagrangian is a decisive element for obtaining a good phenomenological description of the three-pion decays of the tau lepton. We choose it in a two-component form with a flexible mixing parameter sin(theta). In addition to the dominant a_1-> pho pi intermediate states, the a_1->pi sigma ones are included. When fitting the three-pion mass spectra, three data sets are explored: (1) ALEPH 2005 pi-pi-pi+ data, (2) ALEPH 2005 pi-pi0pi0 data, and (3) previous two sets combined and supplemented with the ARGUS 1993, OPAL 1997, and CLEO 2000 data. The corresponding confiden…
We fitted the pi-pi mass distribution in the range 0.5 < mpipi < 1.1 GeV measured in hard exclusive positron-proton reactions at HERA by the form dictated by QCD at leading twist level. Extracted parameters are related to valence quark distribution in the pion, and to the pion and rho meson distribution amplitudes. We obtain, for the first time, a measurement of the second Gegenbauer coefficient of the rho meson distribution amplitude: $a_2^{(ρ)}= -0.10\pm 0.20 $ for a photon virtuality of <Q^2>=21.2 GeV^2.
The electromagnetic form factors of the $π$ and the $ρ$ are obtained using the three forms of relativistic kinematics, instant form, point form and (light) front form. Simple representations of the mass operator together with single quark currents are employed with all the forms. The Poincaré covariant current operators are generated by the dynamics from single-quark currents that are covariant under the kinematic subgroup. Front and instant forms allow to reproduce the available data for the pion form factor. On the other hand point form is not able to reproduce qualitatively the experimental…
Motivated by the planned measurements of the time-like electromagnetic proton form factors an exploratory study of the time-like electromagnetic pion form factor is presented in a formalism which describes mesons as Poincaré-invariant bound states. In the respective quark interaction kernel, beyond the gluon-intermediated interactions for valence-type quarks, non-valence effects are included by allowing the pions to couple back in a self-consistent manner to the quarks. Consequently, the opening of the dominant $ρ$ decay channel, $ρ\to ππ$, and the presence of a multi-particle branch cut, sett…
Within a field theoretical model where all damping width effects are treated self-consistently we study the changes of the spectral properties of rho-mesons due to the finite damping width of the pions in dense hadronic matter at finite temperature. The corresponding effects in the di-lepton yields are presented. Some problems concerning the self consistent treatment of vector or gauge bosons are discussed.
We review the current status of rho-omega mixing and discuss its implication for our understanding of charge-symmetry breaking. In order to place this work in context we also review the photon-hadron coupling within the framework of vector meson dominance. This leads naturally to a discussion of the electromagnetic form-factor of the pion and of nuclear shadowing.
The electromagnetic radius of the charged pion and the transition radius of the neutral pion are calculated in the framework of the nonlocal chiral quark model. It is shown in this model that the contributions of vector mesons to the pion radii are noticeably suppressed in comparison with a similar contribution in the local Nambu--Jona-Lasinio model. The form-factor for the process gamma*pi+pi- is calculated for the -1 GeV^2<q^2<1.6 GeV^2. Our results are in satisfactory agreement with experimental data.
The contribution of the rho^{\pm} vector meson to the tau -> pi pi nu gamma decay is considered as a potential source for the determination of the magnetic dipole moment of this light vector meson. In order to keep gauge-invariance of the whole decay amplitude, a procedure similar to the fermion loop-scheme for charged gauge bosons is implemented to incorporate the finite width effects of the rho^{\pm} vector meson. The absorptive pieces of the one-loop corrections to the propagators and electromagnetic vertices of the rho^{\pm} meson and W^{\pm} gauge boson have identical forms in the limit o…
We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pion-pion scattering amplitude in Chiral Perturbation Theory at finite temperature is unitarized via the Inverse Amplitude Method. Our results predict a clear increase with T of both the rho and sigma widths. The masses decrease slightly for high T, while the rho-pion-pion coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration.
The effective action for light mesons in the external uniform static electromagnetic fields was obtained on the basis of QCD string theory. We imply that in the presence of light quarks the area law of the Wilson loop integral is valid. The approximation of the Nambu-Goto straight-line string is used to simplify the problem. The Coulomb-like short-range contribution which goes from one-gluon exchange is also neglected. We do not take into account spin-orbital and spin-spin interactions of quarks and observe the $ρ$ and $K^*$ mesons. The wave function of the meson ground state is the Airy funct…
We re-examine and extend a recent analysis which showed that the rho-omega mixing amplitude cannot be unambiguously extracted from the pion electromagnetic form-factor in a model independent way. In particular, we focus on the argument that the extraction is sensitive to the presence of any intrinsic omega_I -> 2pi coupling. Our extended analysis confirms the original conclusion, with only minor, quantitative differences. The extracted mixing amplitude is shown to be sensitive to both the intrinsic coupling omega_I -> 2pi and to the value assumed for the mass of the neutral rho meson.
The behavior of the pion dispersion relation in a pion medium is strongly modified by the introduction of a finite chemical potential associated to the finite pion number density. Such behavior is particularly important during the hadronic phase of a relativistic heavy-ion collision, between chemical and thermal freeze-out, where the pion number changing processes, driven by the strong interaction, can be considered to be frozen. We make use of an effective Lagrangian that explicitly respects chiral symmetry through the enforcement of the chiral Ward identities. The pion dispersion relation is…
We calculate the lower moments of the deep-inelastic structure functions of the pion and the rho meson on the lattice. Of particular interest to us are the spin-dependent structure functions of the rho. The calculations are done with Wilson fermions and for three values of the quark mass, so that we can perform an extrapolation to the chiral limit.
We study the effect of rho^0-gamma mixing in e^+e^- to pi^+pi^- and its relevance for the comparison of the square modulus of the pion from-factor |F^(e)_pi|^2, as measured in e^+e^- annihilation experiments, and |F^(tau)_pi|^2 the corresponding quantity obtained after accounting for known isospin breaking effects by an isospin rotation from the tau-decay spectra. After correcting the tau data for the missing rho-gamma mixing contribution, besides the other known isospin symmetry violating corrections, the pi pi I=1 part of the hadronic vacuum polarization contribution to the muon g-2 are full…
We discuss the elastic photo- and leptoproduction of rho^0-mesons from nucleons at Q^2 < 1 GeV^2 as studied in recent experiments at HERA and FNAL. We find that the mass distribution of the measured π^+π^- pairs is determined to a large extent by the two-pion contribution to the photon spectral function as given by the pion form factor. With rising Q^2 the rate of diffractive events decreases and the π^+π^- mass distribution approaches a symmetric shape.
Having calculated the light-cone wave function of the pseudoscalar meson by using two equivalent and fully covariant methods, we generalize such methods to the valence Fock states of the vector meson in the light-cone formalism. We investigate the decay constant of the $ρ$ meson $f_ρ$, the $γ^{\ast} π\to ρ$ and $γ^* ρ\to π$ transition form factors and especially the transition magnetic moments. By using two groups of constraint parameters, we predict the space-like and time-like form factors $F_{πρ}(Q^2)$ and $F_{ρπ}(Q^2)$ at low and moderate energy scale and the electromagnetic radius of thes…
We calculate the processes e+ e- -> 4 pions and tau -> nu_tau + 4 pions to O(p^4) in the low-energy expansion of the standard model. The chiral amplitudes of O(p^4) can be extended via resonance exchange to energies around 1 GeV. Higher-order effects have been included in the form of omega, a_1 and double rho exchange and by performing a resummation of the pion form factor. The predicted cross sections and the branching ratios BR(rho -> 4 pions) are in good agreement with available data.
The aim of this paper is to investigate an efficient strategy that allows to obtain pi-pi phase shifts and rho meson properties from QCD lattice data with high precision. For this purpose we evaluate the levels of the pi-pi system in the rho channel in finite volume using chiral unitary theory. We investigate the dependence on the pi mass and compare with other approaches which use QCD lattice calculations and effective theories. We also illustrate the errors induced by using the conventional Luscher approach instead of a more accurate one recently developed that takes into account exactly the…
We study the contribution of the strong interaction between the two pions in S- and P-waves to the weak B --> pion pion kaon decay amplitudes. The interference between these two waves is analyzed in the pion-pion effective mass range of the rho(770) and f0(980) resonances. We use a unitary pion-pion and antikaon-kaon coupled-channel model to describe the S-wave interactions and a Breit-Wigner function for the P-wave amplitude. The weak B-decay amplitudes, obtained from QCD factorization, are supplemented with charming penguin contributions in both waves. The four complex parameters of these lo…
We study the self-energy amplitudes for the rho-omega meson system produced by an effective field theory model at the quark level characterized by a finite range quark-quark interaction and an isospin breaking bare quark mass difference $m_u - m_d$. Dynamical effects associated with confinement and dressing of quarks and the finite size of the produced $\bar{q}q$ meson modes are treated. Parameters of this approach, previously constrained by soft pion physics, are here supplemented in a minimal way to reproduce $m_ω$ and $g_{ρππ}$. Calculations are carried out up to the one pion loop level and…
We study the propagation properties of the rho vector in a dense and hot pion medium. We introduce a finite value of the chemical potential associated to a conserved pion number and argue that such description is valid during the hadronic phase of a relativistic heavy-ion collision, between chemical and thermal freeze-out, where the strong interaction drives pion number to a fixed value. By invoking vector dominance and rho saturation, we also study the finite pion density effects into the low mass dilepton production rate. We find that the distribution moderately widens and the position of th…
We consider the Olsson sum rule, i.e., the forward dispersion relation for pion-pion scattering with exchange of isospin unity at threshold. We show that, if using the S0, S2 and P wave expressions of Colangelo, Gasser and Leutwyler, then either the sum rule is not satisfied or, if adjusting the residue of the rho exchange Regge amplitude to have the sum rule satisfied (as recently proposed by Caprini, Colangelo and Leutwyler) then the subsequent high energy amplitude is in disagreement with experimental pi-pi cross sections.
We study the influence of the finite damping width of pions on the in-medium properties of the rho-meson in an interacting meson gas model at finite temperature. Using vector dominance also implications on the resulting dilepton spectra from the decay of the rho-meson are presented. A set of coupled Dyson equations with self energies up to the sunset diagram level is solved self consistently. Following a Phi-derivable scheme the self energies are dynamically determined by the self consistent propagators. Some problems concerning the self consistent treatment of vector or gauge bosons on the pr…
We use the one-loop Chiral Perturbation Theory pion-pion scattering amplitude and dispersion theory in the form of the inverse amplitude method, to study the quark mass dependence of the two lightest resonances of the strong interactions, the f_0(600) (sigma) and the rho-meson. As main results we find that the rho-pion-pion coupling constant is almost quark mass independent and that the rho mass shows a smooth quark mass dependence while that of the sigma shows a strong non-analyticity. These findings are important for studies of the meson spectrum on the lattice.
In the framework of the relativistic and gauge invariant spectral integral technique, we calculate radiative decays rho(770)-> gamma pi(140) and omega(780)-> gamma pi(140) supposing all mesons (pi, rho and omega) to be quark-antiquark states. The q anti-q wave functions found for mesons and photon lead to a reasonably good description of data ($Γ^{(exp)}_{ρ^{\pm} \toγπ^{\pm}}=68\pm 30$ keV, $Γ^{(exp)}_{ρ^{0}\toγπ^0}=77\pm 28$ keV, $Γ^{(exp)}_{ω\toγπ^0}=776\pm 45$ keV) that makes it possible to estimate the coupling for the bremsstrahlung emission of pion by quarks $g_π\equiv g_π(u\to d π)$. We…
We determine the magnitude, phase, and $s$-dependence of $ρ$-$ω$ ``mixing'' in the pion form factor in the time-like region through fits to $e^+e^- \ra π^+ π^-$ data. The associated systematic errors in these quantities, arising from the functional form used to fit the $ρ$ resonance, are small. The systematic errors in the $ρ$ mass and width, however, are larger than previously estimated.
We determine the magnetic dipole moment of the rho meson using preliminary data from the BaBar Collaboration for the $e^+ e^- \to π^+ π^- 2 π^0$ process, in the center of mass energy range from 0.9 to 2.2 GeV. We describe the $γ^* \to 4π$ vertex using a vector meson dominance model, including the intermediate resonance contributions relevant at these energies. We find that $μ_ρ= 2.1 \pm 0.5$ in $e/2 m_ρ$ units.
We revisit the evaluations for the spacelike and timelike $ρπ$ transition form factors $F_{ρπ}(Q^2)$ and $G_{ρπ}(Q^2)$ with the inclusion of the the next-to-leading order (NLO) QCD contributions in the framework of the $k_T$ factorization theorem. The infrared divergence is regularized by the transversal momentum carried by external valence quarks, and ultimately absorbed into the meson wave functions. In the region of $ Q^2 \leqslant 2 \, \textrm{GeV}^2 $, where PQCD factorization apporach applicable, the NLO contribution can bring no larger than $ 35\%$ enhancement to the spacelike form fact…
A one parameter, model confined-gluon propagator is employed in a phenomenological application of the Dyson-Schwinger and Bethe-Salpeter equations to the calculation of a range of $π$- and $ρ$-meson observables. Good agreement is obtained with the data. The calculated quark propagator does not have a singularity on the real-$p^2$ axis. A mass formula for the pion, involving only the vacuum, dressed quark propagator, is presented and shown to provide an accurate estimate of the mass obtained via a direct solution of the Bethe-Salpeter equation.
The modification of the rho-meson self-energy due to the coupling to in-medium pions is calculated consistently at finite baryon density and temperature, keeping the full 3-momentum dependence in a gauge invariant way. As a function of nucleon density, the rho-meson spectral function is strongly enhanced in the invariant mass region M < 650 MeV, while the maximum, i.e. the pole mass, is slightly shifted upwards. As a function of temperature, for fixed nucleon density, the imaginary part of the self-energy increases further due to Bose-enhancement. At the same time the mass shift from the real …
We study the pion electromagnetic form factor and the dilepton production rate in hot matter using the hidden local symmetry theory as an effective field theory for pions and rho mesons. In this framework, the chiral symmetry restoration is realized as the vector manifestation (VM) in which the massless vector meson becomes the chiral partner of the pion, giving a theoretical support to the dropping rho a la Brown-Rho scaling. In the VM the vector dominance (VD) is strongly violated near the phase transition point associated with the dropping $ρ$. We show that the effect of the violation of th…
We perform a non-perturbative lattice calculation of the P-wave pion-pion scattering phase in the rho-meson decay channel using two flavors of maximally twisted mass fermions at pion masses ranging from 480 MeV to 290 MeV. Making use of finite-size methods, we evaluate the pion-pion scattering phase in the center-of-mass frame and two moving frames. Applying an effective range formula, we find a good description of our results for the scattering phase as a function of the energy covering the resonance region. This allows us to extract the rho-meson mass and decay width and to study their quark…
