We study the temperature evolution of the ρ and σ mass and width, using a unitary chiral approach. The one-loop ππ scattering amplitude in Chiral Perturbation Theory at T = 0 is unitarized via the Inverse Amplitude Method. Our results predict a clear increase with T of both the ρ and σ widths. The masses decrease slightly for high T , while the ρππ coupling increases. The ρ behavior seems to be favored by experimental results. In the σ case, it signals chiral symmetry restoration.PACS numbers: 11.10. Wx, 12.39.Fe, 11.30.Rd, One of the outstanding phenomena related to heavy ion collisions is the flatness of the dilepton spectrum near the mass of the ρ meson, which is so clearly visible in many processes involving hadrons and electromagnetic probes. This flatness has been observed by the HELIOS and CERES collaborations [1,2] and has been the subject of widespread discussion. Dileptons and photons provide neat signals of the early stages of the quark-gluon plasma and its subsequent evolution into a hadron gas [3]. In fact, the most credible explanation of the absence of a prominent hill in the dilepton spectrum is a change in the mass and width of the ρ due to its interactions with the hot hadron gas [4,5,6,7]. Since the baryons, with a large forward momentum, have almost escaped the central collision region, this gas is composed mainly of pions. Our aim is to study the thermal evolution of the ρ mass M ρ and width Γ ρ , from the first principles of chiral symmetry and unitarity in ππ scattering.What happens to the ρ in extreme conditions is a hadronic physics problem, involving non perturbative physics and hence difficult to be treated. Prior to this work, a copious number of models and estimations have appeared. In most of them Γ ρ increases with temperature, simply as a consequence of stimulated emission in the pion thermal bath or, equivalently, because the effective phase space increases [8,9]. This behavior is often interpreted as a deconfining effect, or hadron "melting". As for the mass, Vector Meson Dominance (VMD) implies that M ρ changes very little at low temperatures [8,10,11]. As T approaches the critical temperature, earlier works claimed that M ρ increases [8,11,12] but the analysis of experimental dilepton data seems to favor a decreasing behavior [5,7]. Let us remark that in all these works, the ρ is introduced as an explicit degree of freedom and often a dilute pion gas is assumed, so that the thermal effects appear, to leading order, only through the pion distribution function and not through the interaction details. Other approaches include the NJL model [13], where M ρ and Γ ρ slightly decrease (but there is an spurious quark threshold near M ρ ) as well as qq wavefunction analysis in the π channel yielding a decreasing width [14].In this work we will use a thermal treatment of the effective degrees of freedom, the pions in the aftermath of the collision at moderate temperatures. The guiding fundamental principles will be just chiral symmetry and unitarity. We will build on a previous work ...

We report an odderon Regge trajectory emerging from a field theoretical Coulomb gauge QCD model for the odd signature J P C (P = C = -1) glueball states (oddballs). The trajectory intercept is clearly smaller than the pomeron and even the ω trajectory's intercept which provides an explanation for the nonobservation of the odderon in high energy scattering data. To further support this result we compare to glueball lattice data and also perform calculations with an alternative model based upon an exact Hamiltonian diagonalization for three constituent gluons.PACS numbers: 11.55. Jy, 12.39.Mk, 12.39.Pn, 12.40.Yx Regge trajectories [1] have long been an effective phenomenological tool in hadronic physics. In Regge theory the scattering amplitude is governed by Regge poles, α n (s), in the complex J (angular momentum) plane. For integer J the amplitude has a pole in the complex s plane and, by crossing symmetry, for t < 0 at high s the cross section is dominated by the Regge trajectory, α(t) = bt + α(0), with the largest intercept, α(0). This conjecture provides a unifying connection between hadron spectroscopy (Chew-Frautschi plot of J vs. t = M 2 J ) and the high energy behavior of the total cross section which scales as s 1−α(0) . For elastic scattering the energy dependence is well described by the leading Regge trajectory, the pomeron, having α P (0) ∼ = 1 and b P = 0.2 − 0.3 GeV −2 (for recent fits see Ref.[2]). Of course the pomeron does not relate to conventional hadron spectra since meson trajectories typically have larger slopes, b M ∼ = .9 GeV −2 , and smaller intercepts, α M (0) ∼ = .55. According to the glueball-pomeron conjecture [3,4], which is supported by lattice data [5] and other models [6], this trajectory is instead connected to glueball spectroscopy. Related, the different pomeron and meson trajectory slopes can be generated [4] by the gluon and quark color factors, respectively, used in confining potential models. Due to the large gluon mass gap, which suppresses relativistic corrections and transverse gluon exchange [7], these models tend to be more robust for glueballs than mesons. They produce a pomeron consisting of even signature J ++ glueballs having maximum intrinsic spin S coupled to minimum possible orbital L.Of active interest is the odd signature, P = C = -1 counterpart to the pomeron, the odderon [8], for which there is no firm experimental evidence. Whereas the pomeron predicts asymptotically equal pp andpp cross sections, the competitive presence of the odderon or any other C = -1 trajectory would produce a difference. However, high energy measurements reveal a minimal difference indicating that the odderon, if it exists, would have a smaller intercept probably at most comparable to the ω value, α ω (0) = 0.5. Indeed, dedicated exclusive searches at HERA [9] exclude an odderon Regge trajectory with an intercept greater than 0.7. Although perturbative QCD calculations [10] based on the BKP equation predict an odderon intercept close to 1, they are only reliable for both s, −t >...

Effective Field Theories (EFTs) constructed as derivative expansions in powers of momentum, in the spirit of Chiral Perturbation Theory (ChPT), are a controllable approximation to strong dynamics as long as the energy of the interacting particles remains small, as they do not respect exact elastic unitarity. This limits their predictive power towards new physics at a higher scale if small separations from the Standard Model are found at the LHC or elsewhere. Unitarized chiral perturbation theory techniques have been devised to extend the reach of the EFT to regimes where partial waves are saturating unitarity, but their uncertainties have hitherto not been addressed thoroughly. Here we take one of the best known of them, the Inverse Amplitude Method (IAM), and carefully following its derivation, we quantify the uncertainty introduced at each step. We compare its hadron ChPT and its electroweak sector Higgs EFT applications. We find that the relative theoretical uncertainty of the IAM at the mass of the first resonance encountered in a partial-wave is of the same order in the counting as the starting uncertainty of the EFT at near-threshold energies, so that its unitarized extension should a priori be expected to be reasonably successful. This is so provided a check for zeroes of the partial wave amplitude is carried out and, if they appear near the resonance region, we show how to modify adequately the IAM to take them into account.

In this review we highlight a few physical properties of neutron stars and their theoretical treatment inasmuch as they can be useful for nuclear and particle physicists concerned with matter at finite density (and newly, temperature). Conversely, we lay out some of the hadron physics necessary to test General Relativity with binary mergers including at least one neutron star, in view of the event GW170817: neutron stars and their mergers reach the highest matter densities known, offering access to the matter side of Einstein's equations. In addition to minimum introductory material for those interested in starting research in the field of neutron stars, we dedicate quite some effort to a discussion of the Equation of State of hadron matter in view of gravitational wave developments; we address phase transitions and how the new data may help; we show why transport is expected to be dominated by turbulence instead of diffusion through most if not all of the star, in view of the transport coefficients that have been calculated from microscopic hadron physics; and we relate many of the interesting physics topics in neutron stars to the radius and tidal deformability.

We show how to fix the renormalization scale for hard-scattering exclusive processes such as deeply virtual meson electroproduction by applying the BLM prescription to the imaginary part of the scattering amplitude and employing a fixed-t dispersion relation to obtain the scale-fixed real part. In this way we resolve the ambiguity in BLM renormalization scale-setting for complex scattering amplitudes. We illustrate this by computing the H generalized parton distribution at leading twist in an analytic quark-diquark model for the parton-proton scattering amplitude which can incorporate Regge exchange contributions characteristic of the deep inelastic structure functions.