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At least 91 records · Page 5Linked to original sources
arXiv2007

Hadron interactions from lattice QCD

Studies on hadron interactions from lattice QCD are reviewed. The $S$-wave $ππ$ scattering lengths of the I=0 and I=2 channels are extracted from various lattice determinations of low energy constants in $N_f=2$ chiral perturbation theory. The results agree with each other and agree also with other non-lattice estimates. Recently the $P$-wave $ππ$ scattering phase shift for the I=1 channel has been calculated. A preliminary estimate of the $ρ$ meson decay width from the phase shift is consistent with the experimental value. Two approaches to potentials between hadrons are discussed. One is a method using static quarks to define the distance between two hadrons. The other is a method to define a potential from a wave function of two hadrons. An application of the latter to the nucleon-nucleon ($NN$) potential turns out to reproduce qualitative features of the phenomenological $NN$ potential such as attraction at long distance and repulsion at short distance. Theoretical issues of this approach are also discussed.

hep-lat↗
arXiv2007

Relativistic corrections to the static potential at O(1/m) and O(1/m^2)

We investigate the relativistic corrections to the static potential, i.e. the O(1/m) potential and the O(1/m^2) velocity-dependent potentials, in SU(3) lattice gauge theory. They are important ingredients of potential nonrelativistic QCD for heavy quarkonium. Utilizing the multi-level algorithm, we obtain remarkably clean signals of these potentials up to r=0.9 fm. We observe long range nonperturbative contributions to these corrections.

hep-lat↗
arXiv2007

Pion--deuteron scattering length in Chiral Perturbation Theory up to order χ^{3/2}

A complete calculation of the corrections to pion-deuteron scattering length up to order $χ^{3/2}$ with $χ=m_π/M_{N}$ is performed. The calculation includes the dispersive contributions and corrections due to the explicit treatment of the $Δ$ resonance. s-wave pion-nucleon scattering parameters are extracted from a combined analysis of modern experimental data.

nucl-th↗
arXiv2007

Progress in NN --> NNpi

We survey the recent developments in the reaction $NN \to NNπ$ in effective field theory. We show that the proper construction of the production operator needs a careful separation of irreducible pieces from reducible ones. The result of this consideration is a complete cancellation of all loops in the production operator at NLO. Moreover, we show that this procedure brings the leading Weinberg-Tomozawa vertex on-shell, thus enhancing the corresponding contribution to the transition amplitude by a factor of 4/3 as compared to the commonly used value. We also discuss the role of the $Δ(1232)$ for the s-wave pion production. Being relatively sizable individually the direct and rescattering mechanisms of the $Δ$ excitation at NLO cancel each other to a large extent. Thus, we conclude that the net effect of the $Δ$ at NLO is very small.

nucl-th↗
arXiv2008

Dissipation in the very early stage of the hydrodynamic evolution in relativistic heavy ion collisions

We propose a modification of the hydrodynamic model of the dynamics in ultrarelativistic nuclear collisions. A modification of the energy-momentum tensor at the initial stage describes the lack of isotropization of the pressure. Subsequently, the pressure is relaxing towards the equilibrium isotropic form in the local comoving frame. Within the Bjorken scaling solution a bound is found on the decay time of the initial anisotropy of the energy-momentum tensor. For the strongest dissipative effect allowed, we find a relative entropy increase of about 30%, a significant hardening of the transverse momentum spectra, and no effect on the HBT radii.

nucl-th↗
arXiv2007

How can we explore the onset of deconfinement by experiment?

There is little doubt that Quantumchromodynamics (QCD) is the theory which describes strong interaction physics. Lattice gauge simulations of QCD predict that in the $μ,T$ plane there is a line where a transition from confined hadronic matter to deconfined quarks takes place. The transition is either a cross over (at low $μ$) or of first order (at high $μ$). It is the goal of the present and future heavy ion experiment at RHIC and FAIR to study this phase transition at different locations in the $μ,T$ plane and to explore the properties of the deconfined phase. It is the purpose of this contribution to discuss some of the observables which are considered as useful for this purpose.

nucl-th↗
arXiv2007

The high density equation of state: constraints from accelerators and astrophysics

The nuclear equation of state (EoS) at high densities and/or extreme isospin is one of the longstanding problems of nuclear physics. In the last years substantial progress has been made to constrain the EoS both, from the astrophysical side and from accelerator based experiments. Heavy ion experiments support a soft EoS at moderate densities while the possible existence of high mass neutron star observations favors a stiff EoS. Ab initio calculations for the nuclear many-body problem make predictions for the density and isospin dependence of the EoS far away from the saturation point. Both, the constraints from astrophysics and accelerator based experiments are shown to be in agreement with the predictions from many-body theory.

nucl-th↗
arXiv2007

How do diquark fluctuations and chiral soft modes affect di-lepton production in the deconfined phase?

We examine diquark fluctuations and chiral soft modes existing in the precritical region of color superconductivity and chiral transition, respectively, at finite temperature and density. We evaluate how they contribute to anomalous di-lepton production; although there appear peaks in the spectral function owing to the existence of the soft modes, the enhancement of the production rate may not be so prominent to be a clear signal of the phsase transitions.

hep-ph↗
arXiv2009

Localization and the interface between quantum mechanics, quantum field theory and quantum gravity

We show that there are significant conceptual differences between QM and QFT which make it difficult to view the latter as just a relativistic extension of the principles of QM. At the root of this is a fundamental distinction between Born-localization in QM (which in the relativistic context changes its name to Newton-Wigner localization) and modular localization which is the localization underlying QFT, after one liberates it from its standard presentation in terms of field coordinates. The first comes with a probability notion and projection operators, whereas the latter describes causal propagation in QFT and leads to thermal aspects of locally reduced finite energy states. The Born-Newton-Wigner localization in QFT is only applicable asymptotically and the covariant correlation between asymptotic in and out localization projectors is the basis of the existence of an invariant scattering matrix. Taking these significant differences serious has not only repercussions for the philosophy of science, but also leads to a new structural properties as a consequence of vacuum polarization: the area law for localization entropy near the the causal localization horizon and a more realistic cutoff independent setting for the cosmological vacuum energy density which is compatible with local covariance. The article presents some observations about the interface between QFT in CST and QG.

hep-th↗
arXiv2009

$^3_ηHe$ nucleus modeling in the frame optical potential model

The conditions, at which quasi-bound $η-^{3}$He state is possible, have been investigated and compared with the available findings about $η$N-scattering length and the information about $^{3}$He nucleus from references. We conclud that the existence of quasi-bound $η-^{3}$He state within the framework of the optical potential model, which doesn`t contradict all collected findings, is not possible, but the observing anomaly of $η^{3}$He-interaction at low energies is a virtual state.

nucl-th↗
arXiv2007

Fragmentation of the fireball and how to observe it

We argue that fragmentation at hadronisation is likely scenario in ultrarelativistic nuclear collisions. In case of crossover phase transition it is driven by a singularity of the bulk viscosity. We claim that such a scenario can explain the ``HBT puzzle'' and can be identified by non-statistical differences between event-wise rapidity distributions and by proton-proton rapidity correlations.

nucl-th↗
arXiv2008

On The Leptons Masses

In this paper we present a connection between the results obtained from a semiclassical study of a relativistic, two-body system, and the leptons masses. Some possible consequences are also discussed.

nucl-th↗
arXiv2007

The High-Z hydrogen-like atom: a model for polarized structure functions

The Dirac equation offers a precise analytical description of relativistic two-particle bound states, when one of the constituent is very heavy and radiative corrections are neglected. Looking at the high-Z hydrogen-like atom in the infinite momentum frame and treating the electron as a "parton", various properties usually attributed to the quark distributions in the nucleon are tested, in particular: Bjørken scaling; charge, helicity, transversity and momentum sum rules; existence of the parton sea; Soffer inequality; correlation between spin and transverse momentum (Sivers and Boer-Mulders effects); transverse displacement of the center-of-charge and its connection with the magnetic moment. Deep inelastic experiments with photon or positron beams at MeV energies, analogous to DIS or Drell-Yan reactions, are considered.

nucl-th↗
arXiv2007

Internal energy in dissipative relativistic fluids

Liu procedure is applied to a first order weakly nonlocal special relativistic fluid. It is shown, that a reasonable relativistic theory is and extended one, where the basic state space contains the momentum density. This property follows from the structure of the energy-momentum balance and the Second Law of thermodynamics. Moreover, the entropy depends on the energy density and the momentum density on a given specific way, indicating that the local rest frame energy density cannot be interpreted as the internal energy, the local rest frame momentum density should be considered, too. The corresponding constitutive relations for the stress and the energy flux are derived.

nucl-th↗