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Register a new userSpectral function of fermions in a highly occupied non-Abelian plasma
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We develop a method to obtain fermion spectral functions non-perturbatively in a non-Abelian gauge theory with high occupation numbers of gauge fields. After recovering the free field case, we extract the spectral function of fermions in a highly occupied non-Abelian plasma close to its non-thermal fixed point, i.e., in a self-similar regime of the non-equilibrium dynamics. We find good agreement with hard loop perturbation theory for medium-induced masses, dispersion relations and quasiparticle residues. We also extract the full momentum dependence of the damping rate of the collective excitations.
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The thesis contains studies of properties quark-gluon plasma, using some non-perturbative techniques. It contains a brief introduction of quark-gluon plasma (QGP) and discussion on various signatures along with a motivation for this thesis work. It presents the basic mathematical tools and ingredients required for the thesis, i.e. basics of QCD, Imaginary and Real Time Formalism, Hard Thermal Loop perturbation theory (HTLpt), Gribov-Zwanziger (GZ) action, the Correlation Function along with the Spectral Function and Operator Product Expansion (OPE) and QCD in magnetized medium. OPE is used to compute the dilepton rate in intermediate mass range by incorporating the non-perturbative dynamics of QCD through the inclusion of non-vanishing quark and gluon condensates in combination with the Green functions in momentum space. Also the magnetic scale (g^2T) in the HTL perturbation theory, related to the confining properties of the QCD is taken into account using the GZ action through a mass parameter, which reflects a new space-like quark mode in the collective excitation. The impact of this new exciting mode on the DPR has been studied and its important consequences has been discussed. A hot magnetized medium introduces another scale in the system in addition to temperature. Electromagnetic spectral properties and DPR are studied completely analytically in presence of both strong and weak background magnetic fields at finite temperature. The Debye screening in a hot and magnetized medium has been studied which reveals some of the intriguing properties of the medium in presence of both strong and weak magnetic field. Also an important quantity that characterizes the QGP, namely quark number susceptibility has been investigated. Most of the non-perturbative results discussed in this thesis are compared with those of perturbative ones and lattice QCD.
We use a holographic method to investigate thermalization of a boost-invariant strongly interacting non-Abelian plasma. Boundary sourcing, a distorsion of the boundary metric, is employed to drive the system far from equilibrium. Thermalization is analyzed through nonlocal probes: the equal-time two-point correlation function of large conformal dimension operators in the boundary theory, and Wilson loops of different shapes. We study the dependence of the thermalization time on the size of the probes, and compare the results to the ones obtained using local observables: the onset of thermalization is first observed at short distances.
Motivated by the boost-invariant Glasma state in the initial stages in heavy-ion collisions, we perform classical-statistical simulations of SU(2) gauge theory in 2+1 dimensional space-time both with and without a scalar field in the adjoint representation. We show that irrespective of the details of the initial condition, the far-from-equilibrium evolution of these highly occupied systems approaches a unique universal attractor at high momenta that is the same for the gauge and scalar sectors. We extract the scaling exponents and the form of the distribution function close to this non-thermal fixed point. We find that the dynamics are governed by an energy cascade to higher momenta with scaling exponents $alpha = 3beta$ and $beta = -1/5$. We argue that these values can be obtained from parametric estimates within kinetic theory indicating the dominance of small momentum transfer in the scattering processes. We also extract the Debye mass non-perturbatively from a longitudinally polarized correlator and observe an IR enhancement of the scalar correlation function for low momenta below the Debye mass.
We have systematically constructed the general structure of the fermion self-energy and the effective quark propagator in presence of a nontrivial background like hot magnetised medium. This is applicable to both QED and QCD. The hard thermal loop approximation has been used for the heat bath. We have also examined transformation properties of the effective fermion propagator under some of the discrete symmetries of the system. Using the effective fermion propagator we have analysed the fermion dispersion spectra in a hot magnetised medium along with the spinor for each fermion mode obtained by solving the modified Dirac equation. The fermion spectra is found to reflect the discrete symmetries of the two-point functions. We note that for a chirally symmetric theory the degenerate left and right handed chiral modes in vacuum or in a heat bath get separated and become asymmetric in presence of magnetic field without disturbing the chiral invariance. The obtained general structure of the two-point functions is verified by computing the three-point function, which agrees with the existing results in one-loop order. Finally, we have computed explicitly the spectral representation of the two-point functions which would be very important to study the spectral properties of the hot magnetised medium corresponding to QED and QCD with background magnetic field.
We study the spectral properties of a highly occupied non-Abelian non-equilibrium plasma appearing ubiquitously in weak coupling descriptions of QCD matter. The spectral function of this far-from-equilibrium plasma is measured by employing linear response theory in classical-statistical real-time lattice Yang-Mills simulations. We establish the existence of transversely and longitudinally polarized quasiparticles and obtain their dispersion relations, effective mass, plasmon frequency, damping rate and further structures in the spectral and statistical functions. Our new method can be interpreted as a non-perturbative generalization of hard thermal loop (HTL) effective theory. We see indications that our results approach leading order HTL in the appropriate limit. The method can also be employed beyond the range of validity of HTL.
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