Samina Masood

Vacuum polarization at finite temperature and density in QED

Abstract We calculate to first order in α, finite temperature and density (FTD) corrections to vacuum polarization in the framework of QED. The limiting values of the vacuum polarization tensor when the temperature of the heat bath T is sufficiently high are subject to physical interpretation and compared to the previously existing works. The FTD corrections to the] electric permittivity, the magnetic permeability of the medium, the anomalous magnetic moment of the electron, the charge renormalization constant Z 3 , and the running coupling constant are also calculated and comparison with the previous work furnished wherever possible.

Second order thermal corrections to electron wavefunction

Abstract Second order perturbative corrections to electron wavefunction are calculated here, for the first time, at generalized temperature. Calculations of electron self energy are important for the renormalizability of electron mass and wavefunction in QED through order by order cancellation of singularities up to order α 2 . Cancellation of temperature dependent singularities is demonstrated by incorporating the results of both orders of integration between cold and hot loops. For finite terms, we have rewritten second order thermal corrections as well, in a concise form, to calculate wavefunction renormalization constant. Our results are in a form that includes intermediate temperatures T ∼ m (where m is electron mass) while limits of high temperature T ≫ m and low temperature T ≪ m are also retrievable from them. A comparison with the existing results is included as well. The renormalized mass and wavefunction are used to calculate particle processes in extremely hot systems such as stellar cores and primordial nucleosynthesis during very early universe. An application to the latter case is also discussed.

Gluon polarization at finite temperature and density

Abstract We calculate the gluon self-mass and the QCD coupling constant at finite temperature in the real-time formalism up to the first loop level. The expressions are derived in a form that is valid for all temperature ranges in QCD. Using these results the dynamically generated mass of gluons and the plasma screening length can be determined from their effective potential.

Renormalization of QED Near Decoupling Temperature

We study the effective parameters of QED near decoupling temperatures and show that the QED perturbative series is convergent, at temperatures below the decoupling temperature. The renormalization constant of QED acquires different values if a system cools down from a hotter system to the electron mass temperature or heats up from a cooler system to the same temperature. At , the first order contribution to the electron self-mass, is 0.0076 for a heating system and 0.0115 for a cooling system and the difference between two values is equal to 1/3 of the low temperature value and 1/2 of the high temperature value around . This difference is a measure of hot fermion background at high temperatures. With the increase in release of more fermions at hotter temperatures, the fermion background contribution dominates and weak interactions have to be incorporated to understand the background effects.

SECOND-ORDER CORRECTIONS TO THE MAGNETIC MOMENT OF ELECTRON AT FINITE TEMPERATURE

Magnetic moment of electron at finite temperature is directly related to the modified electron mass in the background heat bath. Magnetic moment of electron gets modified at finite temperature also, when it couples with the magnetic field, through its temperature-dependent physical mass. We show that the second-order corrections to the magnetic moment of electron is a complicated function of temperature. We calculate the self-mass induced thermal contributions to the magnetic moment of electron, up to the two-loop level, for temperatures valid around the era of primordial nucleosynthesis. A comparison of thermal behavior of the magnetic moment is also quantitatively studied in detail, around the temperatures below and above the nucleosynthesis temperature.

Magnetic moment of neutrinos in the statistical background

Abstract The magnetic moment of neutrinos is found to have nonzero corrections from the background heat bath if we deal with the massive Dirac neutrinos. These statistical corrections are calculated in different extensions of the standard model with the right handed neutrinos. We expect that these statistical corrections may be useful in understanding the physics of superdense media such as supernovae.

Nucleosynthesis in Hot and Dense Media

We study the finite temperature and density effects on beta decay rates to compute their contributions to nucleosynthesis. QED type corrections to beta decay from the hot and dense background are estimated in terms of the statistical corrections to the self-mass of an electron. For this purpose, we re-examine the hot and dense background contributions to the electron mass and compute its effect to the beta decay rate, helium yield, energy density of the universe as well as the change in neutrino temperature from the first order contribution to the self-mass of electrons during these processes. We explicitly show that the thermal contribution to the helium abundance at T = m of a cooling universe (0.045 percent) is higher than the corresponding contribution to helium abundance of a heating universe (0.031 percent) due to the existence of hot fermions before the beginning of nucleosynthesis and their absence after the nucleosynthesis, in the early universe. Thermal contribution to helium abundance was a simple quadratic function of temperature, before and after the nucleosynthesis. However, this quadratic behavior was not the same before the decoupling temperature due to weak interactions; so the nucleosynthesis did not even start before the universe had cooled down to the neutrino decoupling temperatures and QED became a dominant theory in the presence of a high concentration of charged fermions. It is also explicitly shown that the chemical potential in the core of supermassive and superdense stars affect beta decay and their helium abundance but the background contributions depend on the ratio between temperature and chemical potential and not the chemical potential or temperature only. We calculate the hot and dense background contributions for m = T = μ. It has been noticed that temperature plays a role in regulating parameter in an extremely dense systems. Therefore, for extremely dense systems, temperature has to be large enough to get the expected value of helium production in the stellar cores.

Second Order Corrections to QED Coupling at Low Temperature

We calculate the second-order corrections to vacuum polarization tensor of photons at low temperatures, i.e. T ≪ 1010K(T ≪ me). The thermal contributions to the QED coupling constant are evaluated at temperatures below the electron mass that is T < me. Renormalization of QED at these temperatures has explicitly been checked. The electromagnetic properties of such a thermal medium are modified. Parameters like electric permittivity and magnetic permeability of such a medium are no more constant and become functions of temperature.

Two loop low temperature corrections to electron self energy

We recalculate the two loop corrections in the background heat bath using real time formalism. The procedure of the integrations of loop momenta with dependence on finite temperature before the momenta without it has been followed. We determine the mass and wavefunction renormalization constants in the low temperature limit of QED, for the first time with this preferred order of integrations. The correction to electron mass and spinors in this limit is important in the early universe at the time of primordial nucleosynthesis as well as in astrophysics.

Propagation of electromagnetic waves in extremely dense media

We study the propagation of electromagnetic (EM) waves in extremely dense exotic systems with very unique properties. These EM waves develop a longitudinal component due to interactions with the medium. Renormalization scheme of QED is used to understand the propagation of EM waves in both longitudinal and transverse directions. The propagation of EM waves in a quantum statistically treatable medium affects the properties of the medium itself. The electric permittivity and the magnetic permeability of the medium are modified and influence the related behavior of the medium. All the electromagnetic properties of a medium become a function of temperature and chemical potential of the medium. We study in detail the modifications of electric permittivity and magnetic permeability and other related properties of a medium in the superdense stellar objects.