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Title: Particles under extreme conditions
Author: Sehra, A. S.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2006
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In part I we study quantum modified photon trajectories in a Schwarzschild blackhole spacetime. The photon vacuum polarization effect in curved spacetime leads to birefringence, i.e. the photon velocity becomes c±δc depending on its polarization. This velocity shift then results in modified photon trajectories. We find that photon trajectories are shifted by equal and opposite amounts for the two photon polarizations, as expected by the sum rule. Therefore, the critical circular orbit at u =1/3M in Schwarzschild spacetime, is split depending on polarization as u = 1/3M ± (M) (to first order in A), where A is a constant found to be ~ 10-32 for a solar mass blackhole. Then using general quantum modified trajectory equations we find that photons projected into the blackhole for a critical impact parameter tend to the critical orbit associated with that polarization. We then use an impact parameter that is lower than the critical one. In this case the photons tend to the event horizon in coordinate time, and according to the affine parameter the photons fall into the singularity. This means even with the quantum corrections the event horizon behaves in the classic way, as expected from the horizon theorem. We also construct a quantum modified Schwarzschild metric, which encompasses the quantum polarization corrections. This is then used to derive the photons general quantum modified equations of motion, as before. We also show that when this modified metric is used with wave vectors for radically projected photons we obtain the classic equations of motion, as expected, because radial velocities are not modified by the quantum polarization correction. In Part II we use the 2+1d Nambu-Jona-Lasino (NJL) model to study the superfluid behaviour of two-dimensional quark matter. In previous work it was suggested that the high density phase of the 2+1d NJL model could be a relativistic gapless thin film BCS superfluid. In this work we find that as we raise the baryon chemical potential (µ) the baryon supercurrent jumps from a non-superfluid (zero) phase to a superfluid (non-zero) phase. This strongly first order transition is seen to occur at µ = 0.65, which was shown to be the point of chiral symmetry restoration. Therefore, we prove that at high density the 2+ 1d NJL model is in a superfluid phase. We then go on to study the dynamics of the superfluid phase, represented by the helicity modulus (Ү), which is the constant of proportionality between the supercurrent and the gradient of the diquark state function. We find that below the temperature associated with lattice size Lt = 4, the system is in a non-superfluid phase, and above Lt = 24 the system is in a superfluid phase. We also find a possible 2nd order transition at Lt ≈ 6, which corresponds to the critical point as described by Kosterlitz and Thouless’ theory of 2D critical systems with U(1) global symmetry – such as the XY model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available