Interactions of non-Abelian global strings

Non-Abelian global strings are expected to form during the chiral phase transition. They have orientational zero modes in the internal space, associated with the vector-like symmetry SU_(N)L+R$\mathit{SU}{(N)}_{\mathrm{L}+\mathrm{R}}$ broken in the presence of strings. The interaction among two parallel non-Abelian global strings is derived for general relative orientational zero modes, giving a non-Abelian generalization of the Magnus force. It is shown that when the orientations of the strings are the same, the repulsive force reaches the maximum, whereas when the relative orientation becomes the maximum, no force exists between the strings. For the Abelian case we find a finite volume correction to the known result. The marginal instability of the previously known Abelian η^′${\eta }^{\prime }$ strings is discussed.     

Non-Abelian global strings at chiral phase transition

We construct non-Abelian global string solutions in the UL_(N)×UR_(N)$U{(N)}_{\mathrm{L}}\times U{(N)}_{\mathrm{R}}$ linear sigma model. These strings are the most fundamental objects which are expected to form during the chiral phase transitions, because the Abelian η^′${\eta }^{\prime }$ string is marginally decomposed into N   of them. We point out Nambu–Goldstone modes of CPN−1$\mathbf{C}{P}^{N-1}$ for breaking of SUV_(N)$\mathit{SU}{(N)}_{\mathrm{V}}$ arise around a non-Abelian vortex.     

Radiative reaction and quantum mechanics

According to the principles of quantum mechanics, the classical Lorentz-Dirac equations of the electron should follow from quantum electrodynamics in the classical limit. We show this is indeed true for the special case in which the charge does not radiate, provided the momentum operators in the Dirac theory are identified, in the classical limit, with the effective momenta of the Lorentz-Dirac equations.     

On the evolution of global strings in the early universe

We find that a bent global string straightens itself out by dissipation into Nambu-Goldstone (NG) bosons in the order of one oscillation time and that the spectrum of radiated NG bosons is 1/k. In the early universe, the assumption that there is one global string per causal horizon is justified after an initial period during which the effect of the primordial plasma on the motion of the strings is non-negligible. We find that the upper bound that axion radiation by strings places on the axion decay constant is comparable to, but not more stringent than the one derived from coherent oscillations of the axion field, i.e. ∫_a ≲ 10¹²GeV. We also discuss the model-dependence of this bound.     

Quantum tunneling and back reaction

We give a correction to the tunneling probability by taking into account the back reaction effect to the metric of the black hole spacetime. We then show how this gives rise to the modifications in the semiclassical black hole entropy and Hawking temperature. Finally, we reproduce the familiar logarithmic correction to the Bekenstein–Hawking area law.     

Open strings on orbifolds

We consider propagation of type I SO(32) superstrings on orbifolds. It is shown that anomaly cancellation requires the existence of “twisted” open strings and we determine the Chan-Paton factors for these strings in a simple example.     

Particle production, back reaction and singularity avoidance

We consider particle production in Robertson-Walker spacetime as particle-antiparticle rotation. We thereby obtain a scale factor that guarantees particle production. We then study quantum field effects in spatially flat homogeneous and isotropic spacetime with energy density of created particles and one loop quantum correction as back reaction. In the numerical solution initial values are determined from particle production simulated scale factor and obtain the evolution of the universe both at early and late times having a bounce.