윤용성 교수

We use the evolution operator method to find the one-loop effective action of scalar and spinor QED in electric field backgrounds in terms of the Bogoliubov coefficient between the ingoing and the outgoing vacua. We obtain the exact one-loop effective action for a Sauter-type electric field, ${E}_{0}{\mathrm{sech}}^{2}(t/\ensuremath{\tau})$, and show that the imaginary part correctly yields the vacuum persistence. The renormalized effective action shows the general relation between the vacuum pe

We find the Bogoliubov coefficient from the tunneling boundary condition on charged particles in a static electric field ${E}_{0}{\mathrm{sech}}^{2}(z/L)$ and, using the regularization scheme in Phys. Rev. D 78, 105013 (2008), obtain the exact one-loop effective action in scalar and spinor QED. It is shown that the effective action satisfies the general relation between the vacuum persistence and the mean number of produced pairs. We advance an approximation method for general electric fields an

We use the evolution operator method to find the Schwinger pair-production rate at finite temperature in scalar and spinor QED by counting the vacuum production, the induced production, and the stimulated annihilation from the initial ensemble. It is shown that the pair-production rate for each state is factorized into the mean number at zero temperature and the initial thermal distribution for bosons and fermions.

The asymptotic conformal invariance of some SU(2) model and Standard Model in curved space–time are investigated. We have examined the conditions for asymptotic conformal invariance for these models numerically.

Three new Calabi-Yau spaces relevant for superstring compactifications with Euler characteristic -144, -156, and -120 are constructed from the weighted complex projective space ${\mathrm{WCP}}^{5}$. No nontrivial discrete isometry group has been found for these spaces.

We propose a novel method for the effective action of spinor and scalar QED at finite temperature in time-dependent electric fields, where charged pairs evolve in a nonadiabatic way. The imaginary part of the effective action consists of thermal loops of the Fermi-Dirac or Bose-Einstein distribution for the initial thermal ensemble, weighted with factors of the Bogoliubov coefficients for quantum effects. And the real part of the effective action is determined by the mean number of produced pair

It is found that conformally coupled induced gravity with gradient torsion gives dilaton gravity in Riemann geometry. In the Einstein frame of dilaton gravity the conformal symmetry is hidden and a nonvanishing cosmological constant is not plausible due to the constraint of the conformal coupling.

In the present work, perhaps the simplest and the most straightforward new algorithm for generating solutions to the (anti-)self-dual Yang-Mills (YM) equation in the typical gravitational instanton background is proposed and then applied to find solutions to practically all the known gravitational instantons. The solutions thus obtained turn out to be some kind of instanton-meron hybrids possessing mixed features of both. Namely, they are rather exotic type configurations obeying a first order (

We propose a thermal interpretation of the Schwinger effect for charged spinless scalars and spin-1/2 fermions in an extremal and near-extremal Reissner–Nordström (RN) black hole. The emission of charges has the distribution with an effective temperature determined by the Davies–Unruh temperature for accelerating charges by the electric field and the scalar curvature of [Formula: see text] from the near-horizon geometry [Formula: see text]. We find a charge bound for the extremal micro-black hol

We use the evolution operator method to find the one-loop effective action of scalar and spinor QED in electric field backgrounds in terms of the Bogoliubov coefficient between the ingoing and the outgoing vacua. We obtain the exact one-loop effective action for a Sauter-type electric field, E_0 sech^2 (t/tau), and show that the imaginary part correctly yields the vacuum persistence. The renormalized effective action shows the general relation between the vacuum persistence and the total mean nu

We have considered the quantum behavior of a conformally induced gravity in the minimal Riemann-Cartan space. The regularized one-loop effective potential including the quantum fluctuations of the dilaton and the torsion fields in the Coleman-Weinberg sector gives a sensible phase transition for an inflationary phase in de Sitter space. For this effective potential, we have analyzed the semiclassical equation of motion of the dilaton field in the slow-rolling regime.