arXiv subjects

Sang Pyo Kim

Publications and source records attributed to Sang Pyo Kim.

At least 73 records · Page 4Linked to original sources

arXiv2014

Second Quantized Scalar QED in Homogeneous Time-Dependent Electromagnetic Fields

We formulate the second quantization of a charged scalar field in homogeneous, time-dependent electromagnetic fields, in which the Hamiltonian is an infinite system of decoupled, time-dependent oscillators for electric fields, but it is another infinite system of coupled, time-dependent oscillators for magnetic fields. We then employ the quantum invariant method to find various quantum states for the charged field. For time-dependent electric fields, a pair of quantum invariant operators for each oscillator with the given momentum plays the role of the time-dependent annihilation and the creation operators, constructs the exact quantum states, and gives the vacuum persistence amplitude as well as the pair-production rate. We also find the quantum invariants for the coupled oscillators for the charged field in time-dependent magnetic fields and advance a perturbation method when the magnetic fields change adiabatically. Finally, the quantum state and the pair production are discussed when a time-dependent electric field is present in parallel to the magnetic field.

hep-th↗

arXiv2014

QED Actions in Supercritical Fields

In the in-out formalism we advance a new method to represent the gamma function for QED actions in supercritical fields, which is complementary to the proper-time integral representation in Phys. Rev. D 78, 105013 (2008) and Phys. Rev. D 84, 065004 (2011). The new method directly yields the QED action in terms of the Hurwitz zeta function in a constant magnetic field and the complex QED action in a constant electric field. The complex action exactly gives the vacuum polarization and the vacuum persistence and thereby the pair-production rate in the electric field. The QED actions exhibit the electromagnetic duality.

hep-th↗

arXiv2014

Geometric Origin of Pair Production by Electric Field in de Sitter Space

The particle production in a de Sitter space provides an interesting model to understand the curvature effect on Schwinger pair production by a constant electric field or Schwinger mechanism on the de Sitter radiation. For that purpose, we employ the recently introduced complex analysis method, in which the quantum evolution in the complex time explains the pair production via the geometric transition amplitude and gives the pair-production rate as the contour integral. We compare the result by the contour integral with that of the phase-integral method.

gr-qc↗

arXiv2013

Spontaneous Emission of Charged Bosons from Supercritical Point Charges

We study the spontaneous emission of charged bosons from supercritical Coulomb potentials and charged black holes. We find the exact emission rate from the Bogoliubov transformation by applying the tunneling boundary condition on the Jost functions at the asymptotic boundaries. The emission rate for charged bosons in the supercritical Coulomb potential increases as the charge $Zα> 1/2$ of the superatom and the energy of the bosons increase but is suppressed for large angular momenta. We discuss physical implications of the emission of charged bosons from superatoms and charged black holes.

hep-th↗

arXiv2013

Particle Production from Geometric Transition in Expanding Universe

The geometric transitions from the evolution in the complex plane of time provide channels for particle production for a quantum field in expanding universes. The production rate for one pair is obtained by squaring and summing the scattering matrix between the in-vacuum and the transported one over all possible independent closed paths of winding number 1.

gr-qc↗

arXiv2013

Matrix Operator Approach to the Quantum Evolution Operator and the Geometric Phase

The Moody-Shapere-Wilczek's adiabatic effective Hamiltonian and Lagrangian method is developed further into the matrix effective Hamiltonian (MEH) and Lagrangian (MEL) approach to a parameter-dependent quantum system. The matrix-operator approach formulated in the product integral (PI) provides not only a method to find the wave function efficiently in the MEH approach but also higher order corrections to the effective action systematically in the MEL approach, a la the Magnus expansion and the Kubo cumulant expansion. A coupled quantum system of a light particle of a harmonic oscillator is worked out, and as a by-product, a new kind of gauge potential (Berry's connection) is found even for nondegenerate cases (real eigenfunctions). Moreover, in the PI formulation the holonomy of the induced gauge potential is related to Schlesinger's exact formula for the gauge field tensor. A superadiabatic expansion is also constructed, and a generalized Dykhne formula, depending on the contour integrals of the homotopy class of complex degenerate points, is rephrased in the PI formulation.

quant-ph↗

arXiv2013

Landau Levels of Scalar QED in Time-Dependent Magnetic Fields

The Landau levels of scalar QED undergo continuous transitions under a homogeneous, time-dependent magnetic field. We analytically formulate the Klein-Gordon equation for a charged spinless scalar as a Cauchy initial value problem in the two-component first order formalism and then put forth a measure that classifies the quantum motions into the adiabatic change, the nonadiabatic change, and the sudden change. We find the exact quantum motion and calculate the pair-production rate when the magnetic field suddenly changes as a step function.

hep-th↗

arXiv2013

New Geometric Transition as Origin of Particle Production in Time-Dependent Backgrounds

By extending the quantum evolution of a scalar field in time-dependent backgrounds to the complex-time plane and transporting the in-vacuum along a closed path, we argue that the geometric transition from the simple pole at infinity determines the multi-pair production depending on the winding number. We apply the geometric transition to Schwinger mechanism in the time-dependent vector potential for a constant electric field and to Gibbons-Hawking particle production in the planar coordinates of a de Sitter space.

hep-th↗

arXiv2013

Geometric Origin of Stokes Phenomenon for de Sitter Radiation

We propose a geometric interpretation for the Stokes phenomenon in de Sitter spacetime that particles are produced in even dimensions but not in odd dimensions. The scattering amplitude for a quantum field between the in-vacuum and the transported one along a closed path in the complex-time plane gives the particle-production rate that explains not only the Boltzmann factor from the simple pole at infinity, corresponding to the cosmological horizon, but also the sinusoidal behavior from simple poles at the north and south poles of the Euclidean geometry. The Stokes phenomenon is a consequence of interference among four independent closed paths in the complex plane.

hep-th↗

arXiv2013

Massive Scalar Field Quantum Cosmology

We study the third quantized formulation of the massive inflaton quantum cosmology for the Friedmann-Robertson-Walker universe. The Hamiltonian is equivalent to an infinite number of coupled oscillators whose couplings and frequencies are intrinsic time-dependent. We propose the invariant operators whose eigenstates provide the exact wave functions of the universe.

gr-qc↗

arXiv2012

Third Quantization and Quantum Universes

We study the third quantization of the Friedmann-Robertson-Walker cosmology with $N$-minimal massless fields. The third quantized Hamiltonian for the WDW equation in the minisuperspace consists of infinite number of intrinsic time-dependent, decoupled oscillators. The Hamiltonian has a pair of invariant operators for each universe with conserved momenta of the fields that play a role of the annihilation and the creation operators and that construct various quantum states for the universe. The closed universe exhibits an interesting feature of transitions from stable states to tachyonic states depending on the conserved momenta of the fields. In the classical forbidden unstable regime, the quantum states have googolplex growing position and conjugate momentum dispersions, which defy any measurements of the position of the universe.

gr-qc↗

arXiv2012

de Sitter Radiation and Backreaction in Quantum Cosmology

We explore the quantum cosmology description of the de Sitter (dS) radiation and its backreaction to dS space, inherent in the wave function of the Wheeler-DeWitt equation for pure gravity with a cosmological constant. We first investigate the quantum Friedmann-Lemaitre-Robertson-Walker cosmological model and then consider possible effects of inhomogeneities of the universe on the dS radiation. In both the cases we obtain the modified Friedmann equation, including the backreaction from spacetime fluctuations, and the quantum-corrected dS temperature. It is shown that the quantum correction increases the dS temperature with the increment characterized by the ratio of the dS scale to the Planck scale.

gr-qc↗

arXiv2012

Schwinger Pair Production in Pulsed Electric Fields

We numerically investigate the temporal behavior and the structure of longitudinal momentum spectrum and the field polarity effect on pair production in pulsed electric fields in scalar quantum electrodynamics (QED). Using the evolution operator expressed in terms of the particle and antiparticle operators, we find the exact quantum states under the influence of electric pulses and measure the number of pairs of the Minkowski particle and antiparticle. The number of pairs, depending on the configuration of electric pulses, exhibits rich structures in the longitudinal momentum spectrum and undergoes diverse dynamical behaviors at the onset of the interaction but always either converges to a momentum-dependent constant or oscillates around a momentum-dependent time average after the completion of fields.

hep-th↗

arXiv2012

Spontaneous Pair Production in Reissner-Nordstrom Black Holes

We investigate the spontaneous pair production, including the Schwinger mechanism and the Hawking thermal radiation, of charged scalar particles from the near horizon region of a (near) extremal Reissner-Nordström black hole. The paradigm is equivalent to the dynamics of the charged scalar field in a specific AdS$_2 \times S^2$ spacetime with a constant electric field. Two possible boundary conditions are adopted to explicitly compute the corresponding production rate and absorption cross section. It is shown that the Schwinger production rate can be eventually suppressed by the increasing attractive gravitational force as the geometry changes from the extremal to the near extremal black hole. Consequently, the Schwinger mechanism and the Hawking radiation are generically indistinguishable for the near extremal black holes. The holographic description dual to the pair production is also briefly discussed.

hep-th↗

arXiv2012

Lessons from Schwinger Effective Action for Black Holes

We revisit the Hawking radiation by comparing the effective actions in the in-out formalism, and advance an interpretation of the vacuum polarization and the Hawking radiation. The equivalence exists between the spinor QED effective action in a constant electric field and the nonperturbative effective action of a massless boson on the horizon of a Schwarzschild black hole.

hep-th↗

arXiv2012

Quantum Dynamics for de Sitter Radiation

We revisit the Hamiltonian formalism for a massive scalar field and study the particle production in a de Sitter space. In the invariant-operator picture the time-dependent annihilation and creation operators are constructed in terms of a complex solution to the classical equation of motion for the field and the Gaussian wave function for each Fourier mode is found which is an exact solution to the Schrödinger equation. The in-out formalism is reformulated by the annihilation and creation operators and the Gaussian wave functions. The de Sitter radiation from the in-out formalism differs from the Gibbons-Hawking radiation in the planar coordinates, and we discuss the discrepancy of the particle production by the two method

hep-th↗

arXiv2012

Non-adiabatic Quantum Vlasov Equation for Schwinger Pair Production

Using Lewis-Riesenfeld theory, we derive an exact non-adiabatic master equation describing the time evolution of the QED Schwinger pair production rate for a general time-varying electric field. This equation can be written equivalently as a first-order matrix equation, as a Vlasov type integral equation, or as a third-order differential equation. In the last version it relates to the KdV equation, which allows us to construct an exact solution using the well-known one-soliton solution to that equation. The case of time-like delta function pulse fields is also shortly considered. We compare with previous approaches to the purely time-dependent field case.

hep-th↗

arXiv2011

Schwinger mechanism in dS_2 and AdS_2 revisited

Recalculating the Bogoliubov coefficients from the solutions in Phys. Rev. D 78, 103517 (2008), we obtain the mean number of boson pairs in a uniform electric field in the global coordinates dS_2 and AdS_2, which have the correct zero-field and zero-curvature limits, and study the vacuum persistence at one-loop. The mean number in AdS_2 gives the lowest limit to the Breitenloher-Freedman bound in the uniform electric field, and the mean numbers in dS_2 and AdS_2 satisfy the reciprocal relation N_{dS} (R, E) N_{AdS} (R, E) = 1 under the analytical continuation of the scalar curvature R.

hep-th↗