arXiv subjects

Sang Pyo Kim

Publications and source records attributed to Sang Pyo Kim.

At least 19 recordsLinked to original sources

arXiv2026

Scalar QED effective action in dS: implications for primordial magnetogenesis and the running of coupling constants

Particles creation and vacuum polarization under the influence of both an electromagnetic field and a de~Sitter (dS) spacetime nonperturbatively probes quantum electrodynamics (QED) and quantum gravitational effects. By applying the gamma-function regularization to the in-out formulation, we find the exact one-loop effective action in the proper-time integral representation for a charged scalar field in a uniform electric field and a parallel magnetic field in a dS spacetime. It reduces to the one-loop scalar QED Weisskopf-Schwinger effective action in the limit of Minkowski spacetime and the one-loop effective action in the pure dS spacetime. After carefully considering the different limiting cases, a striking result concerns the effective strengths of the coupling constants in the pure strong electric field limit. Our study provides further evidence for evolution of Newton's gravitational constant under the influence of the external fields. Remarkably, the analysis of the effective potential shows that the leading order contributions to the vacuum polarization amplitude, depending on the nonminimal coupling threshold, give a nonzero vacuum expectation value of the magnetic field. This mechanism generates a large magnetic field in the early dS stage of the expansion that may imply primordial magnetogenesis.

hep-th↗

arXiv2026

Energy Loss of Newborn Magnetars by Schwinger Process

We investigate electron--positron pair creation through the Schwinger process in newborn magnetars with millisecond spin periods and surface dipole fields close to or above the QED critical field, $B_{\rm Q} = 4.414\times10^{13}\,\mathrm{G}$. In the unscreened field scenario, we derive the analytical global pair creation flux and recast it into a compact form with accurate analytic approximations. For a fiducial model with $B_{\rm p} = 10^{14}\,\mathrm{G}$ and $P_0 = 1\,\mathrm{ms}$, the Schwinger channel exceeds the classical Goldreich--Julian particle supply by many orders of magnitude and becomes the dominant source of charges at the earliest stage of the magnetar. The associated discharge removes about $90\%$ of the initial rotational energy within 30 ms, suppresses the gravitational-wave loss channel, and implies that the observable millisecond phase is extremely short in this unscreened scenario. The rapid energy release over such a short timescale may also provide a viable power source for astrophysical transients. Extending the same fiducial model to $10^4\,\mathrm{yr}$ gives spin periods of order seconds, linking newborn millisecond magnetars to the mature magnetar population.

astro-ph.HE↗

arXiv2026

Exact one-loop QED actions in global $\mathrm{(A)dS}_2$

Using the in-out formalism, we derive the exact one-loop QED effective actions for spinor field in a uniform electric field in two-dimensional global (anti-)de Sitter (A)dS$_2$ spacetime. The one-loop effective action probed by a scalar or spinor field is determined by the scattering matrix relating the out-vacuum to the in-vacuum, which is in turn fixed by the Bogoliubov coefficients of the corresponding Klein-Gordon or Dirac equation in the presence of both a gauge field and curved spacetime. Remarkably, the vacuum persistence amplitude -- twice the imaginary part of the one-loop effective action -- is related, via the Bogoliubov relations, to the mean number of particle-antiparticle pairs spontaneously produced by the background fields. The Bogoliubov coefficients or mean number of pair-production for charged scalar and spinor fields in global (A)dS$_2$ lead to QED effective actions expressed in terms of both proper-time integrals and Hurwitz zeta functions. These effective actions reveal a strong interplay between the electric field and spacetime curvature and correctly reproduce the limiting cases of pure (A)dS$_2$ spacetime and a uniform electric field in Minkowski space. We further discuss the physical implications and the invariant nature of the resulting QED effective actions in (A)dS$_2$.

hep-th↗

arXiv2025

Saturation of Pauli blocking in near-extremal charged Nariai black holes

We solve the Dirac equation for a massive charged fermion in the near-extremal charged Nariai black hole with the near-horizon geometry $\mathrm{dS}_2 \times \mathrm{S}^2$. At the one-loop level, contrary to the catastrophic emission of charged spinless bosons in [C.-M. Chen \textit{et al.}, Phys. Rev. D 110, 085020 (2024)], we show that the emission of fermions in a narrow time-like inner region between the cosmological horizon and black hole horizon saturates the bound from the Pauli blocking and does not give an amplification (quantum superradiance). Using the reciprocal relation, we find the Schwinger emission of fermions from $\mathrm{AdS}_2 \times \mathrm{S}^2$, and compare the Schwinger emission of fermions and bosons from near-extremal Nariai black holes.

hep-th↗

arXiv2025

Reciprocal relation of Schwinger pair production between $\textrm{dS}_2$ and $\textrm{AdS}_2$

The Klein-Gordon and Dirac equation for a massive charged field in a uniform electric field has a symmetry of two-dimensional global de Sitter (dS) and anti-de Sitter (AdS) space. In the in-out formalism the mean numbers of spinors (spin-1/2 fermions) and scalars (spin-0 bosons) spontaneously produced by the uniform electric field are exactly found from the Bogoliubov relations both in the global and planar coordinates of (A)dS$_2$ space. We show that the uniform electric field enhances the production of charged spinor and scalar pairs in the planar and global dS space while the AdS space reduces the pair production in which weak electric fields below the Breitenlohner-Freedman (BF) bound prohibits pair production. The leading Boltzmann factor in dS space can be written as the Gibbons-Hawking radiation or Schwinger effect enhanced by e-folding factors less than one that give the QED effect or the curvature effect. We observe that dS$_2$ and AdS$_2$ spaces are connected by QED, such as a reciprocal relation between the mean number of spinors and scalars provided that the spacetime curvature is analytically continued. The leading behavior of the mean numbers for spinors and scalars is explained as a residue sum of contour integrals of the frequency or momentum in the phase-integral formulation.

hep-th↗

arXiv2025

3+1 formulation of light modes in nonlinear electrodynamics

We present a 3+1 formulation of the light modes in nonlinear electrodynamics described by Plebanski-type Lagrangians, which include Post-Maxwellian, Born-Infeld, ModMax, and Heisenberg-Euler-Schwinger QED Lagrangians. In nonlinear electrodynamics, strong electromagnetic fields modify the vacuum to acquire optical properties. Such a field-modified vacuum can possess electric permittivity, magnetic permeability, and magneto-electric response, inducing novel phenomena like vacuum birefringence. By exploiting the mathematical structures of Plebanski-type Lagrangians, we obtain a streamlined procedure and explicit formulas to determine light modes, i.e., refractive indices and polarization vectors for a given propagation direction. We also work out the light modes of the mentioned Lagrangians for an arbitrarily strong magnetic field. The 3+1 formulation advanced in this paper has direct applications to the current vacuum birefringence research: terrestrial experiments using permanent magnets/ultra-intense lasers for the subcritical regime and astrophysical observation of the x-rays from highly magnetized neutron stars for the near-critical and supercritical regimes.

gr-qc↗

arXiv2025

Strong Field QED, Astrophysics, and Laboratory Astrophysics

Astrophysical compact objects, such as magnetars, neutron star mergers, etc, have strong electromagnetic fields beyond the Schwinger field ($B_c = 4.4 \times 10^{13}\, {\rm G}$). In strong electric fields, electron-positron pairs are produced from the vacuum, gamma rays create electron-positron pairs in strong magnetic fields, and propagating photons experience vacuum refringence, etc. Astrophysical compact objects with strong electromagnetic fields open a window for probing fundamental physics beyond weak field QED. Ultra-intense lasers and high-energy charged particles may simulate extreme astrophysical phenomena.

astro-ph.HE↗

arXiv2025

Fundamental Physics and Cosmology with TianQin

The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the future? These are the basic questions that press for answers. The space-based gravitational wave detector TianQin will tune in to gravitational waves in the millihertz frequency range ($10^{-4} \sim 1$ Hz, to be specific), opening a new gravitational wave spectrum window to explore many of the previously hidden sectors of the universe. TianQin will discover many astrophysical systems, populating the universe at different redshifts: some will be of new types that have never been detected before, some will have very high signal-to-noise ratios, and some will have very high parameter estimation precision. The plethora of information collected will bring us to new fronts on which to search for the breaking points of general relativity, the possible violation of established physical laws, the signature of possible new gravitational physics and new fundamental fields, and to improve our knowledge on the expansion history of the universe. In this white paper, we highlight the advances that TianQin can bring to fundamental physics and cosmology.

gr-qc↗

arXiv2024

Catastrophic Emission of Charges from Near-Extremal Charged Nariai Black Holes. II. Rotation Effect

Kerr-Newman black holes in a de Sitter (dS) space have the limit of rotating Nariai black holes with the near-horizon geometry of a warped ${\rm dS}_3 \times {\rm S}^1/Z_2$ when the black hole horizon and the cosmological horizon coincide or approach close to each other. We study the rotation effect on the spontaneous emission of charges in the near-extremal rotating charged Nariai black hole and compare it to those from the near-extremal Nariai black hole in Phys. Rev. D \textbf{110}, 085020 (2024) and near-extremal Kerr-Newman black hole in de Sitter space in Eur. Phys. J. C \textbf{83}, 219 (2023). In strong contrast to the near-extremal Kerr-Newman black hole in dS space, the near-extremal rotating Nariai black hole also has an exponential amplification for the emission of high energy charges, which becomes catastrophic regardless of angular momentum when two horizons coincide. The radius of rotating Nariai black holes monotonically increases as the angular momentum and charge of black holes increase, which gives a weaker electric field on the horizon than Nariai black holes. Thus the angular momentum of black holes that drags particles on the horizon decreases the mean number of charges by a factor not by an order. We observe a catastrophic emission of boson condensation for charges with an effective energy equal to the chemical potential in the spacelike outer region of the cosmological horizon. Remarkably, the Schwinger emission of charges in the standard particle model may prevent the rotating Nariai black holes from evolving into spacetimes with a naked singularity when the angular momentum is close to the allowed maximum, which Nariai black holes cannot avoid.

hep-th↗

arXiv2024

Strong-field QED effects on polarization states in dipole and quadrudipole pulsar emissions

Highly magnetized neutron stars have quantum refraction effects on pulsar emission due to the non-linearity of the quantum electrodynamics (QED) action. In this paper, we investigate the evolution of the polarization states of pulsar emission under the quantum refraction effects, combined with the dependence on the emission frequency; we solve a system of evolution equations of the Stokes vector, where the birefringent vector, in which such effects are encoded, acts on the Stokes vector. At a fixed frequency of emission, depending on the magnitude of the birefringent vector, dominated mostly by the magnetic field strength, the evolution of the Stokes vector largely exhibits three different patterns: (i) monotonic, or (ii) half-oscillatory, or (iii) highly oscillatory behaviors. These features are understood and confirmed by means of approximate analytical solutions to the evolution equations.

astro-ph.HE↗

arXiv2024

Catastrophic Emission of Charges from Near-Extremal Nariai Black Holes

Using both the in-out formalism and the monodromy method, we study the emission of charges from near-extremal charged Nariai black holes with the black hole event and cosmological horizons close to each other, whose near-horizon geometry is $\mathrm{dS}_2 \times \mathrm{S}^2$. The emission becomes catastrophic for a charge with energy greater than its chemical potential, whose leading exponential factor increases inversely proportional to the separation of two horizons. This effect may prevent near-extremal Nariai black holes with large charges that evaporate dominantly through the charge emission from evolving to black holes with a naked singularity, in analog to near-extremal RN-dS black holes that have the Breitenlohner-Friedman bound, below which they become stable against Hawking radiation and Schwinger effect of charge emission. The near-extremal Nariai black holes with small charges, which are close to near-extremal Schwarzschild-dS black holes, emit dominantly charge-neutral particles and evolve to black holes with increasing charge to mass ratio. We illuminate the origin of the catastrophic emission in the phase-integral formulation and monodromy method by comparing near-extremal charged Nariai black holes with near-extremal RN-dS black holes.

hep-th↗

arXiv2024

Gravitational and electromagnetic radiations from binary black holes with electric and magnetic charges

The Einstein-Maxwell theory has black hole solutions with electric and magnetic charges. In the standard model for particle physics, dyons with electric and magnetic charges would have been formed in the early universe. We derive the equations of motion of black hole binaries with electric and magnetic charges and explore some features of static orbits. We calculate the total emission rates of energy and angular momentum due to gravitational and electromagnetic radiations from dyonic binary black holes in different cases. It is shown that the emission rates of energy and angular momentum due to gravitational and electromagnetic radiations have the same dependence on the conic angle for different orbits. Moreover, we obtain the evolutions of orbits and find that a circular orbit remains circular while an elliptic orbit becomes quasi-circular due to electromagnetic and gravitational radiations. Our results provide rich information about black hole binaries with electric and magnetic charges and can be used to test black holes with magnetic charges.

gr-qc↗

arXiv2024

Quantum refraction effects in pulsar radio emission

Highly magnetized neutron stars exhibit the vacuum non-linear electrodynamics effects, which can be well described using the one-loop effective action for quantum electrodynamics. In this context, we study the propagation and polarization of pulsar radio emission, based on the post-Maxwellian Lagrangian from the Heisenberg-Euler-Schwinger action. Given the refractive index obtained from this Lagrangian, we determine the leading-order corrections to both the propagation and polarization vectors due to quantum refraction via perturbation analysis. In addition, the effects on the orthogonality between the propagation and polarization vectors and the Faraday rotation angle, all due to quantum refraction are investigated. Furthermore, from the dual refractive index and the associated polarization modes, we discuss quantum birefringence, with the optical phenomenology analogous to its classical counterpart.

gr-qc↗

arXiv2024

WIMP constraints from black hole low-mass X-ray binaries

The abnormally fast orbital decay observed in the black hole (BH) Low-Mass X-ray binaries (BH-LMXB) A0620-00 and XTE J1118+480 can be explained by the dynamical friction between Dark Matter (DM) and the companion star orbiting around the low-mass BH (of a few $M_\odot$) of the system. In this case the value of the index $γ_{\rm sp}$ of the DM spike surrounding the BH can be pinned down with an accuracy of a few percent, way better than that for much bigger systems such as the super massive BHs (SMBHs) in the Galactic Center or in M87. We have used data from XTE J1118+480 to put bounds on the WIMP annihilation cross section times velocity $\langle σv\rangle$, assuming that DM annihilation is driven by the $b\bar{b}$ annihilation channel and that it proceeds in $s$-wave. The bounds are driven by the radio synchrotron signal produced by $e^\pm$ final states propagating in the magnetic field near the BH. For DM masses $m_χ$ up to the TeV scale XTE J1118+480 allows to constrain $\langle σv\rangle$ well below $\langleσv\rangle_{\rm thermal}$, corresponding to the observed DM relic density in the Universe for a thermal WIMP. On the other hand, for $m_χ\gtrsim$ 15 GeV, the bounds from the SMBHs in the GC or in M87 do not reach $\langleσv\rangle_{\rm thermal}$ when the very large uncertainties on the corresponding spike indices are taken into account, in spite of potentially producing much larger DM densities compared to XTE J1118+480. Our bounds for XTE J1118+480 have a mild sensitivity on spatial diffusion, but diffusion enhances the sensitivity of the results upon the intensity of the magnetic field. Taken at face value the bound from XTE J1118+480 on $\langle σv\rangle$ is the most constraining compared to all others for $m_χ\lesssim$ 1 TeV, unless the intensity of the magnetic field is significantly smaller than its equipartition estimation.

hep-ph↗

arXiv2023

Monodromy Approach to Pair Production of Charged Black Holes and Electric Fields

To find the pair production, absorption cross section and quasi-normal modes in background fields, we advance the monodromy method that makes use of the regular singular points of wave equations. We find the mean number of pairs produced in background fields whose mode equations belong to the Riemann differential equation and apply the method to the three particular cases: (i) charges near the horizon of near-extremal black holes, (ii) charges with minimal energy under the static balance in nonextremal charged black holes, and (iii) charges in the Sauter-type electric fields. We then compare the results from the monodromy with those from the exact wave functions in terms of the hypergeometric functions with three regular singular points. The explicit elaboration of monodromy and the model calculations worked out here seem to reveal evidences that the monodromy may provide a practical technique to study the spontaneous pair production in general black holes and electromagnetic fields.

hep-th↗

arXiv2023

Generalized Gelfand-Dikii equation and solitonic electric fields for fermionic Schwinger pair production

In previous work on Schwinger pair creation in purely time-dependent fields, it was shown how to construct ``solitonic'' electric fields that do not create scalar pairs with an arbitrary fixed momentum. We show that this construction can be adapted to the fermionic case in two inequivalent ways, both closely related to supersymmetric quantum mechanics for reflectionless potentials, and both leading to the vanishing of the density of created pairs at certain values of the Pöschl-Teller like index $p$ of the associated Schrödinger equation. For one of them, we are able to demonstrate that the pair non-creation can be interpreted as a quantum interference effect using the phase-integral formalism. Asymptotically for large $p$, here scalar particles are not created for integer $p$ and fermions are not created for half integer $p$. Thus for any given momentum we can construct electric fields that create scalar particles but not spinor particles, and vice versa. In the scalar QED case, the solitonic fields had originally been found using the Gelfand-Dikii equation, which is related to the resolvent of the mode equation, and through it to the (generalized) KdV equation [38]. This motivates us to develop for the spinor QED case, too, an evolution equation that can be considered as a fermionic generalization of the Gelfand-Dikii equation.

hep-th↗

arXiv2023

Schwinger Pair Production and Vacuum Birefringence around High Magnetized Neutron Stars

Highly magnetized neutron stars have magnetic fields of order of the critical field and can lead to measurable QED effects. We consider the Goldreich-Julian pulsar model with supercritical magnetic fields, induced subcritical electric fields, and a period of milliseconds. We then study the strong field physics, such as Schwinger pair production and the vacuum birefringence including the wrench effect, whose X-ray polarimetry will be observed in future space missions.

astro-ph.HE↗

arXiv2023

Gravitational and electromagnetic radiation from binary black holes with electric and magnetic charges: Hyperbolic orbits on a cone

We derive the hyperbolic orbit of binary black holes with electric and magnetic charges. In the low-velocity and weak-field regime, by using the Newtonian method, we calculate the total emission rate of energy due to gravitational and electromagnetic radiation from binary black holes with electric and magnetic charges in hyperbolic orbits. Moreover, we develop a formalism to derive the merger rate of binary black holes with electric and magnetic charges from the two-body dynamical capture. We apply the formalism to investigate the effects of the charges on the merger rate for the near-extremal case and find that the effects cannot be ignored.

gr-qc↗