arXiv subjects

Sen Zhang

Publications and source records attributed to Sen Zhang.

117 records · Page 7Linked to original sources

arXiv2012

Radiation Reaction by Massive Particles and Its Non-Analytic Behavior

We derive a massive analog of the ALD (Abraham, Lorentz and Dirac) equation, i.e., the equation of motion of a relativistic charged particle with a radiation reaction term induced by emissions of massive fields. We show that the radiation reaction term has a non-analytic behavior as a function of the mass M of the radiation field and both expansions with respect of M and 1/M are generally invalid. Hence the massive ALD equation cannot be written as a local equation with derivative expansions. We especially investigate the radiation reaction in three specific motions, uniform acceleration, a circular motion and a scattering process.

hep-th↗

arXiv2011

Stochastic Analysis of an Accelerated Charged Particle -Transverse Fluctuations-

An accelerated particle sees the Minkowski vacuum as thermally excited, and the particle moves stochastically due to an interaction with the thermal bath. This interaction fluctuates the particle's transverse momenta like the Brownian motion in a heat bath. Because of this fluctuating motion, it has been discussed that the accelerated charged particle emits extra radiation (the Unruh radiation) in addition to the classical Larmor radiation, and experiments are under planning to detect such radiation by using ultrahigh intensity lasers constructed in near future. There are, however, counterarguments that the radiation is canceled by an interference effect between the vacuum fluctuation and the fluctuating motion. In fact, in the case of an internal detector where the Heisenberg equation of motion can be solved exactly, there is no additional radiation after the thermalization is completed. In this paper, we revisit the issue in the case of an accelerated charged particle in the scalar-field analog of QED. We prove the equipartition theorem of transverse momenta by investigating a stochastic motion of the particle, and show that the Unruh radiation is partially canceled by an interference effect.

hep-th↗

arXiv2011

Can we detect "Unruh radiation" in the high intensity lasers?

An accelerated particle sees the Minkowski vacuum as thermally excited, which is called the Unruh effect. Due to an interaction with the thermal bath, the particle moves stochastically like the Brownian motion in a heat bath. It has been discussed that the accelerated charged particle may emit extra radiation (the Unruh radiation) besides the Larmor radiation, and experiments are under planning to detect such radiation by using ultrahigh intensity lasers. There are, however, counterarguments that the radiation is canceled by an interference effect between the vacuum fluctuation and the radiation from the fluctuating motion. In this reports, we review our recent analysis on the issue of the Unruh radiation. In this report, we particularly consider the thermalization of an accelerated particle in the scalar QED, and derive the relaxation time of the thermalization.

hep-ph↗

arXiv2011

Unruh radiation and Interference effect

A uniformly accelerated charged particle feels the vacuum as thermally excited and fluctuates around the classical trajectory. Then we may expect additional radiation besides the Larmor radiation. It is called Unruh radiation. In this report, we review the calculation of the Unruh radiation with an emphasis on the interference effect between the vacuum fluctuation and the radiation from the fluctuating motion. Our calculation is based on a stochastic treatment of the particle under a uniform acceleration. The basics of the stochastic equation are reviewed in another report in the same proceeding. In this report, we mainly discuss the radiation and the interference effect.

hep-ph↗

arXiv2010

Non-Equilibrium Fluctuations of Black Hole Horizons

We investigate non-equilibrium nature of fluctuations of black hole horizons by applying the fluctuation theorems and the Jarzynski equality developed in the non-equilibrium statistical physics. These theorems applied to space-times with black hole horizons lead to the generalized second law of thermodynamics. It is also suggested that the second law should be violated microscopically so as to satisfy the Jarzynski equality.

gr-qc↗

arXiv2010

Quiver Chern-Simons Theories, D3-branes and Lorentzian Lie 3-algebras

We show that the Bagger-Lambert-Gustavsson (BLG) theory with two pairs of negative norm generators is derived from the scaling limit of an orbifolded Aharony-Bergman-Jafferis-Maldacena (ABJM) theory. The BLG theory with many Lorentzian pairs is known to be reduced to the Dp-brane theory via Higgs mechanism, so our scaling procedure can be used to derive Dp-branes directly from M2-branes in the field theory language. In this paper, we focus on the D3-brane case and investigate the scaling limits of various quiver Chern-Simons theories obtained from different orbifolding actions. Remarkably, in the case of N=2 quiver CS theories, the resulting D3-brane action covers a larger region in the parameter space of the complex structure moduli than the N=4 quiver CS theories. We also investigate how the SL(2,Z) duality transformation is realized in the resultant D3-brane theory.

hep-th↗

arXiv2008

Scaling limit of N=6 superconformal Chern-Simons theories and Lorentzian Bagger-Lambert theories

We show that the N=8 superconformal Bagger-Lambert theory based on the Lorentzian 3-algebra can be derived by taking a certain scaling limit of the recently proposed N=6 superconformal U(N)xU(N) Chern-Simons-matter theories at level (k, -k). The scaling limit (and Inonu-Wigner contraction) is to scale the trace part of the bifundamental fields as X_0 -> λ^{-1} X_0 and an axial combination of the two gauge fields as B_μ -> λB_μ. Simultaneously we scale the level as k -> λ^{-1} k and then take λ-> 0 limit. Interestingly the same constraint equation \partial^2 X_0=0 is derived by imposing finiteness of the action. In this scaling limit, M2-branes are located far from the origin of C^4/Z_k compared to their fluctuations and Z_k identification becomes a circle identification. Hence the scaled theory describes N=8 supersymmetric theory of 2-branes with dynamical coupling. The coupling constant is promoted to a space-time dependent SO(8) vector X_0^I and we show that the scaled theory has a generalized conformal symmetry as well as manifest SO(8) with the transformation of the background fields X_0^I.

hep-th↗

arXiv2008

Generalized Conformal Symmetry and Recovery of SO(8) in Multiple M2 and D2 Branes

We investigate conformal symmetries of the Aharony-Bergman-Jafferis-Maldacena (ABJM) theory for multiple M2 branes and the Lorentzian Bagger-Lambert-Gustavsson (L-BLG) theory which can be obtained by taking a scaling limit k (>>N) -> \infty of the ABJM theory. The conformal symmetry is maintained in the L-BLG by considering general space-time varying solutions to the constraint equations. The dual geometry is reduced to d=10 AdS4 x CP3 in the scaling limit and has the same conformal symmetry. The curvature radius R satisfies l_{11p} << l_{10p} << R << l_s (l_{dp} and l_s are the d-dimensional Planck lengths and the string scale), and the theory is in a region where an α' expansion is not valid. We also study how the SO(8) covariance is recovered in the AdS4 x CP3 geometry by taking the scaling limit.

hep-th↗

arXiv2008

Janus field theories from multiple M2 branes

Based on the recent proposal of N=8 superconformal gauge theories of the multiple M2 branes, we derive (2+1)-dimensional supersymmetric Janus field theories with a space-time dependent coupling constant. From the original Bagger-Lambert model, we get a supersymmetric field theory with a similar action to the N D2 branes, but the coupling varies with the space-time as a function of the light-cone coordinate, g(t+x). Half of the supersymmetries can be preserved. We further investigate the M2 brane action deformed by mass and Myers-like terms. In this case, the final YM action is deformed by mass and Myers terms and the coupling behaves as exp(μx) where μis a constant mass parameter. Weak coupling gauge theory is continuously changed to strong coupling in the large x region.

hep-th↗