arXiv subjects

Huiquan Li

Publications and source records attributed to Huiquan Li.

23 records · Page 2Linked to original sources

arXiv2012

Strings from geometric tachyon in Rindler space and black hole thermodynamics

The dynamics of a probe particle or wrapped brane moving in the two-dimensional Rindler space can be described by a time-dependent tachyon field theory. Using knowledge of tachyon condensation, we learn that the infalling brane gets thermalised and produces open string pairs at the Hagedorn temperature when entering into the near-horizon Rindler wedge. It is shown that the Hagedorn temperature of the infalling brane is equal to the Hawking temperature of the host black hole detected in the same time coordinate. The infalling brane will decay completely into closed strings, mainly massive modes, when it reaches the horizon in infinitely long time as observed by observers at spatial infinity. Preliminary estimates indicate that the degeneracy of states of the closed strings emitted from the infalling brane should be responsible for the increased entropy in the host black hole due to absorption of the brane.

hep-th↗

arXiv2011

Cosmological evolution of a D-brane

We study the cosmological evolution of a single BPS D-brane in the absence of potential, which is in the category of the Chaplygin gas cosmological model. When such a D-brane coupled to gravity moves in the bulk with a non-vanishing velocity, it tends to slow down to zero velocity via mechanisms like gravitational waves leakage to the bulk, losing its kinetic energy to fuel the expansion of the universe on the D-brane. If the initial velocity of the D-brane is high enough, the universe on the D-brane undergoes a dust-like stage at early times and an acceleration stage at late times, as observed in the original Chaplygin gas model. When the D-brane velocity is initially zero, the D-brane will always remain fixed at some position in the bulk, with the brane tension over the Plank mass squared as a cosmological constant. Interestingly, this kind of fixed brane universe can arise as defects from tachyon inflation on a non-BPS D-brane with one dimension higherWe study the cosmological evolution of a single BPS D-brane coupled to gravity in the absence of potential. When such a D-brane moves in the bulk with non-vanishing velocity, it tends to slow down to zero velocity via mechanisms like gravitational wave leakage to the bulk, losing its kinetic energy to fuel the expansion of the universe on the D-brane. If the initial velocity of the D-brane is high enough, the universe on the D-brane undergoes a dust-like stage at early times and an acceleration stage at late times, realising the original Chaplygin gas model. When the D-brane velocity is initially zero, the D-brane will always remain fixed at some position in the bulk, with the brane tension over the Plank mass squared as a cosmological constant. It is further shown that this kind of fixed brane universe can arise as defects from tachyon inflation on a non-BPS D-brane with one dimension higher.

hep-th↗

arXiv2009

Inhomogeneous tachyon condensation

We investigate the spacetime-dependent condensation of the tachyon in effective field theories. Previous work identified singularities in the field which appear in finite time: infinite gradients at the kinks, and (in the eikonal approximation) caustics near local minima. By performing a perturbation analysis, and with numerical simulations, we demonstrate and explain key features of the condensation process: perturbations generically freeze, and minima develop singular second derivatives in finite time (caustics). This last has previously been understood in terms of the eikonal approximation to the dynamics. We show explicitly from the field equations how this approximation emerges, and how the caustics develop, both in the DBI and BSFT effective actions. We also investigate the equation of state parameter of tachyon matter showing that it is small, but generically non-zero. The energy density tends to infinity near field minima with a charateristic profile. A proposal to regulate infinities by modifying the effective action is also studied. We find that although the infinities at the kinks are successfully regularised in the time-dependent case, caustics still present.

hep-th↗

arXiv2007

Perturbations and moduli space dynamics of tachyon kinks

The dynamic process of unstable D-branes decaying into stable ones with one dimension lower can be described by a tachyon field with a Dirac-Born-Infeld effective action. In this paper we investigate the fluctuation modes of the tachyon field around a two-parameter family of static solutions representing an array of brane-antibrane pairs. Besides a pair of zero modes associated with the parameters of the solution, and instabilities associated with annihilation of the brane-antibrane pairs, we find states corresponding to excitations of the tachyon field around the brane and in the bulk. In the limit that the brane thickness tends to zero, the support of the eigenmodes is limited to the brane, consistent with the idea that propagating tachyon modes drop out of the spectrum as the tachyon field approaches its ground state. Low-lying excited states, including the zero modes, appear to show a 4-fold degeneracy in this limit. Finally, we also discuss the slow motion of the solution corresponding to the decay process in the moduli space, finding a trajectory which oscillates periodically between the unstable D-brane and the brane-antibrane pairs of one dimension lower.

hep-th↗

arXiv2004

A Modification To The Gaseous Pressure Gradients In Spherical Celestial Bodies: Effects Of The Thermal Motion

The atmospherical pressure gradients of spherical celestial bodies are very important in astrophysics and other related areas. The classical form of the gradient in a gravitation-dominated celestial body: $\frac{dp}{dR}=-\frac{GM}{R^2}ρ$ has been widely adopted for quit a long time. But, in this form, a factor has been neglected: the centrifugal force that due to the thermal motion of gaseous particles in a centripetal force field. The pressure gradient is actually caused by the ``effective weight'' $f_g^{^{\prime}}$ of gaseous particles but not by their real gravity $f_g$. For this reason, a modified form of the pressure gradient is given in this paper. Though the changes are very small in most celestial bodies, they may be not negligible in theories of stars, accretion disks, and so on with a cumulative effect.

astro-ph↗