A Note on Tachyons in the D3+D3ˉD3+{\bar {D3}} System

The periodic bounce of Born-Infeld theory of $D3$-branes is derived, and the BPS limit of infinite period is discussed as an example of tachyon condensation. The explicit bounce solution to the Born--Infeld action is interpreted as an unstable fundamental string stretched between the brane and its antibrane.Comment: 10 pages, 2 figures. v2: minor changes, acknowledgement added; v3: explanations and references added. Final version to appear in Mod. Phys. Lett.

Extension of non-minimal derivative coupling theory and Hawking radiation in black-hole spacetime

We study the greybody factor and Hawking radiation with a non-minimal derivative coupling between the scalar field and the curvature in the background of the slowly rotating Kerr-Newman black hole. Our results show that both the absorption probability and luminosity of Hawking radiation of the scalar field increase with the coupling. Moreover, we also find that for the weak coupling $\eta<\eta_c$, the absorption probability and luminosity of Hawking radiation decrease when the black hole's Hawking temperature decreases; while for stronger coupling $\eta>\eta_c$, the absorption probability and luminosity of Hawking radiation increase on the contrary when the black hole's Hawking temperature decreases. This feature is similar to the Hawking radiation in a $d$-dimensional static spherically-symmetric black hole surrounded by quintessence \cite{chensong}.Comment: 17 pages, 6 figures, 1 table, Title changed, Appendix changed, accepted by JHE

Time Variation of the Fine Structure Constant Driven by Quintessence

There are indications from the study of quasar absorption spectra that the fine structure constant $\alpha$ may have been measurably smaller for redshifts $z>2.$ Analyses of other data ($^{149}$Sm fission rate for the Oklo natural reactor, variation of $^{187}$Re $\beta$-decay rate in meteorite studies, atomic clock measurements) which probe variations of $\alpha$ in the more recent past imply much smaller deviations from its present value. In this work we tie the variation of $\alpha$ to the evolution of the quintessence field proposed by Albrecht and Skordis, and show that agreement with all these data, as well as consistency with WMAP observations, can be achieved for a range of parameters. Some definite predictions follow for upcoming space missions searching for violations of the equivalence principle.Comment: Final version, to be published in Phys Rev

Entanglement entropy of black holes

The entanglement entropy is a fundamental quantity which characterizes the correlations between sub-systems in a larger quantum-mechanical system. For two sub-systems separated by a surface the entanglement entropy is proportional to the area of the surface and depends on the UV cutoff which regulates the short-distance correlations. The geometrical nature of the entanglement entropy calculation is particularly intriguing when applied to black holes when the entangling surface is the black hole horizon. I review a variety of aspects of this calculation: the useful mathematical tools such as the geometry of spaces with conical singularities and the heat kernel method, the UV divergences in the entropy and their renormalization, the logarithmic terms in the entanglement entropy in 4 and 6 dimensions and their relation to the conformal anomalies. The focus in the review is on the systematic use of the conical singularity method. The relations to other known approaches such as 't Hooft's brick wall model and the Euclidean path integral in the optical metric are discussed in detail. The puzzling behavior of the entanglement entropy due to fields which non-minimally couple to gravity is emphasized. The holographic description of the entanglement entropy of the black hole horizon is illustrated on the two- and four-dimensional examples. Finally, I examine the possibility to interpret the Bekenstein-Hawking entropy entirely as the entanglement entropy.Comment: 89 pages; an invited review to be published in Living Reviews in Relativit

Experimental Study for Phycoremediation of Botryococcus sp. On Greywater

Abstract. Greywater (GW) is identified as waste disposal from home activites that is discharging from laundry, bath and wash-basin. GW useful in irrigation of a garden and aids to reduce cost as well as maintain the environmental prosperity. This paper discussed the effectiveness of Botryococcus sp. to clean GW in phycoremediation treatment. This process involves as growing the Botryococcus sp. in the GW which is contributing to utilize supplements in GW for its grow. The results indicated that Botryococcus sp. is effective to reduce COD (88%), BOD (82%), TIC (76%), TC (58%), TN (52%), TOC (39%), Phosphate (37.5%) and pH (7%) for 100% concentration of GW. Meanwhile, for the 50% of GW concentration Botryococcus sp. capable to remove such as COD (83%), TIC (82%), BOD (68%), TN (67%), Phosphate (36.8%), TC (34%), TOC (31%) and pH (1.2%). Then, the study concludes that Botryococcus sp. can grow effectively in GW and be able to reduce the rate of nutrient in GW