Introduction to Branes and M-Theory for Relativists and Cosmologists

We review the recent developments in superstrings. We start with a briefsummary of various consistent superstring theories and discuss T-duality whichnecessarily leads to the presence of D-branes. The properties of D-branes aresummarized and we discuss how these suggest the existence of 11-dimensionalquantum theory, M-theory, which is believed to give rise to varioussuperstrings as perturbative expansions around particular backgrounds in thetheory. We also discuss the interpretation of brane solutions as black holes instring theories and statistical explanation of Bekenstein-Hawking entropy. Theidea behind this interpretation is that there is a fundamental duality betweenclosed (gravity) and open (gauge theory) string degrees of freedom, one ofwhose manifestation is what is kown as AdS/CFT correspondence. The idea is usedto discuss the greybody factors for BTZ black holes. Finally the entropy ofvarious balck holes are discussed in connection with Cardy-Verlinde formula.Comment: 28 pages, 7 figures, Latex. Lectures at the international workshop ``Brane world'' at YITP, 15--18 January 2002, to be published in Prog. Theor. Phys. Suppl. ptp style files included. v2: minor corrections, v3: minor corrections and refs. added, v4: eq.(7.14) correcte