Activated Sphalerons and Large Extra Dimensions.pdfVIP

a r X i v : h e p - p h / 0 2 0 5 3 3 1 v 3 7 J u n 2 0 0 2 SIT-HEP/TM-7 Activated Sphalerons and Large Extra Dimensions Tomohiro Matsuda 1 Laboratory of Physics, Saitama Institute of Technology, Fusaiji, Okabe-machi, Saitama 369-0293, Japan Abstract We present a new scenario for the baryon number violation that may take place in models with large extra dimensions. Our idea is interesting because lep- togenesis with a low reheating temperature requires an alternative source of the B + L violation to convert the produced leptons into baryons. If one considers a model with an intermediate compactification radius, the reheating temperature may be allowed to become higher than the critical temperature of the conventional electroweak phase transition. Our mechanism is still important in this case, because it provides the phase boundary, which is an essential ingredient of the electroweak baryogenesis. 1matsuda@sit.ac.jp 1 1 Introduction In spite of the great success in the quantum field theory, there is still no consistent scenario in which the quantum gravity is included. The most promising scenario in this direction would be the string theory, where the consistency is ensured by the require- ment of additional dimensions. Initially the sizes of extra dimensions had been assumed to be as small as M?1p , however it has been observed later that there is no reason to believe such a tiny compactification radius[1]. The large extra dimension may solve the hierarchy problem. Denoting the volume of the n-dimensional compact space by Vn, the observed Planck mass is obtained by the relation M2p = M n+2 ? Vn, where M? denotes the fundamental scale of gravity. If one assumes more than two extra dimensions, M? may be close to the electroweak scale without conflicting any observable bounds. Although such a low fundamental scale considerably improves the situations of the traditional hierarchy problem, the scenario requires some degrees of fine-tuning. The largeness of the quant