Cpt Violation , Strings , and Neutral - Meson Systems

Symmetry under the discrete transformation CPT is a general theoretical condition holding for local relativistic field theories of point particles [1]-[7]. This symmetry has been investigated experimentally under different circumstances and to a high degree of precision [8]. The broad theoretical validity of CPT symmetry for particles and the availability of high-precision tests makes CPT violation an interesting candidate experimental signal for fundamental theories such as string theory [9, 10, 11]. In this talk, I consider the possibility that CPT symmetry might be violated in nature by effects arising in a theory beyond the standard model. One example is string theory, which presently provides the most promising framework for a consistent quantum theory of gravity incorporating also the known interactions and particles. Strings are extended objects, so the usual assumptions underlying proofs of CPT symmetry do not hold. Indeed, spontaneous CPT violation can occur in string theory [9, 10], via a mechanism outlined in the next section. If physics beyond the standard model includes spontaneous CPT violation, it can be described at low energy by additional terms in an effective theory. It is possible to establish the general form of such terms that are compatible with known gauge symmetries [11, 12]. This analysis in turn suggests possible consequences of CPT violation such as baryogenesis [13] and, in particular, quantitative experimental tests of CPT. Among the most promising tests are those involving neutral-meson oscillations, where specific signatures appear in experiments involving either correlated or uncorrelated mesons. These are oulined briefly for the various neutral-meson systems in subsequent sections. Further details about these effects and experiments can be found in the original literature on the K system [9, 10, 11], the two B systems [11, 14, 15], the D system [11, 16].