Robertus Potting

CPT and strings

Abstract We define the string space-time symmetries C,P,T and their products. The effects of nonlocal interactions and the infinite number of particle fields are incorporated using string field theory. At the dynamical level, C,P,T and their products are preserved by the open bosonic string. Only the product CPT is dynamically preserved by the superstring, although a modified action can be constructed to preserve C. We show that these discrete symmetries may be spontaneously broken in a natural way by string interactions. In a favorable scenario, this might lead to CPT violation in the K-K system just below the limits of present experiments.

Analytical construction of a nonperturbative vacuum for the open bosonic string

Using analytical methods, a nonperturbative vacuum is constructed recursively in the field theory for the open bosonic string. Evidence suggests it corresponds to the Lorentz-invariant end point of tachyon condensation on a D25-brane. The corresponding string field is a twisted squeezed state.

CPT , strings, and meson factories

Spontaneous breaking of [ital CPT] is possible in string theory. We show that it can arise at a level within reach of experiments at meson factories currently being built or designed. For [phi], [ital B], and [tau]-charm factories, we discuss the likely experimental string signatures and provide estimates of the bounds that might be attained in these machines.

Expectation values, Lorentz invariance, and CPT in the open bosonic string

The issue of spontaneous breaking of Lorentz and CPT invariance is studied in the open bosonic string using a truncation scheme to saturate the string-field action at successively higher levels. We find strong evidence for the existence of extrema of the action with nonzero expectation values for certain fields. The Lorentz- and CPT-preserving solution previously suggested in the literature is confirmed through level 12 in the action. A family of Lorentz-breaking, CPT-preserving solutions of the equations of motion is found to persist and converge through level 18 in the action. Two sequences of solutions spontaneously breaking both Lorentz invariance and CPT are discussed. The analysis at this level involves the analytical form of over 20,000 terms in the static potential.

CPT violation and baryogenesis

We examine the effects on baryogenesis of spontaneous CPT violation in a string-based scenario. Under suitable circumstances, certain CPT-violating terms can produce a large baryon asymmetry at the grand-unified scale that reduces to the observed value via sphaleron or other dilution mechanisms.

Marginal deformations in string field theory

We describe a method for obtaining analytic solutions corresponding to exact marginal deformations in open bosonic string field theory. For the photon marginal defor- mation we have an explicit analytic solution to all orders. Our construction is based on a pure gauge solution where the gauge field is not in the Hilbert space. We show that the solution itself is nevertheless perfectly regular. We study its gauge transformations and cal- culate some coefficients explicitly. Finally, we discuss howour method can be implemented for other marginal deformations.

Vacuum Cerenkov Radiation

Within the classical Maxwell-Chern-Simons limit of the standard-model extension, the emission of light by uniformly moving charges is studied confirming the possibility of a Cerenkov-type effect. In this context, the exact radiation rate for charged magnetic point dipoles is determined and found in agreement with a phase-space estimate under certain assumptions.

Cosmological acceleration, varying couplings, and Lorentz breaking

Many candidate fundamental theories contain scalar fields that can acquire spacetime-varying expectation values in a cosmological context. Such scalars typically obey Lorentz-violating effective dispersion relations. We illustrate this fact within a simple supergravity model that also exhibits the observed late-time cosmological acceleration and implies varying electromagnetic couplings.

Off-Shell Structure of the String Sigma Model

The off-shell structure of the string sigma model is investigated. In the open bosonic string, nonperturbative effects appear to depend crucially on the regularization scheme. A scheme retaining the notion of string width reproduces the structure of Wittens string field theory.

Gravity from spontaneous Lorentz violation

We investigate a class of theories involving a symmetric two-tensor field in Minkowski spacetime with a potential triggering spontaneous violation of Lorentz symmetry. The resulting massless Nambu-Goldstone modes are shown to obey the linearized Einstein equations in a fixed gauge. Imposing self-consistent coupling to the energy-momentum tensor constrains the potential for the Lorentz violation. The nonlinear theory generated from the self-consistent bootstrap is an alternative theory of gravity, containing kinetic and potential terms along with a matter coupling. At energies small compared to the Planck scale, the theory contains general relativity, with the Riemann-spacetime metric constructed as a combination of the two-tensor field and the Minkowski metric. At high energies, the structure of the theory is qualitatively different from general relativity. Observable effects can arise in suitable gravitational experiments.