Michael G. Schmidt

On the calculation of effective actions by string methods

Abstract Strasslers formulation of the string-derived Bern-Kosower formalism is reconsidered with particular emphasis on effective actions and form factors. Two- and three-point form factors in the nonabelian effective action are calculated and compared with those obtained in the heat aernel approach of Barvinsky, Vilkovisky et al. We discuss the Fock-Schwinger gauge and propose a manifestly covariant calculational scheme for one-loop effective actions in gauge theory.

Electroweak baryogenesis: Concrete in a SUSY model with a gauge singlet

SUSY models with a gauge singlet easily allow for a strong first order electroweak phase transition (EWPT) if the vevs of the singlet and Higgs fields are of comparable size. We discuss the profile of the stationary expanding bubble wall and CP-violation in the effective potential, in particular transitional CP-violation inside the bubble wall during the EWPT. The dispersion relations for charginos contain CP-violating terms in the WKB approximation. These enter as source terms in the Boltzmann equations for the (particle-antiparticle) chemical potentials and fuel the creation of a baryon asymmetry through the weak sphaleron in the hot phase. This is worked out for concrete parameters.

MSSM electroweak baryogenesis and flavour mixing in transport equations

Abstract We make use of the formalism of [T. Konstandin, et al., hep-ph/0410135 ], and calculate the chargino-mediated baryogenesis in the Minimal Supersymmetric Standard Model. The formalism makes use of a gradient expansion of the Kadanoff–Baym equations for mixing fermions. For illustrative purposes, we first discuss the semiclassical transport equations for mixing bosons in a space–time-dependent Higgs background. To calculate the baryon asymmetry, we solve a standard set of diffusion equations, according to which the chargino asymmetry is transported to the top sector, where it biases sphaleron transitions. At the end we make a qualitative and quantitative comparison of our results with the existing work. We find that the production of the baryon asymmetry of the universe by CP-violating currents in the chargino sector is strongly constrained by measurements of electric dipole moments.

First principle derivation of semiclassical force for electroweak baryogenesis

We perform a systematic gradient expansion on kinetic equations and derive the CP-violating semiclassical force for fermions propagating in presence of a CP-violating wall at a first order electroweak phase transition. The force appears at order in the flow term of the kinetic equation and agrees with the semiclassical force used for baryogenesis computations. In particular we consider the force for charginos in both the MSSM and NMSSM. We then study the continuity equations for the vector and axial vector currents and stress the role of the latter as the one containing baryogenesis sources. We also show that there is no CP-violating force for bosons to order in gradient expansion.

Electroweak Phase Transition and Baryogenesis in the nMSSM

We analyze the nMSSM with CP violation in the singlet sector. We study the static and dynamical properties of the electroweak phase transition. We conclude that electroweak baryogenesis in this model is generic in the sense that if the present limits on the mass spectrum are applied, no severe additional tuning is required to obtain a strong first-order phase transition and to generate a sufficient baryon asymmetry. For this we determine the shape of the nucleating bubbles, including the profiles of CP-violating phases. The baryon asymmetry is calculated using the advanced transport theory to first and second order in gradient expansion presented recently. Still, first and second generation sfermions must be heavy to avoid large electric dipole moments.

Orbifolds by cyclic permutations of tensor product conformal field theories

Abstract We present the partition function for orbifold theories obtained by moding cyclic permutational symmetries of a product of identical conformal field theories in two dimensions and read off the spectrum of twisted states. We also shortly discuss applications to tensor products of minimal N = 2 superconformal field theories used in Gepner type superstring compactifications and indicate how the orbifoldization works on the corresponding Calabi-Yau manifolds.

Spectra and Symmetries of Gepner Models Compared to Calabi-yau Compactifications

Abstract The massless spectra of (2, 2) superconformal Gepner models with arbitrary (in particular D-type) affine invariants are presented. The algebraic manifolds corresponding to these models are constructed. The calculation of their Euler numbers and identification of their discrete symmetries is described, and a comparison of these properties with the spectra and discrete symmetries of the Gepner models is made. Orbifoldizing systematically with respect to the discrete symmetries, models with a small number of generations are obtained.

Multiloop calculations in the string inspired formalism: The Single spinor loop in QED

We use the world line path-integral approach to the Bern-Kosower formalism for developing a new algorithm for the calculation of the sum of diagrams with one spinor loop and a fixed number of external and internal photons. The method is based on world line supersymmetry, and on the construction of generalized world line Green functions. The two-loop QED \ensuremath{\beta} function is calculated as an example. \textcopyright{} 1996 The American Physical Society.

Superfield approach to 5D conformal SUGRA and the radion

Abstract We propose that the radion chiral supermultiplet of five-dimensional compactified supergravity is obtained by reduction of the graviphoton gauge multiplet to N = 1 superfields in the off shell 5D superconformal gravity formalism of Fujita, Kugo and Ohashi. We present a superfield Lagrangian of Chern–Simons type (similar to global SUSY), which reproduces all component couplings of gauge fields and the radion. A hypermultiplet superspace action is also proposed which correctly accounts for the coupling of matter multiplets with gauge and radion superfields. 4D supergravity enters by the coupling to the 4D Weyl multiplet, an even orbifold parity multiplet embedded in the 5D Weyl multiplet. We apply this formalism to a discussion of Fayet–Iliopolous terms, and the gauging of orbifold SUGRA to obtain warped solutions.

Kinetic description of fermion flavor mixing and CP-violating sources for baryogenesis

Abstract We derive transport equations for fermionic systems with a space–time dependent mass matrix in flavor space allowing for complex elements leading to CP violation required for electroweak baryogenesis. By constructing appropriate projectors in flavor space of the relevant tree level Kadanoff–Baym equations, we split the constraint equations into “diagonal” and “transversal” parts in flavor space, and show that they decouple. While the diagonal densities exhibit standard dispersion relations at leading order in gradients, the transverse densities exhibit a novel on-shell structure. Next, the kinetic equations are considered to second order in gradients and the CP-violating source terms are isolated. This requires a thorough discussion of a flavor independent definition of charge-parity symmetry operation. To make a link with baryogenesis in the supersymmetric extension of the Standard Model, we construct the Green functions for the leading order kinetic operator and solve the kinetic equations for two mixing fermions (charginos). We take account of flavor blind damping, and consider the cases of inefficient and moderate diffusion. The resulting densities are the CP-violating chargino currents that source baryogenesis.