On nontrivial solutions around a marginal solution in cubic superstring field theory
A bstractWe construct tachyon vacuum and half-brane solutions, using an extension of KBc algebra, in the theory around a type of identity-based marginal solutions in modified cubic superstring field theory. With explicit computations, we find that their vacuum energies are the same as those of corresponding solutions around the original theory. It implies that the vacuum energy for the identity-based marginal solution vanishes although straightforward computation of it is subtle. We also evaluate the gauge invariant overlaps for those nontrivial solutions. The values for them are deformed according to the marginal solution in the same way as the case of bosonic string field theory.

title: On the Generalized Gluing and Resmoothing Theorem
abstract: The generalized gluing and resmoothing theorem originally proved by LeClair, Peskin and Preitschopf, gives a powerful formula for the fused vertex obtained by contracting any two vertices in string field theories. Although the theorem is naturally expected to hold for the vertices at any loop level, the original proof was restricted to the vertices at tree level. Here we present a simplified proof for the tree level theorem and then prove explicitly the extended version at one-loop level. We also find that a non-trivial sign factor, which depends on the string states to be contracted, appears in the theorem. This sign factor turns out to be essential for reproducing correctly the conformal field theory correlation function on the torus.

title: Closed string amplitudes in open string field theory
abstract: We investigate gauge invariant operators corresponding to on-shell closed string states in open string field theory. Using both oscillator representation and conformal mapping techniques, we calculate a two closed string tachyon amplitude that connects two gauge invariant operators by an open string propagator. We find that this amplitude is in a complete agreement with the usual disc amplitude.

title: Tachyon condensation and universal solutions in string field theory
abstract: We investigate a non-perturbative vacuum in open string field theory expanded around the analytic classical solution which has been found in the universal Fock space generated by matter Virasoro generators and ghost oscillators. We carry out level-truncation analyses up to level (6,18) in the theory around one-parameter families of the solution. We observe that the value of the vacuum energy cancels the D-brane tension as the approximation level is increased, but this non-perturbative vacuum disappears at the boundary of the parameter space. These results provide strong evidence for the conjecture that, although the universal solutions are pure gauge in almost all the parameter space, they are regarded as the tachyon vacuum solution at the boundary.

title: Level truncation analysis of exact solutions in open string field theory
abstract: We evaluate vacuum energy density of Schnabl's solution using the level truncation calculation and the total action including interaction terms. The level truncated solution provides vacuum energy density expected both for tachyon vacuum and trivial pure gauge. We discuss the role of the phantom term to reproduce correct vacuum energy.

title: Marginal deformations and closed string couplings in open string field theory
abstract: We investigate analytic classical solutions in open string field theory which are constructed in terms of marginal operators. In the classical background, we evaluate a coupling between an on-shell closed string state and the open string field. The resulting coupling exhibits periodic behavior as expected from the marginal boundary deformation of background Wilson lines or a marginal tachyon lump. We confirm that the solutions in open string field theory correspond to a class of marginal deformations in conformal field theory.

title: Cosmic degeneracy with dark energy equation of state
abstract: We discuss a degeneracy between the geometry of the universe and the dark energy equation of state wX which exists in the power spectrum of the cosmic microwave background. In particular, for the case with wX<−1, this degeneracy has interesting implications to a lower bound on wX from observations. It is also discussed how this degeneracy can be removed using current observations of type Ia supernovae.

title: Extended analysis of CMB constraints on non-Gaussianity in isocurvature perturbations
abstract: We study CMB constraints on non-Gaussianity from isocurvature perturbations of general types. Specifically, we study CDM/neutrino isocurvature perturbations which are uncorrelated or totally correlated with adiabatic ones. Using the data from the WMAP 7-year observation at V and W bands, we obtained optimal constraints on the nonlinearity parameters of adiabatic and isocurvature perturbations. Our result shows that primordial perturbations are consistent with Gaussian ones at around 2σ level for above mentioned isocurvature modes.

title: Relation between inflation and dark energy
abstract: In this talk, we have shown that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.

title: Constraints on natural inflation from cosmic microwave background
abstract: We study constraints on the natural inflation model from the cosmic microwave background radiation (CMBR). Inflaton φ for the natural inflation has a potential of the form V=Λ 4 [1− cos (φ/ 2 f φ )] , which is parametrized by two parameters f φ and Λ . Various cosmological quantities, like the primordial curvature perturbation and the CMBR anisotropy, are determined as functions of these two parameters. Using recent observations of the CMBR anisotropy by BOOMERANG and MAXIMA (as well as those from COBE), constraints on the parameters f φ and Λ are derived. The model with f φ lower than 8.5×10 18 (5.4×10 18 , 4.5×10 18 ) GeV predicts a power spectrum with index n S smaller than 0.95 (0.9, 0.85) which suppresses the CMBR anisotropy for smaller angular scale. With such a small n S , height of the second acoustic peak can become significantly lower than the case of the scale-invariant Harrison–Zeldovich spectrum.

title: Gravitino dark matter and non-Gaussianity
abstract: We investigate density fluctuations in a scenario with gravitino dark matter in the framework of modulated reheating, which is known to generate large non-Gaussianity. We show that gravitino dark matter is disfavored in this framework. We also briefly discuss the case with the curvaton mechanism and some other possible dark matter scenarios.