Observables for identity-based tachyon vacuum solutions
We consider a modified KBc algebra in bosonic open string field theory expanded around identity-based scalar solutions. By use of the algebra, classical solutions on the background are constructed and observables for them, including energy densities and gauge invariant overlaps, are calculable. These results are applied to evaluate observables analytically for both of the identity-based trivial pure gauge solution and the identity-based tachyon vacuum solution.

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: 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: 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: 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: Dark energy from inflation
abstract: We show that a very light scalar field experiencing quantum fluctuations during primordial inflation can explain the current cosmic acceleration. 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. Assuming this scenario to be correct, and using supernovae data, the model predicts the energy scale of primordial inflation to be around a few TeV and suggests that it has lasted for an extremely long period. Dark energy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.

title: Constraining SuperWIMPy and Warm Subhalos with Future Submillilensing
abstract: We propose to observe QSO-galaxy strong lens systems to give a new constraint on the damping scale of the initial fluctuations. We find that the future observation of submilliarc scale astrometric shifts of the multiple lensed images of QSOs would find ∼ 10 ( 3 – 9 ) M ⊙ subhalos inside the macrolens halo. The superweakly interacting massive particles (superWIMPs) produced from a WIMP decay and the warm dark matter (WDM) particles that predict a comoving damping scale larger than ∼ 2 kpc can be constrained if ∼ 10 3 M ⊙ subhalos are detected.

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: Signatures of non-Gaussianity in the curvaton model
abstract: We discuss the signatures of non-Gaussianity in the curvaton model where the potential includes also a non-quadratic term. In such a case the non-linearity parameter fNL can become very small, and we show that non-Gaussianity is then encoded in the non-reducible non-linearity parameter gNL of the trispectrum, which can be very large. Thus the place to look for the non-Gaussianity in the curvaton model may be the trispectrum rather than the bispectrum. We also show that gNL measures directly the deviation of the curvaton potential from the purely quadratic form. While gNL depends on the strength of the non-quadratic terms relative to the quadratic one, we find that for reasonable cases roughly –, which are values that may well be accessible by future observations.

title: Cosmic Microwave Background from Late-Decaying Scalar Condensations
abstract: We study the cosmic microwave background (CMB) anisotropy in the scenario with late-decaying scalar condensations which arise in many class of cosmological scenarios based on supersymmetric models. With such a scalar condensation \phi, the CMB radiation we observe today originates to \phi and hence the CMB anisotropy is affected if \phi has a primordial fluctuation. In particular, if all the components in the universe (i.e., radiation, baryon, cold dark matter, and so on) are generated from the decay product of \phi, the dominant source of the cosmic density perturbations can be the primordial fluctuation of \phi, not the fluctuation of the inflaton field. In this case, the constraints on the inflation models can be drastically relaxed. In other case, the baryon or the CDM may not be from the decay product of \phi and correlated mixture of the adiabatic and isocurvature fluctuations can be generated. If so, the CMB angular power spectrum may not be the same as the adiabatic result and the on-going MAP experiment may observe a deviation from the prediction of the standard inflationary scenario.