ONE-LOOP TACHYON AMPLITUDE IN UNORIENTED OPEN-CLOSED STRING FIELD THEORY
We calculate one-loop 2-point tachyon amplitudes in unoriented open-closed string field theory, and determine all the coupling constants of the interaction vertices in the theory. It is shown that the planar, nonplanar and nonorientable amplitudes are all reproduced correctly, and nontrivial consistencies among the determined coupling constants are observed. The necessity for the gauge group to be SO(2 13 = 8192)is also reconfirmed. field theory (SFT)for an unoriented open-closed string mixed system and proved the BRS/gauge invariance of the action at the ‘tree level’; namely, we have classified the terms in the BRS transform of the action into two categories, ‘tree terms’ and ‘loop terms’, and have shown that all the tree terms indeed cancel among themselves. For the loop terms, we have identified which anomalous one-loop diagrams they are expected to cancel. It was left for a future work to show that the loop diagrams are indeed anomalous and that the loop terms actually cancel them. However, the task to show this BRS invariance for general one-loop diagrams is technically rather difficult, and we have not yet completed it. In this paper, we address an easier problem: to compute the one-loop 2-point (open-string)tachyon amplitudes in our SFT. These one-loop amplitudes already suffer from a BRS anomaly, and so the present calculation gives partially an affirmative answer to the expected cancellation between the loop terms and the one-loop anomaly. Moreover, with this computation we confirm that the one-loop tachyon amplitudes are correctly reproduced in our SFT, and we are able to determine all the remaining coupling constants left undetermined in the previous work; in particular, we show that the gauge group must be SO(2 13 = 8192). 3) - 8) The action of the present system, containing seven interaction terms, is given by S = − 1 �Ψ | ˜

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: 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: 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: 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: Primordial Helium Abundance from CMB: a constraint from recent observations and a forecast
abstract: We studied a constraint on the primordial helium abundance Y{sub p} from current and future observations of CMB. Using the currently available data from WMAP, ACBAR, CBI, and BOOMERANG, we obtained the constraint as Y{sub p}=0.25{sub -0.07}{sup +0.10} at 68% confidence level. We also provide a forecast for the Planck experiment using the Markov chain Monte Carlo approach. In addition to forecasting the constraint on Y{sub p}, we investigate how assumptions for Y{sub p} affect constraints on the other cosmological parameters.

title: Runnings in the Curvaton
abstract: We investigate the scale-dependence, or the runnings, of linear and second order density perturbations generated in various curvaton scenarios. We argue that the second order perturbations, i.e. non-Gaussianity, can strongly depend on the scale, even when the linear perturbations are nearly scale-invariant. We present analytic formulae for the runnings from curvatons with general energy potentials, and clarify the conditions under which fNL becomes strongly scale-dependent. From the point of view of the fNL running, curvaton potentials can be classified into roughly two categories by whether the potential flattens or steepens compared to a quadratic one. As such examples, we study pseudo-Nambu-Goldstone curvatons, and self-interacting curvatons, respectively. The dynamics of non-quadratic curvatons and the behaviors of the resulting density perturbations are clarified by analytical methods. Then we also study models where multiple source can be responsible for density perturbations such as the multi-curvaton, and mixed curvaton and inflaton models where the running of fNL can also be large due to their multi-source nature. We make quantitative analysis for each curvaton scenario and discuss in what cases the scale-dependence, in particular, of fNL can be large enough to be probed with future CMB experiments.

title: Higher order corrections to the primordial gravitational wave spectrum and its impact on parameter estimates for inflation
abstract: We study the impact of the use of the power series expression for the primordial tensor spectrum on parameter estimation from future direct detection gravitational wave experiments. The spectrum approximated by the power series expansion may give large deviation from the true (fiducial) value when it is normalized at CMB scale because of the large separation between CMB and direct detection scales. We derive the coefficients of the higher order terms of the expansion up to the sixth order within the framework of the slow-roll approximation and investigate how well the inclusion of higher order terms improves the analytic prediction of the spectrum amplitude by comparing with numerical results. Using the power series expression, we consider future constraints on inflationary parameters expected from direct detection experiments of the inflationary gravitational wave background and show that the truncation of the higher order terms can lead to incorrect evaluation of the parameters. We present two example models; a quadratic chaotic inflation model and mixed inflaton and curvaton model with a quartic inflaton potential.

title: Effect of background evolution on the curvaton non-Gaussianity
abstract: We investigate how the background evolution affects the curvature perturbations generated by the curvaton, assuming a curvaton potential that may deviate slightly from the quadratic one, and parameterizing the background fluid density as ?a??, where a is the scale factor, and ? depends on the background fluid. It turns out that the more there is deviation from the quadratic case, the more pronounced is the dependence of the curvature perturbation on ?. We also show that the background can have a significant effect on the nonlinearity parameters fNL and gNL. As an example, if at the onset of the curvaton oscillation there is a dimension 6 contribution to the potential at 5 % level and the energy fraction of the curvaton to the total one at the time of its decay is at 1%, we find variations ?fNL ~ (10) and ?gNL ~ (104) between matter and radiation dominated backgrounds. Moreover, we demonstrate that there is a relation between fNL and gNL that can be used to probe the form of the curvaton potential and the equation of state of the background fluid.

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.