Marginal and Scalar Solutions in Cubic Open String Field Theory
We find marginal and scalar solutions in cubic open string field theory by using left-right splitting properties of a delta function. The marginal solution represents a marginal deformation generated by a U(1) current, and it is a generalized solution of the Wilson lines one given by the present authors. The scalar solution has a well-defined universal Fock space expression, and it is expressed as a singular gauge transform of the trivial vacuum. The expanded theory around it is unable to be connected with the original theory by the string field redefinition.

title: Open String Field Theory around Universal Solutions
abstract: We study the physical spectrum of cubic open string field theory around universal solutions, which are constructedusing the matter Virasoro operators andthe ghost andantighost fields. We find the cohomology of the new BRS charge around the solutions, which appear with a ghost number that differs from that of the original theory. Considering the gauge-unfixedstring fieldtheory, we conclud e that open string excitations perturbatively disappear after the condensation of the string field to the solutions.

title: Unoriented open - closed string field theory
abstract: The string field theory for unoriented open-closed string mixed system is constructed up to quadratic order based on the joining-splitting type vertices. The gauge invariance with closed string transformation parameter is proved. The infinity cancellation mechanism between disk and projective plane amplitudes plays an essential role for the gauge invariance of the theory.

title: ONE-LOOP TACHYON AMPLITUDE IN UNORIENTED OPEN-CLOSED STRING FIELD THEORY
abstract: 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: Comments on observables for identity-based marginal solutions in Berkovits’ superstring field theory
abstract: A bstractWe construct an analytic solution for tachyon condensation around identity-based marginal solutions in Berkovits’ WZW-like open superstring field theory. Using this, which is a kind of wedge-based solution, the gauge invariant overlaps for the identity-based marginal solutions can be calculated analytically. This is a straightforward extension of a method in bosonic string field theory, which has been elaborated by the authors, to superstring. We also comment on a gauge equivalence relation between the tachyon vacuum solution and its marginally deformed one. From this viewpoint, we can find the vacuum energy of the identity-based marginal solutions to be zero, which agrees with the previous result as a consequence of ξ zero mode counting.

title: Cosmic Microwave Background Anisotropy in models with Quintessence
abstract: We study the Cosmic Microwave Background (CMB) anisotropies produced by cosine-type quintessence models. In our analysis, effects of the adiabatic and isocurvature fluctuations are both taken into account. For purely adiabatic fluctuations with scale invariant spectrum, we obtain a stringent constraint on the model parameters using the CMB data from COBE, BOOMERanG and MAXIMA. Furthermore, it is shown that isocurvature fluctuations have significant effects on the CMB angular power spectrum at low multipoles in some parameter space, which may be detectable in future satellite experiments. Such a signal may be used to test the cosine-type quintessence models.

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: 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: Dark energy from primordial inflationary quantum fluctuations.
abstract: We show 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: The fate of dark energy
abstract: By studying the present cosmological data, particularly on CMB, SNeIA and LSS, we find that the future fate of the universe, for simple linear models of the dark energy equation-of-state, can vary between the extremes of (I) a divergence of the scale factor in as little as 7 Gyr; (II) an infinite lifetime of the universe with dark energy dominant for all future time; (III) a disappearing dark energy where the universe asymptotes as t →∞ to a ( t )∼ t 2/3 , i.e., matter domination. Our dreadful conclusion is that no amount of data from our past light-cone can select between these future scenarios.