Cosmology at the top of the α′ tower

Abstract

The cosmology of the fully α′-corrected duality-invariant action for the Neveu-Schwarz sector of string theory is revisited, with special emphasis on its coupling to matter sources. The role of the duality covariant pressure and dilatonic charge of the matter sector is explored in various contexts, from the low-curvature regime to non-perturbative solutions in α′. We comment on how an infinite tower of α′ corrections allows for fixed-dilaton de Sitter solutions, even in vacuum. We further investigate the necessary conditions for accelerated expansion in the Einstein frame, as well as for non-singular bounces that could resolve the big bang singularity. In particular, explicit examples are constructed, which show that the tower of α′ corrections may support an Einstein-frame non-singular cosmological bouncing background, even when the matter sector respects the null energy condition.

Kalb-Ramond backgrounds in α′-complete cosmology

“…For comparison, a solution to the Ddimensional Friedmann equations with such scale factor corresponds to an effective equation of state w = (2 − d)/d, and so for d = 3 the solution is the same we would obtain from the Friedmann equations with a winding equation of state. This solution saturates the strong energy condition (see [15]).…”

“…This approach has been first implemented in [7], establishing the framework of α -complete cosmology. Many applications to string cosmology have been considered so far [2,[8][9][10][11][12][13][14][15], including the construction of a realistic cosmological model [13] which describes the dynamics of a universe that evolves from a phase with topology R × T 9 towards four large spacetime dimensions, while keeping the remaining dimensions confined close to the string length, thus making use of the nonperturbative classical regime of the framework. Nonetheless, all those works have assumed that one of the massless degrees of freedom of the string to vanish.…”

“…Hence, the O(d, d) covariant energy-momentum tensor T will have T ij among its components, and not T t ij . See [15] for a detailed discussion. In the following, note that the index-suppressed T stands for T j i , while J corresponds to J ij .…”

“…In this section, after a brief overview of the EF formulae, we consider two types of solutions for the dilaton (the linear and logarithmic evolutions obtained in the previous sections), derive their corresponding cosmologies in the EF, and compare them with the solutions of the D-dimensional Friedmann's equations. Note that this sort of analysis was considered in [2,7,15] as well.…”

Supersymmetry breaking, brane dynamics and Swampland conjectures

“…Aside from cases where the leading contribution vanishes, one can expect that couplings of this type be required to all orders, at least in α , in order to circumvent a Dine-Seiberg-like argument [121]. Some progress along these lines has been achieved via all-order string-amplitude computations (see, e.g., [122,123]) and via T-duality in the context of cosmology [124][125][126][127][128][129][130][131][132][133]. Furthermore, from the perspective of holography, it would be interesting to understand whether the IR fixed-point structure exhibited by the JHEP10(2021)080 near-horizon AdS throats discussed in section 3 can be reproduced via strong-coupling effects in the putative dual gauge theory.…”