119114774
On non-Gaussianities in two-field poly-instanton inflation
A bstractIn the context of Type IIB LARGE volume orientifold setup equipped with poly-instanton corrections, the standard single-field poly-instanton inflation driven by a ‘Wilson’ divisor volume modulus is generalized by the inclusion of respective axion modulus. This two-field dynamics results in a “Roulette” type inflation with the presence of several inflationary trajectories which could produce 50 (or more) e-foldings. The evolution of various trajectories along with physical observables are studied. The possibility of generating primordial non-Gaussianities in the slow-roll as well as in the beyond slow-roll region is investigated. We find that although the non-linearity parameters are quite small during the slow-roll regime, the same are significantly enhanced in the beyond slow-roll regime investigated up to the end of inflation.
119188664
On classifying the divisor involutions in Calabi-Yau threefolds
A bstractIn order to support the odd moduli in models of (type IIB) string compactification, we classify the Calabi-Yau threefolds with h1,1 ≤ 4 which exhibit pairs of identical divisors, with different line-bundle charges, mapping to each other under possible divisor exchange involutions. For this purpose, the divisors of interest are identified as completely rigid surface, Wilson surface, K3 surface and some other deformation surfaces. Subsequently, various possible exchange involutions are examined under the symmetry of Stanley-Reisner Ideal. In addition, we search for the Calabi-Yau theefolds which contain a divisor with several disjoint components. Under certain reflection involution, such spaces also have nontrivial odd components in (1,1)-cohomology class. String compactifications on such Calabi-Yau orientifolds with non-zero $ h_{-}^{1,1}\left( {{{{C{Y_3}}} \left/ {\sigma } \right.}} \right) $ could be promising for concrete model building in both particle physics and cosmology. In the spirit of using such Calabi-Yau orientifolds in the context of LARGE volume scenario, we also present some concrete examples of (strong/weak) swiss-cheese type volume form.
118438338
A note on poly-instanton effects in type IIB orientifolds on Calabi-Yau threefolds
A bstractThe zero mode structure for the generation of poly-instanton corrections for Euclidian D3-branes wrapping complex surfaces in Type IIB orientifolds with O7- and O3-planes is analyzed. Working examples of such surfaces and explicit embeddings into compact Calabi-Yau threefolds are presented, with special emphasis on geometries capable of realizing the LARGE volume scenario.
118684924
Analytical computation of critical exponents in several holographic superconductors
It is very interesting that all holographic superconductors, such as s-wave, p-wave and d-wave holographic superconductors, show the universal mean-field critical exponent 1/2 at the critical temperature, just like Gindzburg-Landau (G-L) theory for second order phase transitions. Now it is believed that the universal critical exponents appear because the dual gravity theory is classic in the large N limit. However, even in the large N limit there is an exception called “non-mean-field theory”: an extension of the s-wave model with a cubic term of the charged scalar field shows a different critical exponent 1. In this paper, we try to use analytical methods to obtain the critical exponents for these models to see how the properties of the gravity action decides the appearance of the mean-field behaviors. It will be seen that just like the G-L theory, it is the fundamental symmetries rather than the detailed parameters of the bulk theory that lead to the universal properties of the holographic superconducting phase transition. The feasibility of the called “non-mean-field theory” is also discussed.
119118248
Moduli stabilization and inflationary cosmology with poly-instantons in type IIB orientifolds
A bstractEquipped with concrete examples of Type IIB orientifolds featuring polyinstanton corrections to the superpotential, the effects on moduli stabilization and inflationary cosmology are analyzed. Working in the framework of the LARGE volume scenario, the Kähler modulus related to the size of the four-cycle supporting the poly-instanton contributes sub-dominantly to the scalar potential. It is shown that this Kähler modulus gets stabilized and, by displacing it from its minimum, can play the role of an inflaton. Subsequent cosmological implications are discussed and compared to experimental data.
119246227
Cosmological observables in multi-field inflation with a non-flat field space
Using delta N formalism in the context of a generic multi-field inflation driven on a non-flat field space background, we revisit the analytic expressions of the various cosmological observables such as scalar tensor power spectra, scalar/tensor spectral tilts, non-Gaussianity parameters, tensor-to-scalar ratio, and the various runnings of these observables. In our backward formalism approach, the subsequent expressions of observables automatically include the terms beyond the leading order slow-roll expansion correcting many of the expression at subleading order. To connect our analysis properly with the earlier results, we rederive the (well) known (single field) expressions in the limiting cases of our generic formulae. Further, in the light of PLANCK results, we examine for the compatibility of the consistency relations within the slow-roll regime of a two-field roulette poly-instanton inflation realized in the context, of large volume scenarios.
14271056
Cosmological Perturbations and Non-Gaussianities in Ho\v{r}ava-Lifshitz Gravity
We investigate cosmological perturbations and non-gaussianities in Ho\v{r}ava-Lifshitz theory of gravitation. In the UV limit, the scalar perturbation in Ho\v{r}ava theory is naturally scale-invariant, ignoring the details of the expansion of the universe. Thus one may relax the exponential inflation and the slow-roll conditions for the inflaton field. Moreover, in the absence of slow-roll conditions, it is possible that the "slow-roll suppressed" non-gaussianities resume to become large. We calculate the non-gaussianities from the bispectrum of the perturbation and find that, the equilateral-type non-gaussianity is of order unity, while the local-type non-gaussianity remains small as in usual single-field slow-roll inflation model in general relativity.
15618257
Reheating and Cosmic String Production
Abstract We compute the string production rate at the end of inflation, using the string spectrum obtained in [M. Li, W. Song, Y. Song, Quantizing strings in de Sitter space, JHEP 0704 (2007) 042, hep-th/0701258 ] in a near-de Sitter space. Our result shows that highly excited strings are hardly produced, thus the simple slow-roll inflation alone does not offer a cosmic string production mechanism.
118382047
On cross-correlations between curvature and isocurvature perturbations during inflation
We investigate the effects of couplings between curvature and isocurvature perturbations before and around horizon-crossings during cosmological inflation. We consider a generalized two-field inflation model, in which the non-canonical kinetic term allows us arbitrary sound speeds of curvature and isocurvature perturbations. By using the field-theoretical perturbative analysis, we calculate the cross-spectrum between curvature and isocurvature perturbations and the corrections to curvature and isocurvature power spectra due to the presence of couplings between them. Our analysis confirms previous results that the cross-correlations are generated and amplified when perturbations cross the horizons. Moreover, we find the cross-correlation, which was previously shown to be first-order in slow-roll parameter, can be enhanced when the sound speed of curvature perturbation is much larger than that of the isocurvature perturbation. This is because in this case the isocurvature perturbation exits its horizon much earlier than the curvature perturbation and acts as a nearly constant source on the curvature perturbation.
119234091
Full bispectra from primordial scalar and tensor perturbations in the most general single-field inflation model
We compute the full bispectra, namely both auto- and cross- bispectra, of primordial curvature and tensor perturbations in the most general single-field inflation model whose scalar and gravitational equations of motion are of second order. The formulae in the limits of k-inflation and potential-driven inflation are also given. These expressions are useful for estimating the full bispectra of temperature and polarization anisotropies of the cosmic microwave background radiation.
749285
Non-supersymmetric attractors in Born-Infeld black holes with a cosmological constant
We investigate the attractor mechanism for spherically symmetric extremal black holes in Einstein-Born-Infeld-dilaton theory of gravity in four-dimensions, in the presence of a cosmological constant. We look for solutions analytic near the horizon by using perturbation method. It is shown that the values of the scalar fields at the horizon are only dependent on the charges carried by the black hole and are irrelevant in their asymptotic values. This analysis supports the validity of non-supersymmetric attractors in the presence of higher derivative interactions in the gauge fields part and in non-asymptotically flat spacetime.