A central theme in string cosmology in recent years has been the construction of realistic large field inflationary models through axions. In this talk we will discuss a set-up with both closed and open string axions in Type IIA string theory in which strong dynamical effects determine the inflaton candidate. The interplay of Nambu-Jona-Lasinio type interactions, gauge instantons and chiral...
We develop a new class of supergravity cosmological models where inflation is induced by terms in the K\"ahler potential which mix a nilpotent superfield $S$ with a chiral sector $\Phi$. As the new terms are non-(anti)holomorphic, and hence cannot be removed by a K\"ahler transformation, these models are intrinsically K\"ahler potential driven. Such terms could arise for example due to a...
My talk is devoted to superstring cosmology and moduli stabilization, and is based on arXiv:1607.05293 (published in JHEP), and 1703.08993 (submitted to PTEP). We search for dS vacua and slow roll inflation in a class of flux compactifications of type IIA strings on rigid Calabi-Yau manifolds with local N=2 supersymmetry in four spacetime dimensions. These theories represent a nice theoretical...
In this talk I will start by studying some general aspects of String Theory compactifications to four dimensions, focusing on the the constraints to obtain 4 dimensional de Sitter vacua. These microscopic constraints will then be applied to some existing mechanisms to uplift the cosmological constant, that will allow us to understand the mechanisms and their limitations better.
We study Kahler moduli stabilizations in semi-realistic magnetized D-brane models based on Z2 × Z'2 toroidal orbifolds. In type IIB compactifications, 3-form fluxes can stabilize the dilaton and complex structure moduli fields, but there remain some massless closed string moduli fields, K¨ahler moduli. The magnetic fluxes generate Fayet-Iliopoulos terms, which can fix ratios of K¨ahler moduli....
We discuss the possible realizations of $\alpha$-attractor in Maximal supersymmetric theory/string theory/M-theory. The $\alpha$-attractor is realized with the Kahler potential $K=-3\alpha\log (T+\bar{T})$, which describes hyperbolic geometry. The tensor-to-scalar ratio $r$ in this model is proportional to $\alpha$. It is known that the 4-dimesional supersymmetric truncation of maximal...
Axion monodromy models can always be described in terms of an axion coupled to 3-form gauge fields with non-canonical kinetic terms. The presence of the saxions parametrising the kinetic metrics of the 3-form fields leads to backreaction effects in the inflationary dynamics. We analyse
the case in which saxions backreact on the Kähler metric of the inflaton leading to a logarithmic scaling of...
The electric Weak Gravity Conjecture demands that axions with large decay constant $f$ couple to light instantons. The resulting large instantonic corrections pose problems for natural inflation. We explore an alternative argument based on the magnetic Weak Gravity Conjecture for axions, which we try to make more precise. Roughly speaking, it demands that the minimally charged string coupled...
The Weak Gravity Conjecture (WGC) has recently received much attention for its potential applications to models of large field inflation. Unfortunately, generic motivations behind the WGC remain somewhat weak. In this talk, I will discuss suggestive arguments hinting at the WGC in two different contexts: extremal black holes in Einstein-Maxwell theories, and 'axionic black holes' in theories...
Triple Chern-Simons terms are a generic feature of stringy compactifications, where they are usually responsible for topological masses, or branes ending in branes. Another piece of common lore says that one should not expect exact global symmetries in quantum gravity, and in fact this is the case in every known stringy compactification. I will argue that these two seemingly disconnected...
I will discuss two ways in which revising the notion of time at the Big Bang will lead to testable predictions. I will then contrast these predictions against standard ΛCDM scenario, and cosmological observations. The first model, Holographic Cosmology, is based on a 3d quantum field theory without time, suggesting the possibility of nonperturbative effects on large angles (l<30) in the CMB...
We find the explicit form of two-point function for the conformal spin-2 energy momentum operators on the near horizon of a near extremal Kerr black hole by variation of a proper boundary action. In this regard, we consider an appropriate boundary action for the gravitational perturbation of the Kerr black hole. We show that the variation of the boundary action with respect to the boundary...
The supersymmetry arises in certain theories of fermions coupled to gauge fields and gravity in a spacetime of eleven dimensions. The dynamical M-brane backgrounds have mainly been studied for the class of purely bosonic solutions only, but developments involving time-dependent supersymmetric solution have made it clear that one can get more information by asking what happens on dynamical...
We complete the renormalization program of (projectable) Horava gravity. We show that the theory is renormalizable in any space-time dimension, preserving scaling and gauge invariance of the counter-terms at any order in the loop expansion. Later, we focus on 2+1 dimensions, where we show that the renormalization group flow of the marginal couplings contains a UV fixed point leading to...
We study all translationally and rotationally invariant local theories involving massless spin 2 and spin 1 particles that mediate long range forces, allowing for general energy relations and violation of boost invariance. Although gauge invariance is not a priori required to describe non Lorentz invariant theories, we first establish that locality requires `soft gauge invariance'. Then by...
We study moduli stabilization of F-theory compactified on an elliptically fibered Calabi-Yau fourfold arising from open mirror symmetry prescription including the brane deformation.
We focus on a particular background and utilize associated fourfold periods to determine the properties of resulting $4$D ${\cal{N}}=1$ effective theory for moduli fields. We find that the F-theory vacua has a...
A unified theory of the non-Abelian gauge interactions with gravity in the framework of a discretized Kaluza-Klein theory is constructed with a modified Dirac operator and wedge product. All the couplings of chiral spinors to the non-Abelian gauge fields emerge naturally as components of the couplings of the chiral spinors to the generalized gravity together with some new interactions. In...
Nature is full of examples pairings of small but massive compact objects (of linear size R) interacting with and controlling the motions of their neighbours over within a much larger surrounding domain (of size a ≫ R). For such systems familiar arguments (such as the multipole expansion) show that only a few features of the compact object are relevant to understanding motions in their larger...
Combining the ideas of quantum scale invariance with the absence of new particle thresholds between the Planck and the Electroweak (EW) scales leads to stability of the latter against quantum corrections. However, the large discrepancy between the scales remains unexplained. We suggest a non-perturbative mechanism of generation of the EW scale that is able to reproduce naturally this hierarchy.
In quantum mechanics and quantum field theory the perturbative series usually have factorially growing coefficients, hence being non-convergent asymptotic expansions. In order to go beyond the approximation given by the optimal truncation one can Borel-resum the series but generically extra contributions (non-perturbative in the coupling) such as instantons, must be included to reproduce the...
I will describe a modified version of the dimensional regularization of a classically scale invariant theory, motivated by the requirement to preserve scale invariance at the quantum level. The role of the subtraction scale $\mu$ is played be a dynamic scalar field. This field is assumed to have non-zero VEV thus triggering spontaneous breakdown of scale symmetry which in turn triggers EWSB....
There are results that suggest a connection between gauged maximal supergravities and asymmetric toroidal orbifolds. By looking at several examples we argue that a similar relationship exists between 4D N=2 gauged supergravities and asymmetric Gepner models. Going further we conjecture that the asymmetric CFTs we construct are the fully backreacted string uplifts of N=1 Minkowski vacua in a...
