Tibra Ali

Natural Inflation from Near Alignment in Heterotic String Theory

We propose a model for large field inflation in heterotic string theory. The construction applies the near alignment mechanism of Kim, Nilles, and Peloso. By including gaugino condensates and world-sheet instanton non-perturbative effects, we obtain a large effective axion decay constant.

The Ricci curvature of half-flat manifolds

We derive expressions for the Ricci curvature tensor and scalar in terms of intrinsic torsion classes of half-flat manifolds by exploiting the relationship between half-flat manifolds and non-compact G2 holonomy manifolds. Our expressions are tested for Iwasawa and more general nilpotent manifolds. We also derive expressions, in the language of Calabi-Yau moduli spaces, for the torsion classes and the Ricci curvature of the particular half-flat manifolds that arise naturally via mirror symmetry in flux compactifications. Using these expressions we then derive a constraint on the Kahler moduli space of type II string theories on these half-flat manifolds.

A note on a standard embedding on half-flat manifolds

It is argued that the ten dimensional solution that corresponds to the compactification of E8 × E8 heterotic string theory on half-flat manifolds is the product space-time 1,2 × 7 where 7 is a generalized cylinder with G2 holonomy. Standard embedding on 7 then implies an embedding on the half-flat manifold which involves the torsionful connection rather than the Levi-Civita connection. This leads to the breakdown of E8 × E8 to E6 × E8, as in the case of the standard embedding on Calabi-Yau manifolds, which agrees with the result derived recently by Gurrieri, Lukas and Micu [1] using a different approach. Green-Schwarz anomaly cancellation is then implemented via the torsionful connection on half-flat manifolds.

On a NAHE variation

Abstract We present a variation of the NAHE-basis for free fermionic heterotic string models. By rotating some of the boundary conditions of the NAHE periodic/anti-periodic fermions { y m , y ¯ m , w m , w ¯ m } , for m = 1 to 6, associated with the six compact dimensions of a bosonic lattice/orbifold model, we show an additional method for enhancing the standard NAHE gauge group of SO ( 10 ) back to E 6 . This rotation transforms ( SO ( 10 ) ⊗ SO ( 6 ) 3 ) obs ⊗ ( E 8 ) hid into ( E 6 ⊗ U ( 1 ) 5 ) obs ⊗ SO ( 22 ) hid . When SO ( 10 ) is enhanced to E 6 in this manner, the i th MSSM matter generation in the SO ( 10 ) 16 i rep, originating in the twisted basis vector b i , recombines with both its associated untwisted MSSM Higgs in a 10 i rep and an untwisted non-Abelian singlet ϕ i , to form a 27 i rep of E 6 . Beginning instead with the E 6 model, the inverse transformation of the fermion boundary conditions corresponds to partial GUT breaking via boundary rotation. Correspondence between free fermionic models with Z 2 ⊗ Z 2 twist (especially of the NAHE class) and orbifold models with a similar twist has received further attention recently. Our NAHE variation also involves a Z 2 ⊗ Z 2 twist and offers additional understanding regarding the free fermion/orbifold correspondence. Further, models based on this NAHE variation offer some different phenomenological features compared to NAHE-based models. In particular, the more compact Z 2 ⊗ Z 2 twist of the NAHE variation offers a range of mirror models not possible from NAHE-based models. Examples of such models are presented.

Holographic entanglement entropy for gravitational anomaly in four dimensions

A bstractWe compute the holographic entanglement entropy for the anomaly polynomial TrR2 in 3+1 dimensions. Using the perturbative method developed for computing entanglement entropy for quantum field theories, we also compute the parity odd contribution to the entanglement entropy of the dual field theory that comes from a background gravitational Chern-Simons term. We find that, in leading order in the perturbation of the background geometry, the two contributions match except for a logarithmic divergent term on the field theory side. We interpret this extra contribution as encoding our ignorance of the source which creates the perturbation of the geometry.

Branes in the MD × Md+ × Md− compactification of type II string on S1/Z2 and their cosmological applications

In this paper, we study the implementation of brane worlds in type II string theory. Starting with the NS/NS sector of type II string, we first compactify the (D + d+ + d?)-dimensional spacetime, and reduce the corresponding action to a D-dimensional effective action, where the topologies and geometries of Md+ and Md? are arbitrary. We further compactify one of the (D ? 1) spatial dimensions on an S1/Z2 orbifold, and derive the gravitational and matter field equations both in the bulk and on the branes. Then, we investigate two key issues in such a setup: the radion stability and radion mass; and the localization of gravity, and the corresponding Kaluza-Klein (KK) modes. We show explicitly that the radion is stable and its mass can be in the order of TeV. In addition, the gravity is localized on the visible brane, and its spectrum of the gravitational KK towers is discrete and can have a mass gap of TeV, too. The high order Yukawa corrections to the 4-dimensional Newtonian potential is exponentially suppressed, and can be negligible. Applying such a setup to cosmology, we obtain explicitly the field equations in the bulk and the generalized Friedmann equations on the branes.