Gravitational resonances on f(T)-branes

In this work, we investigate the gravitational resonances in various f(T)-brane models with the warp factor $$\text {e}^{A(y)}=\tanh \big (k(y+b)\big )-\tanh \big (k(y-b)\big )$$ e A ( y ) = tanh ( k ( y + b ) ) - tanh ( k ( y - b ) ) , where f(T) is an arbitrary function of the torsion scalar T. For three kinds of f(T), we give the solutions to the system. Besides, we consider the tensor perturbation of the vielbein and obtain the effective potentials by the Kaluza–Klein (KK) decomposition. Then we analyze what kind of effective potential can produce the gravitational resonances. The effects of different parameters on the gravitational resonances are analyzed. The lifetimes of the resonances could be long enough as regards the age of our universe in some ranges of the parameters. This indicates that the gravitational resonances might be considered as one of the candidates for dark matter. Combining the current experimental observations, we constrain the parameters for these brane models.

Tachyon condensation in magnetic compactifications

Intersecting D-brane models and their T-dual magnetic compactifications provide an attractive framework for particle physics, allowing for chiral fermions and supersymmetry breaking. Generically, magnetic compactifications have tachyons that are usually removed by Wilson lines. However, quantum corrections prevent local minima for Wilson lines. We therefore study tachyon condensation in the simplest case, the magnetic compactification of type I string theory on a torus to eight dimensions. We find that tachyon condensation restores supersymmetry, which is broken by the magnetic flux, and we compute the Kaluza-Klein mass spectrum. The gauge group SO(32) is broken to USp(16). We give arguments that the vacuum reached by tachyon condensation corresponds to the unique 8d superstring theory already known in the literature, with discrete Bab background or, in the T-dual version, the type IIB orientifold with three O7−-planes, one O7+-plane and eight D7-branes coincident with the O7+-plane. The ground state after tachyon condensation is supersymmetric and has no chiral fermions.

“Lagrangian disks” in M-theory

While the study of bordered (pseudo-)holomorphic curves with boundary on Lagrangian submanifolds has a long history, a similar problem that involves (special) Lagrangian submanifolds with boundary on complex surfaces appears to be largely overlooked in both physics and math literature. We relate this problem to geometry of coassociative submanifolds in G2 holonomy spaces and to Spin(7) metrics on 8-manifolds with T2 fibrations. As an application to physics, we propose a large class of brane models in type IIA string theory that generalize brane brick models on the one hand and 2d theories T[M4] on the other.

Dark matter from Starobinsky supergravity

We review our recent results on dark matter from Starobinsky supergravity. In this context, a natural candidate for cold dark matter is the gravitino. On the other hand, assuming the supersymmetry broken at scales much higher than the electroweak scale, gravitinos are superheavy particles. In this case, they may be non-thermally produced during inflation, in turn originated by the scalaron field with Starobinsky’s potential. Assuming gravitinos as Lightest Supersymmetric Particles (LSSP), the non-thermal production naturally accounts for the right amount of cold dark matter. Metastability of the gravitino LSSP leads to observable effects of their decay, putting constraints on the corresponding Unstable or Decaying Dark Matters scenarios. In this model, the gravitino mass is controlled by the inflaton field and it runs with it. This implies that a continuous spectrum of superheavy gravitinos is produced during the slow-roll epoch. Implications in phenomenology, model building in Grand Unified Theory (GUT) scenarios, intersecting D-brane models and instantons in string theories are discussed.