Related papers: Stringy constraints on primordial electromagnetic …
Spontaneous breaking of Lorentz invariance may take place in string theories, possibly endowing the photon with a mass. This leads to the breaking of the conformal symmetry of the electromagnetic action allowing for the generation within…
In this thesis I present applications of the Born-Infeld action to the description of D-branes, mostly in the context of type IIB string theory. First I present the Callan-Maldacena construction of a fundamental string attached to a…
We study general class of small-field axion inflations which are the mixture of polynomial and sinusoidal functions suggested by the natural and axion monodromy inflations. The axion decay constants leading to the successful axion…
The Dirac-Born-Infeld (DBI) action has been widely studied as an interesting example of a model of k-inflation in which the sound speed of the cosmological perturbations differs from unity. In this article we consider a scalar-tensor theory…
We revisit the mechanism of primordial magnetogenesis during inflation by taking into account the dynamics of the stochastic noises of the electromagnetic perturbations. We obtain the associated Langevin and Fokker-Planck equations for the…
The primordial density fluctuation inevitably couples to all forms of matter via loop corrections and depends on the ambient conditions while inflation was ongoing. This gives us an opportunity to observe processes which were in progress…
The recent measurements of cosmological parameters by the Planck collaboration favors inflationary models with a redshifted spectrum and a very low tensor-to-scalar ratio. Two well-studied scenarios in the particle physics/string theory…
The origin of magnetic fields observed on both astrophysical and cosmological scales is a compelling problem that has the potential to shed light on the early Universe. We analytically investigate inflationary magnetogenesis in scenarios…
Recent BICEP2 detection of low-multipole B-mode polarization anisotropy in the cosmic microwave background radiation supports the inflationary universe scenario and suggests a large inflaton field range. The latter feature can be achieved…
The interplay between string theory and early-universe cosmology offers promising avenues to explore high-energy regimes where the standard single-field slow-roll model may no longer provide an accurate description. One intriguing scenario…
We investigate primordial magnetogenesis by assuming the gauge field is prepared in a thermal state during inflation rather than the standard Bunch-Davies vacuum. The temperature $\mathcal{T}$ introduces a physical scale that breaks…
Cosmological inflation provides the initial conditions for the structure formation. However, the origin of large-scale magnetic fields cannot be addressed in this framework. The key issue for this long-standing problem is the conformal…
We consider the nonlinearly extended Einstein-Maxwell-axion theory, which is based on the account for two symmetries: first, the discrete symmetry associated with the properties of the axion field, second, the Jackson's symmetry,…
We consider gravitational wave production during inflation in type IIB string theory, and the possibility of observable gravitational waves in small field inflation. We show that the gauge field excitations on a set of coincident D7 branes,…
Generation of primordial magnetic fields during inflation typically requires the breaking of conformal invariance of the Electromagnetic action. In this paper this has been achieved naturally in a higher dimensional cosmological model with…
We investigate real-time tachyon dynamics of unstable D-brane carrying fundamental string charge. We construct the boundary state relevant for rolling of modulated tachyon with gauge fields excited on the world-volume, and study spatial…
String theory gives rise to various mechanisms to generate primordial inflation, of which ``brane inflation'' is one of the most widely considered. In this scenario, inflation takes place while two branes are approaching each other, and the…
We present a single-field string inflationary model which allows for the generation of primordial black holes in the low mass region where they can account for a significant fraction of the dark matter abundance. The potential is typical of…
I discuss tree-level amplitudes in cubic topological string field theory, showing that a certain family of gauge conditions leads to an A-infty algebra of tree-level string products which define a potential describing the dynamics of…
In this talk, I review briefly a scenario for the evolution of a string-inspired cosmological model, in which condensates of primordial gravitational waves (GW), formed at the very early eras after the Big Bang, are considered responsible…