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Davoud Kamani

Publications and source records attributed to Davoud Kamani.

At least 19 recordsLinked to original sources
arXiv2025

The Inflationary Dynamics with the Scalar-Tensor Model

We investigate the cosmic inflation within a class of the scalar-tensor model with the scalar-dependent non-minimal kinetic couplings. The inflationary dynamical potential will be applied. Using the slow-roll approximation, we compute theoretical predictions for the key observables, like the spectral indexes $n_s$, scalar-to-tensor ratio $r$ and the running of the scalar spectral index $α_s$ in terms of the free parameters of the model. Besides, we find the limitations of these parameters. In addition, these quantities will be compared with the latest observational data from the Planck data. Furthermore, we analyze the sensitivity of $r$, $n_s$ and $α_s$ in terms of the model's free parameters.

gr-qc↗
arXiv2025

Observational Restrictions and Slow-Roll D-brane Inflation in the Special $F(ϕ,T)$ Gravity

We shall investigate the inflation for the D-brane model, motivated by the modified gravity $F(ϕ,T)$. This gravity has been recently introduced in the literature. The feasibility of the D-brane inflation theory in the $F(ϕ,T)$-gravity has been studied in conjunction with the most recent Planck data. We shall analyze the slow-roll inflation in the context of the $F(ϕ)T$-gravity, via the D-brane model. Then, we shall calculate the inflation dynamics to obtain the scalar spectral index ``$n_s$'' and the tensor-to-scalar ratio ``$r$''. Besides, we investigate the dynamics of the reheating for this model. Our model accurately covers the left-hand side of the Planck data and the D-brane inflation.

gr-qc↗
arXiv2025

$F(ϕ)T$-Gravity and Inflationary Natural Model

By applying a particular kind of modified gravity, we study the inflation. Precisely, we extend our investigations beyond the Einstein's gravity to explore the Natural inflation model via the term $F(ϕ)T$. We compute the inflation dynamics to derive the slow-roll parameters, i.e., the tensor-to-scalar ratio ``$r$'' and the scalar spectral index ``$n_s$''. This modified form of the gravity yields not only the predictions of the original models but also better-fitting with the Planck/BICEP/Keck data.

gr-qc↗
arXiv2025

The Inflationary Quartic Hilltop Model in a Modified Gravity and Its Comparison with the Observations

We investigate the inflation for the quartic hilltop model via a certain type of modified gravity. Precisely, we analyze the $F(ϕ) T$ term in the Einstein's gravity to examine the quartic hilltop inflation model. $T$ is the trace of the energy-momentum tensor, and $ϕ$ is the inflaton field. Next, we calculate the inflation dynamics for the foregoing model and obtain the slow-roll parameters, i.e., the scalar spectral index ``$n_s$'' and the tensor-to-scale ratio ``$r$'', which these parameters exhibit high sensitivity to the $F(ϕ) T$ term. This modified form of the gravity is not only in accordance with the predictions of the original model but also allows for better prediction of the Planck/BICEP/Keck data.

gr-qc↗
arXiv2025

Dressed D-strings with Instability and Transverse Rotation: The Open String Pair Production

Motivated by the Schwinger effect in the QED, we investigate the open string pair creation for the dressed D1-branes, incorporating electric and tachyonic fields and also transverse rotation in the presence of the antisymmetric (Kalb-Ramond) background field. The background spacetime is partially compact on a torus. Our first observation is that the presence of the tachyonic field together with the transverse rotation prevents the open string production. Consequently, we shall quench the tachyonic field. Thus, we find that the pair creation arises only when the angular frequencies of the D-strings satisfy a rational relation. Besides, we observe that the compactification enhances the production rate of the open strings. Finally, we study various special cases of the system.

hep-th↗
arXiv2024

LREE of a Dressed D$p$-brane with Transverse Motion in the Partially Compact Spacetime

In the context of the type IIA/IIB superstring theories, we derive the left-right entanglement entropy (LREE) of a BPS D$p$-brane with transverse motion in the presence of a $U(1)$ gauge potential and the Kalb-Ramond field in the partially compact spacetime $\mathbf{T}^n \otimes \mathbb R^{1,9-n}$. At first we employ the replica trick to compute the Rényi entropy and then we obtain the entanglement entropy. We examine the results for the special case, i.e. for the D6-brane. Besides, we investigate the thermodynamical entropy, associated with the LREE. This demonstrates that the LREE is precisely equivalent to its thermodynamic counterpart.

hep-th↗
arXiv2023

Open String Pair Production from the Interacting Dressed-Angled D-Strings

We calculate the rate of the open string pair production from the interaction of two non-intersecting D-strings at angle. The D-strings have been equipped with the $U(1)$ gauge potentials in the presence of the Kalb-Ramond field. This rate will be discussed when the D-strings intersect each other. Our computations is in the framework of the bosonic string theory.

hep-th↗
arXiv2023

Pair Creation of Open Strings between the Unstable-Dressed D$p$-branes

We study the open string pair production via the interaction of two parallel D$p$-branes. The branes have been dressed by the Kalb-Ramond field, a specific $U(1)$ gauge potential and a tachyon field of the open string spectrum. We shall apply the boundary state formalism, in the context of the bosonic string theory.

hep-th↗
arXiv2023

Closed String Radiation from the Interaction of the Moving D$p$-branes with Background Fields

At first, we derive a boundary state, associated with a moving D$p$-brane, in the presence of the Kalb-Ramond field and a $U(1)$ gauge potential. Then, from the interaction of such D$p$-branes, we obtain the radiation amplitude for a massless closed string. The behavior of the radiation amplitude for the large distance of the branes will be studied. Our calculations is in the framework of the bosonic string theory.

hep-th↗
arXiv2022

Radiation of a Massless Closed String from Interacting D$p$-branes with Background Fields in the Superstring Theory

In the context of the superstring theory, we calculate the radiation amplitude of a general massless closed string from the interaction of two parallel D$p$-branes. The background field is the constant antisymmetric tensor $B_{μν}$, and the branes have been equipped with the different $U(1)$ gauge fields. For the large distance of the branes, the Kalb-Ramond emission will be investigated.

hep-th↗
arXiv2022

Closed String Radiation from the Interacting Fractional-Dressed D$p$-Branes with the Transverse Motions

We determine the boundary states, associated with a fractional D$p$-brane in the presence of the Kalb-Ramond field and a $U(1)$ gauge potential. The background spacetime is the non-compact orbifold $ \mathbb{R}^{1, 21} \otimes \mathbb{R}^4/ \mathbb{Z}_2$. Besides, the brane has a transverse velocity. We compute the radiation amplitude of a massless closed string from the interaction of two fractional D$p$-branes with the previous background fields. The branes have been dressed by different fields and have transverse motions. The total radiation amplitude will be investigated for large inter-brane separation. Finally, the graviton, Kalb-Ramond (axion) and dilaton emissions will be distinctly studied. Our calculations are in the context of the bosonic string theory.

hep-th↗
arXiv2022

Gravitational and Dilatonic Radiations from the Parallel Dressed-Dynamical Unstable Dp-Branes

In the context of the bosonic string theory, we shall extract the general radiation amplitude of a massless closed string from the interaction of two parallel unstable D$p$-branes. The branes are non-stationary and have been dressed by background fields. The foregoing amplitude will be rewritten for the massless state radiation from the branes with the large distance. Besides, we shall study the gravitational and dilatonic radiations from this configuration.

hep-th↗
arXiv2022

Radiation of Closed Strings between the Parallel Dynamical-Dressed Unstable Dp-Branes

We introduce a boundary state which is corresponding to a D$p$-brane with tangential dynamics in the presence of the Kalb-Ramond field, a tachyonic field and a $U(1)$ gauge potential in a special gauge. From the interaction of such branes radiation amplitude of a general massless closed string will be computed. The effects of the large distances of the branes on this radiation will be studied. In the large distances of the branes, the possibility of axion radiation will be investigated. Our calculations will be in the context of the bosonic string theory.

hep-th↗
arXiv2021

LREE of an Unstable Dressed-Dynamical D$p$-brane: Superstring Calculations

We obtain the left-right entanglement entropy (LREE) for a D$p$-brane with tangential motion in the presence of a $U(1)$ gauge potential, the Kalb-Ramond field and an open string tachyon field. Thus, at first we extract the Rényi entropy and then by taking a special limit of it we acquire the entanglement entropy. We shall investigate the behavior of the LREE under the tachyon condensation phenomenon. We observe that the deformation of the LREE, through this process, reveals the collapse of the brane. Besides, we examine the second law of thermodynamics for the LREE under tachyon condensation, and we extract the imposed constraints. Note that our calculations will be in the context of the type IIA/IIB superstring theories.

hep-th↗
arXiv2020

LREE of a Dynamical Unstable D$p$-brane

We derive the left-right entanglement entropy (LREE) for a bosonic D$p$-brane. This brane has tangential dynamics and has been dressed by a $U(1)$ gauge potential, the Kalb-Ramond field and a tachyon field. For this purpose, the Rényi entropy will be computed and then, by taking a special limit of it, the LREE will be obtained. Besides, the behavior of the LREE under the tachyon condensation process will be evaluated. In addition, after the transition of the system, i.e. the collapse of the unstable brane, the second law of the thermodynamics on the LREE will be checked. We find that preserving the second law imposes some conditions on the parameters of the setup.

hep-th↗
arXiv2020

Brane with Transverse Rotation and Background Fields: Boundary State and Tachyon Condensation

The boundary state corresponding to the D$p$-brane with a transverse rotation in the presence of the Kalb-Ramond and tachyon background fields and a $U(1)$ internal field will be constructed. We shall investigate effects of the open string tachyon condensation on this brane via its boundary state. We demonstrate that the background fields and transverse rotation cannot protect the brane against the collapse. Our calculations are in the context of the bosonic string theory.

hep-th↗
arXiv2020

Left-Right Entanglement Entropy for a Dp-brane with Dynamics and Background Fields

We investigate the left-right entanglement entropy of a boundary state, corresponding to a dynamical D$p$-brane with the internal and background fields. We assume that the brane has a tangential linear motion and a rotation, and is dressed with an internal $U(1)$ gauge potential and the Kalb-Ramond tensor field $B_{μν}$. We derive the entanglement entropy via the Rényi entropy by applying the replica trick. Our calculations will be in the context of the bosonic string theory.

hep-th↗