arXiv subjects

Hamid Razaghian

Publications and source records attributed to Hamid Razaghian.

4 recordsLinked to original sources

arXiv2020

Complexity Growth of Dyonic Black holes with Quartic Field Strength Corrections

In this paper, according to CA duality, we study the complexity growth of dyonic RN-type black holes with quartic field strength corrections ($F^4$ corrections) to the matter action in general $D\geq4$-dimensions and find the behavior of action growth, similar to the case of the normal RN black holes, is different between electric and magnetic black holes which is unexpected since violates the electromagnetic duality. For restoring this duality, we add the Maxwell boundary term (at order 3-derivative) to the action and discuss the outcomes of the addition. Also, we have used another method that introduces UV finite cut off at AdS boundary to evaluate the complexity growth rate of dyonic black holes with and without $F^4$ corrections. In this method, without adding a surface term, late time growth rate of complexity exhibits expected behavior.

hep-th↗

arXiv2019

Minimal independent couplings at order $α'^2$

Using field redefinitions and Bianchi identities on the general form of the effective action for metric, $B$-field and dilaton, we have found that the minimum number of independent couplings at order $α'^2$ is 60. We write these couplings in two different schemes in the string frame. In the first scheme, each coupling does not include terms with more than two derivatives and it does not include structures $R,\,R_{μν},\,\nabla_μH^{μαβ}$, $ \nabla_μ\nabla^μΦ$. In this scheme, 20 couplings which are the minimum number of couplings for metric and $B$-field, include dilaton trivially as the overall factor of $e^{-2Φ}$, and all other couplings include derivatives of dilaton. In the second scheme, the dilaton appears in all 60 coupling only as the overall factor of $e^{-2Φ}$. In this scheme, 20 of the couplings are exactly the same as those in the previous scheme.

hep-th↗

arXiv2018

$R^4 $ terms in supergravities via T-duality constraint

It has been speculated in the literature that the effective actions of string theories at any order of $α'$ should be invariant under the Buscher rules plus their higher covariant derivative corrections. This may be used as a constraint to find effective actions at any order of $α'$, in particular, the metric, the B-field and the dilaton couplings in supergravities at order $α'^3$ up to an overall factor. For the simple case of zero B-field and diagonal metric in which we have done the calculations explicitly, we have found that the constraint fixes almost all the seven independent Riemann curvature couplings. There is only one term which is not fixed, because when metric is diagonal, the reduction of two $R^4$ terms become identical. The Riemann curvature couplings that the T-duality constraint produces for both type II and Heterotic theories are fully consistent with the existing couplings in the literature which have been found by the S-matrix and by the sigma-model approaches.

hep-th↗

arXiv2018

T-duality invariant effective actions at orders $ α', α'^2$

We use compatibility of the $D$-dimensional effective actions for diagonal metric and for dilaton with the T-duality when theory is compactified on a circle, to find the the $D$-dimensional couplings of curvatures and dilaton as well as the higher derivative corrections to the $(D-1)$-dimensional Buscher rules at orders $ α' $ and $α'^2$. We observe that the T-duality constraint on the effective actions fixes the covariant effective actions at each order of $α'$ up to field redefinitions and up to an overall factor. Inspired by these results, we speculate that the $D$-dimensional effective actions at any order of $α'$ must be consistent with the standard Buscher rules provided that one uses covariant field redefinitions in the corresponding reduced $(D-1)$-dimensional effective actions. This constraint may be used to find effective actions at all higher orders of $α'$.

hep-th↗