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Filipe Moura

Publications and source records attributed to Filipe Moura.

29 records · Page 2Linked to original sources
arXiv2010

Higher-order string effective actions and off-shell d=4 supergravity

We start by a concise yet thorough revision of four-dimensional superspace supergravity. We present curved superspace geometry, for arbitrary N, including torsion, curvature and Bianchi identities. We motivate the choice of torsion constraints. We then consider the particular cases of N=1,2. In both cases we show how Poincare supergravity can be obtained from conformal supergravity. We see how to obtain the different versions of the Poincare off-shell theory, with distinct compensating multiplets and sets of auxiliary fields. For those versions of N=1,2 supergravities known as "old minimal", we present the solutions to the Bianchi identities, their field content and we show how to write superspace actions for these theories and their extensions using chiral densities and chiral projectors. As concrete applications, we study the supersymmetrization of the two possible R^4 terms in d=4, which are both required as string corrections to supergravity. We conclude by discussing possible applications of these results to open problems on black holes in string theory.

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arXiv2007

One loop superstring effective actions and d=4 supergravity

We review our recent work on the existence of a new independent R^4 term, at one loop, in the type IIA and heterotic effective actions, after reduction to four dimensions, besides the usual square of the Bel-Robinson tensor. We discuss its supersymmetrization.

hep-th↗
arXiv2007

One loop superstring effective actions and N=8 supergravity

In a previous article we have shown the existence of a new independent R^4 term, at one loop, in the type IIA and heterotic effective actions, after reduction to four dimensions, besides the usual square of the Bel-Robinson tensor. It had been shown that such a term could not be directly supersymmetrized, but we showed that was possible after coupling to a scalar chiral multiplet. In this article we study the extended (N=8) supersymmetrization of this term, where no other coupling can be taken. We show that such supersymmetrization cannot be achieved at the linearized level. This is in conflict with the theory one gets after toroidal compactification of type II superstrings being N=8 supersymmetric. We interpret this result in face of the recent claim that perturbative supergravity cannot be decoupled from string theory in d>=4, and N=8, d=4 supergravity is in the swampland.

hep-th↗
arXiv2007

Higher-Derivative Corrected Black Holes: Perturbative Stability and Absorption Cross-Section in Heterotic String Theory

This work addresses spherically symmetric, static black holes in higher-derivative stringy gravity. We focus on the curvature-squared correction to the Einstein-Hilbert action, present in both heterotic and bosonic string theory. The string theory low-energy effective action necessarily describes both a graviton and a dilaton, and we concentrate on the Callan-Myers-Perry solution in d-dimensions, describing stringy corrections to the Schwarzschild geometry. We develop the perturbation theory for the higher-derivative corrected action, along the guidelines of the Ishibashi-Kodama framework, focusing on tensor type gravitational perturbations. The potential obtained allows us to address the perturbative stability of the black hole solution, where we prove stability in any dimension. The equation describing gravitational perturbations to the Callan-Myers-Perry geometry also allows for a study of greybody factors and quasinormal frequencies. We address gravitational scattering at low frequencies, computing corrections arising from the curvature-squared term in the stringy action. We find that the absorption cross-section receives α' corrections, even though it is still proportional to the area of the black hole event-horizon. We also suggest an expression for the absorption cross-section which could be valid to all orders in α'.

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arXiv2007

Type II and heterotic one loop string effective actions in four dimensions

We analyze the reduction to four dimensions of the R^4 terms which are part of the ten-dimensional string effective actions, both at tree level and one loop. We show that there are two independent combinations of R^4 present, at one loop, in the type IIA four dimensional effective action, which means they both have their origin in M-theory. The d=4 heterotic effective action also has such terms. This contradicts the common belief thathere is only one R^4 term in four-dimensional supergravity theories, given by the square of the Bel-Robinson tensor. In pure N=1 supergravity this new R^4 combination cannot be directly supersymmetrized, but we show that, when coupled to a scalar chiral multiplet (violating the U(1) $R$-symmetry), it emerges in the action after elimination of the auxiliary fields.

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arXiv2004

Four dimensional supersymmetrization of R^4

We review our recent works on the supersymmetrization of the leading string correction (the R^4 term) to N=1,2 supergravity theories in four dimensions. We show that, in the "old minimal" formulations of these theories, when going on-shell in the presence of this correction, the auxiliary fields which come from multiplets with physical fields cannot be eliminated, but those ones that come from compensating multiplets without any physical fields can be eliminated. We conjecture similar results for other versions of these theories.

hep-th↗
arXiv2003

Four dimensional "old minimal" N=2 supersymmetrization of R^4

We write in superspace the lagrangian containing the fourth power of the Weyl tensor in the "old minimal" d=4, N=2 supergravity, without local SO(2) symmetry. Using gauge completion, we analyze the lagrangian in components. We find out that the auxiliary fields which belong to the Weyl and compensating vector multiplets have derivative terms and therefore cannot be eliminated on-shell. Only the auxiliary fields which belong to the compensating nonlinear multiplet do not get derivatives and could still be eliminated; we check that this is possible in the leading terms of the lagrangian. We compare this result to the similar one of "old minimal" N=1 supergravity and we comment on possible generalizations to other versions of N=1,2 supergravity.

hep-th↗
arXiv2002

Four dimensional R^4 superinvariants through gauge completion

We fully compute the N=1 supersymmetrization of the fourth power of the Weyl tensor in d=4 x-space with the auxiliary fields. In a previous paper, we showed that their elimination requires an infinite number of terms; we explicitely compute those terms to order κ^4 (three loop). We also write, in superspace notation, all the possible N=1 actions, in four dimensions, that contain pure R^4 terms (with coupling constants). We explicitely write these actions in terms of the θcomponents of the chiral density εand the supergravity superfields R, G_m, W_{ABC}. Using the method of gauge completion, we compute the necessary θcomponents which allow us to write these actions in x-space. We discuss under which circumstances can these extra R^4 correction terms be reabsorbed in the pure supergravity action, and their relevance to the quantum supergravity/string theory effective actions.

hep-th↗
arXiv2001

Four dimensional N=1 supersymmetrization of R^4 in superspace

We write an action, in four dimensional N=1 curved superspace, which contains a pure R^4 term with a coupling constant. Starting from the off-shell solution of the Bianchi identities, we compute the on-shell torsions and curvatures with this term. We show that their complete solution includes, for some of them, an infinite series in the R^4 coupling constant, which can only be computed iteratively. We explicitly compute the superspace torsions and curvatures up to second order in this coupling constant. Finally, we comment on the lifting of this result to higher dimensions.

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