Searcharxiv⌕ Search

arXiv subjects

Kasper Peeters

Publications and source records attributed to Kasper Peeters.

At least 37 records · Page 2Linked to original sources
arXiv2007

A field-theory motivated approach to symbolic computer algebra

Field theory is an area in physics with a deceptively compact notation. Although general purpose computer algebra systems, built around generic list-based data structures, can be used to represent and manipulate field-theory expressions, this often leads to cumbersome input formats, unexpected side-effects, or the need for a lot of special-purpose code. This makes a direct translation of problems from paper to computer and back needlessly time-consuming and error-prone. A prototype computer algebra system is presented which features TeX-like input, graph data structures, lists with Young-tableaux symmetries and a multiple-inheritance property system. The usefulness of this approach is illustrated with a number of explicit field-theory problems.

cs.SC↗
arXiv2006

Holographic decays of large-spin mesons

We study the decay process of large-spin mesons in the context of the gauge/string duality, using generic properties of confining backgrounds and systems with flavour branes. In the string picture, meson decay corresponds to the quantum-mechanical process in which a string rotating on the IR "wall" fluctuates, touches a flavour brane and splits into two smaller strings. This process automatically encodes flavour conservation as well as the Zweig rule. We show that the decay width computed in the string picture is in remarkable agreement with the decay width obtained using the phenomenological Lund model.

hep-th↗
arXiv2005

Loop quantum gravity: an outside view

We review aspects of loop quantum gravity in a pedagogical manner, with the aim of enabling a precise but critical assessment of its achievements so far. We emphasise that the off-shell (`strong') closure of the constraint algebra is a crucial test of quantum space-time covariance, and thereby of the consistency, of the theory. Special attention is paid to the appearance of a large number of ambiguities, in particular in the formulation of the Hamiltonian constraint. Developing suitable approximation methods to establish a connection with classical gravity on the one hand, and with the physics of elementary particles on the other, remains a major challenge.

hep-th↗
arXiv2005

Higher-derivative gauge field terms in the M-theory action

We use superparticle vertex operator correlators in the light-cone gauge to determine the (DF)^2 R^2 and (DF)^4 terms in the M-theory effective action. Our results, when compactified on a circle, reproduce terms in the type-IIA string effective action obtained through string amplitude calculations.

hep-th↗
arXiv2005

Superfield integrals in high dimensions

We present an efficient, covariant, graph-based method to integrate superfields over fermionic spaces of high dimensionality. We illustrate this method with the computation of the most general sixteen-dimensional Majorana-Weyl integral in ten dimensions. Our method has applications to the construction of higher-derivative supergravity actions as well as the computation of string and membrane vertex operator correlators.

hep-th↗
arXiv2005

Splitting strings and chains

We review a study of the semiclassical decay of macroscopic spinning strings in AdS_5 x S^5 as well as its dual gauge theory description. The conservation of the infinite tower of commuting charges in the semiclassical string sigma-model description of the process suggests that the decay channel of maximal probability should preserve integrability in the gauge theory.

hep-th↗
arXiv2005

Splitting spinning strings in AdS/CFT

We study the semiclassical decay of macroscopic spinning strings in AdS_5 x S^5 through spontaneous splitting of the folded string worldsheet. Based on similar considerations in flat space this decay channel is expected to dominate the full quantum computation. The outgoing strings are uniquely specified by an infinite set of conserved (local) charges with a regular expansion in inverse powers of the initial angular momentum. We compute these charges and determine functional relations between them. Finally, a preliminary discussion of the corresponding calculation in the non-planar sector of the dual gauge theory is presented.

hep-th↗
arXiv2005

AdS/CFT description of D-particle decay

Unstable D-particles in type-IIB string theory correspond to sphaleron solutions in the dual gauge theory. We construct an explicit time-dependent solution for the sphaleron decay on S^3 x R, as well as the coherent state corresponding to the decay product. We develop a method to count the number of bulk particles in the AdS/CFT setup. When applied to our coherent state, the naive number operator O^\dagger O is shown to be inappropriate, even in the large-N limit. The reason is that the final state consists of a large number of particles. By computing all probabilities for finding multi-particle states in the coherent state, we deduce the bulk particle content of the final state of the sphaleron decay. The qualitative features of this spectrum are compared with the results expected from the gravity side, and agreement is found.

hep-th↗
arXiv2004

Holographic dynamics of unstable branes in AdS

The gauge theory dual to the decay of an unstable D-particle in AdS is analysed in terms of coherent states. We discuss in detail how to count the number of particles in the decay product. We find, in agreement with the analysis in flat space, that the emission amplitude is suppressed as the mass of the radiated particles increases.

hep-th↗
arXiv2003

The Ramond-Ramond sector of string theory beyond leading order

Present knowledge of higher-derivative terms in string effective actions is, with a few exceptions, restricted to the NS-NS sector, a situation which prevents the development of a variety of interesting applications for which the RR terms are relevant. We here provide the formalism as well as efficient techniques to determine the latter directly from string-amplitude calculations. As an illustration of these methods, we compute the dependence of the type-IIB action on the three- and five-form RR field strengths at four-point, genus-one, order-(alpha')^3 level. We explicitly verify that our results are in accord with the SL(2,Z) S-duality invariance of type-IIB string theory. Extensions of our method to other bosonic terms in the type-II effective actions are discussed as well.

hep-th↗
arXiv2003

Anti-de-Sitter vacua require fermionic brane charges

We argue that a modification of the super-AdS algebras which accounts for the presence of D-branes requires not only the inclusion of bosonic brane charges, but also the inclusion of new fermionic ones. We show that such fermionic brane charges are indeed present in the matrix model and the supermembrane in the pp-wave limit of the corresponding backgrounds. We briefly comment on an AdS version of Sezgin's M-algebra inspired by this observation.

hep-th↗
arXiv2003

Supersymmetric higher-derivative actions in ten and eleven dimensions, the associated superalgebras and their formulation in superspace

Higher-derivative terms in the string and M-theory effective actions are strongly constrained by supersymmetry. Using a mixture of techniques, involving both string amplitude calculations and an analysis of supersymmetry requirements, we determine the supersymmetric completion of the R^4 action in eleven dimensions to second order in the fermions, in a form compact enough for explicit further calculations. Using these results, we obtain the modifications to the field transformation rules and determine the resulting field-dependent modifications to the coefficients in the supersymmetry algebra. We then make the link to the superspace formulation of the theory and discuss the mechanism by which higher-derivative interactions lead to modifications to the supertorsion constraints. For the particular interactions under discussion we find that no such modifications are induced.

hep-th↗
arXiv2003

Chiral splitting and world-sheet gravitinos in higher-derivative string amplitudes

We report on progress made in the construction of higher-derivative superinvariants for type-II theories in ten dimensions. The string amplitude calculations required for this analysis exhibit interesting features which have received little attention in the literature so far. We discuss two examples from a forthcoming publication: the construction of the (H_{NS})^2 R^3 terms and the fermionic completion of the εεR^4 terms. We show that a correct answer requires very careful treatment of the chiral splitting theorem, implies unexpected new relations between fermionic correlators, and most interestingly, necessitates the use of worldsheet gravitino zero modes in the string vertex operators. In addition, we discuss the relation of our results to the predictions of the linear scalar superfield of the type-IIB theory and find (and explain) an interesting discrepancy.

hep-th↗
arXiv2003

On non-perturbative extensions of anti-de-Sitter algebras

Motivated by the study of branes in curved backgrounds, we investigate the construction of non-perturbative extensions of the super-isometry algebra osp*(8|4) of the AdS_7xS^4 background of M-theory. This algebra is not a subalgebra of osp(1|32) and its non-perturbative extension can therefore not be obtained by embedding in this simple superalgebra. We show how, instead, it is possible to construct an extension directly by solving the Jacobi identities. This requires, in addition to the expected non-perturbative charges, the introduction of new charges which appear in the {Q,Q} bracket only via a linear combination with the bosonic generators of the isometry algebra. The resulting extended algebra has the correct flat-space limit, but it is not simple and the non-perturbative charges do not commute with the super-isometry generators. We comment on the consequences of this structure for the representation theory and on possible alternatives to our construction.

hep-th↗
arXiv2003

D-branes in a plane wave from covariant open strings

We derive boundary conditions for the covariant open string corresponding to D-branes in an Hpp-wave, by requiring kappa symmetry of its bulk action. Both half-supersymmetric and quarter-supersymmetric branes are seen to arise in this way, and the analysis furthermore agrees fully with the existing probe brane and supergravity computations. We elaborate on the origin of dynamical and kinematical supersymmetries from the covariant point of view. In particular we focus on the D-string which only preserves half of the dynamical supersymmetries and none of the kinematical ones. We discuss its origin in AdS_5 x S^5 and its world-volume spectrum.

hep-th↗
arXiv2002

Motion on moduli spaces with potentials

In the limit of small velocities, the dynamics of half-BPS Yang-Mills-Higgs solitons can be described by the geodesic approximation. Recently, it has been shown that quarter-BPS states require the addition of a potential term to this approximation. We explain the logic behind this modification for a larger class of models and then analyse in detail the dynamics of two five-dimensional dyonic instantons, using both analytical and numerical techniques. Nonzero-modes are shown to play a crucial role in the analysis of these systems, and we explain how these modes lead to qualitatively new types of dynamics.

hep-th↗