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M. Porrati

Publications and source records attributed to M. Porrati.

At least 55 records · Page 3Linked to original sources
arXiv2000

Holographic Duals of 4D Field Theories

We discuss various aspect of the holographic correspondence between 5-d gravity and 4-d field theory. First of all, we describe deformations of N=4 Super Yang-Mills (SYM) theories in terms of 5-d gauged supergravity. In particular, we describe N=0 and N=1 deformations of N=4 SYM to confining theories. Secondly, we describe recent proposals for the holographic dual of the renormalization group and for 4-d central charges associated to it. We conclude with a ``holographic'' proof of the Goldstone theorem.

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arXiv2000

A Note on the Holographic Beta and C Functions

The holographic RG flow in AdS/CFT correspondence naturally defines a holographic scheme in which the central charge c and the beta function are related by a universal formula. We perform some checks of that formula and we compare it with quantum field theory expectations. We discuss alternative definitions of the c-function. In particular, we compare, for a particular supersymmetric flow, the holographic c-function with the central charge computed directly from the two-point function of the stress-energy tensor.

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arXiv2000

A Comment on Brane Bending and Ghosts in Theories with Infinite Extra Dimensions

Theories with infinite volume extra dimensions open exciting opportunities for particle physics. We argued recently that along with attractive features there are phenomenological difficulties in this class of models. In fact, there is no graviton zero-mode in this case and 4D gravity is obtained by means of continuum bulk modes. These modes have additional degrees of freedom which do not decouple at low energies and lead to inconsistent predictions for light bending and the precession of Mercury's perihelion. In a recent papers, [hep-th/0003020] and [hep-th/0003045] the authors made use of brane bending in order to cancel the unwanted physical polarization of gravitons. In this note we point out that this mechanism does not solve the problem since it uses a {\it ghost} which cancels the extra degrees of freedom. In order to have a consistent model the ghost should be eliminated. As soon as this is done, 4D gravity becomes unconventional and contradicts General Relativity. New mechanisms are needed to cure these models. We also comment on the possible decoupling of the ghost at large distances due to an apparent flat-5D nature of space-time and on the link between the presence of ghosts and the violation of positive-energy conditions.

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arXiv2000

Metastable Gravitons and Infinite Volume Extra Dimensions

We address the issue of whether extra dimensions could have an infinite volume and yet reproduce the effects of observable four-dimensional gravity on a brane. There is no normalizable zero-mode graviton in this case, nevertheless correct Newton's law can be obtained by exchanging bulk gravitons. This can be interpreted as an exchange of a single {\it metastable} 4D graviton. Such theories have remarkable phenomenological signatures since the evolution of the Universe becomes high-dimensional at very large scales. Furthermore, the bulk supersymmetry in the infinite volume limit might be preserved while being completely broken on a brane. This gives rise to a possibility of controlling the value of the bulk cosmological constant. Unfortunately, these theories have difficulties in reproducing certain predictions of Einstein's theory related to relativistic sources. This is due to the van Dam-Veltman-Zakharov discontinuity in the propagator of a massive graviton. This suggests that all theories in which contributions to effective 4D gravity come predominantly from the bulk graviton exchange should encounter serious phenomenological difficulties.

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arXiv1999

The Supergravity Dual of N=1 Super Yang-Mills Theory

We find an exact, N=1 supersymmetric kink solution of 5d gauged supergravity. We associate this solution with the RG flow from N=4 super Yang-Mills theory, deformed by a relevant operator, to pure N=1 super Yang-Mills in the IR. We test this identification by computing various QFT quantities using the supergravity dual: the tension of electric and magnetic strings and the gaugino condensate. As demanded by our identification, our kink solution is a true deformation of N=4, that exhibits confinement of quarks, magnetic screening, and spontaneous chiral symmetry breaking.

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arXiv1999

AdS Superalgebras with Brane Charges

We consider the inclusion of brane charges in AdS_5 superalgebras that contain the maximal central extension of the super-Poincaré algebra on the boundary of AdS_5. For theories with N supersymmetries on the boundary, the maximal extension is OSp(1/8N,R), which contains the group $Sp(8N,R)\supset U(2N,2N) \supset SU(2,2)\times U(N)$ as extension of the conformal group. An ``intermediate'' extension to U(2N,2N/1) is also discussed, as well as the inclusion of brane charges in AdS_7 and AdS_4 superalgebras. BPS conditions in the presence of brane charges are studied in some details.

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arXiv1999

Confinement and Condensates Without Fine Tuning in Supergravity Duals of Gauge Theories

We discuss a solution of the equations of motion of five-dimensional gauged type IIB supergravity that describes confining SU(N) gauge theories at large N and large 't Hooft parameter. We prove confinement by computing the Wilson loop, and we show that our solution is generic, independent of most of the details of the theory. In particular, the Einstein-frame metric near its singularity, and the condensates of scalar, composite operators are universal. Also universal is the discreteness of the glueball mass spectrum and the existence of a mass gap. The metric is also identical to a generically confining solution recently found in type 0B theory.

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arXiv1999

RG Fixed Points in Supergravity Duals of 4-d Field Theory and Asymptotically AdS Spaces

Recently, it has been conjectured that supergravity solutions with two asymptotically AdS regions describe the RG flow of a 4-d field theory from a UV fixed point to an interacting IR fixed point. In this paper we lend support to this conjecture by showing that, in the UV (IR) limit, the two-point function of a minimally-coupled scalar field depends only on the UV (IR) region of the metric, asymptotic to AdS_5. This result is consistent with the interpretation of the radial coordinate of Anti de Sitter space as an energy scale, and it may provide an analog of the Callan-Symanzik equation for supergravity duals of strongly coupled field theories.

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arXiv1999

Novel Local CFT and Exact Results on Perturbations of N=4 Super Yang Mills from AdS Dynamics

We find new, local, non-supersymmetric conformal field theories obtained by relevant deformations of the N=4 super Yang Mills theory in the large $N$ limit. We contruct interpolating supergravity solutions that naturally represent the flow from the N=4 super Yang Mills UV theory to these non-supersymmetric IR fixed points. We also study the linearization around the N=4 superconformal point of N=1 supersymmetric, marginal deformations. We show that they give rise to N=1 superconformal fixed points, as expected from field-theoretical arguments.

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arXiv1998

N=6 Supergravity on $AdS_5$ and the $SU(2,2/3)$ Superconformal Correspondence

It is argued that N=6 supergravity on $AdS_5$, with gauge group $SU(3)\times U(1)$ corresponds, at the classical level, to a subsector of the ``chiral'' primary operators of N=4 Yang-Mills theories. This projection involves a ``duality transformation'' of N=4 Yang-Mills theory and therefore can be valid if the coupling is at a self-dual point, or for those amplitudes that do not depend on the coupling constant.

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arXiv1997

Central Extensions of Supersymmetry in Four and Three Dimensions

We consider the maximal central extension of the supertranslation algebra in d=4 and 3, which includes tensor central charges associated to topological defects such as domain walls (membranes) and strings. We show that for all N-extended superalgebras these charges are related to nontrivial configurations on the scalar moduli space. For N=2 theories obtained from compactification on Calabi-Yau threefolds, we give an explicit realization of the moduli-dependent charges in terms of wrapped branes.

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arXiv1997

Bound States at Threshold in Supersymmetric Quantum Mechanics

We propose a general method that allows to detect the existence of normalizable ground states in supersymmetric quantum mechanical systems with non-Fredholm spectrum. We apply our method to show the existence of bound states at threshold in two important cases: 1) the quantum mechanical system describing H-monopoles; 2) the quantum mechanics of D0 branes.

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arXiv1997

Spontaneously Broken N=2 Supergravity Without Light Mirror Fermions

We present a spontaneously broken N=2 supergravity model that reduces in the flat limit to a globally supersymmetric N=2 system with explicit soft supersymmetry breaking terms. These soft terms generate a mass O(100 GeV) for mirror quarks and leptons, while leaving the physical fermions light, thereby overcoming one of the major obstacles towards the construction of a realistic N=2 model of elementary interactions.

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arXiv1996

M-Theory Origin of Mirror Symmetry in Three Dimensional Gauge Theories

We present M-theory compactifications on $K_3 \times K_3$ with membranes near the $A_n$ or $D_n$ singularities of the $K_3$ spaces. By realizing each of these compactifications in two different ways as type I' models with 2- and 6-branes, we explain the three-dimensional duality between gauge theories recently found by Intriligator and Seiberg. We also find new pairs of dual gauge theories, which we briefly describe.

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arXiv1996

How to Find H-Monopoles in Brane Dynamics

We prove in two different ways that brane dynamics gives rise to all H-monopoles predicted by S-duality of N=4, 4-dimensional superstring compactifications. One method uses heterotic-type II duality and the self-dual 3-brane dynamics, the other uses the 5-brane description of small instantons in SO(32) superstrings.

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arXiv1996

Aspects of Space-Time Dualities

Duality groups of Abelian gauge theories on four manifolds and their reduction to two dimensions are considered. The duality groups include elements that relate different space-times in addition to relating different gauge-coupling matrices. We interpret (some of) such dualities as the geometrical symmetries of compactified theories in higher dimensions. In particular, we consider compactifications of a (self-dual) 2-form in 6-D, and compactifications of a self-dual 4-form in 10-D. Relations with a self-dual superstring in 6-D and with the type IIB superstring are discussed.

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