arXiv subjects

E. Gava

Publications and source records attributed to E. Gava.

At least 19 recordsLinked to original sources

arXiv2007

1/8 BPS States in Ads/CFT

We study a class of exact supersymmetric solutions of type IIB Supergravity. They have an SO(4) x SU(2) x U(1) isometry and preserve generically 4 of the 32 supersymmetries of the theory. Asymptotically AdS_5 x S^5 solutions in this class are dual to 1/8 BPS chiral operators which preserve the same symmetries in the N=4 SYM theory. They are parametrized by a set of four functions that satisfy certain differential equations. We analyze the solutions to these equations in a large radius asymptotic expansion: they carry charges with respect to two U(1) KK gauge fields and their mass saturates the expected BPS bound.

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arXiv2007

BPS Solutions in AdS/CFT

We study a class of exact supersymmetric solutions of type IIB Supergravity. They have an SO(4) x SU(2) x U(1) isometry and preserve generically 4 of the 32 supersymmetries of the theory. Asymptotically AdS_5 x S^5 solutions in this class are dual to 1/8 BPS chiral operators which preserve the same symmetries in the N=4 SYM theory. We analyse the solutions to these equations in a large radius asymptotic expansion: they carry charges with respect to two U(1) KK gauge fields and their mass saturates the expected BPS bound. We also show how the same formalism is suitable for the description of the AdS_5 x Y^{p,q} geometries and a class of their excitations.

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arXiv2005

Spacetime Properties of ZZ D-Branes

We study the tachyon and the RR field sourced by the $(m,n)$ ZZ D-branes in type 0 theories using three methods. We first use the mini-superspace approximation of the closed string wave functions of the tachyon and the RR scalar to probe these fields. These wave functions are then extended beyond the mini-superspace approximation using mild assumptions which are motivated by the properties of the corresponding wave functions in the mini-superspace limit. These are then used to probe the tachyon and the RR field sourced. Finally we study the space time fields sourced by the $(m,n)$ ZZ D-branes using the FZZT brane as a probe. In all the three methods we find that the tension of the $(m,n)$ ZZ brane is $mn$ times the tension of the $(1,1)$ ZZ brane. The RR charge of these branes is non-zero only for the case of both $m$ and $n$ odd, in which case it is identical to the charge of the $(1,1)$ brane. As a consistency check we also verify that the space time fields sourced by the branes satisfy the corresponding equations of motion.

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arXiv2002

Open Strings on Plane waves and their Yang-Mills duals

We study the plane wave limit of $AdS_5\times S^5/Z_2$ which arises as the near horizon geometry of D3-branes at an orientifold 7-plane in type I' theory. We analyze string theory in the resulting plane wave background which contains open strings. We identify gauge invariant operators in the dual $Sp(N)$ gauge theory with unoriented closed and open string states.

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arXiv2002

Little String Theories in Heterotic Backgrounds

We study Little String Theories (LST) with ${\cal N}=(1,0)$ supersymmetry arising, in a suitable double scaling limit, from 5-branes in heterotic string theory or in the heterotic-like type II/$(-)^{F_L}\times {\rm shift}$. The limit in question, previously studied in the type II case, is such that the resulting holographically dual pairs, i.e. bulk string theory and LST are at a finite effective coupling. In particular, the internal $(2,2)$ SCFT on the string theory side is non-singular and given by $SL(2)/U(1)\times SU(2)/U(1)$ coset. In the type II orbifold case, we determine the orbifold action on the internal SCFT and construct the boundary states describing the non-BPS massive states of a completely broken $SO$ gauge theory, in agreement with the dual picture of D5-branes in type II/$Ω\times {\rm shift}$. We also describe a different orbifold action which gives rise to a $Sp$ gauge theory with $(1,1)$ supersymmetry. In both the heterotic SO(32) and $E_8\times E_8$ cases, we determine the gauge bundles which correspond to the above SCFT and break down the gauge groups to $SU(2)\times SO(28)$ and $E_7\times E_8$ respectively. The double scaling limit in this case involves taking small instanton together with small string coupling constant limit. We determine the spectrum of chiral gauge invariant operators with the corresponding global symmetry charges on the LST side and compare with the massless excitations on the string theory side, finding agreement for multiplicities and global charges.

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arXiv2001

AdS/CFT correspondence and D1/D5 systems in theories with 16 supercharges

We discuss spectra of $AdS_3$ supergravities, arising in the near horizon geometry of D1/D5 systems in orbifolds/orientifolds of type IIB theory with 16 supercharges. These include models studied in a recent paper (hep-th/0012118), where the group action involves also a shift along a transversal circle, as well as IIB/$ΩI_4$, which is dual to IIB on $K3$. After appropriate assignements of the orbifold group eigenvalues and degrees to the supergravity single particle spectrum, we compute the supergravity elliptic genus and find agreement, in the expected regime of validity, with the elliptic genus obtained using U-duality map from (4,4) CFTs of U-dual backgrounds. Since this U-duality involves the exchange of KK momentum $P$ and D1 charge $N$, it allows us to test the (4,4) CFTs in the $P < N/4$ and $N < P/4$ regimes by two different supergravity duals.

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arXiv2000

D1/D5 systems in ${\cal N}=4$ string theories

We propose CFT descriptions of the D1/D5 system in a class of freely acting Z_2 orbifolds/orientifolds of type IIB theory, with sixteen unbroken supercharges. The CFTs describing D1/D5 systems involve N=(4,4) or N=(4,0) sigma models on $(R^3\times S^1\times T^4\times (T^4)^N/S_N)/Z_2$, where the action of Z_2 is diagonal and its precise nature depends on the model. We also discuss D1(D5)-brane states carrying non-trivial Kaluza-Klein charges. The resulting multiplicities for two-charge bound states are shown to agree with the predictions of U-duality. We raise a puzzle concerning the multiplicities of three-charge systems, which is generically present in all vacuum configurations with sixteen unbroken supercharges studied so far, including the more familiar type IIB on K3 case: the constraints put on BPS counting formulae by U-duality are apparently in contradiction with any CFT interpretation. We argue that the presence of RR backgrounds appearing in the symmetric product CFT may provide a resolution of this puzzle.

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arXiv1999

Instantons in ${\cal N}=2$ $Sp(N)$ Superconformal Gauge Theories and the AdS/CFT Correspondence

We study, using ADHM construction, instanton effects in an ${\CN}=2$ superconformal $Sp(N)$ gauge theory, arising as effective field theory on a system of $N$ D-3-branes near an orientifold 7-plane and 8 D-7-branes in type I' string theory. We work out the measure for the collective coordinates of multi-instantons in the gauge theory and compare with the measure for the collective coordinates of $(-1)$-branes in the presence of 3- and 7-branes in type I' theory. We analyse the large-N limit of the measure and find that it admits two classes of saddle points: In the first class the space of collective coordinates has the geometry of $AdS_5\times S^3$ which on the string theory side has the interpretation of the D-instantons being stuck on the 7-branes and therefore the resulting moduli space being $AdS_5\times S^3$, In the second class the geometry is $AdS_5\times S^5/Z_2$ and on the string theory side it means that the D-instantons are free to move in the 10-dimensional bulk. We discuss in detail a correlator of four O(8) flavour currents on the Yang-Mills side, which receives contributions from the first type of saddle points only, and show that it matches with the correlator obtained from $F^4$ coupling on the string theory side, which receives contribution from D-instantons, in perfect accord with the AdS/CFT correspondence. In particular we observe that the sectors with odd number of instantons give contribution to an O(8)-odd invariant coupling, thereby breaking O(8) down to SO(8) in type I' string theory. We finally discuss correlators related to $R^4$, which receive contributions from both saddle points.

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arXiv1999

D-strings in unconventional type I vacuum configurations

We determine the spectrum of D-string bound states in various classes of generalized type I vacuum configurations with sixteen and eight supercharges. The precise matching of the BPS spectra confirms the duality between unconventional type IIB orientifolds with quantized NS-NS antisymmetric tensor and heterotic CHL models in D=8. A similar analysis puts the duality between type II (4,0) models and type I strings {\it without open strings} on a firmer ground. The analysis can be extended to type II (2,0) asymmetric orbifolds and their type I duals that correspond to unconventional K3 compactifications. Finally we discuss BPS-saturated threshold corrections to the correponding low-energy effective lagrangians. In particular we show how the exact moduli dependence of some F^4 terms in the eight-dimensional type II (4,0) orbifold is reproduced by the infinite sum of D-instanton contributions in the dual type I theory.

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arXiv1999

On the perturbative corrections around D-string instantons

We study ${\cal F}^4$-threshold corrections in an eight dimensional S-dual pair of string theories, as a prototype of dual string vacua with sixteen supercharges. We show that the orbifold CFT description of D-string instantons gives rise to a perturbative expansion similar to the one appearing on the fundamental string side. By an explicit calculation, using the Nambu-Goto action in the static gauge, we show that the first subleading term agrees precisely on the two sides. We then give a general argument to show that the agreement extends to all orders.

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arXiv1998

Bound States of Type I D-Strings

We study the infra-red limit of the O(N) gauge theory that describes the low energy modes of a system of $N$ type I D-strings and provide some support to the conjecture that, in this limit, the theory flows to an orbifold conformal theory. We compute the elliptic genus of the orbifold theory and argue that its longest string sector describes the bound states of D-strings. We show that, as a result, the masses and multiplicities of the bound states are in agreement with the predictions of heterotic-type I duality in 9 dimensions, for all the BPS charges in the lattice $Γ_{(1,17)}$.

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arXiv1997

Duality in Superstring Compactifications with Magnetic Field Backgrounds

Motivated by the work of Polchinski and Strominger on type IIA theory, where the effect of non-trivial field strengths for p-form potentials on a Calabi-Yau space was discussed, we study four-dimensional heterotic string theory in the presence of magnetic field on a 2-cycle in the internal manifold, for both N=4 and N=2 cases. We show that at special points in the moduli space, certain perturbative charged states become tachyonic and stabilize the vacuum by acquiring vacuum expectation values, thereby restoring supersymmetry. We discuss both the cases where the tachyons appear with a tower of Landau levels, which become light in the limit of large volume of the 2-cycle, and the case where such Landau levels are not present. In the latter case it is sufficient to restrict the analysis to the quartic potential for the tachyon. On the other hand, in the former case it is necessary to include the Landau levels in the analysis of the potential; for toroidal and orbifold examples, we give an explicit CFT description of the new supersymmetric vacuum. The resulting new vacuum turns out to be in the same class as the original supersymmetric one. Finally, using duality, we discuss the role of the Landau levels on the type IIA side.

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arXiv1997

On the Bound States of p- and (p+2)-Branes

We study bound states of D-p-branes and D-(p+2)-branes. By switching on a large magnetic field F on the (p+2) brane, the problem is shown to admit a perturbative analysis in an expansion in inverse powers of F. It is found that, to the leading order in 1/F, the quartic potential of the tachyonic state from the open string stretched between the p- and (p+2)-brane gives a vacuum energy which agrees with the prediction of the BPS mass formula for the bound state. We generalize the discussion to the case of m p-branes plus 1 (p+2)-brane with magnetic field. The T dual picture of this, namely several (p+2)-branes carrying some p-brane charges through magnetic flux is also discussed, where the perturbative treatment is available in the small F limit. We show that once again, in the same approximation, the tachyon condensates give rise to the correct BPS mass formula. The role of 't Hooft's toron configurations in the extension of the above results beyond the quartic approximation as well as the issue of the unbroken gauge symmetries are discussed. We comment on the connection between the present bound state problem and Kondo-like problems in the context of relevant boundary perturbations of boundary conformal field theories.

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arXiv1996

D-branes and the Conifold Singularity

We analyze in detail the description of type IIB theory on a Calabi-Yau three-fold near a conifold singularity in terms of intersecting D-branes. In particular we study the singularity structure of higher derivative $F$-terms of the form $F_g W^{2g}$ where $W$ is the gravitational superfield. This singularity is expected to be due to a one -loop contribution from a charged soliton hypermultiplet becoming massless at the conifold point. In the intersecting D-brane description this soliton is described by an open string stretched between the two D-branes. After identifying the graviphoton vertex as a closed string operator we show that $F_g$'s have the expected singularity structure in the limit of vanishing soliton mass.

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arXiv1996

Topological Amplitudes in Heterotic Superstring Theory

We show that certain heterotic string amplitudes are given in terms of correlators of the twisted topological (2,0) SCFT, corresponding to the internal sector of the N=1 spacetime supersymmetric background. The genus g topological partition function $F^g$ corresponds to a term in the effective action of the form $W^{2g}$, where W is the gauge or gravitational superfield. We study also recursion relations related to holomorphic anomalies, showing that, contrary to the type II case, they involve correlators of anti-chiral superfields. The corresponding terms in the effective action are of the form $W^{2g}Π^n$, where $Π$ is a chiral superfield obtained by chiral projection of a general superfield. We observe that the structure of the recursion relations is that of N=1 spacetime supersymmetry Ward identity. We give also a solution of the tree level recursion relations and discuss orbifold examples.

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arXiv1995

Duality Symmetries in N=2 Heterotic Superstring

We review the derivation and the basic properties of the perturbative prepotential in N=2 compactifications of the heterotic superstring. We discuss the structure of the perturbative monodromy group and the embedding of rigidly supersymmetric monodromies associated with enhanced gauge groups, at both perturbative and non-perturbative level.

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arXiv1995

N=2 Type II- Heterotic duality and Higher derivative F-terms

We test the recently conjectured duality between $N=2$ supersymmetric type II and heterotic string models by analysing a class of higher dimensional interactions in the respective low-energy Lagrangians. These are $F$-terms of the form $F_g W^{2g}$ where $W$ is the gravitational superfield. On the type II side these terms are generated at the $g$-loop level and in fact are given by topological partition functions of the twisted Calabi-Yau sigma model. We show that on the heterotic side these terms arise at the one-loop level. We study in detail a rank 3 example and show that the corresponding couplings $F_g$ satisfy the same holomorphic anomaly equations as in the type II case. Moreover we study the leading singularities of $F_g$'s on the heterotic side, near the enhanced symmetry point and show that they are universal poles of order $2g{-}2$ with coefficients that are given by the Euler number of the moduli space of genus-$g$ Riemann surfaces. This confirms a recent conjecture that the physics near conifold singularity is governed by $c{=}1$ string theory at the self-dual point.

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arXiv1995

Perturbative Prepotential and Monodromies in N=2 Heterotic Superstring

We discuss the prepotential describing the effective field theory of N=2 heterotic superstring models. At the one loop-level the prepotential develops logarithmic singularities due to the appearance of charged massless states at particular surfaces in the moduli space of vector multiplets. These singularities modify the classical duality symmetry group which now becomes a representation of the fundamental group of the moduli space minus the singular surfaces. For the simplest two-moduli case, this fundamental group turns out to be a certain braid group and we determine the resulting full duality transformations of the prepotential, which are exact in perturbation theory.

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