arXiv subjects

Ruben Minasian

Publications and source records attributed to Ruben Minasian.

87 records · Page 5Linked to original sources

arXiv2002

Kaluza-Klein bundles and manifolds of exceptional holonomy

We show how in the presence of RR two-form field strength the conditions for preserving supersymmetry on six- and seven-dimensional manifolds lead to certain generalizations of monopole equations. For six dimensions the string frame metric is Kaehler with the complex structure that descends from the octonions if in addition we assume F^{(1,1)}=0. The susy generator is a gauge covariantly constant spinor. For seven dimensions the string frame metric is conformal to a G_2 metric if in addition we assume the field strength to obey a selfduality constraint. Solutions to these equations lift to geometries of G_2 and Spin(7) holonomy respectively.

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arXiv2002

Variations on stability

We explore the effects of non-abelian dynamics of D-branes on their stability and introduce Hitchin-like modifications to previously-known stability conditions. The relation to brane-antibrane systems is used in order to rewrite the equations in terms of superconnections and arrive at deformed vortex equations.

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arXiv2001

Hopf reductions, fluxes and branes

We use a series of reductions, T-dualities and liftings to construct connections between fractional brane solutions in IIA, IIB and M-theory. We find a number of phantom branes that are not supported by the geometry, however materialize upon untwisting and/or Hopf-reduction.

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arXiv2001

Closed Strings from SO(8) Yang-Mills Instantons

When eight-dimensional instantons, satisfying F \wedge F = \pm \star_8 (F\wedge F), shrink to zero size, we find stringy objects in higher order ten-dimensional Yang-Mills (viewed as a low-energy limit of open string theory). The associated F^4 action is a combination of two independent parts having a single-trace and a double-trace structure. As a result we get a D-string from the single-trace term and a fundamental string from the double-trace. The latter has (8,0) supersymmetry on the worldsheet and couplings to the background gauge fields of a heterotic string. A correlation between the conformal factor of the instanton and the tachyon field is conjectured.

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arXiv2001

M5-branes, Special Lagrangian Submanifolds and sigma-models

We study M-theory fivebranes wrapped on Special Lagrangian submanifolds ($§_n$) in Calabi-Yau three- and fourfolds. When the M5 wraps a four-cycle, the resulting theory is a two-dimensional domain wall embedded in three-dimensional bulk with four supercharges. The theory on the wall is specified in terms of the geometry of the CY manifold and the cycle $§_4$. It is chiral and anomalous, however the presence of a three-dimensional gravitational Chern-Simons terms with a coefficient that jumps when crossing the wall allows to cancel the anomaly by inflow. Kahler manifolds of special type, where the potential depends only on the real part of the complex coordinate, are shown to emerge as the target spaces of two-dimensional sigma-models when the M5 is wrapped on $§_3 \times S^1$, thus providing a physical realization of some recent symplectic construction by Hitchin.

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arXiv2001

On non-commutative N=2 super Yang-Mills

We discuss the Seiberg-Witten solution of the non-commutative N=2 U(N) SYM model. The solution is described in terms of the ordinary Seiberg-Witten curve of the SU(N) theory plus an additional free U(1). Hence, at the two-derivative approximation the theory flows to the ordinary commutative theory in the infra-red (k<1/sqrt(theta)). In particular, the center U(1) is free and it decouples from the other U(1)'s. In addition, no UV/IR mixing is found.

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arXiv2000

On the geometry of non-trivially embedded branes

We present a formal supersymmetric solution of type IIB supergravity generalizing previously known solutions corresponding to D3 branes to geometries without an orthogonal split between parallel and transverse directions. The metric is given implicitly as one with respect to which a certain connection is compatible. The case of the deformed conifold is discussed in detail.

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arXiv2000

Anomalous D-Brane Charge in F-Theory Compactifications

Tadpole cancellation in F-theory on an elliptic Calabi-Yau fourfold $X\to B_3$ demands some spacetime-filling three-branes (points in $B_3$). If moved to the discriminant surface, which supports the gauge group, and dissolved into a finite size instanton, the second Chern class of the corresponding bundle $E$ is expected to give a compensating contribution. However the dependence of D-brane charge on the geometry of $W$ and on the embedding $i: W\to B_3$ gives a correction to $c_2(E)$. We show how this is reconciled by considering the torsion sheaf $i_*E$ and discuss some integrality issues related to global properties of $X$ as well as the moduli space of this object.

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arXiv1999

K-theory and Ramond-Ramond charge

We discuss the relation between the Ramond-Ramond charges of D-branes and the topology of Chan-Paton vector bundles. We show that a topologically nontrivial normal bundle induces RR charge and that the result fits in perfectly with the proposal that D-brane charge is the topology of the Chan-Paton bundle, regarded as an element of K-theory.

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arXiv1999

Calabi-Yau black holes and (0,4) sigma models

When an M-theory fivebrane wraps a holomorphic surface $\mathcal{P}$ in a Calabi-Yau 3-fold $X$ the low energy dynamics is that of a black string in 5 dimensional $\mathcal{N}=1$ supergravity. The infrared dynamics on the string worldsheet is an $\mathcal{N} = (0,4)$ 2D conformal field theory. Assuming the 2D CFT can be described as a nonlinear sigma model, we describe the target space geometry of this model in terms of the data of $X$ and $\mathcal{P}$. Variations of weight two Hodge structures enter the construction of the model in an interesting way.

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arXiv1999

Black holes and membranes in AdS_7

We investigate maximal gauged supergravity in seven dimensions and some of its solitonic solutions. By focusing on a truncation of the gauged SO(5) R-symmetry group to its U(1)^2 Cartan subgroup, we construct general two charge black holes that are asymptotically anti-de Sitter. We demonstrate that 1- and 2-charge black holes preserve 1/2 and 1/4 of the supersymmetries respectively. Additionally, we examine the odd-dimensional self-duality equation governing the three-form potential transforming as the 5 of SO(5), and provide some insight on the construction of membrane solutions in anti-de Sitter backgrounds.

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arXiv1997

U-branes and T^3 fibrations

We describe eight-dimensional vacuum configurations with varying moduli consistent with the U-duality group $SL(2,Z) \times SL(3,Z)$. Focusing on the latter less-well understood SL(3,Z) properties, we construct a class of fivebrane solutions living on lines on a three-dimensional base space. The resulting U-manifolds, with five scalars transforming under SL(3), admit a Ricci-flat Kahler metric. Based on the connection with special lagrangian $T^3$ fibered Calabi-Yau 3-folds, this construction provides a simple framework for the investigation of Calabi-Yau mirrors.

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arXiv1996

Low-Energy Analysis of $M$ and $F$ Theories on Calabi-Yau Threefolds

We elucidate the interplay between gauge and supersymmetry anomalies in six-dimensional $N=1$ supergravity with generalized couplings between tensor and vector multiplets. We derive the structure of the five-dimensional supergravity resulting from the $S_1$ reduction of these models and give the constraints on Chern-Simons couplings that follow from duality to $M$ theory compactified on a Calabi-Yau threefold. The duality is supported only on a restricted class of Calabi-Yau threefolds and requires a special type of intersection form. We derive five-dimensional central-charge formulas and discuss briefly the associated phase transitions. Finally, we exhibit connections with $F$-theory compactifications on Calabi-Yau manifolds that admit elliptic fibrations. This analysis suggests that $F$ theory unifies Type-$IIb$ three-branes and $M$-theory five-branes.

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arXiv1996

M-Theory on a Calabi-Yau Manifold

We compactify $M$-theory on a Calabi-Yau manifold to five dimensions by wrapping the membrane and fivebrane solitons of the eleven-dimensional supergravity limit around Calabi-Yau two-cycles and four-cycles respectively. We identify the perturbative and non-perturbative BPS states thus obtained with those of heterotic string theory compactified on $K3\times S^1$. Quantum aspects of the five-dimensional theory are discussed.

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arXiv1993

New Black Hole, String and Membrane Solutions of the Four-Dimensional Heterotic String

We present solutions of the low-energy four-dimensional heterotic string corresponding to $p$-branes with $p=0,1,2$, which are characterized by a mass per unit $p$-volume, ${\cal M}_{p+1}$, and topological ``magnetic'' charge, $g_{p+1}$. In the extremal limit, $\sqrt{2} κ{\cal M}_{p+1} = g_{p+1}$, they reduce to the recently discovered non-singular supersymmetric monopole, string and domain wall solutions. A novel feature is that the solutions involve both the dilaton and the modulus fields. In particular, the effective scalar coupling to the Maxwell field, $e^{-αϕ} F_{μν} F^{μν}$, gives rise to a new string black hole with $α= \sqrt{3}$, in contrast to the pure dilaton black hole solution which has $α=1$. This means that electric/magnetic duality in $D=4$ may be seen as a consequence of string/fivebrane duality in $D=10$.

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