arXiv subjects

Ralph Blumenhagen

Publications and source records attributed to Ralph Blumenhagen.

At least 145 records · Page 8Linked to original sources

arXiv2000

Asymmetric Orbifolds, Noncommutative Geometry and Type I String Vacua

We investigate the D-brane contents of asymmetric orbifolds. Using T-duality we find that the consistent description of open strings in asymmetric orbifolds requires to turn on background gauge fields on the D-branes. We derive the corresponding noncommutative geometry arising on such D-branes with mixed Neumann-Dirichlet boundary conditions directly by applying an asymmetric rotation to open strings with pure Dirichlet or Neumann boundary conditions. As a concrete application of our results we construct asymmetric type I vacua requiring open strings with mixed boundary conditions for tadpole cancellation.

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arXiv2000

A New Class of Supersymmetric Orientifolds with D-Branes at Angles

We describe a new class of supersymmetric orientifolds which combine the world-sheet parity transformation with a complex conjugation in the compact directions. As an example, we investigate in detail the orientifold of the Z_3 toroidal orbifold in six and four dimensions. We demonstrate how the solution to the tadpole cancellation conditions, the resulting gauge groups and the massless spectra depend on the choice of the complex structures on the tori, giving rise to a variety of inequivalent models. We also summarize the results for the orientifolds of the Z_4, Z_6 and Z_6' orbifolds in four and six dimensions.

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arXiv2000

Supersymmetric 4D Orientifolds of Type IIA with D6-branes at Angles

We study a certain class of four-dimensional N=1 supersymmetric orientifolds for which the world-sheet parity transformation is combined with a complex conjugation in the compact directions. We investigate in detail the orientifolds of the Z_3, Z_4, Z_6 and Z_6' toroidal orbifolds finding solutions to the tadpole cancellation conditions for all models. Generically, all the massless spectra turn out to be non-chiral.

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arXiv1999

Discrete Deformations in Type I Vacua

We study supersymmetric orientifolds where the world-sheet parity transformation is combined with a conjugation of some compact complex coordinates. We investigate their T-duality relation to standard orientifolds and discuss the origin of continuous and discrete moduli. In contrast to standard orientifolds, the antisymmetric tensor describes a continuous deformation, while the off-diagonal part of the metric is frozen to quantized values and is responsible for the rank reduction of the gauge group. We also give a geometrical interpretation of some recently constructed six-dimensional permutational orientifolds.

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arXiv1999

Supersymmetric Orientifolds in 6D with D-Branes at Angles

We study a new class of N=1 supersymmetric orientifolds in six space-time dimensions. The world-sheet parity transformation is combined with a permutation of the internal complex coordinates. In contrast to ordinary orientifolds the twisted sectors contribute to the Klein bottle amplitude leading to new tadpoles to be cancelled by twisted open string sectors. They arise from open strings stretched between D7-branes intersecting at non-trivial angles. We study in detail the Z_3, Z_4 and Z_6 permutational orientifolds obtaining in all cases anomaly free massless spectra.

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arXiv1999

Continuous Gauge and Supersymmetry Breaking for Open Strings on D-branes

We consider freely acting orbifold compactifications, which interpolate in two possible decompactification limits between the supersymmetric type II string and the non-supersymmetric type 0 string. In particular we discuss how D-branes are incorporated into these orbifold models. Investigating the open string spectrum on D3-branes, we will show that one can interpolate in this way between N=4 supersymmetric U(N) respectively U(2N) Yang-Mills theories and non-supersymmetric U(N)*U(N) gauge theories with adjoint massless scalar fields plus bifundamental massless fermions in a smooth way. Finally, by lifting the orbifold construction to M-theory, we conjecture some duality relations and show that in particular a new supersymmetric branch of gauge like theories emanate for the non-supersymmetric model.

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arXiv1999

A Note on Orientifolds and Dualities of Type 0B String Theory

We generalize the construction of four dimensional non-tachyonic orientifolds of type 0B string theory to non-supersymmetric backgrounds. We construct a four dimensional model containing self-dual D3 and D9-branes and leading to a chiral anomaly-free massless spectrum. Moreover, we discuss a further tachyon-free six dimensional model with only D5 branes. Eventually, we speculate about strong coupling dual models of the ten-dimensional orientifolds of type 0B.

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arXiv1999

Non-Supersymmetric Gauge Theories from D-Branes in Type 0 String Theory

We construct non-supersymmetric four dimensional gauge theories arising as effective theories of D-branes placed on various singularities in Type 0B string theory. We mostly focus on models which are conformal in the large N limit and present both examples appearing on self-dual D3-branes on orbifold singularities and examples including orientifold planes. Moreover, we derive type 0 Hanany-Witten setups with NS 5-branes intersected by D-branes and the corresponding rules for determining the massless spectra. Finally, we discuss possible duality symmetries (Seiberg-duality) for non-supersymmetric gauge theories within this framework.

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arXiv1999

Tachyon-free Orientifolds of Type 0B Strings in Various Dimensions

We construct non-tachyonic, non-supersymmetric orientifolds of Type 0B strings in ten, six and four space-time dimensions. Typically, these models have unitary gauge groups with charged massless fermionic and bosonic matter fields. However, generically there remains an uncancelled dilaton tadpole.

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arXiv1999

Orientifolds of Non-Supersymmetric Asymmetric Orbifolds

We consider certain four dimensional supersymmetric and non-supersymmetric asymmetric orbifolds with vanishing cosmological constant up to two loops and gauge the world sheet parity transformation. This leads to new string vacua, in which Dp and D(p-4) branes or Dp and anti-D(p-4) are identified. Moreover, it is shown that different degrees of supersymmetry can be realized in the bulk and on the brane. We show that for non-supersymmetric models the cosmological constant still vanishes at one loop order.

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arXiv1999

Issues of Heterotic (0,2) Compactifications

A brief review of some aspects of heterotic (0,2) compactifications in the framework of exactly solvable superconformal field theories and gauged linear sigma models is presented.

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arXiv1998

Spectra of 4D, N=1 Type I String Vacua on Non-Toroidal CY Threefolds

We compute the massless spectra of some four dimensional, N=1 supersymmetric compactifications of the type I string. The backgrounds are non-toroidal Calabi-Yau manifolds described at special points in moduli space by Gepner models. Surprisingly, the abstract conformal field theory computation reveals Chan-Paton gauge groups as big as SO(12) x SO(20) or SO(8)^4 x SO(4)^3.

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arXiv1997

(0,2) Target Space Duality, CICYs and Reflexive Sheaves

It is shown that the recently proposed target space duality for (0,2) models is not limited to models admitting a Landau-Ginzburg description. By studying some generic examples it is established for the broader class of vector bundles over complete intersections in toric varieties. Instead of sharing a common Landau-Ginzburg locus, a pair of dual models agrees in more general non-geometric phases. The mathematical tools for treating reflexive sheaves are provided, as well.

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arXiv1997

Target Space Duality for (0,2) Compactifications

The moduli spaces of two (0,2) compactifications of the heterotic string can share the same Landau-Ginzburg model even though at large radius they look completely different. It was argued that such a pair of (0,2) models might be connected via a perturbative transition at the Landau-Ginzburg point. Situations of this kind are studied for some explicit models. By calculating the exact dimensions of the generic moduli spaces at large radius, strong indications are found in favor of a different scenario. The two moduli spaces are isomorphic and complex, Kähler and bundle moduli get exchanged.

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arXiv1997

Aspects of (0,2) Orbifolds and Mirror Symmetry

We study orbifolds of (0,2) models and their relation to (0,2) mirror symmetry. In the Landau-Ginzburg phase of a (0,2) model the superpotential features a whole bunch of discrete symmetries, which by quotient action lead to a variety of consistent (0,2) vacua. We study a few examples in very much detail. Furthermore, we comment on the application of (0,2) mirror symmetry to the calculation of Yukawa couplings in the space-time superpotential.

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arXiv1996

On Orbifolds of (0,2) Models

We study orbifolds of (0,2) models, including some cases with discrete torsion. Our emphasis is on models which have a Landau-Ginzburg realization, where we describe part of the massless spectrum by computing the elliptic genus for the orbifolded theory. Somewhat surprisingly, we find simple examples of (0,2) mirror pairs that are related by a quotient action. We present a detailed description of a family of such pairs.

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arXiv1996

(0,2) Mirror Symmetry

We generalize the previously established (0,2) triality of exactly solvable models, Landau-Ginzburg theories and Calabi-Yau manifolds to a number of different classes of (0,2) compactifications derived from (2,2) vacua. For the resulting models we show that the known (2,2) mirror constructions induce mirror symmetry in the (0,2) context.

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arXiv1996

Exploring the Moduli Space of (0,2) Strings

We use an exactly solvable (0,2) supersymmetric conformal field theory with gauge group SO(10) to investigate the superpotential of the corresponding classical string vacuum. We provide evidence that the rational point lies in the Landau-Ginzburg phase of the linear sigma-model and calculate exactly all three- and four-point functions of the gauge singlets. These couplings already put severe constraints on the possible flat directions of the superpotential. Finally, we contemplate about the flat direction related to Kahler deformations of the underlying linear sigma-model.

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