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48
Recombination of intersecting Dbranes and cosmological inflation
, 2002
"... We consider the interactions between Dpbranes intersecting at an arbitrary number of angles in the context of typeII string theory. For cosmology purposes we concentrate in the theory on R 3,1 ×T 6. Interpreting the distance between the branes as the inflaton field, the branes can intersect at mos ..."
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Cited by 17 (0 self)
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We consider the interactions between Dpbranes intersecting at an arbitrary number of angles in the context of typeII string theory. For cosmology purposes we concentrate in the theory on R 3,1 ×T 6. Interpreting the distance between the branes as the inflaton field, the branes can intersect at most at two angles on the compact space. If the configuration is non supersymmetric we will have an interbrane potential that provides an effective cosmological inflationary epoch at the fourdimensional intersection between the branes. The end of inflation occurs when the interbrane distance becomes small compared with the string scale, where a tachyon develops triggering the recombination of the branes. We study this recombination due to tachyon instabilities and we find the possibility for the final configuration to be again branes intersecting at two angles. This preserves the interesting features that are present in the intersecting brane models from the string model building point of view also after the end of inflation. This fact was not present in the models of branes intersecting at just one angle. This kind of recombination can be also important in other string contexts.
Overproduction of cosmic superstrings
"... Abstract: We show that the naive application of the Kibble mechanism seriously underestimates the initial density of cosmic superstrings that can be formed during the annihilation of Dbranes in the early universe, as in models of braneantibrane inflation. We study the formation of defects in effec ..."
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Cited by 16 (2 self)
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Abstract: We show that the naive application of the Kibble mechanism seriously underestimates the initial density of cosmic superstrings that can be formed during the annihilation of Dbranes in the early universe, as in models of braneantibrane inflation. We study the formation of defects in effective field theories of the string theory tachyon both analytically, by solving the equation of motion of the tachyon field near the core of the defect, and numerically, by evolving the tachyon field on a lattice. We find that defects generically form with correlation lengths of order M −1 s rather than H−1. Hence, defects localized in extra dimensions may be formed at the end of inflation. This implies that braneantibrane inflation models where inflation is driven by branes which wrap the compact manifold may have problems
Dterms and Dstrings in open string models
 JHEP 0410 (2004) 056 [arXiv:hepth/0409284
"... We study the FayetIliopoulos (FI) Dterms on Dbranes in type II CalabiYau backgrounds. We provide a simple worldsheet proof of the fact that, at tree level, these terms only couple to scalars in closed string hypermultiplets. At the oneloop level, the Dterms get corrections only if the gauge gr ..."
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Cited by 12 (1 self)
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We study the FayetIliopoulos (FI) Dterms on Dbranes in type II CalabiYau backgrounds. We provide a simple worldsheet proof of the fact that, at tree level, these terms only couple to scalars in closed string hypermultiplets. At the oneloop level, the Dterms get corrections only if the gauge group has an anomalous spectrum, with the anomaly cancelled by a GreenSchwarz mechanism. We study the local type IIA model of D6branes at SU(3) angles and show that, as in field theory, the oneloop correction suffers from a quadratic divergence in the open string channel. By studying the closed string channel, we show that this divergence is related to a closed string tadpole, and is cancelled when the tadpole is cancelled. Next, we study the cosmic strings that arise in the supersymmetric phases of these systems in light of recent work of Dvali et. al. In the type IIA intersecting D6brane examples, we identify the Dterm strings as D4branes ending on the D6branes. Finally, we use N = 1 dualities to relate these results to previous work on the FI Dterm of heterotic strings. September
Localized instabilities at conifolds
, 2002
"... We consider the Mtheory lifts of configurations of type IIA D6branes intersecting at angles. In supersymmetry preserving cases, the lifts correspond to special holonomy geometries, like conifolds and G2 holonomy singularities. Transitions in which D6branes approach and recombine lift to topology c ..."
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Cited by 12 (1 self)
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We consider the Mtheory lifts of configurations of type IIA D6branes intersecting at angles. In supersymmetry preserving cases, the lifts correspond to special holonomy geometries, like conifolds and G2 holonomy singularities. Transitions in which D6branes approach and recombine lift to topology changing transition in these geometries. In some instances nonsupersymmetric configurations can be reliably lifted, leading to the same topological manifolds, but endowed with nonsupersymmetric metrics. In these cases the phase transitions are driven dynamically, due to instabilities localized at the singularities. Even though in noncompact setups the instabilities relax to infinity, in compact situations there exist nearby minima where the instabilities dissappear and the decay reaches a welldefined (in general supersymmetric) endpoint. 1
Multiple inflation, cosmic string networks and the string landscape
 JHEP
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Spectral flow and boundary string field theory for angled dbranes
 JHEP
"... Abstract: Dbranes intersecting at an arbitrary fixed angle generically constitute a configuration unstable towards recombination. The reconnection of the branes nucleates at the intersection point and involves a generalization of the process of brane decay of interest to nonperturbative string dyn ..."
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Cited by 10 (1 self)
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Abstract: Dbranes intersecting at an arbitrary fixed angle generically constitute a configuration unstable towards recombination. The reconnection of the branes nucleates at the intersection point and involves a generalization of the process of brane decay of interest to nonperturbative string dynamics as well as cosmology. After reviewing the string spectrum of systems of angled branes, we show that worldsheet twist superfields may be used in the context of Boundary Superstring Field Theory to describe the dynamics. Changing the angle between the branes is seen from the worldsheet as spectral flow with boundary insertions flowing from bosonic to fermionic operators. We calculate the complete tachyon potential and the low energy effective action as a function of angle and find an expression that interpolates between the braneantibrane and the DiracBornInfeld actions. The potential captures the mechanism of Dbrane recombination and provides for interesting new
Aspects of stability and phenomenology in type IIA orientifolds with intersecting D6branes,” Fortsch. Phys
"... Intersecting branes have been the subject of an elaborate string model building for several years. After a general introduction into string theory, this work introduces in detail the toroidal and ZNorientifolds. The picture involving D9branes with Bfluxes is shortly reviewed, but the main discuss ..."
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Cited by 9 (2 self)
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Intersecting branes have been the subject of an elaborate string model building for several years. After a general introduction into string theory, this work introduces in detail the toroidal and ZNorientifolds. The picture involving D9branes with Bfluxes is shortly reviewed, but the main discussion employs the Tdual picture of intersecting D6branes. The derivation of the RR and NSNS tadpole cancellation conditions in the conformal field theory is shown in great detail. Various aspects of the open and closed chiral and nonchiral massless spectrum are discussed, involving spacetime anomalies and the generalized GreenSchwarz mechanism. An introduction into possible gauge breaking mechanisms is given, too. Afterwards, both N=1 supersymmetric and nonsupersymmetric approaches to low energy model building are treated. Firstly, the problem of complex structure instabilities in toroidal ΩRorientifolds is approached by a Z3orbifolded model. In particular, a stable nonsupersymmetric standardlike model with three fermion generations is discussed. This model features the standard model gauge groups at the same time as having a massless hypercharge, but possessing an additional global BL
Coupling hybrid inflation to moduli
 JCAP 0609 (2006) 012 [hepth/0606140
"... Abstract. Hybrid inflation can be realised in lowenergy effective string theory, as described using supergravity. We find that the coupling of moduli to the hybrid inflation sector in supergravity leads to a slope and a curvature for the inflaton potential. The ǫ and η parameters receive contributi ..."
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Cited by 8 (5 self)
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Abstract. Hybrid inflation can be realised in lowenergy effective string theory, as described using supergravity. We find that the coupling of moduli to the hybrid inflation sector in supergravity leads to a slope and a curvature for the inflaton potential. The ǫ and η parameters receive contributions at tree and one loop level which are not compatible with slow roll inflation. Furthermore the coupling to the moduli sector can even prevent inflation from ending at all. We show that introducing shift symmetries in the inflationary sector and taking the moduli sector to be noscale removes most of these problems. If the moduli fields are fixed during inflation, as is usually assumed, it appears that viable slowroll inflation can then be obtained with just one finetuning of the moduli sector parameters. However, we show this is not a reasonable assumption, and that the small variation of the moduli fields during inflation gives a significant contribution to the effective inflaton potential. This typically implies that η ≈ −6.
Strings between branes
, 2003
"... Dbrane configurations containing fundamental strings are constructed as classical solutions of YangMills theory. The fundamental strings in these systems stretch between Dbranes. In the case of D1branes, this construction gives smooth (classical) resolutions of string junctions and string netw ..."
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Cited by 7 (0 self)
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Dbrane configurations containing fundamental strings are constructed as classical solutions of YangMills theory. The fundamental strings in these systems stretch between Dbranes. In the case of D1branes, this construction gives smooth (classical) resolutions of string junctions and string networks. Using a nonabelian YangMills analysis of the string current, the string charge density is computed and is shown to have support in the region between the Dbrane worldvolumes. The ’t HooftPolyakov monopole is analyzed using similar methods, and is shown to contain Dstrings whose flux has support off the Dbrane worldvolume defined by the Higgs scalar field, when this field is interpreted in terms of a transverse dimension. The constructions presented here are used to give a qualitative picture of tachyon condensation in the YangMills limit, where fundamental strings and lowerdimensional Dbranes arise in a volume of spacetime where braneantibrane annihilation has occurred.
Warped tachyonic inflation in type IIB flux compactifications and the openstring completeness conjecture
 JHEP
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