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S. -H. Henry Tye

Publications and source records attributed to S. -H. Henry Tye.

At least 73 records · Page 4Linked to original sources
arXiv2006

Observational Constraints on Cosmic String Production During Brane Inflation

Overall, brane inflation is compatible with the recent analysis of the WMAP data. Here we explore the constraints of WMAP and 2dFGRS data on the various brane inflationary scenarios. Brane inflation naturally ends with the production of cosmic strings, which may provide a way to distinguish these models observationally. We argue that currently available data cannot exclude a non-negligible contribution from cosmic strings definitively. We perform a partial statistical analysis of mixed models that include a sub-dominant contribution from cosmic strings. Although the data favor models without cosmic strings, we conclude that they cannot definitively rule out a cosmic-string-induced contribution of $\sim 10 %$ to the observed temperature, polarization and galaxy density fluctuations. These results imply that $Gμ\lesssim 3.5\times 10^{-7}(λ/0.25)\sqrt{B/0.1}$, where $λ$ is a dimensionless parameter related to the interstring distance, and $B$ measures the importance of perturbations induced by cosmic strings. We argue that, conservatively, the data available currently still permit $B\lesssim 0.1$. Precision measurements sensitive to the B-mode polarization produced by vector density perturbation modes driven by the string network could provide evidence for these models. Accurate determinations of $n_s(k)$, the scalar fluctuation index, could also distinguish among various brane inflation models.

hep-th↗
arXiv2006

A Note on the Quantum Creation of Universes

We elucidate the nature of the correction to the Hartle-Hawking wavefunction presented in hep-th/$0505104$ and hep-th/$0406107$. The correction comes from the quantum fluctuation of the metric that spontaneously breaks the classical deSitter symmetry. This converts the tunneling from nothing to a deSitter-like universe via a $S^{4}$ instantion to that via a barrel instanton, which is bounded from below. Its generalization to 10 dimensional spacetime allows us to find the preferred sites in the stringy cosmic landscape. We comment on how some of the problems of the Hartle-Hawking wavefunction are avoided with the new modified wavefunction of the universe, when applied to the spontaneous creation of an inflationary universe. We also summarize our arguments on the validity of the Hartle-Hawking wavefunction in the minisuperspace approximation, as opposed to the WKB formula suggested by Linde and Vilenkin.

hep-th↗
arXiv2006

The (p,q) String Tension in a Warped Deformed Conifold

We find the tension spectrum of the bound states of p fundamental strings and q D-strings at the bottom of a warped deformed conifold. We show that it can be obtained from a D3-brane wrapping a 2-cycle that is stabilized by both electric and magnetic fluxes. Because the F-strings are Z_M-charged with non-zero binding energy, binding can take place even if (p,q) are not coprime. Implications for cosmic strings are briefly discussed.

hep-th↗
arXiv2005

The Shape of Gravity in a Warped Deformed Conifold

We study the spectrum of the gravitational modes in Minkowski spacetime due to a 6-dimensional warped deformed conifold, i.e., a warped throat, in superstring theory. After identifying the zero mode as the usual 4D graviton, we present the KK spectrum as well as other excitation modes. Gluing the throat to the bulk (a realistic scenario), we see that the graviton has a rather uniform probability distribution everywhere while a KK mode is peaked in the throat, as expected. Due to the suppressed measure of the throat in the wave function normalization, we find that a KK mode's probability in the bulk can be comparable to that of the graviton mode. We also present the tunneling probabilities of a KK mode from the inflationary throat to the bulk and to another throat. Due to resonance effect, the latter may not be suppressed as natively expected. Implication of this property to reheating after brane inflation is discussed.

hep-th↗
arXiv2005

Cosmic String Lensing and Closed Time-like Curves

In an analysis of the gravitational lensing by two relativistic cosmic strings, we argue that the formation of closed time-like curves proposed by Gott is unstable in the presence of particles (e.g. the cosmic microwave background radiation). Due to the attractor-like behavior of the closed time-like curve, we argue that this instability is very generic. A single graviton or photon in the vicinity, no matter how soft, is sufficient to bend the strings and prevent the formation of closed time-like curves. We also show that the gravitational lensing due to a moving cosmic string is enhanced by its motion, not suppressed.

hep-th↗
arXiv2005

Scaling of Multi-Tension Cosmic Superstring Networks

Brane inflation in superstring theory ends when branes collide, initiating the hot big bang. Cosmic superstrings are produced during the brane collision. The cosmic superstrings produced in a D3-brane-antibrane inflationary scenario have a spectrum: $(p,q)$ bound states of $p$ fundamental (F) strings and $q$ D-strings, where $p$ and $q$ are coprime. By extending the velocity-dependent one-scale network evolution equations for abelian Higgs cosmic strings to allow a spectrum of string tensions, we construct a coupled (infinite) set of equations for strings that interact through binding and self-interactions. We apply this model to a network of $(p,q)$ superstrings. Our numerical solutions show that $(p,q)$ networks rapidly approach a stable scaling solution. We also extract the relative densities of each string type from our solutions. Typically, only a small number of the lowest tension states are populated substantially once scaling is reached. The model we study also has an interesting new feature: the energy released in $(p,q)$ string binding is by itself adequate to allow the network to reach scaling. This result suggests that the scaling solution is robust. To demonstrate that this result is not trivial, we show that choosing a different form for string interactions can lead to network frustration.

astro-ph↗
arXiv2005

The Boundedness of Euclidean Gravity and the Wavefunction of the Universe

When the semi-positive cosmological constant is dynamical, the naive Euclidean Einstein action is unbounded from below and the Hartle-Hawking wavefunction of the universe is not normalizable. With the inclusion of back-reaction (a crucial point), the presence of the metric perturbative modes (as well as matter fields) as the environment (that is, to be integrated or traced out) introduces a correction term that provides a bound to the Euclidean action. So the improved wavefunction is normalizable. That is, decoherence plays an essential role in the consistency of quantum gravity. In the spontaneous creation of the universe, this improved wavefunction allows one to compare the tunneling probabilities from absolute nothing (i.e., not even classical spacetime) to various vacua (with different large spatial dimensions and different low energy spectra) in the stringy cosmic landscape.

hep-th↗
arXiv2005

Brane Inflation and Cosmic String Tension in Superstring Theory

In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll condition in the D3-anti-D3-brane inflationary scenario in superstring theory requires no more than a moderate tuning. The cosmic string tension is very sensitive to the conformal coupling: with less fine-tuning, the cosmic string tension (as well as the ratio of tensor to scalar perturbation mode) increases rapidly and can easily saturate the present observational bound. In a multi-throat brane inflationary scenario, this feature substantially improves the chance of detecting and measuring the properties of the cosmic strings as a window to the superstring theory and our pre-inflationary universe.

hep-th↗
arXiv2005

Inter-brane Interactions in Compact Spaces and Brane Inflation

It was pointed out that brane-anti-brane inflation without warped geometry is not viable due to compactification effects (in the simplified scenario where the inflaton is decoupled from the compactification moduli). We show that the inflationary scenario with branes at a small angle in this simplified scenario remains viable. We also point out that brane-anti-brane inflation may still be viable under some special conditions. We also discuss a way to treat potentials in compact spaces that should be useful in the analysis of more realistic brane inflationary scenarios.

hep-th↗
arXiv2004

Spontaneous Creation of Inflationary Universes and the Cosmic Landscape

We study some gravitational instanton solutions that offer a natural realization of the spontaneous creation of inflationary universes in the brane world context in string theory. Decoherence due to couplings of higher (perturbative) modes of the metric as well as matter fields modifies the Hartle-Hawking wavefunction for de Sitter space. Generalizing this new wavefunction to be used in string theory, we propose a principle in string theory that hopefully will lead us to the particular vacuum we live in, thus avoiding the anthropic principle. As an illustration of this idea, we give a phenomenological analysis of the probability of quantum tunneling to various stringy vacua. We find that the preferred tunneling is to an inflationary universe (like our early universe), not to a universe with a very small cosmological constant (i.e., like today's universe) and not to a 10-dimensional uncompactified de Sitter universe. Such preferred solutions are interesting as they offer a cosmological mechanism for the stabilization of extra dimensions during the inflationary epoch.

hep-th↗
arXiv2004

Stability of D1-Strings Inside a D3-Brane

Within the tachyon condensation approach, we find that a D(p-2)-brane is stable inside Dp-branes when the bulk is compactified. It is a codimension-2 soliton of the Dp-brane action with coupling to the bulk (p-1)-form RR field. We discuss the properties of such solitons. They may appear as detectable cosmic strings in our universe.

hep-th↗
arXiv2003

Closer towards inflation in string theory

In brane inflation, the relative brane position in the bulk of a brane world is the inflaton. For branes moving in a compact manifold, the approximate translational (or shift) symmetry is necessary to suppress the inflaton mass, which then allows a slow-roll phase for enough inflation. Following recent works, we discuss how inflation may be achieved in superstring theory. Imposing the shift symmetry, we obtain the condition on the superpotential needed for inflation and suggest how this condition may be naturally satisfied.

hep-th↗
arXiv2003

Spectral flow and boundary string field theory for angled D-branes

D-branes intersecting at an arbitrary fixed angle generically constitute a configuration unstable toward recombination. The reconnection of the branes nucleates at the intersection point and involves a generalization of the process of brane decay of interest to non-perturbative 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 brane-antibrane and the Dirac-Born-Infeld actions. The potential captures the mechanism of D-brane recombination and provides for interesting new physics for tachyon decay.

hep-th↗
arXiv2003

Adding a Brane to the Brane-Anti-Brane Action in BSFT

We attempt to generalize the effective action for the D-brane-anti-D-brane system obtained from boundary superstring field theory (BSFT) by adding an extra D-brane to it to obtain a covariantized action for 2 D-branes and 1 anti-D-brane. We discuss the approximations made to obtain the effective action in closed form. Among other properties, this effective action admits solitonic solutions of codimension 2 (vortices) when one of the D-brane is far separated from the brane-anti-brane pair.

hep-th↗
arXiv2003

Inter-Brane Potential and the Decay of a non-BPS-D-brane to Closed Strings

We calculate the potential for $Dp-\Dbar p$ pair and show that the coincident $Dp-\Dbar p$ system has $(11-p)$ tachyonic modes, with $(9-p)$ of them due to radiative corrections. We propose that the decay width of an unstable non-BPS-$Dp$-brane to closed strings is given by the imaginary part of the one-loop contribution to the effective potential of the open string tachyon mode.

hep-th↗
arXiv2003

The Production, Spectrum and Evolution of Cosmic Strings in Brane Inflation

Brane inflation in superstring theory predicts that cosmic strings (but not domain walls or monopoles) are produced towards the end of the inflationary epoch. Here, we discuss the production, the spectrum and the evolution of such cosmic strings, properties that differentiate them from those coming from an abelian Higgs model. As D-branes in extra dimensions, some type of cosmic strings will dissolve rapidly in spacetime, while the stable ones appear with a spectrum of cosmic string tensions. Moreover, the presence of the extra dimensions reduces the interaction rate of the cosmic strings in some scenarios, resulting in an order of magnitude enhancement of the number/energy density of the cosmic string network when compared to the field theory case.

hep-th↗
arXiv2002

An Improved Brane Anti-Brane Action from Boundary Superstring Field Theory and Multi-Vortex Solutions

We present an improved effective action for the D-brane-anti-D-brane system obtained from boundary superstring field theory. Although the action looks highly non-trivial, it has simple explicit multi-vortex (i.e. codimension-2 multi-BPS D-brane) multi-anti-vortex solutions. The solutions have a curious degeneracy corresponding to different ``magnetic'' fluxes at the core of each vortex. We also generalize the brane anti-brane effective action that is suitable for the study of the inflationary scenario and the production of defects in the early universe. We show that when a brane and anti-brane are distantly separated, although the system is classically stable it can decay via quantum tunneling through the barrier.

hep-th↗