Dynamical classicalization

We integrate numerically the nonlinear equation of motion for a collapsing spherical wavepacket in the context of theories that are expected to display behavior characteristic of classicalization. The classicalization radius sets the scale for the onset of significant deformations of the collapsing configuration, which result in the formation of shock fronts. A characteristic observable feature of the classicalization process is the creation of an outgoing field configuration that extends far beyond the classicalization radius. This feature develops before the deformed wavepacket reaches distances of the order of the fundamental scale. We find that in some models the scattering problem may not have real solutions over the whole space at late times. We determine the origin of this behavior and discuss the consistency of the underlying models.Comment: 16 pages, 6 figures, published versio

On the dynamics of classicalization

We discuss the mechanism through which classicalization may occur during the collapse of a spherical field configuration modelled as a wavepacket. We demonstrate that the phenomenon is associated with the dynamical change of the equation of motion from a second-order partial differential equation of hyperbolic to one of elliptic type. Within this approach, we rederive the known expression for the classicalization radius. We also find indications that classicalization is associated with the absence of wave propagation at distances below the classicalization radius and the generation of shock fronts. The full quantitative picture can be obtained only through the numerical integration of a partial differential equation of mixed type.Comment: enhanced version, 6 pages, 2 figure

Black Hole Entropy and Gravity Cutoff

We study the black hole entropy as entanglement entropy and propose a resolution to the species puzzle. This resolution comes out naturally due to the fact that in the presence of $N$ species the universal gravitational cutoff is $\Lambda=M_{\rm Planck}/\sqrt{N}$, as opposed to $M_{\rm Planck}$. We demonstrate consistency of our solution by showing the equality of the two entropies in explicit examples in which the relation between $M_{\rm Planck}$ and $\Lambda$ is known from the fundamental theory.Comment: 11 pages, no figure

Consistency of Relevant Cosmological Deformations on all Scales

Using cosmological perturbation theory we show that the most relevant defor- mation of gravity is consistent at the linear level. In particular, we prove the absence of uni- tarity violating negative norm states in the weak coupling regime from sub- to super-Hubble scales. This demonstrates that the recently proposed classical self-protection mechanism of deformed gravity extends to the entire kinematical domain.Comment: 22 pages, 4 figure

Infinitely Large New Dimensions

We construct intersecting brane configurations in Anti-de-Sitter space localizing gravity to the intersection region, with any number $n$ of extra dimensions. This allows us to construct two kinds of theories with infinitely large new dimensions, TeV scale quantum gravity and sub-millimeter deviations from Newton's Law. The effective 4D Planck scale $M_{Pl}$ is determined in terms of the fundamental Planck scale $M_*$ and the $AdS$ radius of curvature $L$ via the familiar relation $M_{Pl}^2 \sim M_{*}^{2+n} L^n$; $L$ acts as an effective radius of compactification for gravity on the intersection. Taking $M_* \sim$ TeV and $L \sim$ sub-mm reproduces the phenomenology of theories with large extra dimensions. Alternately, taking $M_* \sim L^{-1} \sim M_{Pl}$, and placing our 3-brane a distance $\sim 100 M_{Pl}^{-1}$ away from the intersection gives us a theory with an exponential determination of the Weak/Planck hierarchy.Comment: 4 pages, revtex, no figure

Braneworld Flattening by a Cosmological Constant

We present a model with an infinite volume bulk in which a braneworld with a cosmological constant evolves to a static, 4-dimensional Minkowski spacetime. This evolution occurs for a generic class of initial conditions with positive energy densities. The metric everywhere outside the brane is that of a 5-dimensional Minkowski spacetime, where the effect of the brane is the creation of a frame with a varying speed of light. This fact is encoded in the structure of the 4-dimensional graviton propagator on the braneworld, which may lead to some interesting Lorentz symmetry violating effects. In our framework the cosmological constant problem takes a different meaning since the flatness of the Universe is guaranteed for an arbitrary negative cosmological constant. Instead constraints on the model come from different concerns which we discuss in detail.Comment: 18 pages, 3 figures RevTe

Regularization of Brane Induced Gravity

We study the regularization of theories of ``brane induced'' gravity in codimension $N>1$. The brane can be interpreted as a thin dielectric with a large dielectric constant, embedded in a higher dimensional space. The kinetic term for the higher dimensional graviton is enhanced over the brane. A four dimensional gravitation is found on the brane at distances smaller than a critical distance $r<r_c$, and is due to the exchange of a massive resonant graviton. The crossover scale $r_c$ is determined by the mass of the resonance. The suppression of the couplings of light Kaluza-Klein modes to brane matter results in a higher dimensional force law at large distances. We show that the resulting theory is free of ghosts or tachyons.Comment: One reference added. To appear in PRD. 20 pages, 3 figure

On Sub-Millimeter Forces From Extra Dimensions

We show that in theories with large extra dimensions forces mediated by a bulk dilaton and bulk gauge fields may be parametrically (exponentially) weaker than gravity due to the suppression of their wave-functions on a brane. This is the case when dilaton gets stabilized by certain strongly coupled dynamics on the brane, or the bulk gauge symmetries are spontaneously broken by the Higgs mechanism on the worldvolume. At distances smaller than the size of a largest extra dimension these particles produce the force-law which decreases with distance faster than high-dimensional gravity. For a millimeter size extra dimensions predicted deviations are in the range which may be detected in sub-millimeter gravity measurements.Comment: 11 page

New Dimensions at a Millimeter to a Fermi and Superstrings at a TeV

Recently, a new framework for solving the hierarchy problem has been proposed which does not rely on low energy supersymmetry or technicolor. The gravitational and gauge interactions unite at the electroweak scale, and the observed weakness of gravity at long distances is due the existence of large new spatial dimensions. In this letter, we show that this framework can be embedded in string theory. These models have a perturbative description in the context of type I string theory. The gravitational sector consists of closed strings propagating in the higher-dimensional bulk, while ordinary matter consists of open strings living on D3-branes. This scenario raises the exciting possibility that the LHC and NLC will experimentally study both ordinary aspects of string physics such as the production of narrow Regge-excitations of all standard model particles, as well more exotic phenomena involving strong gravity such as the production of black holes. The new dimensions can be probed by events with large missing energy carried off by gravitons escaping into the bulk. We finally discuss some important issues of model building, such as proton stability, gauge coupling unification and supersymmetry breaking.Comment: 12 pages, late

On the long-range gravity in warped backgrounds

In this paper the Randall-Sundrum model with brane-localized curvature terms is considered. Within some range of parameters a compact extra dimension in this model can be astronomically large. In this case the model predicts small deviation from Newton's law at astronomical scales, caused by the massive modes. The existence of this deviation can result in a slight affection on the planetary motion trajectories.Comment: LaTeX, 9 pages, typos corrected, reference adde