arXiv subjects

Thomas S. Levi

Publications and source records attributed to Thomas S. Levi.

At least 19 recordsLinked to original sources

arXiv2011

Observing the Multiverse with Cosmic Wakes

Current theories of the origin of the Universe, including string theory, predict the existence of a multiverse containing many bubble universes. These bubble universes will generically collide, and collisions with ours produce cosmic wakes that enter our Hubble volume, appear as unusually symmetric disks in the cosmic microwave background (CMB) and disturb large scale structure (LSS). There is preliminary observational evidence consistent with one or more of these disturbances on our sky. However, other sources can produce similar features in the CMB temperature map and so additional signals are needed to verify their extra-universal origin. Here we find, for the first time, the detailed three-dimensional shape and CMB temperature and polarization signals of the cosmic wake of a bubble collision in the early universe consistent with current observations. The predicted polarization pattern has distinctive features that when correlated with the corresponding temperature pattern are a unique and striking signal of a bubble collision. These features represent the first verifiable prediction of the multiverse paradigm and might be detected by current experiments such as Planck and future CMB polarization missions. A detection of a bubble collision would confirm the existence of the Multiverse, provide compelling evidence for the string theory landscape, and sharpen our picture of the Universe and its origins.

astro-ph.CO↗

arXiv2011

Vacuum decay in multidimensional field landscapes: thin, thick and intersecting walls

We study tunneling between vacua in multi-dimensional field spaces. Working in the strict thin wall approximation, we find that the conventional instantons for false vacuum decay develop a new vanishing eigenvalue in their fluctuation determinant, arising from decorations of the nucleating bubble wall with small spots of the additional vacua. Naively, this would suggest that the presence of additional vacua in field space leads to a substantial enhancement of the nucleation rate. However, we argue that this potential enhancement is regulated away by the finite thickness of physical bubble wall intersections. We then discuss novel saddle points of the thin wall action that, in some regimes of parameter space, have the potential to destabilize the conventional instantons for false vacuum decay.

hep-th↗

arXiv2011

Polarizing Bubble Collisions

We predict the polarization of cosmic microwave background (CMB) photons that results from a cosmic bubble collision. The polarization is purely E-mode, symmetric around the axis pointing towards the collision bubble, and has several salient features in its radial dependence that can help distinguish it from a more conventional explanation for unusually cold or hot features in the CMB sky. The anomalous "cold spot" detected by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite is a candidate for a feature produced by such a collision, and the Planck satellite and other proposed surveys will measure the polarization on it in the near future. The detection of such a collision would provide compelling evidence for the string theory landscape.

astro-ph.CO↗

arXiv2010

Bubble, Bubble, Flow and Hubble: Large Scale Galaxy Flow from Cosmological Bubble Collisions

We study large scale structure in the cosmology of Coleman-de Luccia bubble collisions. Within a set of controlled approximations we calculate the effects on galaxy motion seen from inside a bubble which has undergone such a collision. We find that generically bubble collisions lead to a coherent bulk flow of galaxies on some part of our sky, the details of which depend on the initial conditions of the collision and redshift to the galaxy in question. With other parameters held fixed the effects weaken as the amount of inflation inside our bubble grows, but can produce measurable flows past the number of efolds required to solve the flatness and horizon problems.

hep-th↗

arXiv2010

Twisted Inflation

We present a new mechanism for slow-roll inflation based on higher dimensional supersymmetric gauge theory compactified to four dimensions with twisted (supersymmetry breaking) boundary conditions. These boundary conditions lead to a potential for directions in field space that would have been flat were supersymmetry preserved. For field values in these directions much larger than the supersymmetry-breaking scale, the flatness of the potential is nearly restored. Starting in this nearly flat region, inflation can occur as the theory relaxes towards the origin of field space. Near the origin, the potential becomes steep and the theory quickly descends to a confining gauge theory in which the inflaton does not exist as a particle. This confining gauge theory could be part of the Standard Model (QCD) or a natural dark matter sector; we comment on various scenarios for reheating. As a specific illustration of this mechanism, we discuss 4+1 dimensional maximally supersymmetric gauge theory on a circle with antiperiodic boundary conditions for fermions. When the theory is weakly coupled at the compactification scale, we calculate the inflaton potential directly in field theory by integrating out the heavy W-bosons and their superpartners. At strong coupling the model can be studied using a gravity dual, which realizes a new model of brane inflation on a non-supersymmetric throat geometry. Assuming there exists a UV completion that avoids the eta-problem, predictions from our model are consistent with present observations, and imply a small tensor-to-scalar ratio.

hep-th↗

arXiv2009

Godel space from wrapped M2-branes

We show that M-theory admits a supersymmetric compactification to the Godel universe of the form Godel3 x S2 x CY3. We interpret this geometry as coming from the backreaction of M2-branes wrapping the S2 in an AdS3 x S2 x CY3 flux compactification. In the black hole deconstruction proposal similar states give rise to the entropy of a D4-D0 black hole. The system is effectively described by a three-dimensional theory consisting of an axion-dilaton coupled to gravity with a negative cosmological constant. Other embeddings of the three-dimensional theory imply similar supersymmetric Godel compactifications of type IIA/IIB string theory and F-theory.

hep-th↗

arXiv2009

Watching Worlds Collide: Effects on the CMB from Cosmological Bubble Collisions

We extend our previous work on the cosmology of Coleman-de Luccia bubble collisions. Within a set of approximations we calculate the effects on the cosmic microwave background (CMB) as seen from inside a bubble which has undergone such a collision. We find that the effects are always qualitatively similar--an anisotropy that depends only on the angle to the collision direction--but can produce a cold or hot spot of varying size, as well as power asymmetries along the axis determined by the collision. With other parameters held fixed the effects weaken as the amount of inflation which took place inside our bubble grows, but generically survive order 10 efolds past what is required to solve the horizon and flatness problems. In some regions of parameter space the effects can survive arbitrarily long inflation.

hep-th↗

arXiv2007

When Worlds Collide

We analyze the cosmological signatures visible to an observer in a Coleman-de Luccia bubble when another such bubble collides with it. We use a gluing procedure to generalize the results of Freivogel, Horowitz, and Shenker to the case of a general cosmological constant in each bubble and study the resulting spacetimes. The collision breaks the isotropy and homogeneity of the bubble universe and provides a cosmological "axis of evil" which can affect the cosmic microwave background in several unique and potentially detectable ways. Unlike more conventional perturbations to the inflationary initial state, these signatures can survive even relatively long periods of inflation. In addition, we find that for a given collision the observers in the bubble with smaller cosmological constant are safest from collisions with domain walls, possibly providing another anthropic selection principle for small positive vacuum energy.

hep-th↗

arXiv2007

Black Ring Deconstruction

We present a sample microstate for a black ring in four and five dimensional language. The microstate consists of a black string microstate with an additional D6-brane. We show that with an appropriate choice of parameters the piece involving the black string microstate falls down a long AdS throat, whose M-theory lift is AdS_3 X S^2. We wrap a spinning dipole M2-brane on the S^2 in the probe approximation. In IIA, this corresponds to a dielectric D2-brane carrying only D0-charge. We conjecture this is the first approximation to a cloud of D0-branes blowing up due to their non-abelian degrees of freedom and the Myers effect.

hep-th↗

arXiv2007

Geometry of non-supersymmetric three-charge bound states

We study the smooth non-supersymmetric three-charge microstates of Jejjala, Madden, Ross and Titchener [hep-th/0504181] using Kaluza-Klein reductions of the solutions to five and four dimensions. Our aim is to improve our understanding of the relation between these non-supersymmetric solutions and the well-studied supersymmetric cases. We find some surprising qualitative differences. In the five-dimensional description, the solution has orbifold fixed points which break supersymmetry locally, so the geometries cannot be thought of as made up of separate half-BPS centers. In the four-dimensional description, the two singularities in the geometry are connected by a conical singularity, which makes it impossible to treat them independently and assign unambiguous brane charges to these centers.

hep-th↗

arXiv2007

Mesons and Flavor on the Conifold

We explore the addition of fundamental matter to the Klebanov-Witten field theory. We add probe D7-branes to the ${\cal N}=1$ theory obtained from placing D3-branes at the tip of the conifold and compute the meson spectrum for the scalar mesons. In the UV limit of massless quarks we find the exact dimensions of the associated operators, which exhibit a simple scaling in the large-charge limit. For the case of massive quarks we compute the spectrum of scalar mesons numerically.

hep-th↗

arXiv2007

Four Dimensional Black Hole Microstates: From D-branes to Spacetime Foam

We propose that every supersymmetric four dimensional black hole of finite area can be split up into microstates made up of primitive half-BPS "atoms''. The mutual non-locality of the charges of these "atoms'' binds the state together. In support of this proposal, we display a class of smooth, horizon-free, four dimensional supergravity solutions carrying the charges of black holes, with multiple centers each carrying the charge of a half-BPS state. At vanishing string coupling the solutions collapse to a bound system of intersecting D-branes. At weak coupling the system expands into the non-compact directions forming a topologically complex geometry. At strong coupling, a new dimension opens up, and the solutions form a "foam'' of spheres threaded by flux in M-theory. We propose that this transverse growth of the underlying bound state of constitutent branes is responsible for the emergence of black hole horizons for coarse-grained observables. As such, it suggests the link between the D-brane and "spacetime foam'' approaches to black hole entropy.

hep-th↗

arXiv2005

Supergravity Microstates for BPS Black Holes and Black Rings

We demonstrate a solution generating technique, modulo some constraints, for a large class of smooth supergravity solutions with the same asymptotic charges as a five dimensional 3-charge BPS black hole or black ring, dual to a D1/D5/P system. These solutions are characterized by a harmonic function with both positive and negative poles, which induces a geometric transition whereby singular sources have disappeared and all of the net charge at infinity is sourced by fluxes through two-cycles joining the poles of the harmonic function.

hep-th↗

arXiv2004

Beyond the veil: Inner horizon instability and holography

We show that scalar perturbations of the eternal, rotating BTZ black hole should lead to an instability of the inner (Cauchy) horizon, preserving strong cosmic censorship. Because of backscattering from the geometry, plane wave modes have a divergent stress tensor at the event horizon, but suitable wavepackets avoid this difficulty, and are dominated at late times by quasinormal behavior. The wavepackets have cuts in the complexified coordinate plane that are controlled by requirements of continuity, single-valuedness and positive energy. Due to a focusing effect, regular wavepackets nevertheless have a divergent stress-energy at the inner horizon, signaling an instability. This instability, which is localized behind the event horizon, is detected holographically as a breakdown in the semiclassical computation of dual CFT expectation values in which the analytic behavior of wavepackets in the complexified coordinate plane plays an integral role. In the dual field theory, this is interpreted as an encoding of physics behind the horizon in the entanglement between otherwise independent CFTs.

hep-th↗

arXiv2004

Open Strings from N=4 Super Yang-Mills

Exploiting insights on strings moving in pp-wave backgrounds, we show how open strings emerge from N = 4 SU(M) Yang-Mills theory as fluctuations around certain states carrying R-charge of order M. These states are dual to spherical D3-branes of AdS_5 x S^5 and we reproduce the spectrum of small fluctuations of these states from Yang Mills theory. When G such D3-branes coincide, the expected G^2 light degrees of freedom emerge. The open strings running between the branes can be quantized easily in a Penrose limit of the spacetime. Taking the corresponding large charge limit of the Yang-Mills theory, we reproduce the open string worldsheets and their spectra from field theory degrees of freedom.

hep-th↗

arXiv2003

A comment on multiple vacua, particle production and the time dependent AdS/CFT correspondence

We give an explicit formulation of the time dependent AdS/CFT correspondence when there are multiple vacua present in Lorentzian signature. By computing sample two point functions we show how different amplitudes are related by cosmological particle production. We illustrate our methods in two example spacetimes: (a) a ``bubble of nothing'' in AdS space, and (b) an asymptotically locally AdS spacetime with a bubble of nothing on the boundary. In both cases the alpha vacua of de Sitter space make an interesting appearance.

hep-th↗

arXiv2003

Holography beyond the horizon and cosmic censorship

We investigate the description of the region behind the event horizon in rotating black holes in the AdS/CFT correspondence, using the rotating BTZ black hole as a concrete example. We extend a technique introduced by Kraus, Ooguri and Shenker [hep-th/0212277], based on analytically continuing amplitudes defined in a Euclidean space, to include rotation. In the rotating case, boundary amplitudes again have two different bulk descriptions, involving either integration only over the regions outside the black holes' event horizon, or integration over this region and the region between the event horizon and the Cauchy horizon (inner horizon). We argue that generally, the holographic map will relate the field theory to the region bounded by the Cauchy horizons in spacetime. We also argue that these results suggest that the holographic description of black holes will satisfy strong cosmic censorship.

hep-th↗

arXiv2002

Gauged Fermionic Q-balls

We present a new model for a non-topological soliton (NTS) that contains interacting fermions, scalar particles and a gauge field. Using a variational approach, we estimate the energy of the localized configuration, showing that it can be the lowest energy state of the system for a wide range of parameters.

hep-ph↗