Closed String Tachyon Research Articles

Solvable time-dependent model and rolling closed string tachyon

We investigate the $SL(2,\mathbb{R})/U(1)$ WZW model with level $0<k<2$ as a solvable time-dependent background in string theory. This model is expected to be dual to the one describing a rolling closed string tachyon with a timelike linear dilaton. We examine its exact metric and minisuperspace wave functions. Two point functions and the one-loop vacuum amplitude are computed and their relation to the closed string emission is discussed. Comparing with the results from the minisuperspace approximation, we find a physical interpretation of our choice to continue the Euclidean model into the Lorentzian one. Three point functions are also examined.

Hartle-Hawking Vacuum for c=1 Tachyon Condensation

Quantum vacua are constructed for a time-symmetric cosmology describing closed string tachyon condensation in two-dimensional string theory. Due to the Euclidean periodicity of the solution, and despite its time dependence, we are able to construct thermal states at discrete values of the temperature. The asymptotic thermal Green functions and stress energy tensor are computed and found to have an intriguing resemblance to those in the Hartle-Hawking vacuum of a black hole.

Localized Tachyons and the Quantum McKay Correspondence

The condensation of closed string tachyons localized at the fixed point of a d/Γ orbifold can be studied in the framework of renormalization group flow in a gauged linear sigma model. The evolution of the Higgs branch along the flow describes a resolution of singularities via the process of tachyon condensation. The study of the fate of D-branes in this process has lead to a notion of a ``quantum McKay correspondence.'' This is a hypothetical correspondence between fractional branes in an orbifold singularity in the ultraviolet with the Coulomb and Higgs branch branes in the infrared. In this paper we present some nontrivial evidence for this correspondence in the case 2/n by relating the intersection form of fractional branes to that of ``Higgs branch branes,'' the latter being branes which wrap nontrivial cycles in the resolved space.

Localized tachyons inC3/ZN

We study the condensation of localized closed string tachyons in C^3/Z_N nonsupersymmetric noncompact orbifold singularities via renormalization group flows that preserve supersymmetry in the worldsheet conformal field theory and their interrelations with the toric geometry of these orbifolds. We show that for worldsheet supersymmetric tachyons, the endpoint of tachyon condensation generically includes ``geometric'' terminal singularities (orbifolds that do not have any marginal or relevant Kahler blowup modes) as well as singularities in codimension two. Some of the various possible distinct geometric resolutions are related by flip transitions. For Type II theories, we show that the residual singularities that arise under tachyon condensation in various classes of Type II theories also admit a Type II GSO projection. We further show that Type II orbifolds entirely devoid of marginal or relevant blowup modes (Kahler or otherwise) cannot exist, which thus implies that the endpoints of tachyon condensation in Type II theories are always smooth spaces.

Vacuum States in 2D Tachyon Effective Action

In this paper we will study ground states of the toy model of 2D closed string tachyon effective action. We will firstly construct the classical solutions of the tachyon effective action that do not induce backreaction on metric and dilaton. Then we will study the quantum mechanics of the zero mode of the tachyon field. We will find family of vacuum states that are labeled with single parameter. We will also perform the quantum mechanical analysis of the tachyon effective action when we take into account dynamics of nonzero modes. We will calculate the vacuum expectation values of components of the stress energy tensor and dilaton source and we will argue that there is not any backreaction on metric and dilaton.

Closed String Tachyons and Their Implications for Non-Supersymmetric Strings

Closed string tachyons have long been somewhat mysterious. We note that there is often a regime in the classical moduli space in which one can systematically compute the effective action for such fields. In this regime, the tachyon is light, and cannot be integrated out. Instead, one must consider the combined dynamics of gravitons, moduli, tachyons and other light fields. We compute the action and find that the quartic term for the tachyon is positive in the field definition where the tachyon has no derivative coupling to the radion. We study the evolution of isotropic, homogeneous configurations and find that typically the system is driven to regions where the calculation is no longer under control.

Twisting S-branes

Smooth time dependent supergravity solutions corresponding to analytic continuations of Kerr black holes are constructed and limits with a local de Sitter phase are found. These solutions are non-singular due to a helical twist in space and a fine tuning of the energy flow in the spacetime. For the extremal limit in which the mass and twist parameters are equal the S-brane undergoes de Sitter expansion. Subextremal limits show the formation and decay of a twisted circle and closed string tachyon condensation backreaction effects can be followed. For small values of the twist deformation, a short lived ergosphere envelopes the S-brane and leads to the production of closed timelike curves.

Closed String Tachyon Condensation atc=1

The c=1 matrix model, with or without a type 0 hat, has an exact quantum solution corresponding to closed string tachyon condensation along a null surface. The condensation occurs, and spacetime dissolves, at a finite retarded time on I^+. The outgoing quantum state of tachyon fluctuations in this time-dependent background is computed using both the collective field and exact fermion pictures. Perturbative particle production induced by the moving tachyon wall is shown to be similar to that induced by a soft moving mirror. Hence, despite the fact that I^+ for the tachyon is geodesicaly incomplete, quantum correlations in the incoming state are unitarily transmitted to the outgoing state in perturbation theory. It is also shown that, non-perturbatively, information can leak across the tachyon wall, and tachyon scattering is not unitary. Exact unitarity remains intact only in the free fermion picture.

Off-Shell Interactions for Closed-String Tachyons

Off-shell interactions for localized closed-string tachyons in C/Z_N superstring backgrounds are analyzed and a conjecture for the effective height of the tachyon potential is elaborated. At large N, some of the relevant tachyons are nearly massless and their interactions can be deduced from the S-matrix. The cubic interactions between these tachyons and the massless fields are computed in a closed form using orbifold CFT techniques. The cubic interaction between nearly-massless tachyons with different charges is shown to vanish and thus condensation of one tachyon does not source the others. It is shown that to leading order in N, the quartic contact interaction vanishes and the massless exchanges completely account for the four point scattering amplitude. This indicates that it is necessary to go beyond quartic interactions or to include other fields to test the conjecture for the height of the tachyon potential.

UV/IR mixing, noncommutative instabilites and closed strings

AbstractThe leading UV/IR mixing effects on noncommutative field theories modify the dispersion relations and, depending on their sign, may cause the appearance of unstable modes. For noncommutative gauge theories on D‐branes, this phenomenon is able to capture important information about the closed string spectrum of the parent string theory. We analyse noncommutative D‐branes on nonsupersymmetric orbifolds and twisted circle backgrounds. We find that the sign of the leading UV/IR mixing effects is governed by the mass gap between the lowest modes in the NSNS and RR closed string towers. For noncommutative D3‐branes at orbifolds we obtain a stronger result: a one to one correspondence between noncommutative instabilities and closed string tachyons.

Matrix Cosmology

Exact time-dependent solutions of c=1 string theory are described using the free fermion formulation. One such class of solutions describes draining of the Fermi sea and has a spacetime interpretation as closed string tachyon condensation. A second class of solutions, corresponding to droplets of Fermi liquid orbiting in phase space, describes closed cosmologies which bounce through singularities.

Closed string tachyon condensation: an overview

These notes are an expanded version of a review paper on closed string tachyon condensation at the RTN workshop in Copenhagen in September 2003. We begin with a lightning review of open string tachyon condensation, and then proceed to review recent results on localized closed string tachyon condensation, focusing on two simple systems, C/Zn orbifolds and twisted circle compactifications.

Decay Rates of Fixed Planes and Closed-String Tachyons on Unstable Orbifolds

We consider closed-string tachyon condensation in the twisted sectors on the C/Z_{2n+1} \times R^{7,1} orbifold. We calculate the localized energy density in the fixed plane on the orbifold at the one-loop level, and we obtain the decay rate per unit volume of the fixed plane to leading order. We show that the decay rate increases monotonically as a function of n.

THE SCHRÖDINGER WAVE FUNCTIONAL AND CLOSED STRING ROLLING TACHYON

In this paper we apply a Schrödinger picture description of the minisuperspace approach to the closed string tachyon condensation. We will calculate the rate of produced closed string and we will show that the density of high massive closed string modes reaches the string density in time of order one in string units.

Toward an open-closed string theoretical description of a rolling tachyon

We consider how the time-dependent decay process of an unstable D-brane should be described in the full (quantum) open-closed string theory. It is argued that the system, starting from the unstable D-brane configuration, will evolve in time into the time-independent open string tachyon vacuum configuration which we assume to be finite, with the total energy conserved. As a concrete realization of this idea, we construct a toy model describing the open and closed string tachyons which admits such a time-dependent solution. The structure of our model has some resemblance to that of open-closed string field theory.

Decay of type 0 Neveu-Schwarz 5-branes to nothing

The perturbative vacuum of type 0 string theory is unstable due to the existence of the closed string tachyon. This instability can be removed by ${\mathbf{S}}^{1}$ compactification with the twisted boundary condition for the tachyon field. We show that even in this situation unwrapped NS5-branes are unstable and decay to bubbles of nothing smoothly without tunneling any potential barrier. We discuss a relation between the closed string tachyon condensation and the instability of NS5-branes.

Tachyon condensation in open-closed p-adic string theory

We study a simple model of p-adic closed and open strings. It sheds some light on the dynamics of tachyon condensation for both types of strings. We calculate the effect of static and decaying D-brane configurations on the closed string background. For closed string tachyons we find lumps analogous to D-branes. By studying their fluctuation spectrum and the D-branes they admit, we argue that closed string lumps should be interpreted as spacetimes of lower dimensionality described by some noncritical p-adic string theory.

Rolling tachyons from Liouville theory

In this work we propose an exact solution of the c=1 Liouville model, i.e. of the world-sheet theory that describes the homogeneous decay of a closed string tachyon. Our expressions are obtained through careful extrapolation from the correlators of Liouville theory with c > 25. In the c=1 limit, we find two different theories which differ by the signature of Liouville field. The Euclidean limit coincides with the interacting c=1 theory that was constructed by Runkel and Watts as a limit of unitary minimal models. The couplings for the Lorentzian limit are new. In contrast to the behavior at c > 1, amplitudes in both c=1 models are non-analytic in the momenta and consequently they are not related by Wick rotation.

Engineering a Bosonic AdS/CFT Correspondence

We search for a bosonic (nonsupersymmetric) string/gauge theory correspondence by using the ten-dimensional IIB and 0B strings as a guide. Our construction is based on the low-energy bosonic string effective action modified by an extra form flux. We prove that the closed string tachyon can be stabilized in this context, when the AdS scalem L does not exceed a certain critical value, L<L c . The extra form may be nonperturbatively generated as a soliton from 3-string junctions, similarly to the known nonperturbative (Jackiw–Rebbi–'t Hooft–Hasenfratz) mechanism in gauge theories, as was recently argued by David, Minwalla and Núñez. We find a stable AdS 13×S13 solution that implies the existence of a 12-dimensional AdS-boundary conformal field theory with the SO(14) global symmetry in the large N't Hooft limit, which is similar to the recently proposed bosonic M-theory of Horowitz and Susskind. Taking the proposed bosonic AdS/CFT correspondence for granted, we generalize it to finite temperature. The corresponding "glueball" masses in higher space–time dimensions are calculated from the dilaton wave equation in the AdS black hole background.

Closed string tachyon condensation and worldsheet inflation

Closed string tachyon condensation in spacetime generates potentials on the worldsheet that model two-dimensional inflationary cosmology. These models illustrate and elucidate a variety of aspects of inflation, in particular the generation of quantum fluctuations and their back reaction on geometry. We exhibit a class of Liouville gravity models coupled to matter that can exhibit, for example, (a) pure de Sitter gravity, (b) slow-roll inflation, (c) topological inflation, and (d) graceful exit into a Friedmann-Robertson-Walker (FRW) phase. The models also provide a quantitative testing ground for ideas about the origin of inflation, such as the various ``no-boundary or tunnelling'' proposals, and the ``eternal or chaotic'' inflationary scenario. We suggest an alternative mechanism for quantum creation of cosmological spacetimes which, in the context of the model, provides a natural explanation for why the typical FRW cosmology at large scales underwent a period of inflation at small scale.