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Brane Gas Cosmology, M-Theory and Little String Theory Provided by CERN Document Server View metadata,∗ citation and similar papers at core.ac.uk brought to you by CORE Brane Gas Cosmology, M-theory and Little String Theory provided by CERN Document Server Stephon H.S Alexander SLAC and Institute for Theoretical Physics, Stanford University, Stanford,CA 94305 We generalize the Brane Gas Cosmological Scenario to M-theory degrees of freedom, namely M5 and M2 branes. Without brane intersections, the Brandenberger Vafa(BV) arguments applied to M-theory degrees of freedom generically predict a large 6 dimensional spacetime. We show that intersections of M5andM2 branes can instead lead to a large 4 dimensional spacetime. One dimensional intersections in 11D is related to (2,0) little strings (LST) on NS5 branes in type IIA. The gas regime of membranes in M-theory corresponds to the thermodynamics of LST obtained from holography. We propose a mechanism whereby LST living on the worldvolume of NS5 (M5)-branes wrapping a five dimensional torus, annihilate most efficiently in 3+1 dimensions leading to a large 3+1 dimensional spacetime. We also show that this picture is consistent with the gas approximation in M-theory. I. INTRODUCTION where strings are not present as fundamental degrees of freedom†. We are also motivated to see how hologra- The Brane Gas Cosmological scenario (BGC) provides phy can play a role in describing the thermodynamics of a unification of Cosmology with String Theory [1–8]. the early universe. What we will discover is that these This is acheived by addressing the dimensionality prob- two motivations are intimately connected and leads to a lem present in String theory by a dynamical decompact- picture which dovetails the original proposal of Branden- ification mechanism which involves the unwinding of an- berger and Vafa on string gases in the early universe. nihilating D-branes. BGC also resolves the initial cur- The original paper on BGC examined a cosmological vature singularities which plague the standard big bang scenario where a gas of strings and branes were wrapped scenario by implementing T-duality of the space-time as over all cycles of T 9. While further research has ad- the radius of the Universe tends to zero∗. dressed more general background topologies such as orb- A key ingredient in BGC is that strings dominate the ifolds and inhomogenous space-times [5,7,9], no proce- dynamics of the universe leading to decompactification dure has yet emerged that generalizes brane gases in of 3 large spatial dimensions. The Brandenberger-Vafa which the dynamics of M2andM5 branes play a central (BV) mechanism which is central to BGC, posits that role. A related problem is that typical scenarios based on strings see each other most efficiently in 2(p +1)(p=1 string theory contain a plethora of extended objects. By for strings) dimensions [1,2,11]. Therefore, their winding reducing the dynamics to that of only two fundamental modes will annihilate most efficiently in 3 + 1 dimensions degrees of freedom, one hopes to obtain a clearer picture and this leads to a decompactification in those dimen- of the BGC mechanism. In an earlier version of BGC, sions. The strings moving in higher dimensions eventu- to evade the complications of dealing with complex con- ally cease to interact efficiently and will fall out of equi- figurations and interactions of brane gases, the authors librium. Their winding modes will prevent those higher of [3](ABE) only considered parallel interactions of D- dimensions from further expanding. branes with the same RR charges. The BV mechanism was originally analyzed in the con- It is the purpose of this paper to initiate an investi- text of perturbative string theory. We know that type II gation of some of the above mentioned outstanding is- string theories at strong coupling becomes M-theory in sues in BGC. We will show that, by going directly to the 11 dimensions. In this, M5andM2 branes play a funda- fundamental states of M-theory, the BGC scenario sim- mental role. It is, therefore, important to reconsider the plifies and also generalizes to intersections and a strong ubiquity of the BGC mechanism in all corners of mod- coupling regime. In this situation we can use 11D su- uli space and, in particular, the 11 dimensional corner pergravity and the worldvolume actions of M2andM5 branes to analyze BGC. ∗The issue of implementing T-duality for timelike singulari- ties is still under investigation and is not as yet resolved. In yBrane Gases in 11D Supergravity was recently investigated our case we assume that for each constant time slice one can by [6]. map winding states on small radius to momentum states on large radius. [10] 1 II. BRANE GASES IN M-THEORY:GENERAL The general setting starts with all branes and their SETTING intersections wrapping cycles of all dimensions small with respect to the string length scale. In this case all branes 10;1 Brane Gases have been formulated in the weak string wrap T ‡ . The equilibrium condition coupling regime in Type IIA where g < 1 [3]. In this s * regime BGC was studied using IIA supergravity. The wp +¯wp ) loops; radiation (2) zero mode fluctuation of p-brane winding and momentum states that there is an equal number of branes and anti- states were obtained from linearized fluctuations of the branes in the system interacting. However, we expect Dira-Born-Infeld (DBI) action. In a toroidal geometry the system to fall out of equilibrium when the wind- ABE [3] were able to show that a hierarchy of dimensions ing degrees of freedom cease to interact. Moreover, the decompactify resulting in three large spatial dimensions breakdown of thermal equlibrium is suggested by exceed- with two smaller extra dimensions. However, the exact ing the Hagedorn temperature which is lower for higher scaling of the hierarchy was not determined. Can we dimensional branes, so they are expected to fall out of gain more information about the scaling in dimensions equilibrium faster than lower dimensional branes. Hence by going to strong coupling? we expect the five-branes to fall out of equilibrium faster The strong coupling limit of IIA is 11 dimensional than the membranes. supergravity(SUGRA), whose fundamental degrees of We are working in 11 dimensional supergravity and freedom are M2andM5 branes. We wish to study gases there is no dilaton which in ten dimensional string theory, of intersecting M2andM5 branes and generalize the na- plays a key role to dynamically prevent cycles from ex- ture of the intersection. While our philosophy is rooted in panding in the presence of winding modes. Therefore, in the standard big bang scenario where the early universe the 11 dimensional regime, it is necessary to to show that existed in a hot dense state with all degrees of freedom branes wrapped on cycles will keep the dimensions from excited, it is not a prediction of M-theory as to how extra expanding; in other words there exists a confining poten- spatial dimensions could start off small. tial for the modulus of the cycle. The most straightfor- Our starting point closely dovetails the standard hot ward way to show this is to work in a toroidal coordinate big bang where all fundamental degrees of freedom are system that is time dependent in an 11-d SUGRA back- excited and in thermal equilibrium with all dimensions ground. For simplicity we shall assume homogeneity of small and compact. While we do not know what the the background and adiabacity of the evolution. We will quantum version of M-theory is, 11-D SUGRA is ex- discover that these assumptions are to weak to explain pected to be the classical limit. We shall analyze our how membrane winding states can prevent expansion of cosmology with an interplay between 11-D SUGRA and the cycles they wrap. Nonetheless, one will be able to the effective worldvolume actions of M2andM5 branes. isolate exactly where the assumptions break down. The Let us start with the bosonic sector of 11D SUGRA. issue of the confining nature of wrapping membranes in 1 M-theory was resolved by [6]. S = d11x√ g(R + F 2 + F F A )(1) κ9 Z − [4] [4] ∧ [4] ∧ [3] We consider the wrapping of a membrane at rest along a two cycle. We want to find its equation of state which where dA = F is a four form field strength tensor. [3] [4] can be obtained from finding the energy-momemtum ten- The dual of F is a seven form which couples to the [4] sor of the membrane in its wrapped configuration. The worldvolume of the fivebrane. This state in 11-D is iden- relevant bosonic part of the membrane action is described tified with the M5 brane, which is the magnetic dual by the Nambu-Goto action of the M2 brane. The potential A is a threeform and therefore couples to a M2 brane. Now consider a gas T d3σ detg (3) of M5andM2 branes which are not interacting with 2 ab Z p− each other. Since the five branes are heavier they will fall out of equilibrium faster than the M2 branes and where T2 is the tension of the membrane. To find its their winding modes will cease to annihilate. Membranes energy momentum tensor with respect to the 11 dimen- will dominate the dynamics at later times and according sion space-time we will vary the membrane action with to the BV topological arguments, 6 larger space-time di- respect to the background metric Gµν defined as mensions will get big since the membrane winding modes a b Gµν = gabX X (4) annihilate most efficiently in these dimensions. At this ,µ ,ν point, it is still not clear to realize three large spatial di- The action is then mensions directly from M-theory dynamics.
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