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Extremal N=2 2D CFT’s and Constraints of Modularity . IAS, October 3, 2008 . Work done with M. Gaberdiel, S. Gukov, C. Keller and H. Ooguri arXiv:0805.4216. …. TexPoint fonts used in EMF: A A A A A A A A A A A A A. Outline. 1. Two Motivations 2. Results

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## Extremal N=2 2D CFT’s and Constraints of Modularity

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**Extremal N=2 2D CFT’s and Constraints of Modularity**IAS, October 3, 2008 Work done with M. Gaberdiel, S. Gukov, C. Keller and H. Ooguri arXiv:0805.4216 … TexPoint fonts used in EMF: AAAAAAAAAAAAA**Outline**1. Two Motivations 2. Results 3. Extremal N=0 and N=1 theories 4. 2D N=2 Theories: Elliptic Genus + Polarity 5. Counting Polar Terms 6. Search for Extremal N=2 theories 7. Near Extremal N=2 Theories 8. Possible Applications to the Landscape 9. Summary & Concluding Remarks**Motivation 1**• An outstanding question in theoretical physics is the existence of three-dimensional AdS ``pure quantum gravity.’’ • Witten proposed that it should be defined by a holographically dual ``extremal CFT.’’ • We do not know if such CFT’s exist for general central charge c=24 k, k> 1. • In AdS3 one can defineOSp(p|2)xOSp(q|2) sugra dual to theories • with (p,q) supersymmetry. • What can we say about those?**Motivation 2**• There are widely-accepted claims of the existence of a • ``landscape’’ of d=4 N=1 AdS solutions of string theory • with all moduli fixed. • The same techniques should apply to M-theory • compactifications on – say – CY 4-folds to AdS3. • Such backgrounds would be holographically dual to 2D CFT • Does modularity of partition functions put any interesting • constraints on the landscape?**Result 1**• We give a natural definition of an ``extremal N=(2,2) CFT’’ • And we then show that there are at most a finite number of ``exceptional’’ examples**Result -2**We present evidence for the following conjecture: Any N=(2,2) CFT must contain a state of the form:**Result - 3**The bound is nearly optimal: There are candidate partition functions (elliptic genera) where all states with are descendents of the vacuum.**Extremal Conformal Field Theory**Definition: An extremal conformal field theory of level k is a CFT with c=24k with a (weight zero) modular partition function ``as close as possible’’ to the vacuum Virasoro character. Not modular**Reconstruction Theorem**Define the polar polynomial of Zk to be the sum of terms with nonpositive powers of q. The weight zero modular function Zk can be uniquely reconstructed from its polar polynomial: This is the step which will fail (almost always) in the N=(2,2) case.**Witten’s proposal for pure 3D quantum gravity**The holographic dual of pure AdS3 quantum gravity is a left-right product of extremal conformal field theories. Justification: Chern-Simons form of action Polar terms: Chiral edge states (Brown-Henneaux) Nonpolar terms: Black holes (c.f. Fareytail)**N=1 Theories**Witten already pointed out that there is an analog of the j-function for the modular group preserving a spin structure on the torus. Therefore one can construct the analog of extremal N=1 partition functions for the NS and R sectors. We will return to N=1 later, but for now let us focus on N=2.**Pure N=(2,2) AdS3 supergravity**N=(2,2) AdS3 supergravity can be written as a Chern-Simons theory for OSp(2|2) x OSp(2|2) A natural extension of Witten’s conjecture is that pure N=(2,2) sugra is dual to an ``extremal (2,2) SCFT’’**Extremal N=(2,2) SCFT**Define an extremal N=(2,2) theory to be a theory whose partition function is ``as close as possible’’ to the vacuum character: It is useful to parametrize c= 6 m This is neither spectral flow invariant, nor modular invariant.**Extremal N=(2,2) SCFT – II**Impose spectral flow by hand So, more precisely, an extremal N=(2,2) CFT is a CFT with a modular and spectral flow invariant partition function of the above form.**Cosmic Censorship Bound**Black holes with near horizon geometry Must satisfy the cosmic censorship bound Cvetic & Larsen**Elliptic Genus**Modular: Spectral flow invariant: (Assume: m integer, U(1) charges integral.)**Do such weak Jacobi forms exist?**Extremal Elliptic Genus**Reconstruction Theorem**Dijkgraaf, Maldacena, Moore, Verlinde; Manschot & Moore**Obstructions**However, some polar polynomials cannot be extended to a full weak Jacobi form! Does not converge. It must be regulated. The regularization can spoil modular invariance Knopp; Niebur; Manschot & Moore**Computer Search**Recall P(m)>j(m) for m>4. Is there magic?**Not Much Magic**We find five ``exceptional solutions’’**Finiteness Theorem**Theorem: There is an M such that for m> M an extremal elliptic genus does not exist. Difficult proof. Compare the elliptic genus at The NS and R cusps to derive the constraint**Numerical analysis strongly indicates**that our five exceptional solutions are indeed the only ones. All this suggests that there are at most a finite number of pure N=(2,2) supergravity theories. But….**Near-Extremal Theories**Perhaps our definition of ``extremal’’ was too restrictive… Maybe there are quantum corrections to the cosmic censorship bound… Define a b-extremal N=2 CFT by only demanding agreement of the polar terms with the vacuum character for polarity less than or equal to - b**Escape Hatch for Pure N=2 Sugra?**suggests a loophole: Perhaps there are quantum corrections to the cosmic censorship bound. Perhaps pure N=2 sugra exists, and P(m)-j(m) polar quantum numbers in fact admit states which are semiclassically described as black holes (or other nondescendent geometries).**Bound on Conformal Weight**Also implies an interesting bound on the conformal weight of the first N=2 primary. There must be some polar-state which is NOT a descendent and satisfies**Bound on Conformal Weight-2**Conclusion: The conjecture implies that for any unitary N=(2,2) theory there must exist a state of the form**Explicit Construction of Nearly Extremal Elliptic Genera**We can explicitly construct elliptic genera so that only descendents of the vacuum contribute to the polar subregion: So our bound is close to optimal. Gritsenko**Flux Compactifications**(Discussions with T. Banks, F. Denef M. Gaberdiel, C. Keller, J. Maldacena)**Existence of a Hauptmodul K: There are**no restrictions on the polar polynomial However, given the polar piece, modularity does make predictions about the degeneracies at h=c/24 +a, a=1/2, 1,3/2,… Characterize the flux vacuum by c & J**Single Particle Spectrum**Planck scale Kaluza-Klein mode Complex modulus Kahler modulus Vacuum Large c, moderate J: ``Near extremal’’**Supergravity Fock Space**Supplies polar polynomial**Optimistically – one could estimate the**degeneracies at h= c/24 + a, a=1/2, 1, 3/2,… Modularity: Descendents: • J<<1: Contradiction with EFT • J>>1: No contradiction. But large • degeneracy might possibly invalidate EFT

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