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Miao Li

Publications and source records attributed to Miao Li.

At least 271 records · Page 15Linked to original sources
arXiv2002

Note on Holographic RG Flow in String Cosmology

We propose a new holographic C-function for the accelerating universe defined in the stringy frame motivated mainly by the fact that the number of degrees of freedom should be infinite for a physical system of infinite size. This is the generalization of Strominger's recent proposal of the holographic C-function to the asymptotically non-de Sitter universe. We find that the corresponding C-theorem holds true if the universe accelerates toward the weak coupling regime driven by the exponential dilaton potential. It also holds in other simple cases.

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arXiv2001

Matrix Model for De Sitter

Based on a heuristic boost argument, we propose that the 4 dimensional de Sitter space can be described by a spherical Chern-Simons matrix model near the cosmological horizon, or models generalizing this simple choice. The dimension of the Hilbert space is naturally finite. We also make some comments on possible realization of holography in this approach, and on possible relation to the conformal field theory approach.

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arXiv2001

Dimensional Reduction via Noncommutative Spacetime: Bootstrap and Holography

Unlike noncommutative space, when space and time are noncommutative, it seems necessary to modify the usual scheme of quantum mechanics. We propose in this paper a simple generalization of the time evolution equation in quantum mechanics to incorporate the feature of a noncommutative spacetime. This equation is much more constraining than the usual Schrödinger equation in that the spatial dimension noncommuting with time is effectively reduced to a point in low energy. We thus call the new evolution equation the spacetime bootstrap equation, the dimensional reduction called for by this evolution seems close to what is required by the holographic principle. We will discuss several examples to demonstrate this point.

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arXiv2000

Quantum Corrections to Noncommutative Solitons

Noncommutative solitons are easier to find in a noncommutative field theory. Similarly, the one-loop quantum corrections to the mass of a noncommutative soliton are easier to compute, in a real scalar theory in 2+1 dimensions. We carry out this computation in this paper. We also discuss the model with a double-well potential, and conjecture that there is a partial symmetry restoration in a vacuum state.

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arXiv2000

Note on Noncommutative Tachyon in Matrix Models

The solution representing a brane-anti-brane system in matrix models breaks the usual matrix spacetime symmetry. We show that the spacetime symmetry on the branes is not breaking, rather appears as a combination of the matrix spacetime transformation and a gauge transformation. As a result, the tachyon field, itself an off-diagonal entry in longitudinal matrices, transforms nontrivially under rotations, decomposing into tensors of different ranks. We also show that the tachyon field can never be gauged away, and conjecture that this field is related to the usual complex scalar tachyon by a field redefinition. We also briefly discuss tachyon condensation.

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arXiv2000

Black Holes and Spacetime Physics in String/M Theory

In addition to briefly reviewing recent progress in studying black hole physics in string/M theory, we describe several robust features pertaining to spacetime physics that one can glean by studying quantum physics of black holes. In particular, we review 't Hooft's S-matrix ansatz which results in a noncommutative horizon. A recent construction of fuzzy AdS2 is emphasized, this is a nice toy model for fuzzy black hole horizon. We demonstrate that this model captures some nonperturbative features of quantum gravity.

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arXiv2000

Large N Expansion From Fuzzy AdS_2

We study the quantum analogue of primary fields and their descendants on fuzzy AdS_2, proposed in hep-th/0004072. Three-point vertices are calculated and shown to exhibit the conventional 1/N expansion as well as nonperturtive effects in large N, thus providing a strong consistency check of the fuzzy AdS_2 model. A few new physical motivations for this model are also presented.

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arXiv2000

Fuzzy Spheres in AdS/CFT Correspondence and Holography from Noncommutativity

We show that the existent fuzzy S^2 and S^4 models are natural candidates for the quantum geometry on the corresponding spheres in AdS/CFT correspondence. These models fit nicely the data from the dipole mechanism for the stringy exclusion principle. In the AdS_2 X S^2 case, we show that a wrapped fractional membrane can be used to count for the large ground state degeneracy. We also propose a fuzzy AdS_2 model whose fundamental commutation relation may underlie the UV/IR connection.

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arXiv2000

Fuzzy Gravitons From Uncertain Spacetime

The recently proposed remarkable mechanism explaining ``stringy exclusion principle" on an Anti de Sitter space is shown to be another beautiful manifestation of spacetime uncertainty principle in string theory as well as in M theory. Put in another way, once it is realized that the graviton of a given angular momentum is represented by a spherical brane, we deduce the maximal angular momentum directly from either the relation $ΔtΔx^2>l_p^3$ in M theory or $ΔtΔx>\ap$ in string theory. We also show that the result of hep-th/0003075 is similar to results on D2-branes in SU(2) WZW model. Using the dual D2-brane representation of a membrane, we obtain the quantization condition for the size of the membrane.

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arXiv1999

Matrix Theory in a Constant C Field Background

D0-branes moving in a constant antisymmetric C field are found to be described by quantum mechanics of the supersymmetric matrix model with a similarity transformation. Sometimes this similarity transformation is singular or ill-defined and cannot be ignored. As an example, when there are non-vanishing C_{-ij} components, we obtain the theory for Dp-branes which is effectively the noncommutative super Yang-Mills theory. We also briefly discuss the effects of other non-vanishing components such as C_{+ij} and C_{ijk}.

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arXiv1999

Holography and Noncommutative Yang-Mills

In this note a lately proposed gravity dual of noncommutative Yang-Mills theory is derived from the relations, recently suggested by Seiberg and Witten, between closed string moduli and open string moduli. The only new input one needs is a simple form of the running string tension as a function of energy. This derivation provides convincing evidence that string theory integrates with the holographical principle, and demonstrates a direct link between noncommutative Yang-Mills theory and holography.

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arXiv1999

On the Quantization of Nambu Brackets

We present several non-trivial examples of the three-dimensional quantum Nambu bracket which involve square matrices or three-index objects. Our examples satisfy two fundamental properties of the classical Nambu bracket: they are skew-symmetric and they obey the Fundamental Identity. We contrast our approach to the existing literature on the quantum deformations of Nambu mechanics. We also discuss possible applications of our results in M-theory.

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arXiv1999

Energy-Momentum Conservation and Holographic S-Matrix

We investigate the consequence of the energy-momentum conservation law for the holographic S-matrix from AdS/CFT correspondence. It is shown that the conservation law is not a natural consequence of conformal invariance in the large N limit. We predict a new singularity for the four point correlation function of a marginal operator. Only the two point scattering amplitude is explicitly calculated, and the result agrees with what is expected.

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arXiv1999

Ten Dimensional Black Hole and the D0-brane Threshold Bound State

We discuss the ten dimensional black holes made of D0-branes in the regime where the effective coupling is large, and yet the 11D geometry is unimportant. We suggest that these black holes can be interpreted as excitations over the threshold bound state. Thus, the entropy formula for the former is used to predict a scaling region of the wave function of the latter. The horizon radius and the mass gap predicted in this picture agree with the formulas derived from the classical geometry.

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arXiv1999

Large N Strong/Weak Coupling Phase Transition and the Correspondence Principle

We argue that the large N strong/weak phase transition is a generic phenomenon in a finite temperature supersymmetric Yang-Mills theory of maximal supersymmetry. ${\cal N}=4$, D=4 SYM is the canonical example, where we also argue that the large N Hawking-Page phase transition disappears for a sufficiently small coupling. The Hawking-Page transition temperature is lowered by the first $\ap$ correction. Physically, the strong/weak phase transition is identified with the correspondence point of Horowitz and Polchinski. We also try to construct toy models to demonstrate the large N phase transitions, with limited success.

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arXiv1998

Introduction to M Theory

This is an introduction to some recent developments in string theory and M theory. We try to concentrate on the main physical aspects, and often leave more technical details to the original literature.

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arXiv1998

Black Holes and the SYM Phase Diagram

Making combined use of the Matrix and Maldacena conjectures, the relation between various thermodynamic transitions in super Yang-Mills (SYM) and supergravity is clarified. The thermodynamic phase diagram of an object in DLCQ M-theory in four and five non-compact space dimensions is constructed; matrix strings, matrix black holes, and black $p$-branes are among the various phases. Critical manifolds are characterized by the principles of correspondence and longitudinal localization, and a triple point is identified. The microscopic dynamics of the Matrix string near two of the transitions is studied; we identify a signature of black hole formation from SYM physics.

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