28,456 research outputs found

    A New Model of Holographic Dark Energy with Action Principle

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    We propose a new model of holographic dark energy with an action. It is the first time that one can derive a HDE model from the action principle. The puzzles of causality and circular logic about HDE have been completely solved in this model. The evolution of the universe only depends on the present state of the universe, clearly showing that it obeys the law of causality. Furthermore, the use of future event horizon as a present cut-off is not an input but automatically follows from equations of motion. Interestingly, this new model is very similar to the initial one of Li except a new term which may be explained as dark radiation.Comment: 11 pages, no figures, typo corrected, English improve

    Degrees of freedom of f(T)f(T) gravity

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    We investigate the Hamiltonian formulation of f(T)f(T) gravity and find that there are five degrees of freedom. The six first class constraints corresponding to the local Lorentz transformation in Teleparallel gravity become second class constraints in f(T)f(T) gravity, which leads to the appearance of three extra degrees of freedom and the violation of the local Lorentz invariance in f(T)f(T) gravity. In general, there are D1D-1 extra degrees of freedom for f(T)f(T) gravity in DD dimensions, and this implies that the extra degrees of freedom correspond to one massive vector field or one massless vector field with one scalar field.Comment: 18 pages, some references added, minor revision to appear in JHE

    Quantum Corrections to Noncommutative Solitons

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    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.Comment: 19 pages, harvmac. v2: a ref. added, minor typos correcte

    Energy-Momentum Conservation and Holographic S-Matrix

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    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.Comment: 16 pages, harvma

    Comments on Supersymmetric Yang-Mills Theory on a Noncommutative Torus

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    D0-brane theory on a torus with a nonvanishing B field is embedded into a string theory in the weak coupling limit. It is shown that the usual supersymmetric Yang-Mills theory on a noncommutative torus can not be the whole story. The Born-Infeld action survives the noncommutative torus limit.Comment: 11 pages, two attached figures, harvma

    A proposal on the topological sector of 2d string

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    The field content of the two dimensional string theory consists of the dynamical tachyon field and some nonpropagating fields which consist in the topological sector of this theory. We propose in this paper to study this topological sector as a spacetime gauge theory with a simple centrally extended ww_\infty algebra. This ww_\infty algebra appears in both the world sheet BRST analysis and the matrix model approach. Since the two dimensional centrally extended Poincar\'e algebra is naturally embedded in the centrally extended ww_\infty algebra, the low energy action for the metric and dilaton appears naturally when the model is truncated at this level. We give a plausible explanation of emergence of discrete states in this formulation. This theory is again the effective theory at zero slope limit. To include higher order α\alpha' corrections, we speculate that the whole theory is a gauge theory of a deformed ww_\infty algebra, and the deformation parameter is just α\alpha'.Comment: no major changes in revisio

    Correlators of Special States in c=1 Liouville Theory

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    We generalize the ground ring structure to all special BRST invariant operators in the right branch in the c=1 Liouville theory. We also discuss correlation functions of special states on the sphere.Comment: 17 page

    Gluino Condensation in F-theory

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    Coupling of bilinears of gauginos on D-branes to anti-symmetric tensor fields can be deduced by comparing F-theory compactified to 8 dimensions with the heterotic string on R8×T2R^8\times T^2. Application to SUSY breaking in F-theory triggered by gaugino condensation is discussed. Compactification to four dimensions with a warp factor is briefly discussed. In this case some 3-branes whose world-volume coincides with the open spacetime must be introduced, in addition to 7-branes.Comment: 11 pages, harvmac. One mistake and some typos corrected, two references adde

    Black Holes and Spacetime Physics in String/M Theory

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    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.Comment: 33 pages, harvma

    Dirichlet String Theory and Singular Random Surfaces

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    We show that string theory with Dirichlet boundaries is equivalent to string theory containing surfaces with certain singular points. Surface curvature is singular at these points. A singular point is resolved in conformal coordinates to a circle with Dirichlet boundary conditions. We also show that moduli parameters of singular surfaces coincide with those of smooth surfaces with boundaries. Singular surfaces with saddle points indeed arise in the strong coupling expansion in lattice QCD. The kind of saddle point, which may be the origin of a singular point we need, is of infinite order.Comment: 8 pages, BROWN-HET-923, a minor error is correcte
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