142 research outputs found
Supersymmetric Extension of GCA in 2d
We derive the infinite dimensional Supersymmetric Galilean Conformal Algebra
(SGCA) in the case of two spacetime dimensions by performing group contraction
on 2d superconformal algebra. We also obtain the representations of the
generators in terms of superspace coordinates. Here we find realisations of the
SGCA by considering scaling limits of certain 2d SCFTs which are non-unitary
and have their left and right central charges become large in magnitude and
opposite in sign. We focus on the Neveu-Schwarz sector of the parent SCFTs and
develop, in parallel to the GCA studies recently in (arXiv:0912.1090), the
representation theory based on SGCA primaries, Ward identities for their
correlation functions and their descendants which are null states.Comment: La TeX file, 32 pages; v2: typos corrected, journal versio
Asymptotic W-symmetries in three-dimensional higher-spin gauge theories
We discuss how to systematically compute the asymptotic symmetry algebras of
generic three-dimensional bosonic higher-spin gauge theories in backgrounds
that are asymptotically AdS. We apply these techniques to a one-parameter
family of higher-spin gauge theories that can be considered as large N limits
of SL(N) x SL(N) Chern-Simons theories, and we provide a closed formula for the
structure constants of the resulting infinite-dimensional non-linear
W-algebras. Along the way we provide a closed formula for the structure
constants of all classical W_N algebras. In both examples the higher-spin
generators of the W-algebras are Virasoro primaries. We eventually discuss how
to relate our basis to a non-primary quadratic basis that was previously
discussed in literature.Comment: 61 page
Universality of Phases in QCD and QCD-like Theories
We argue that the whole or the part of the phase diagrams of QCD and QCD-like
theories should be universal in the large-N_c limit through the orbifold
equivalence. The whole phase diagrams, including the chiral phase transitions
and the BEC-BCS crossover regions, are identical between SU(N_c) QCD at finite
isospin chemical potential and SO(2N_c) and Sp(2N_c) gauge theories at finite
baryon chemical potential. Outside the BEC-BCS crossover region in these
theories, the phase diagrams are also identical to that of SU(N_c) QCD at
finite baryon chemical potential. We give examples of the universality in some
solvable cases: (i) QCD and QCD-like theories at asymptotically high density
where the controlled weak-coupling calculations are possible, (ii) chiral
random matrix theories of different universality classes, which are solvable
large-N (large volume) matrix models of QCD. Our results strongly suggest that
the chiral phase transition and the QCD critical point at finite baryon
chemical potential can be studied using sign-free theories, such as QCD at
finite isospin chemical potential, in lattice simulations.Comment: v1: 35 pages, 6 figures; v2: 37 pages, 6 figures, minor improvements,
conclusion unchanged; v3: version published in JHE
Fermionic Coset, Critical Level W^(2)_4-Algebra and Higher Spins
The fermionic coset is a limit of the pure spinor formulation of the AdS5xS5
sigma model as well as a limit of a nonlinear topological A-model, introduced
by Berkovits. We study the latter, especially its symmetries, and map them to
higher spin algebras.
We show the following. The linear A-model possesses affine
\AKMSA{pgl}{4}{4}_0 symmetry at critical level and its \AKMSA{psl}{4}{4}_0
current-current perturbation is the nonlinear model. We find that the
perturbation preserves -algebra symmetry at critical
level. There is a topological algebra associated to \AKMSA{pgl}{4}{4}_0 with
the properties that the perturbation is BRST-exact. Further, the
BRST-cohomology contains world-sheet supersymmetric symplectic fermions and the
non-trivial generators of the -algebra. The Zhu functor
maps the linear model to a higher spin theory. We analyze its
\SLSA{psl}{4}{4} action and find finite dimensional short multiplets.Comment: 25 page
Static Charges in the Low-Energy Theory of the S-Duality Twist
We continue the study of the low-energy limit of N=4 super Yang-Mills theory
compactified on a circle with S-duality and R-symmetry twists that preserve N=6
supersymmetry in 2+1D. We introduce external static supersymmetric quark and
anti-quark sources into the theory and calculate the Witten Index of the
resulting Hilbert space of ground states on a torus. Using these results we
compute the action of simple Wilson loops on the Hilbert space of ground states
without sources. In some cases we find disagreement between our results for the
Wilson loop eigenvalues and previous conjectures about a connection with
Chern-Simons theory.Comment: 73 pages, two paragraphs added, one to the introduction and one to
the discussio
Lorentzian and Euclidean Quantum Gravity - Analytical and Numerical Results
We review some recent attempts to extract information about the nature of
quantum gravity, with and without matter, by quantum field theoretical methods.
More specifically, we work within a covariant lattice approach where the
individual space-time geometries are constructed from fundamental simplicial
building blocks, and the path integral over geometries is approximated by
summing over a class of piece-wise linear geometries. This method of
``dynamical triangulations'' is very powerful in 2d, where the regularized
theory can be solved explicitly, and gives us more insights into the quantum
nature of 2d space-time than continuum methods are presently able to provide.
It also allows us to establish an explicit relation between the Lorentzian- and
Euclidean-signature quantum theories. Analogous regularized gravitational
models can be set up in higher dimensions. Some analytic tools exist to study
their state sums, but, unlike in 2d, no complete analytic solutions have yet
been constructed. However, a great advantage of our approach is the fact that
it is well-suited for numerical simulations. In the second part of this review
we describe the relevant Monte Carlo techniques, as well as some of the
physical results that have been obtained from the simulations of Euclidean
gravity. We also explain why the Lorentzian version of dynamical triangulations
is a promising candidate for a non-perturbative theory of quantum gravity.Comment: 69 pages, 16 figures, references adde
Numerical studies of the ABJM theory for arbitrary N at arbitrary coupling constant
We show that the ABJM theory, which is an N=6 superconformal U(N)*U(N)
Chern-Simons gauge theory, can be studied for arbitrary N at arbitrary coupling
constant by applying a simple Monte Carlo method to the matrix model that can
be derived from the theory by using the localization technique. This opens up
the possibility of probing the quantum aspects of M-theory and testing the
AdS_4/CFT_3 duality at the quantum level. Here we calculate the free energy,
and confirm the N^{3/2} scaling in the M-theory limit predicted from the
gravity side. We also find that our results nicely interpolate the analytical
formulae proposed previously in the M-theory and type IIA regimes. Furthermore,
we show that some results obtained by the Fermi gas approach can be clearly
understood from the constant map contribution obtained by the genus expansion.
The method can be easily generalized to the calculations of BPS operators and
to other theories that reduce to matrix models.Comment: 35 pages, 20 figures; reference added. The simulation code is
available upon request to [email protected]
Super-W(infinity) Asymptotic Symmetry of Higher-Spin AdS(3) Supergravity
We consider (2+1)-dimensional (N, M)-extended higher-spin anti-de Sitter
supergravity and study its asymptotic symmetries. The theory is described by
the Chern-Simons action based on a real, infinite-dimensional higher-spin
superalgebra. We specify consistent boundary conditions on the higher-spin
super-gauge connection corresponding to asymptotically anti-de Sitter
spacetimes. We then determine the residual gauge transformations that preserve
these asymptotic conditions and compute their Poisson bracket algebra. We find
that the asymptotic symmetry is enhanced from the higher-spin superalgebra to
some (N,M)-extended super-W(infinity) nonlinear superalgebra. The latter has
the same classical central charge as pure Einstein gravity. Special attention
is paid to the (1,1)-case. Truncation to the bosonic sector yields the
previously found W(infinity) algebra, while truncation to the underlying
finite-dimensional superalgebra reproduces the N-extended superconformal
algebra (in its nonlinear version for N>2). We discuss string theory
realization of these higher-spin anti-de Sitter supergravity theories as well
as relations to previous treatments of super-W(infinity) in the literature.Comment: References added. (N>2)-Extended supersymmetric models argued to be
rigid with respect to lambda-deformation. Comments on G(3)-case adde
Microtubules Remodel Actomyosin Networks in Xenopus Egg Extracts via Two Mechanisms of F-Actin Transport
Interactions between microtubules and filamentous actin (F-actin) are crucial for many cellular processes, including cell locomotion and cytokinesis, but are poorly understood. To define the basic principles governing microtubule/F-actin interactions, we used dual-wavelength digital fluorescence and fluorescent speckle microscopy to analyze microtubules and F-actin labeled with spectrally distinct fluorophores in interphase Xenopus egg extracts. In the absence of microtubules, networks of F-actin bundles zippered together or exhibited serpentine gliding along the coverslip. When microtubules were nucleated from Xenopus sperm centrosomes, they were released and translocated away from the aster center. In the presence of microtubules, F-actin exhibited two distinct, microtubule-dependent motilities: rapid (∼250–300 nm/s) jerking and slow (∼50 nm/s), straight gliding. Microtubules remodeled the F-actin network, as F-actin jerking caused centrifugal clearing of F-actin from around aster centers. F-actin jerking occurred when F-actin bound to motile microtubules powered by cytoplasmic dynein. F-actin straight gliding occurred when F-actin bundles translocated along the microtubule lattice. These interactions required Xenopus cytosolic factors. Localization of myosin-II to F-actin suggested it may power F-actin zippering, while localization of myosin-V on microtubules suggested it could mediate interactions between microtubules and F-actin. We examine current models for cytokinesis and cell motility in light of these findings
Nonlinear W(infinity) Algebra as Asymptotic Symmetry of Three-Dimensional Higher Spin Anti-de Sitter Gravity
We investigate the asymptotic symmetry algebra of (2+1)-dimensional higher
spin, anti-de Sitter gravity. We use the formulation of the theory as a
Chern-Simons gauge theory based on the higher spin algebra hs(1,1). Expanding
the gauge connection around asymptotically anti-de Sitter spacetime, we specify
consistent boundary conditions on the higher spin gauge fields. We then study
residual gauge transformation, the corresponding surface terms and their
Poisson bracket algebra. We find that the asymptotic symmetry algebra is a
nonlinearly deformed W(infinity) algebra with classical central charges. We
discuss implications of our results to quantum gravity and to various
situations in string theory.Comment: 25 pages, no figure; v2. minor corrections, references added, v3.
JHEP published versio
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