16 research outputs found
On Normal Modes of a Warped Throat
As shown in arXiv:hep-th/0405282, the warped deformed conifold has two
bosonic massless modes, a pseudoscalar and a scalar, that are dual to the phase
and the modulus of the baryonic condensates in the cascading gauge theory. We
reconsider the scalar mode sector, mixing fluctuations of the NS-NS 2-form and
the metric, and include non-zero 4-d momentum . The resulting pair of
coupled equations produce a discrete spectrum of which is
interpreted as the spectrum of glueballs in the gauge theory.
Similarly, we derive the spectrum of certain pseudoscalar glueballs with
, which originate from the decoupled fluctuations of the RR
2-form. We argue that each of the massive scalar or pseudoscalar modes we find
belongs to a 4-d massive axial vector or vector supermultiplet. We also discuss
our results in the context of a finite length throat embedded into a type IIB
flux compactification.Comment: LaTeX, 29 pages, 4 eps figure
On the Strong Coupling Scaling Dimension of High Spin Operators
We give an exact analytic solution of the strong coupling limit of the
integral equation which was recently proposed to describe the universal scaling
function of high spin operators in N = 4 gauge theory. The solution agrees with
the prediction from string theory, confirms the earlier numerical analysis and
provides a basis for developing a systematic perturbation theory around strong
coupling.Comment: 26 pages, 2 figure
Charges of Monopole Operators in Chern-Simons Yang-Mills Theory
We calculate the non-abelian R-charges of BPS monopole operators in
three-dimensional gauge theories with N=3 supersymmetry. This class of models
includes ABJM theory, the proposed gauge theory dual of M-theory on AdS_4 x
S^7/Z_k, as a special case. In the UV limit of the N=3 theories the Yang-Mills
coupling becomes weak and the monopole operators are described by classical
backgrounds. This allows us to find their SU(2)_R charges in a one-loop
computation which by virtue of the non-renormalization of non-abelian R-charges
yields the exact result for any value of the coupling. The spectrum of SU(2)_R
charges is found by quantizing the SU(2)/U(1) collective coordinate of the BPS
background, whose dynamics is that of a charged particle on a sphere with a
Wess-Zumino term representing a magnetic monopole at its center. If the
Wess-Zumino coefficient is h, then the smallest possible SU(2)_R representation
for BPS monopole operators has spin |h|/2. We find, in agreement with earlier
proposals, that h is proportional to the sum of the U(1)_R charges of all the
fermion fields weighted by the effective monopole charges determined by their
gauge representations. The field content of ABJM theory is such that h=0. This
proves for any Chern-Simons level k the existence of monopole operators which
are singlets under all global symmetries and have vanishing scaling dimensions.
These operators are essential for matching the spectrum of the ABJM theory with
supergravity and for the supersymmetry enhancement to N=8.Comment: 31 pages, 3 figures, v2: reference added, discussion of collective
coordinate wave-function adde
Baryonic Condensates on the Conifold
We provide new evidence for the gauge/string duality between the baryonic
branch of the cascading SU(k(M+1)) \times SU(kM) gauge theory and a family of
type IIB flux backgrounds based on warped products of the deformed conifold and
R^{3,1}. We show that a Euclidean D5-brane wrapping all six deformed conifold
directions can be used to measure the baryon expectation values, and present
arguments based on kappa-symmetry and the equations of motion that identify the
gauge bundles required to ensure worldvolume supersymmetry of this object.
Furthermore, we investigate its coupling to the pseudoscalar and scalar modes
associated with the phase and magnitude, respectively, of the baryon
expectation value. We find that these massless modes perturb the
Dirac-Born-Infeld and Chern-Simons terms of the D5-brane action in a way
consistent with our identification of the baryonic condensates. We match the
scaling dimension of the baryon operators computed from the D5-brane action
with that found in the cascading gauge theory. We also derive and numerically
evaluate an expression that describes the variation of the baryon expectation
values along the supergravity dual of the baryonic branch.Comment: 34 pages, 1 figure; v2 typos corrected, references added; v3 added
comment on \kappa-symmetry of Euclidean D5-brane, published in JHE
Place cells may simply be memory cells: Memory compression leads to spatial tuning and history dependence.
Place cells may simply be memory cells: Memory compression leads to spatial tuning and history dependence
The observation of place cells has suggested that the hippocampus plays a special role in encoding spatial information. However, place cell responses are modulated by several nonspatial variables and reported to be rather unstable. Here, we propose a memory model of the hippocampus that provides an interpretation of place cells consistent with these observations. We hypothesize that the hippocampus is a memory device that takes advantage of the correlations between sensory experiences to generate compressed representations of the episodes that are stored in memory. A simple neural network model that can efficiently compress information naturally produces place cells that are similar to those observed in experiments. It predicts that the activity of these cells is variable and that the fluctuations of the place fields encode information about the recent history of sensory experiences. Place cells may simply be a consequence of a memory compression process implemented in the hippocampus
Face familiarity detection with complex synapses
Summary: Synaptic plasticity is a complex phenomenon involving multiple biochemical processes that operate on different timescales. Complexity can greatly increase memory capacity when the variables characterizing the synaptic dynamics have limited precision, as shown in simple memory retrieval problems involving random patterns. Here we turn to a real-world problem, face familiarity detection, and we show that synaptic complexity can be harnessed to store in memory a large number of faces that can be recognized at a later time. The number of recognizable faces grows almost linearly with the number of synapses and quadratically with the number of neurons. Complex synapses outperform simple ones characterized by a single variable, even when the total number of dynamical variables is matched. Complex and simple synapses have distinct signatures that are testable in experiments. Our results indicate that a system with complex synapses can be used in real-world tasks such as face familiarity detection