81 research outputs found
The Large N Harmonic Oscillator as a String Theory
We propose a duality between the large-N gauged harmonic oscillator and a
novel string theory in two dimensions.Comment: 31 pages, 2 figures; v2: fixed typo
Non-Fermi liquids from holography
We report on a potentially new class of non-Fermi liquids in
(2+1)-dimensions. They are identified via the response functions of composite
fermionic operators in a class of strongly interacting quantum field theories
at finite density, computed using the AdS/CFT correspondence. We find strong
evidence of Fermi surfaces: gapless fermionic excitations at discrete shells in
momentum space. The spectral weight exhibits novel phenomena, including
particle-hole asymmetry, discrete scale invariance, and scaling behavior
consistent with that of a critical Fermi surface postulated by Senthil.Comment: 10 pages, 16 figures. v2: added references, corrected figures, some
minor changes. v3: figure 5 replace
Gravity duals for non-relativistic CFTs
We attempt to generalize the AdS/CFT correspondence to non-relativistic
conformal field theories which are invariant under Galilean transformations.
Such systems govern ultracold atoms at unitarity, nucleon scattering in some
channels, and more generally, a family of universality classes of quantum
critical behavior. We construct a family of metrics which realize these
symmetries as isometries. They are solutions of gravity with negative
cosmological constant coupled to pressureless dust. We discuss realizations of
the dust, which include a bulk superconductor. We develop the holographic
dictionary and compute some two-point correlators. A strange aspect of the
correspondence is that the bulk geometry has two extra noncompact dimensions.Comment: 12 pages; v2, v3, v4: added references, minor corrections; v3:
cleaned up and generalized dust; v4: closer to published versio
A controlled expansion for certain non-Fermi liquid metals
The destruction of Fermi liquid behavior when a gapless Fermi surface is
coupled to a fluctuating gapless boson field is studied theoretically. This
problem arises in a number of different contexts in quantum many body physics.
Examples include fermions coupled to a fluctuating transverse gauge field
pertinent to quantum spin liquid Mott insulators, and quantum critical metals
near a Pomeranchuk transition. We develop a new controlled theoretical approach
to determining the low energy physics. Our approach relies on combining an
expansion in the inverse number (N) of fermion species with a further expansion
in the parameter \epsilon = z_b -2 where z_b is the dynamical critical exponent
of the boson field. We show how this limit allows a systematic calculation of
the universal low energy physics of these problems. The method is illustrated
by studying spinon fermi surface spin liquids, and a quantum critical metal at
a second order electronic nematic phase transition. We calculate the low energy
single particle spectra, and various interesting two particle correlation
functions. In some cases deviations from the popular Random Phase Approximation
results are found. Some of the same universal singularities are also calculated
to leading non-vanishing order using a perturbative renormalization group
calculation at small N extending previous results of Nayak and Wilczek.
Implications for quantum spin liquids, and for Pomeranchuk transitions are
discussed. For quantum critical metals at a nematic transition we show that the
tunneling density of states has a power law suppression at low energies.Comment: 19 pages, 15 figure
New Dimensions for Wound Strings: The Modular Transformation of Geometry to Topology
We show, using a theorem of Milnor and Margulis, that string theory on
compact negatively curved spaces grows new effective dimensions as the space
shrinks, generalizing and contextualizing the results in hep-th/0510044.
Milnor's theorem relates negative sectional curvature on a compact Riemannian
manifold to exponential growth of its fundamental group, which translates in
string theory to a higher effective central charge arising from winding
strings. This exponential density of winding modes is related by modular
invariance to the infrared small perturbation spectrum. Using self-consistent
approximations valid at large radius, we analyze this correspondence explicitly
in a broad set of time-dependent solutions, finding precise agreement between
the effective central charge and the corresponding infrared small perturbation
spectrum. This indicates a basic relation between geometry, topology, and
dimensionality in string theory.Comment: 28 pages, harvmac big. v2: references and KITP preprint number added,
minor change
Supersymmetric Three-cycles and (Super)symmetry Breaking
We describe physical phenomena associated with a class of transitions that
occur in the study of supersymmetric three-cycles in Calabi-Yau threefolds. The
transitions in question occur at real codimension one in the complex structure
moduli space of the Calabi-Yau manifold. In type IIB string theory, these
transitions can be used to describe the evolution of a BPS state as one moves
through a locus of marginal stability: at the transition point the BPS particle
becomes degenerate with a supersymmetric two particle state, and after the
transition the lowest energy state carrying the same charges is a
non-supersymmetric two particle state. In the IIA theory, wrapping the cycles
in question with D6-branes leads to a simple realization of the Fayet model:
for some values of the CY modulus gauge symmetry is spontaneously broken, while
for other values supersymmetry is spontaneously broken.Comment: 10 pages, harvmac big; v2, minor change
Stringy Instantons and Quiver Gauge Theories
We explore contributions to the 4D effective superpotential which arise from
Euclidean D3 branes (``instantons'') that intersect space-filling D-branes.
These effects can perturb the effective field theory on the space-filling
branes by nontrivial operators composed of charged matter fields, changing the
vacuum structure in a qualitative way in some examples. Our considerations are
exemplified throughout by a careful study of a fractional brane configuration
on a del Pezzo surface.Comment: 30 pages, 4 figures; v2: reference added; v3: confusing minor error
in axion charges fixed (thanks to D. Green for pointing it out
Strings from Tachyons
We propose a new interpretation of the c=1 matrix model as the world-line
theory of N unstable D-particles, in which the hermitian matrix is provided by
the non- abelian open string tachyon. For D-particles in 1+1-d string theory,
we find a direct quantitative match between the closed string emission due to a
rolling tachyon and that due to a rolling eigenvalue in the matrix model. We
explain the origin of the double-scaling limit, and interpret it as an extreme
representative of a large equivalence class of dual theories. Finally, we
define a concrete decoupling limit of unstable D-particles in IIB string theory
that reduces to the c=1 matrix model, suggesting that 1+1-d string theory
represents the near-horizon limit of an ultra-dense gas of IIB D-particles.Comment: 30 pages, 4 figures; v2: added references, improved discussion of
Liouville boundary states, v3: small correction
A Quantum Mechanical Model of Spherical Supermembranes
We present a quantum mechanical model of spherical supermembranes. Using
superfields to represent the cartesian coordinates of the membrane, we are able
to exactly determine its supersymmetric vacua. We find there are two classical
vacua, one corresponding to an extended membrane and one corresponding to a
point-like membrane. For the case, instanton effects then
lift these vacua to massive states. For the case, there is
no instanton tunneling, and the vacua remain massless. Similarities to
spherical supermembranes as giant gravitons and in Matrix theory on pp-waves is
discussed.Comment: 9 page
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