108 research outputs found
Instantons and Toric Quiver Gauge Theories
We show how to construct the general action coupling (multi)instantons to
gauge theories arising from branes probing arbitrary toric singularities. We
give a general set of rules for how to construct such an action given the
knowledge of the superpotential for the gauge theory. The main idea is to
obtain the action by higgsing a theory whose instanton dynamics is known,
namely an orbifold of N=4 super Yang-Mills. We find that the couplings of the
fermionic zero-modes with the holomorphic fields are dictated by the structure
of the superpotential describing the toric singularity. We present explicit
examples such as the Suspended Pinch Point, the Conifold and the first three
del Pezzo's. We perform various checks on these results by further higgsing to
smaller orbifolds and present some applications, including both gauge theory
and stringy instantons.Comment: 42 pages, footnote 2 added, references upgrade
Superstring Theory on AdS_3 x G/H and Boundary N=3 Superconformal Symmetry
Superstrings propagating on backgrounds of the form AdS_3 x G/H are studied
using the coset CFT approach. We focus on seven dimensional cosets which have a
semiclassical limit, and which give rise to N=3 superconformal symmetry in the
dual CFT. This is realized for the two cases AdS_3 x SU(3)/U(1) and AdS_3 x
SO(5)/SO(3), for which we present an explicit construction. We also provide
sufficient conditions on a CFT background to enable a similar construction, and
comment on the geometrical interpretation of our results.Comment: 22 pages, harvmac; added reference
Brane Physics in M-theory
The thesis begins with an introduction to M-theory (at a graduate student's
level), starting from perturbative string theory and proceeding to dualities,
D-branes and finally Matrix theory. The following chapter treats, in a
self-contained way, of general classical p-brane solutions. Black and extremal
branes are reviewed, along with their semi-classical thermodynamics. We then
focus on intersecting extremal branes, the intersection rules being derived
both with and without the explicit use of supersymmetry. The last three
chapters comprise more advanced aspects of brane physics, such as the dynamics
of open branes, the little theories on the world-volume of branes and how the
four dimensional Schwarzschild black hole can be mapped to an extremal
configuration of branes, thus allowing for a statistical interpretation of its
entropy. The original results were already reported in hep-th/9701042,
hep-th/9704190, hep-th/9710027 and hep-th/9801053.Comment: 206 pages, Latex (three times), no figures. PhD thesis (Universite
Libre de Bruxelles). One reference modifie
Superstrings on AdS_3 and Symmetric Products
Some properties of N=2 superstrings on AdS_3 x N are studied. Their spectrum
has the same pattern as 2-d CFTs in the moduli space of symmetric products
M^p/S_p, where p is associated with the number of long fundamental strings
required to construct the AdS_3 background, and M is the spacetime CFT
corresponding to short string excitations of a single long string. Worldsheet
operators associated with w long strings correspond to twisted sectors of
M^p/S_p.Comment: 43 pages, harvma
Are there Goldstone bosons in ?
We study the viability of spontaneous breaking of continuous symmetries in
theories with Lifshitz scaling, according to the number of space-time
dimensions and the dynamical scaling . Then, the answer to the question
in the title is no (quantum field theoretically) and yes (holographically).
With field theory tools, we show that symmetry breaking is indeed prevented by
large quantum fluctuations when , as expected from scaling
arguments. With holographic tools, on the other hand, we find nothing that
prevents the existence of a vacuum expectation value. This difference is made
possible by the large limit of holography. An important subtlety in this
last framework is that in order to get a proper description of a conserved
current, renormalization of the temporal mode of the bulk vector requires an
alternative quantization. We also comment on the implications of turning on
temperature.Comment: 18 pages. v2: a few clarifying comments added, matches published
versio
Massless fermionic bound states and the gauge/gravity correspondence
We study the equations of motion of fermions in type IIB supergravity in the
context of the gauge/gravity correspondence. The main motivation is the search
for normalizable fermionic zero modes in such backgrounds, to be interpreted as
composite massless fermions in the dual theory. We specialize to backgrounds
characterized by a constant dilaton and a self-dual three-form. In the specific
case of the Klebanov--Strassler solution we construct explicitly the fermionic
superpartner of the Goldstone mode associated with the broken baryonic
symmetry. The fermionic equations could also be used to search for goldstinos
in theories that break supersymmetry dynamically.Comment: 25 pages. V2: ref. added; V3: ref. adde
On the Exotic Phases of M-theory
We study aspects of the new phases of M-theory recently conjectured using
generalised dualities such as timelike T-duality. Our focus is on brane
solutions. We derive the intersection rules in a general framework and then
specialise to the new phases of M-theory. We discuss under which conditions a
configuration with several branes leads to a regular extremal black hole under
compactification. We point out that the entropy seems not to be constant when
the radius of the physical timelike direction is varied. This could be
interpreted as a non-conservation of the entropy (and the mass) under at least
some of the new dualities.Comment: 13 pages, LaTeX file, no figure
Symmetry breaking in holographic theories with Lifshitz scaling
We study holographically Lifshitz-scaling theories with broken symmetries. In
order to do this, we set up a bulk action with a complex scalar and a massless
vector on a background which consists in a Lifshitz metric and a massive
vector. We first study separately the complex scalar and the massless vector,
finding a similar pattern in the two-point functions that we can compute
analytically. By coupling the probe complex scalar to the background massive
vector we can construct probe actions that are more general than the usual
Klein--Gordon action. Some of these actions have Galilean boost symmetry.
Finally, in the presence of a symmetry breaking scalar profile in the bulk, we
reproduce the expected Ward identities of a Lifshitz-scaling theory with a
broken global continuous symmetry. In the spontaneous case, the latter imply
the presence of a gapless mode, the Goldstone boson, which will have dispersion
relations dictated by the Lifshitz scaling.Comment: 39 pages, 3 figures. v2: a few clarifying comments added, matches
published versio
Why not a di-NUT? or Gravitational duality and rotating solutions
We study how gravitational duality acts on rotating solutions, using the
Kerr-NUT black hole as an example. After properly reconsidering how to take
into account both electric (i.e. mass-like) and magnetic (i.e. NUT-like)
sources in the equations of general relativity, we propose a set of definitions
for the dual Lorentz charges. We then show that the Kerr-NUT solution has
non-trivial such charges. Further, we clarify in which respect Kerr's source
can be seen as a mass M with a dipole of NUT charges.Comment: 20 pages. v2: minor clarifications in section 4, version to appear in
PR
Analytic pseudo-Goldstone bosons
We consider the interplay between explicit and spontaneous symmetry breaking
in strongly coupled field theories. Some well-known statements, such as the
Gell-Mann-Oakes-Renner relation, descend directly from the Ward identities and
have thus a general relevance. Such Ward identities are recovered in
gauge/gravity dual setups through holographic renormalization. In a simple
paradigmatic three dimensional toy-model, we find analytic expressions for the
two-point correlators which match all the quantum field theoretical
expectations. Moreover, we have access to the full spectrum, which is
reminiscent of linear confinement.Comment: 20 pages, 4 figures, v2 minor correction
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