62 research outputs found
New extended superconformal sigma models and Quaternion Kahler manifolds
Quaternion Kahler manifolds are known to be the target spaces for matter
hypermultiplets coupled to N=2 supergravity. It is also known that there is a
one-to-one correspondence between 4n-dimensional quaternion Kahler manifolds
and those 4(n+1)-dimensional hyperkahler spaces which are the target spaces for
rigid superconformal hypermultiplets (such spaces are called hyperkahler
cones). In this paper we present a projective-superspace construction to
generate a hyperkahler cone M^{4(n+1)}_H of dimension 4(n+1) from a
2n-dimensional real analytic Kahler-Hodge manifold M^{2n}_K. The latter emerges
as a maximal Kahler submanifold of the 4n-dimensional quaternion Kahler space
M^{4n}_Q such that its Swann bundle coincides with M^{4(n+1)}_H. Our approach
should be useful for the explicit construction of new quaternion Kahler
metrics. The results obtained are also of interest, e.g., in the context of
supergravity reduction N=2 --> N=1, or alternatively from the point of view of
embedding N=1 matter-coupled supergravity into an N=2 theory.Comment: 30 page
Relaxed super self-duality and effective action
A closed-form expression is obtained for a holomorphic sector of the two-loop
Euler-Heisenberg type effective action for N = 2 supersymmetric QED derived in
hep-th/0308136. In the framework of the background-field method, this sector is
singled out by computing the effective action for a background N = 2 vector
multiplet satisfying a relaxed super self-duality condition. The approach
advocated in this letter can be applied, in particular, to the study of the N =
4 super Yang-Mills theory on its Coulomb branch.Comment: 8 pages, latex; V2: comments, references added, typos correcte
Active Topology Inference using Network Coding
Our goal is to infer the topology of a network when (i) we can send probes
between sources and receivers at the edge of the network and (ii) intermediate
nodes can perform simple network coding operations, i.e., additions. Our key
intuition is that network coding introduces topology-dependent correlation in
the observations at the receivers, which can be exploited to infer the
topology. For undirected tree topologies, we design hierarchical clustering
algorithms, building on our prior work. For directed acyclic graphs (DAGs),
first we decompose the topology into a number of two-source, two-receiver
(2-by-2) subnetwork components and then we merge these components to
reconstruct the topology. Our approach for DAGs builds on prior work on
tomography, and improves upon it by employing network coding to accurately
distinguish among all different 2-by-2 components. We evaluate our algorithms
through simulation of a number of realistic topologies and compare them to
active tomographic techniques without network coding. We also make connections
between our approach and alternatives, including passive inference, traceroute,
and packet marking
Anomalous Magnetic Properties of Sr2YRuO6
Anomalous magnetic properties of the double perovskite ruthenates compound
Sr2YRuO6 are reported here. Magnetization measurements as a function of
temperature in low magnetic fields show clear evidence for two components of
magnetic order (TM1 ~ 32K and TM2 ~ 27K) aligned opposite to each other with
respect to the magnetic field direction even though only Ru5+moments can order
magnetically in this compound. The second component of the magnetic order at
TM2 ~ 27K results only in a magnetization reversal, and not in the negative
magnetization when the magnetization is measured in the field cooled (FC) mode.
Isothermal magnetization (M-H) measurements show hysteresis with maximum
coercivity (Hc) and remnant magnetization (Mr) at T ~ 27 K, corroborating the
presence of the two oppositely aligned magnetic moments, each with a
ferromagnetic component. The two components of magnetic ordering are further
confirmed by the double peak structure in the heat capacity measurements. These
anomalous properties have significance to some of the earlier results obtained
for the Cu-substituted superconducting Sr2YRu1-xCuxO6 compounds.Comment: 6 figur
Polar supermultiplets, Hermitian symmetric spaces and hyperkahler metrics
We address the construction of four-dimensional N=2 supersymmetric nonlinear
sigma models on tangent bundles of arbitrary Hermitian symmetric spaces
starting from projective superspace. Using a systematic way of solving the
(infinite number of) auxiliary field equations along with the requirement of
supersymmetry, we are able to derive a closed form for the Lagrangian on the
tangent bundle and to dualize it to give the hyperkahler potential on the
cotangent bundle. As an application, the case of the exceptional symmetric
space E_6/SO(10) \times U(1) is explicitly worked out for the first time.Comment: 17 page
Variant supercurrents and Noether procedure
Consistent supercurrent multiplets are naturally associated with linearized
off-shell supergravity models. In arXiv:1002.4932 we presented the hierarchy of
such supercurrents which correspond to all the models for linearized 4D N = 1
supergravity classified a few years ago. Here we analyze the correspondence
between the most general supercurrent given in arXiv:1002.4932 and the one
obtained eight years ago in hep-th/0110131 using the superfield Noether
procedure. We apply the Noether procedure to the general N = 1 supersymmetric
nonlinear sigma-model and show that it naturally leads to the so-called
S-multiplet, revitalized in arXiv:1002.2228.Comment: 6 page
Different representations for the action principle in 4D N = 2 supergravity
Within the superspace formulation for four-dimensional N = 2 matter-coupled
supergravity developed in arXiv:0805.4683, we elaborate two approaches to
reduce the superfield action to components. One of them is based on the
principle of projective invariance which is a purely N = 2 concept having no
analogue in simple supergravity. In this approach, the component reduction of
the action is performed without imposing any Wess-Zumino gauge condition, that
is by keeping intact all the gauge symmetries of the superfield action,
including the super-Weyl invariance. As a simple application, the c-map is
derived for the first time from superfield supergravity. Our second approach to
component reduction is based on the method of normal coordinates around a
submanifold in a curved superspace, which we develop in detail. We derive
differential equations which are obeyed by the vielbein and the connection in
normal coordinates, and which can be used to reconstruct these objects, in
principle in closed form. A separate equation is found for the
super-determinant of the vielbein, which allows one to reconstruct it without a
detailed knowledge of the vielbein. This approach is applicable to any
supergravity theory in any number of space-time dimensions. As a simple
application of this construction, we reduce an integral over the curved N = 2
superspace to that over the chiral subspace of the full superspace. We also
give a new representation for the curved projective-superspace action principle
as a chiral integral.Comment: 44 pages; V2: typos corrected, a comment added; V3: eq. (3.16)
corrected, version published in JHEP; V4: more typos correcte
The SU(N) Matrix Model at Two Loops
Multi-loop calculations of the effective action for the matrix model are
important for carrying out tests of the conjectured relationship of the matrix
model to the low energy description of M-theory. In particular, comparison with
N-graviton scattering amplitudes in eleven-dimensional supergravity requires
the calculation of the effective action for the matrix model with gauge group
SU(N). A framework for carrying out such calculations at two loops is
established in this paper. The two-loop effective action is explicitly computed
for a background corresponding to the scattering of a single D0-brane from a
stack of N-1 D0-branes, and the results are shown to agree with known results
in the case N=2.Comment: 30 pages, 1 figure; v2 - typos corrected, references update
On the two-loop four-derivative quantum corrections in 4D N = 2 superconformal field theories
In \cN = 2, 4 superconformal field theories in four space-time dimensions,
the quantum corrections with four derivatives are believed to be severely
constrained by non-renormalization theorems. The strongest of these is the
conjecture formulated by Dine and Seiberg in hep-th/9705057 that such terms are
generated only at one loop. In this note, using the background field
formulation in \cN = 1 superspace, we test the Dine-Seiberg proposal by
comparing the two-loop F^4 quantum corrections in two different superconformal
theories with the same gauge group SU(N): (i) \cN = 4 SYM (i.e. \cN = 2 SYM
with a single adjoint hypermultiplet); (ii) \cN = 2 SYM with 2N hypermultiplets
in the fundamental. According to the Dine-Seiberg conjecture, these theories
should yield identical two-loop F^4 contributions from all the supergraphs
involving quantum hypermultiplets, since the pure \cN = 2 SYM and ghost sectors
are identical provided the same gauge conditions are chosen. We explicitly
evaluate the relevant two-loop supergraphs and observe that the F^4 corrections
generated have different large N behaviour in the two theories under
consideration. Our results are in conflict with the Dine-Seiberg conjecture.Comment: 26 pages, 4 EPS figures. V2: comments, appendix added. V3: a misprint
removed, discussion in the appendix of cancellation of divergences improved.
V4: typos corrected, the version to appear in NPB. V5: error in eq. (4.12)
corrected, conclusions unchange
On conformal supergravity and projective superspace
The projective superspace formulation for four-dimensional N = 2
matter-coupled supergravity presented in arXiv:0805.4683 makes use of the
variant superspace realization for the N = 2 Weyl multiplet in which the
structure group is SL(2,C) x SU(2) and the super-Weyl transformations are
generated by a covariantly chiral parameter. An extension to Howe's realization
of N = 2 conformal supergravity in which the tangent space group is SL(2,C) x
U(2) and the super-Weyl transformations are generated by a real unconstrained
parameter was briefly sketched. Here we give the explicit details of the
extension.Comment: 17 pages, no figure; V2: comments and references added, published
versio
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