1,523 research outputs found
Suppression of nuclear spin diffusion at a GaAs/AlGaAs interface measured with a single quantum dot nano-probe
Nuclear spin polarization dynamics are measured in optically pumped
individual GaAs/AlGaAs interface quantum dots by detecting the time-dependence
of the Overhauser shift in photoluminescence (PL) spectra. Long nuclear
polarization decay times of ~ 1 minute have been found indicating inefficient
nuclear spin diffusion from the GaAs dot into the surrounding AlGaAs matrix in
externally applied magnetic field. A spin diffusion coefficient two orders
lower than that previously found in bulk GaAs is deduced.Comment: 5 pages, 3 figures, submitted to Phys Rev
Quantum Deconstruction of a 5D SYM and its Moduli Space
We deconstruct the fifth dimension of the 5D SYM theory with SU(M) gauge
symmetry and Chern-Simons level k=M and show how the 5D moduli space follows
from the non-perturbative analysis of the 4D quiver theory. The 5D coupling
h=1/(g_5)^2 of the un-broken SU(M) is allowed to take any non-negative values,
but it cannot be continued to h<0 and there are no transitions to other phases
of the theory. The alternative UV completions of the same 5D SYM -- via M
theory on the C^3/Z_2M orbifold or via the dual five-brane web in type IIB
string theory -- have identical moduli spaces: h >= 0 only, and no flop
transitions. We claim these are intrinsic properties of the SU(M) SYM theory
with k=M.Comment: 46 Page
Three-Point Functions of Quarter BPS Operators in N=4 SYM
In a recent paper hep-th/0109064, quarter-BPS chiral primaries were
constructed in the fully interacting four dimensional N=4 Super-Yang-Mills
theory with gauge group SU(N). These operators are annihilated by four
supercharges, and at order g^2 have protected scaling dimension and
normalization. Here, we compute three-point functions involving these
quarter-BPS operators along with half-BPS operators. The combinatorics of the
problem is rather involved, and we consider the following special cases: (1)
correlators of two half-BPS primaries with an arbitrary
chiral primary; (2) certain classes of and < quarter
quarter quarter > three-point functions; (3) three-point functions involving
the Delta
correlators with the special quarter-BPS operator made of single and double
trace operators only. The analysis in cases (1)-(3) is valid for general N,
while (4) is a large N approximation. Order g^2 corrections to all three-point
functions considered in this paper are found to vanish.
In the AdS/CFT correspondence, quarter-BPS chiral primaries are dual to
threshold bound states of elementary supergravity excitations. We present a
supergravity discussion of two- and three-point correlators involving these
bound states.Comment: 44 pages, Latex, eps figures, uses epsfig.sty; references adde
Deconstruction, Lattice Supersymmetry, Anomalies and Branes
We study the realization of anomalous Ward identities in deconstructed
(latticized) supersymmetric theories. In a deconstructed four-dimensional
theory with N=2 supersymmetry, we show that the chiral symmetries only appear
in the infrared and that the anomaly is reproduced in the usual framework of
lattice perturbation theory with Wilson fermions. We then realize the theory on
the world-volume of fractional D-branes on an orbifold. In this brane
realization, we show how deconstructed theory anomalies can be computed via
classical supergravity. Our methods and observations are more generally
applicable to deconstructed/latticized supersymmetric theories in various
dimensions.Comment: 1+27 pages, 2 figures, references adde
Non-renormalization of next-to-extremal correlators in N=4 SYM and the AdS/CFT correspondence
We show that next-to-extremal correlators of chiral primary operators in N=4
SYM theory do not receive quantum corrections to first order in perturbation
theory. Furthermore we consider next-to-extremal correlators within AdS
supergravity. Here the exchange diagrams contributing to these correlators
yield results of the same free-field form as obtained within field theory. This
suggests that quantum corrections vanish at strong coupling as well.Comment: 21 pages, LaTex, 9 eps figures, typos corrected and references adde
Preliminary studies of sediments from the Dobczyce drinking water reservoir
The analysis of river and lake sediments indicates that the physical, chemical, biochemical and geochemical
processes that influence the fate of toxic compounds and elements in sediments are numerous and complex
(for example: sorption - desorption, oxidation - reduction, ion-exchange, biological activity). Due to the
above-mentioned general statement, only a long term and complex research programme can lead to satisfactory
answers to the questions relating to possible changes of water and environmental quality in the future.
The aim of our study consisted in physical and chemical characterisation of sediments in in-depth profiles
taken from the Dobczyce reservoir in southern Poland that is a main source of drinking water for the city
of Kraków. Due to morphological reasons, 7 layers of sediment samples were distinguished from the ground
level to about 90 cm below (total thickness of the sediments in the sampling site). Analysis of grain size distribution
and application of x-ray diffraction method, enabled mineralogical description of sediments.
The use of proton-induced x-ray emission (PIXE) and atomic absorption spectrometry (AAS) revealed
elemental composition of the samples (Al, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn). Concentrations
of natural 40K and artificial 137Cs radionuclides were determined by the use of gamma spectrometry.
The following facts were established: 1) the oldest (deepest) and newest, recently deposited layers of
sediments are similar in their physical and chemical properties. It means that the inflow of contaminants
and biogenic compounds to the reservoir has changed little since it was constructed and filled with water;
2) the severe flood in 1997 changed significantly sediment composition and, in fact, led to purification of
sediments in the Dobczyce reservoir
Multi giant graviton systems, SUSY breaking and CFT
In this article, we describe giant gravitons in AdS_5 x S^5 moving along
generic trajectories in AdS_5. The giant graviton dynamics is solved by proving
that the D3-brane effective action reduces to that of a massive point particle
in AdS_5 and therefore the solutions are in one to one correspondence with
timelike geodesics of AdS_5. All these configurations are related via
isometries of the background, which induce target space symmetries in the world
volume theory of the D-brane. Hence, all these configurations preserve the same
amount of supersymmetry as the original giant graviton, i.e. half of the
maximal supersymmetry. Multiparticle configurations of two or more giant
gravitons are also considered. In particular, a binary system preserving one
quarter of the supersymmetries is found, providing a non trivial time-dependent
supersymmetric solution. A short study on the dual CFT description of all the
above states is given, including a derivation of the exact induced isometry map
in the CFT side of the correspondence.Comment: latex, 27+1 pages. v2: comment on mixing of states in section 4.3
added, reference added, typos corrected, final versio
Giant Gravitons, BPS bounds and Noncommutativity
It has been recently suggested that gravitons moving in
spacetimes along the blow up into spherical branes whose radius
increases with increasing angular momentum. This leads to an upper bound on the
angular momentum, thus ``explaining'' the stringy exclusion principle. We show
that this bound is present only for states which saturate a BPS-like condition
involving the energy and angular momentum , , where is
the radius of . Restriction of motion to such states lead to a
noncommutativity of the coordinates on . As an example of motions which do
not obey the exclusion principle bound, we show that there are finite action
instanton configurations interpolating between two possible BPS states. We
suggest that this is consistent with the proposal that there is an effective
description in terms of supergravity defined on noncommutative spaces and
noncommutativity arises here because of imposing supersymmetry.Comment: 15 pages, harvmac, corrected some typo
Smoking-gun signatures of little Higgs models
Little Higgs models predict new gauge bosons, fermions and scalars at the TeV
scale that stabilize the Higgs mass against quadratically divergent one-loop
radiative corrections. We categorize the many little Higgs models into two
classes based on the structure of the extended electroweak gauge group and
examine the experimental signatures that identify the little Higgs mechanism in
addition to those that identify the particular little Higgs model. We find that
by examining the properties of the new heavy fermion(s) at the LHC, one can
distinguish the structure of the top quark mass generation mechanism and test
the little Higgs mechanism in the top sector. Similarly, by studying the
couplings of the new gauge bosons to the light Higgs boson and to the Standard
Model fermions, one can confirm the little Higgs mechanism and determine the
structure of the extended electroweak gauge group.Comment: 59 pages, 10 figures. v2: refs added, typos fixed, JHEP versio
Reconstructing Sparticle Mass Spectra using Hadronic Decays
Most sparticle decay cascades envisaged at the Large Hadron Collider (LHC)
involve hadronic decays of intermediate particles. We use state-of-the art
techniques based on the \kt jet algorithm to reconstruct the resulting hadronic
final states for simulated LHC events in a number of benchmark supersymmetric
scenarios. In particular, we show that a general method of selecting
preferentially boosted massive particles such as W, Z or Higgs bosons decaying
to jets, using sub-jets found by the \kt algorithm, suppresses QCD backgrounds
and thereby enhances the observability of signals that would otherwise be
indistinct. Consequently, measurements of the supersymmetric mass spectrum at
the per-cent level can be obtained from cascades including the hadronic decays
of such massive intermediate bosons.Comment: 1+29 pages, 12 figure
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