1,378 research outputs found
Higher Derivative Corrections to Eleven Dimensional Supergravity via Local Supersymmetry
In this paper we derive higher derivative corrections to the eleven
dimensional supergravity by applying the Noether method with respect to the N=1
local supersymmetry. An ansatz for the higher derivative effective action,
which includes quartic terms of the Riemann tensor, is parametrized by 132
parameters. Then we show that by the requirement of the local supersymmetry,
the higher derivative effective action is essentially described by two
parameters. The bosonic parts of these two superinvariants completely match
with the known results obtained by the perturbative calculations in the type
IIA superstring theory. Since the calculations are long and systematic, we
build the computer programming to check the cancellation of the variations
under the local supersymmetry. This is an extended version of our previous
paper hep-th/0508204.Comment: 67 pages, no figure, references added, typos correcte
Spinorial cohomology and maximally supersymmetric theories
Fields in supersymmetric gauge theories may be seen as elements in a
spinorial cohomology. We elaborate on this subject, specialising to maximally
supersymmetric theories, where the superspace Bianchi identities, after
suitable conventional constraints are imposed, put the theories on shell. In
these cases, the spinorial cohomologies describe in a unified manner gauge
transformations, fields and possible deformations of the models, e.g.
string-related corrections in an alpha' expansion. Explicit cohomologies are
calculated for super-Yang-Mills theory in D=10, for the N=(2,0) tensor
multiplet in D=6 and for supergravity in D=11, in the latter case from the
point of view of both the super-vielbein and the super-3-form potential. The
techniques may shed light on some questions concerning the alpha'-corrected
effective theories, and result in better understanding of the role of the
3-form in D=11 supergravity.Comment: 23 pp, plain tex. v2: Minor changes, references adde
Comments on Heterotic Flux Compactifications
In heterotic flux compactification with supersymmetry, three different
connections with torsion appear naturally, all in the form .
Supersymmetry condition carries , the Dirac operator has , and
higher order term in the effective action involves . With a view toward
the gauge sector, we explore the geometry with such torsions. After reviewing
the supersymmetry constraints and finding a relation between the scalar
curvature and the flux, we derive the squared form of the zero mode equations
for gauge fermions. With \d H=0, the operator has a positive potential term,
and the mass of the unbroken gauge sector appears formally positive definite.
However, this apparent contradiction is avoided by a no-go theorem that the
compactification with and \d H=0 is necessarily singular, and the
formal positivity is invalid. With \d H\neq 0, smooth compactification
becomes possible. We show that, at least near smooth supersymmetric solution,
the size of should be comparable to that of \d H and the consistent
truncation of action has to keep term. A warp factor equation of
motion is rewritten with contribution included precisely, and
some limits are considered.Comment: 31 pages, a numerical factor correcte
On the absence of BPS preonic solutions in IIA and IIB supergravities
We consider the present absence of 31 out of 32 supersymmetric solutions in
supergravity i.e., of solutions describing BPS preons. A recent result
indicates that (bosonic) BPS preonic solutions do not exist in type IIB
supergravity. We reconsider this analysis by using the G-frame method, extend
it to the IIA supergravity case, and show that there are no (bosonic) preonic
solutions for type IIA either. For the classical D=11 supergravity no
conclusion can be drawn yet, although the negative IIA results permit
establishing the conditions that preonic solutions would have to satisfy. For
supergravities with `stringy' corrections, the existence of BPS preonic
solutions remains fully open.Comment: plain latex, 12 pages Minor misprints corrected. Published in JHEP 09
(2006) 00
The One-loop Open Superstring Massless Five-point Amplitude with the Non-Minimal Pure Spinor Formalism
We compute the massless five-point amplitude of open superstrings using the
non-minimal pure spinor formalism and obtain a simple kinematic factor in pure
spinor superspace, which can be viewed as the natural extension of the
kinematic factor of the massless four-point amplitude. It encodes bosonic and
fermionic external states in supersymmetric form and reduces to existing
bosonic amplitudes when expanded in components, therefore proving their
equivalence. We also show how to compute the kinematic structures involving
fermionic states.Comment: 38 pages, harvmac TeX, v2: fix typo in (4.2) and add referenc
Probing the Shape of Quantum Dots with Magnetic Fields
A tool for the identification of the shape of quantum dots is developed. By
preparing a two-electron quantum dot, the response of the low-lying excited
states to a homogeneous magnetic field, i.e. their spin and parity
oscillations, is studied for a large variety of dot shapes. For any geometric
configuration of the confinement we encounter characteristic spin singlet -
triplet crossovers. The magnetization is shown to be a complementary tool for
probing the shape of the dot.Comment: 11 pages, 4 figure
Aspects of higher curvature terms and U-duality
We discuss various aspects of dimensional reduction of gravity with the
Einstein-Hilbert action supplemented by a lowest order deformation formed as
the Riemann tensor raised to powers two, three or four. In the case of R^2 we
give an explicit expression, and discuss the possibility of extended coset
symmetries, especially SL(n+1,Z) for reduction on an n-torus to three
dimensions. Then we start an investigation of the dimensional reduction of R^3
and R^4 by calculating some terms relevant for the coset formulation, aiming in
particular towards E_8(8)/(Spin(16)/Z_2) in three dimensions and an
investigation of the derivative structure. We emphasise some issues concerning
the need for the introduction of non-scalar automorphic forms in order to
realise certain expected enhanced symmetries.Comment: 26 pp., 15 figs., plain te
A note on the quartic effective action of type IIB superstring
We recast the result of our recent computation of the quartic action of
ten-dimensional IIB supergravity in a manifestly SL(2,R)-covariant form. This
affords us a critical assessment of an earlier conjecture in the literature.Comment: 15 pages; v2: some clarifications and a rerence adde
Holographic rho mesons in an external magnetic field
We study the rho meson in a uniform magnetic field eB using a holographic
QCD-model, more specifically a D4/D8/Dbar8 brane setup in the confinement phase
at zero temperature with two quenched flavours. The parameters of the model are
fixed by matching to corresponding dual field theory parameters at zero
magnetic field. We show that the up- and down-flavour branes respond
differently to the presence of the magnetic field in the dual QCD-like theory,
as expected because of the different electromagnetic charge carried by up- and
down-quark. We discuss how to recover the Landau levels, indicating an
instability of the QCD vacuum at eB = m_rho^2 towards a phase where charged rho
mesons are condensed, as predicted by Chernodub using effective QCD-models. We
improve on these existing effective QCD-model analyses by also taking into
account the chiral magnetic catalysis effect, which tells us that the
constituent quark masses rise with eB. This turns out to increase the value of
the critical magnetic field for the onset of rho meson condensation to eB = 1.1
m_rho^2 = 0.67 GeV^2. We briefly discuss the influence of pions, which turn out
to be irrelevant for the condensation in the approximation made.Comment: 26 pages, 10 .pdf figures, v2: version accepted for publication in
JHE
Community sensitization and decision-making for trial participation: A mixed-methods study from The Gambia
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