53,262 research outputs found
A Classical Manifestation of the Pauli Exclusion Principle
The occupied and unoccupied fermionic BPS quantum states of a type-IIA string
stretched between a D6-brane and an orthogonal D2-brane are described in
M-theory by two particular holomorphic curves embedded in a Kaluza-Klein
monopole. The absence of multiply-occupied fermionic states --- the Pauli
exclusion principle --- is manifested in M-theory by the absence of any other
holomorphic curves satisfying the necessary boundary conditions. Stable,
non-BPS states with multiple strings joining the D6-brane and D2-brane are
described M-theoretically by non-holomorphic curves.Comment: harvmac 6 pages. Final version as published in JHE
When Is it Wrong to Trade Stocks on the Basis of Non-Public Information?: Public Views of the Morality of Insider Trading
Curvature terms in D-brane actions and their M-theory origin
We derive the complete terms of effective D-brane actions,
for arbitrary ambient geometries and world-volume embeddings, at lowest order
(disk-level) in the string-loop expansion. These terms reproduce the
corrections to string scattering amplitudes, and are consistent
with duality conjectures. In the particular case of the D3-brane with trivial
normal bundle, considerations of invariance lead to a
complete sum of D-instanton corrections for both the parity-conserving and the
parity-violating parts of the effective action. These corrections are required
for the cancellation of the modular anomalies of massless modes, and are
consistent with the absence of chiral anomalies in the intersection domain of
pairs of D-branes. We also show that the parity-conserving part of the
non-perturbative R^2 action follows from a one-loop quantum calculation in the
six-dimensional world-volume of the M5-brane compactified on a two-torus.Comment: tex file, 31 pages, uses harvmac. Some rewriting of section 2,
conclusions and appendix B, in particular in what concerns the discussion of
seven-branes in the conclusions and the structure of terms in
appendix B. Other minor corrections plus added reference
(8,0) Quantum mechanics and symmetry enhancement in type I' superstrings
The low-energy supersymmetric quantum mechanics describing D-particles in the
background of D8-branes and orientifold planes is analyzed in detail, including
a careful discussion of Gauss' law and normal ordering of operators. This
elucidates the mechanism that binds D-particles to an orientifold plane, in
accordance with the predictions of heterotic/type I duality. The ocurrence of
enhanced symmetries associated with massless bound states of a D-particle with
one orientifold plane is illustrated by the enhancement of
to and to at strong type I' coupling.
Enhancement to higher-rank groups involves both orientifold planes. For
example, the enhanced symmetry at the self-dual
radius of the heterotic string is seen as the result of two D8-branes
coinciding midway between the orientifold planes, while the enhanced
symmetry results from the coincidence of all sixteen D8-branes and
when they also coincide with an orientifold plane. As a separate by-product,
the s-rule of brane-engineered gauge theories is derived by relating it through
a chain of dualities to the Pauli exclusion principle.Comment: 30 pages LaTeX, Five figures. Two references added as well as some
Comments in section4. v4: Missing backslashes added to four reference
citations
Supersymmetry Constraints on Type IIB Supergravity
Supersymmetry is used to derive conditions on higher derivative terms in the
effective action of type IIB supergravity. Using these conditions, we are able
to prove earlier conjectures that certain modular invariant interactions of
order alpha' **3 relative to the Einstein-Hilbert term are proportional to
eigenfunctions of the Laplace operator on the fundamental domain of SL(2,Z). We
also discuss how these arguments generalize to terms of higher order in alpha',
as well as to compactifications of supergravity.Comment: 31 pages, harvmac (b); minor correction
An Early Universe Model with Stiff Matter and a Cosmological Constant
In the present work, we study the quantum cosmology description of a
Friedmann-Robertson-Walker model in the presence of a stiff matter perfect
fluid and a negative cosmological constant. We work in the Schutz's variational
formalism and the spatial sections have constant negative curvature. We
quantize the model and obtain the appropriate Wheeler-DeWitt equation. In this
model the states are bounded therefore we compute the discrete energy spectrum
and the corresponding eigenfunctions. In the present work, we consider only the
negative eigenvalues and their corresponding eigenfunctions. This choice
implies that the energy density of the perfect fluid is negative. A stiff
matter perfect fluid with this property produces a model with a bouncing
solution, at the classical level, free from an initial singularity. After that,
we use the eigenfunctions in order to construct wave packets and evaluate the
time-dependent expectation value of the scale factor. We find that it
oscillates between maximum and minimum values. Since the expectation value of
the scale factor never vanishes, we confirm that this model is free from an
initial singularity, also, at the quantum level.Comment: 12 Pages, 4 Figures. Final version. Accepted for publication in the
Proceedings of the 8th Friedmann Seminar, Rio de Janeiro, 2011. We restricted
our attention to treat the case where the stiff matter has negative energy
eigenvalues, following the referee's suggestio
Non-commutative Complex Projective Spaces and the Standard Model
The standard model fermion spectrum, including a right handed neutrino, can
be obtained as a zero-mode of the Dirac operator on a space which is the
product of complex projective spaces of complex dimension two and three. The
construction requires the introduction of topologically non-trivial background
gauge fields. By borrowing from ideas in Connes' non-commutative geometry and
making the complex spaces `fuzzy' a matrix approximation to the fuzzy space
allows for three generations to emerge. The generations are associated with
three copies of space-time. Higgs' fields and Yukawa couplings can be
accommodated in the usual way.Comment: Contribution to conference in honour of A.P. Balachandran's 65th
birthday: "Space-time and Fundamental Interactions: Quantum Aspects", Vietri
sul Mare, Italy, 25th-31st May, 2003, 10 pages, typset in LaTe
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