7,153 research outputs found
Moving Five-Branes in Low-Energy Heterotic M-Theory
We construct cosmological solutions of four-dimensional effective heterotic
M-theory with a moving five-brane and evolving dilaton and T modulus. It is
shown that the five-brane generates a transition between two asymptotic
rolling-radii solutions. Moreover, the five-brane motion always drives the
solutions towards strong coupling asymptotically. We present an explicit
example of a negative-time branch solution which ends in a brane collision
accompanied by a small-instanton transition. The five-dimensional origin of
some of our solutions is also discussed.Comment: 16 pages, Latex, 3 eps figure
Heterotic M-Theory Cosmology in Four and Five Dimensions
We study rolling radii solutions in the context of the four- and
five-dimensional effective actions of heterotic M-theory. For the standard
four-dimensional solutions with varying dilaton and T-modulus, we find
approximate five-dimensional counterparts. These are new, generically
non-separating solutions corresponding to a pair of five-dimensional domain
walls evolving in time. Loop corrections in the four-dimensional theory are
described by certain excitations of fields in the fifth dimension. We point out
that the two exact separable solutions previously discovered are precisely the
special cases for which the loop corrections are time-independent. Generically,
loop corrections vary with time. Moreover, for a subset of solutions they
increase in time, evolving into complicated, non-separating solutions. In this
paper we compute these solutions to leading, non-trivial order. Using the
equations for the induced brane metric, we present a general argument showing
that the accelerating backgrounds of this type cannot evolve smoothly into
decelerating backgrounds.Comment: 15 pages, Latex, 1 eps figur
Torus-Fibered Calabi-Yau Threefolds with Non-Trivial Fundamental Group
We construct smooth Calabi-Yau threefolds Z, torus-fibered over a dP_9 base,
with fundamental group Z_2 X Z_2. To do this, the structure of rational
elliptic surfaces is studied and it is shown that a restricted subset of such
surfaces admit at least a Z_2 X Z_2 group of automorphisms. One then constructs
Calabi-Yau threefolds X as the fiber product of two such dP_9 surfaces,
demonstrating that the involutions on the surfaces lift to a freely acting Z_2
X Z_2 group of automorphisms on X. The threefolds Z are then obtained as the
quotient Z=X/(Z_2 X Z_2). These Calabi-Yau spaces Z admit stable, holomorphic
SU(4) vector bundles which, in conjunction with Z_2 X Z_2 Wilson lines, lead to
standard-like models of particle physics with naturally suppressed nucleon
decay.Comment: 60 pages, 13 figures, Typos correcte
Higher order corrections to Heterotic M-theory inflation
We investigate inflation driven by dynamical five-branes in Heterotic
M-theory using the scalar potential derived from the open membrane instanton
sector. At leading order the resulting theory can be mapped to power law
inflation, however more generally one may expect higher order corrections to be
important. We consider a simple class of such corrections, which imposes tight
bounds on the number of branes required for inflation.Comment: 10 pages, 2 figure
Sub-Kelvin Parametric Feedback Cooling of a Laser-Trapped Nanoparticle
Recent experiments have demonstrated the ability to optically cool a
macroscopic mechanical oscillator to its quantum ground state by means of
dynamic backaction. Such experiments allow quantum mechanics to be tested with
mesoscopic objects, and represent an essential step toward quantum optical
memories, transducers, and amplifiers. Most oscillators considered so far are
rigidly connected to their thermal environment, fundamentally limiting their
mechanical Q-factors and requiring cryogenic precooling to liquid helium
temperatures. Here we demonstrate parametric feedback cooling of a
laser-trapped nanoparticle which is entirely isolated from the thermal bath.
The lack of a clamping mechanism provides robust decoupling from internal
vibrations and makes it possible to cool the nanoparticle in all degrees of
freedom by means of a single laser beam. Compared to laser-trapped
microspheres, nanoparticles have the advantage of higher resonance frequencies
and lower recoil heating, which are favorable conditions for quantum ground
state coolin
Five-Branes in Heterotic Brane-World Theories
The effective action for five-dimensional heterotic M-theory in the presence
of five-branes is systematically derived from Horava-Witten theory coupled to
an M5-brane world-volume theory. This leads to a five-dimensional N=1 gauged
supergravity theory on S^1/Z_2 coupled to four-dimensional N=1 theories
residing on the two orbifold fixed planes and an additional bulk three-brane.
We analyse the properties of this action, particularly the four-dimensional
effective theory associated with the domain-wall vacuum state. The moduli
Kahler potential and the gauge-kinetic functions are determined along with the
explicit relations between four-dimensional superfields and five-dimensional
component fields.Comment: 19 pages, Latex, typos corrected, reference adde
Classification and Moduli Kahler Potentials of G_2 Manifolds
Compact manifolds of G_2 holonomy may be constructed by dividing a
seven-torus by some discrete symmetry group and then blowing up the
singularities of the resulting orbifold. We classify possible group elements
that may be used in this construction and use this classification to find a set
of possible orbifold groups. We then derive the moduli Kahler potential for
M-theory on the resulting class of G_2 manifolds with blown up co-dimension
four singularities.Comment: 30 pages, Latex, references adde
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