2,599 research outputs found
Classical and Quantum Cosmology of Multigravity
Recently, a multigraviton theory on a simple closed circuit graph
corresponding to the discretization of compactification of the
Kaluza-Klein (KK) theory has been considered. In the present paper, we extend
this theory to that on a general graph and study what modes of particles are
included. Furthermore, we generalize it in a possible nonlinear theory based on
the vierbein formalism and study classical and quantum cosmological solutions
in the theory. We found that scale factors in a solution for this theory repeat
acceleration and deceleration.Comment: 17 pages, 15 figures, RevTeX4.1, revised versio
An anisotropic hybrid non-perturbative formulation for 4D N = 2 supersymmetric Yang-Mills theories
We provide a simple non-perturbative formulation for non-commutative
four-dimensional N = 2 supersymmetric Yang-Mills theories. The formulation is
constructed by a combination of deconstruction (orbifold projection), momentum
cut-off and matrix model techniques. We also propose a moduli fixing term that
preserves lattice supersymmetry on the deconstruction formulation. Although the
analogous formulation for four-dimensional N = 2 supersymmetric Yang-Mills
theories is proposed also in Nucl.Phys.B857(2012), our action is simpler and
better suited for computer simulations. Moreover, not only for the
non-commutative theories, our formulation has a potential to be a
non-perturbative tool also for the commutative four-dimensional N = 2
supersymmetric Yang-Mills theories.Comment: 32 pages, final version accepted in JHE
Effect of activated alloys on hydrogen discharge kinetics of MgH2 nanocrystals
This is the post-print version of the final paper published in Journal of Alloys and Compounds. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2007 Elsevier B.V.Activated alloys synthesized by arc-melting were examined as catalysts for improving the hydrogen sorption characteristics of nanostructured magnesium hydride, proposed as a reversible hydrogen storage material. The MgH2-catalyst absorbing materials were prepared by ball milling of pure MgH2 with hydrided Zr47Ni53, Zr9Ni11, and other investigated alloys. The nanostructured MgH2-intermetallic systems were tested at 250 °C and catalyst addition of eutectoid Zr47Ni53 resulted in the fastest desorption time and highest initial desorption rate. Also, the catalyzed Mg-hydride with activated Zr9Ni11 and Zr7Ni10 phases showed fast desorption kinetics. Moreover, the results demonstrated that the composition of dispersed ZrxNiy catalysts has a strong influence on the amount of accumulated hydrogen and desorption rate of Mg-nanocomposite.National Research Council Canad
Absence of sign problem in two-dimensional N=(2,2) super Yang-Mills on lattice
We show that N=(2,2) SU(N) super Yang-Mills theory on lattice does not have
sign problem in the continuum limit, that is, under the phase-quenched
simulation phase of the determinant localizes to 1 and hence the phase-quench
approximation becomes exact. Among several formulations, we study models by
Cohen-Kaplan-Katz-Unsal (CKKU) and by Sugino. We confirm that the sign problem
is absent in both models and that they converge to the identical continuum
limit without fine tuning. We provide a simple explanation why previous works
by other authors, which claim an existence of the sign problem, do not capture
the continuum physics.Comment: 27 pages, 24 figures; v2: comments and references added; v3: figures
on U(1) mass independence and references added, to appear in JHE
Hydrogen in Cyclotron-Irradiated Niobium
開始ページ、終了ページ: 冊子体のページ付
Nonperturbative studies of supersymmetric matrix quantum mechanics with 4 and 8 supercharges at finite temperature
We investigate thermodynamic properties of one-dimensional U(N)
supersymmetric gauge theories with 4 and 8 supercharges in the planar large-N
limit by Monte Carlo calculations. Unlike the 16 supercharge case, the
threshold bound state with zero energy is widely believed not to exist in these
models. This led A.V. Smilga to conjecture that the internal energy decreases
exponentially at low temperature instead of decreasing with a power law. In the
16 supercharge case, the latter behavior was predicted from the dual black
0-brane geometry and confirmed recently by Monte Carlo calculations. Our
results for the models with 4 and 8 supercharges indeed support the exponential
behavior, revealing a qualitative difference from the 16 supercharge case.Comment: 16 pages, 7 figures, LaTeX2e, minor corrections in section 3, final
version accepted in JHE
On the shape of a D-brane bound state and its topology change
As is well known, coordinates of D-branes are described by NxN matrices. From
generic non-commuting matrices, it is difficult to extract physics, for
example, the shape of the distribution of positions of D-branes. To overcome
this problem, we generalize and elaborate on a simple prescription, first
introduced by Hotta, Nishimura and Tsuchiya, which determines the most
appropriate gauge to make the separation between diagonal components (D-brane
positions) and off-diagonal components. This prescription makes it possible to
extract the distribution of D-branes directly from matrices. We verify the
power of it by applying it to Monte-Carlo simulations for various lower
dimensional Yang-Mills matrix models. In particular, we detect the topology
change of the D-brane bound state for a phase transition of a matrix model; the
existence of this phase transition is expected from the gauge/gravity duality,
and the pattern of the topology change is strikingly similar to the counterpart
in the gravity side, the black hole/black string transition. We also propose a
criterion, based on the behavior of the off-diagonal components, which
determines when our prescription gives a sensible definition of D-brane
positions. We provide numerical evidence that our criterion is satisfied for
the typical distance between D-branes. For a supersymmetric model, positions of
D-branes can be defined even at a shorter distance scale. The behavior of
off-diagonal elements found in this analysis gives some support for previous
studies of D-brane bound states.Comment: 29 pages, 16 figure
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