26,788 research outputs found
Potentially Good Reduction of Barsotti-Tate Groups
Let R be a complete discrete valuation ring of mixed characteristic (0, p)
with perfect residue field, K the fraction field of R. Suppose G is a
Barsotti-Tate group (p-divisible group) defined over K which acquires good
reduction over a finite extension K' of K. We prove that there exists a
constant c which depends on the absolute ramification index e(K'/Q_p) and the
height of G such that G has good reduction over K if and only if G[p^c] can be
extended to a finite flat group scheme over R. For abelian varieties with
potentially good reduction, this result generalizes Grothendieck's p-adic
Neron-Ogg-Shafarevich criterion to finite level. We use methods that can be
generalized to study semi-stable p-adic Galois representations with general
Hodge-Tate weights, and in particular leads to a proof of a conjecture of
Fontaine and gives a constant c as above that is independent of the height of
G
The K\"ahler Potential of Abelian Higgs Vortices
We calculate the K\"ahler potential for the Samols metric on the moduli space
of Abelian Higgs vortices on \mathbbm{R}^{2}, in two different ways. The
first uses a scaling argument. The second is related to the Polyakov conjecture
in Liouville field theory. The K\"ahler potential on the moduli space of
vortices on \mathbbm{H}^{2} is also derived, and we are led to a geometrical
reinterpretation of these vortices. Finally, we attempt to find the K\"ahler
potential for vortices on \mathbbm{R}^{2} in a third way by relating the
vortices to SU(2) Yang-Mills instantons on \mathbbm{R}^{2}\times S^{2}. This
approach does not give the correct result, and we offer a possible explanation
for this.Comment: 25 page
Self-reproduction in k-inflation
We study cosmological self-reproduction in models of inflation driven by a
scalar field with a noncanonical kinetic term (-inflation). We
develop a general criterion for the existence of attractors and establish
conditions selecting a class of -inflation models that admit a unique
attractor solution. We then consider quantum fluctuations on the attractor
background. We show that the correlation length of the fluctuations is of order
, where is the speed of sound. By computing the magnitude
of field fluctuations, we determine the coefficients of Fokker-Planck equations
describing the probability distribution of the spatially averaged field .
The field fluctuations are generally large in the inflationary attractor
regime; hence, eternal self-reproduction is a generic feature of -inflation.
This is established more formally by demonstrating the existence of stationary
solutions of the relevant FP equations. We also show that there exists a
(model-dependent) range within which large
fluctuations are likely to drive the field towards the upper boundary
, where the semiclassical consideration breaks down. An exit
from inflation into reheating without reaching will occur almost
surely (with probability 1) only if the initial value of is below
. In this way, strong self-reproduction effects constrain models of
-inflation.Comment: RevTeX 4, 17 pages, 1 figur
Intersecting branes from 7-manifolds with G_2 holonomy
In this talk I discuss intersecting brane configurations coming from explicit
metrics with G_2 holonomy. An example of a 7-manifold which representing a R^3
bundle over a self-dual Einstein space is described and the potential appearing
after compactification over the 6-d twistor space is derived.Comment: 7 pages, Latex, talk presented at the 35th Symposium Ahrenshoop,
August 200
Detectable primordial non-gaussianities and gravitational waves in k-inflation
An inflationary single field model with a non-trivial kinetic term for the
inflaton is discussed. It is shown that it is possible to have large primordial
non-gaussianities and large tensor-to-scalar ratio in a simple concrete model
with just a scalar field and a generalized kinetic term for the inflaton field.
This is potentially interesting in the prospect of new forthcoming
observations.Comment: 4 pages, 1 figure, REVTEX, to appear in PR
Possible link of a structurally driven spin flip transition and the insulator-metal transition in the perovskite LaBaCoO
The complex nature of the magnetic ground state in LaACoO
(A = Ca, Sr, Ba) has been investigated via neutron scattering. It was
previously observed that ferromagnetic (FM) as well as antiferromagnetic (AFM)
correlations can coexist prior to the insulator-metal transition (IMT). We
focused on a unique region in the Ba phase diagram, from x = 0.17 - 0.22, in
which a commensurate AFM phase appears first with a propagation vector, k = (0,
-0.5, 0.5), and the Co moment in the (001) plane of the rhombohedral
lattice. With increasing x, the AFM component weakens while an FM order appears
with the FM Co moment directed along the (001) (=(111)) axis. By x
= 0.22, a spin flip to new FM component appears as the crystal fully transforms
to an orthorhombic (Pnma) structure, with the Co moments pointing along a new
direction, (001) (=(110)). It is the emergence of the magnetic Pnma
phase that leads to IMT.Comment: 5 page
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