57 research outputs found
On equivariant Serre problem for principal bundles
Let be a --equivariant algebraic principal --bundle over a
normal complex affine variety equipped with an action of , where
and are complex linear algebraic groups. Suppose is
contractible as a topological --space with a dense orbit, and is a --fixed point. We show that if is reductive, then
admits a --equivariant isomorphism with the product principal
--bundle , where is a homomorphism between algebraic groups. As a
consequence, any torus equivariant principal -bundle over an affine toric
variety is equivariantly trivial. This leads to a classification of torus
equivariant principal -bundles over any complex toric variety.Comment: References added. To appear in the International Journal of
Mathematic
A classification of equivariant principal bundles over nonsingular toric varieties
We classify holomorphic as well as algebraic torus equivariant principal
-bundles over a nonsingular toric variety , where is a complex linear
algebraic group. It is shown that any such bundle over an affine, nonsingular
toric variety admits a trivialization in equivariant sense. We also obtain some
splitting results.Comment: 14 page
Tannakian classification of equivariant principal bundles on toric varieties
Let be a complete toric variety equipped with the action of a torus
and a reductive algebraic group, defined over an algebraically closed field
. We introduce the notion of a compatible --filtered algebra
associated to , generalizing the notion of a compatible --filtered
vector space due to Klyachko, where denotes the fan of . We combine
Klyachko's classification of --equivariant vector bundles on with Nori's
Tannakian approach to principal --bundles, to give an equivalence of
categories between --equivariant principal --bundles on and certain
compatible --filtered algebras associated to , when the
characteristic of is .Comment: 22 pages, revised version, to appear in Transform. Group
Reviewing the prospect of fermion triplets as dark matter and source of baryon asymmetry in non-standard cosmology
Indirect searches of Dark Matter (DM), in conjugation with `missing track
searches' at the collider seem to confine SU(2) fermion triplet DM (FTDM)
mass within a narrow range around 1 TeV. The canonical picture of the pure FTDM
is in tension since it is under-abundant for the said mass range. Several
preceding studies have reported that an extra species (), redshifts
faster than the radiation ( where ), leads to a faster
expanding early Universe by dominating in the energy density with an enhanced
Hubble parameter. This has the potential to revive the under-abundant FTDM
( odd, lightest generation) by causing freeze-out earlier without
modifying the interaction strength between DM and thermal bath. On the other
hand, although the CP asymmetry produced due to the decay of
even heavier generations of the triplet remains unaffected, its evolution is
greatly affected by the non-standard cosmology. It has been observed through
numerical estimations that the minimum mass of the triplet, required to produce
sufficient baryon asymmetry of the Universe (BAU), can be lowered up to two
orders (compared to the standard cosmology) in this fast expansion scenario.
The non-standard parameters and (a reference temperature below which
radiation dominance prevails), which simultaneously control DM abundance as
well as the frozen value of BAU, are tightly constrained from the observed
experimental values. We have found that is strictly bounded within the
interval where the upper bound is imposed by the
BAU constraint whereas the lower bound arises to satisfy the correct DM
abundance. It has been noticed that the restriction on is not so
stringent as it can vary from sub-GeV to a few tens of GeV.Comment: 40 pages, 10 figures, 1 table, minor changes, version published in
JCA
Structural segments and residue propensities in protein-RNA interfaces: Comparison with protein-protein and protein-DNA complexes
The interface of a protein molecule that is involved in binding another protein, DNA or RNA has been characterized in terms of the number of unique secondary structural segments (SSSs),
made up of stretches of helix, strand and non-regular (NR) regions. On average 10-11 segments define the protein interface in protein-protein (PP) and protein-DNA (PD) complexes, while the
number is higher (14) for protein-RNA (PR) complexes. While the length of helical segments in PP interaction increases with the interface area, this is not the case in PD and PR complexes.
The propensities of residues to occur in the three types of secondary structural elements (SSEs) in the interface relative to the corresponding elements in the protein tertiary structures
have been calculated. Arg, Lys, Asn, Tyr, His and Gln are preferred residues in PR complexes; in addition, Ser and Thr are also favoured in PD interfaces
On stability of tangent bundle of toric varieties
Let be a nonsingular complex projective toric variety. We address the
question of semi-stability as well as stability for the tangent bundle .
In particular, a complete answer is given when is a Fano toric variety of
dimension four with Picard number at most two, complementing earlier work of
Nakagawa. We also give an infinite set of examples of Fano toric varieties for
which is unstable; the dimensions of this collection of varieties are
unbounded. Our method is based on the equivariant approach initiated by
Klyachko and developed further by Perling and Kool.Comment: Revised version. To appear in Proc. Indian Acad. Sci. Math. Sc
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