277 research outputs found
Localized Tachyons and the g_cl conjecture
We consider C/Z_N and C^2/Z_N orbifolds of heterotic string theories and Z_N
orbifolds of AdS_3. We study theories with N=2 worldsheet superconformal
invariance and construct RG flows. Following Harvey, Kutasov, Martinec and
Moore, we compute g_cl and show that it decreases monotonically along RG flows-
as conjectured by them. For the heterotic string theories, the gauge degrees of
freedom do not contribute to the computation of g_cl.Comment: Corrections and clarifications made, 19 page
Twistfield Perturbations of Vertex Operators in the Z_2-Orbifold Model
We apply Kadanoff's theory of marginal deformations of conformal field
theories to twistfield deformations of Z_2 orbifold models in K3 moduli space.
These deformations lead away from the Z_2 orbifold sub-moduli-space and hence
help to explore conformal field theories which have not yet been understood. In
particular, we calculate the deformation of the conformal dimensions of vertex
operators for p^2<1 in second order perturbation theory.Comment: Latex2e, 19 pages, 1 figur
Domestic Rivalry and Export Performance: Theory and Evidence from International Airline Markets
The much-studied relationship between domestic rivalry and export performance consists of those supporting a national-champion rationale, and those supporting a rivalry rationale. While the empirical literature generally supports the positive effects of domestic rivalry, the national-champion rationale actually rests on firmer theoretical ground. We address this inconsistency by providing a theoretical framework that illustrates three paths via which domestic rivalry translates into enhanced international exports. Furthermore, empirical tests on the world airline industry elicit the existence of one particular path - an enhanced firm performance effect - that connects domestic rivalry with improved international exports
Family Unification in Five and Six Dimensions
In family unification models, all three families of quarks and leptons are
grouped together into an irreducible representation of a simple gauge group,
thus unifying the Standard Model gauge symmetries and a gauged family symmetry.
Large orthogonal groups, and the exceptional groups and have been
much studied for family unification. The main theoretical difficulty of family
unification is the existence of mirror families at the weak scale. It is shown
here that family unification without mirror families can be realized in simple
five-dimensional and six-dimensional orbifold models similar to those recently
proposed for SU(5) and SO(10) grand unification. It is noted that a family
unification group that survived to near the weak scale and whose coupling
extrapolated to high scales unified with those of the Standard model would be
evidence accessible in principle at low energy of the existence of small
(Planckian or GUT-scale) extra dimensions.Comment: 13 pages, 2 figures, minor corrections, references adde
An Effect of Corrections on Racetrack Inflation
We study the effects of corrections to the K\"ahler potential on
volume stabilisation and racetrack inflation. In a region where classical
supergravity analysis is justified, stringy corrections can nevertheless be
relevant for correctly analyzing moduli stabilisation and the onset of
inflation.Comment: 13 pages, 4 figures. Typos corrected, references added, this version
to appear in JHE
Affine and toric hyperplane arrangements
We extend the Billera-Ehrenborg-Readdy map between the intersection lattice
and face lattice of a central hyperplane arrangement to affine and toric
hyperplane arrangements. For arrangements on the torus, we also generalize
Zaslavsky's fundamental results on the number of regions.Comment: 32 pages, 4 figure
Towards a Stringy Resolution of the Cosmological Singularity
We study cosmological solutions to the low-energy effective action of
heterotic string theory including possible leading order corrections
and a potential for the dilaton. We consider the possibility that including
such stringy corrections can resolve the initial cosmological singularity.
Since the exact form of these corrections is not known the higher-derivative
terms are constructed so that they vanish when the metric is de Sitter
spacetime. The constructed terms are compatible with known restrictions from
scattering amplitude and string worldsheet beta-function calculations. Analytic
and numerical techniques are used to construct a singularity-free cosmological
solution. At late times and low-curvatures the metric is asymptotically
Minkowski and the dilaton is frozen. In the high-curvature regime the universe
enters a de Sitter phase.Comment: 6 pages, 2 Figures; minor revisions; references added; REVTeX 4;
version to appear in Phys. Rev.
Four Dimensional String/String/String Triality
In six spacetime dimensions, the heterotic string is dual to a Type
string. On further toroidal compactification to four spacetime dimensions, the
heterotic string acquires an SL(2,\BbbZ)_S strong/weak coupling duality and
an SL(2,\BbbZ)_T \times SL(2,\BbbZ)_U target space duality acting on the
dilaton/axion, complex Kahler form and the complex structure fields
respectively. Strong/weak duality in interchanges the roles of and
in yielding a Type string with fields . This suggests
the existence of a third string (whose six-dimensional interpretation is more
obscure) that interchanges the roles of and . It corresponds in fact to
a Type string with fields leading to a four-dimensional
string/string/string triality. Since SL(2,\BbbZ)_S is perturbative for the
Type string, this triality implies -duality for the heterotic
string and thus fills a gap left by duality. For all three strings the
total symmetry is SL(2,\BbbZ)_S \times O(6,22;\BbbZ)_{TU}. The
O(6,22;\BbbZ) is {\it perturbative} for the heterotic string but contains the
conjectured {\it non-perturbative} SL(2,\BbbZ)_X, where is the complex
scalar of the Type string. Thus four-dimensional triality also
provides a (post-compactification) justification for this conjecture. We
interpret the Bogomol'nyi spectrum from all three points of view. In
particular we generalize the Sen-Schwarz formula for short multiplets to
include intermediate multiplets also and discuss the corresponding black hole
spectrum both for the theory and for a truncated ---- symmetric
theory. Just as the first two strings are described by the
four-dimensional {\it elementary} and {\it dual solitonic} solutions, so theComment: 36 pages, Latex, 2 figures, some references changed, minor changes in
formulas and tables; to appear in Nucl. Phys.
Mirror Manifolds in Higher Dimension
We describe mirror manifolds in dimensions different from the familiar case
of complex threefolds. We emphasize the simplifying features of dimension three
and supply more robust methods that do not rely on such special characteristics
and hence naturally generalize to other dimensions. The moduli spaces for
Calabi--Yau -folds are somewhat different from the ``special K\"ahler
manifolds'' which had occurred for , and we indicate the new geometrical
structures which arise. We formulate and apply procedures which allow for the
construction of mirror maps and the calculation of order-by-order instanton
corrections to Yukawa couplings. Mathematically, these corrections are expected
to correspond to calculating Chern classes of various parameter spaces (Hilbert
schemes) for rational curves on Calabi--Yau manifolds. Our results agree with
those obtained by more traditional mathematical methods in the limited number
of cases for which the latter analysis can be carried out. Finally, we make
explicit some striking relations between instanton corrections for various
Yukawa couplings, derived from the associativity of the operator product
algebra.Comment: 44 pages plus 3 tables using harvma
Broad activation of the ubiquitin-proteasome system by Parkin is critical for mitophagy
Parkin, an E3 ubiquitin ligase implicated in Parkinson's disease, promotes degradation of dysfunctional mitochondria by autophagy. Using proteomic and cellular approaches, we show that upon translocation to mitochondria, Parkin activates the ubiquitin–proteasome system (UPS) for widespread degradation of outer membrane proteins. This is evidenced by an increase in K48-linked polyubiquitin on mitochondria, recruitment of the 26S proteasome and rapid degradation of multiple outer membrane proteins. The degradation of proteins by the UPS occurs independently of the autophagy pathway, and inhibition of the 26S proteasome completely abrogates Parkin-mediated mitophagy in HeLa, SH-SY5Y and mouse cells. Although the mitofusins Mfn1 and Mfn2 are rapid degradation targets of Parkin, we find that degradation of additional targets is essential for mitophagy. These results indicate that remodeling of the mitochondrial outer membrane proteome is important for mitophagy, and reveal a causal link between the UPS and autophagy, the major pathways for degradation of intracellular substrates
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