1,026 research outputs found
Accidental SUSY: Enhanced Bulk Supersymmetry from Brane Back-reaction
We compute how bulk loops renormalize both bulk and brane effective
interactions for codimension-two branes in 6D gauged chiral supergravity, as
functions of the brane tension and brane-localized flux. We do so by explicitly
integrating out hyper- and gauge-multiplets in 6D gauged chiral supergravity
compactified to 4D on a flux-stabilized 2D rugby-ball geometry, specializing
the results of a companion paper, arXiv:1210.3753, to the supersymmetric case.
While the brane back-reaction generically breaks supersymmetry, we show that
the bulk supersymmetry can be preserved if the amount of brane-localized flux
is related in a specific BPS-like way to the brane tension, and verify that the
loop corrections to the brane curvature vanish in this special case. In these
systems it is the brane-bulk couplings that fix the size of the extra
dimensions, and we show that in some circumstances the bulk geometry
dynamically adjusts to ensure the supersymmetric BPS-like condition is
automatically satisfied. We investigate the robustness of this residual
supersymmetry to loops of non-supersymmetric matter on the branes, and show
that supersymmetry-breaking effects can enter only through effective brane-bulk
interactions involving at least two derivatives. We comment on the relevance of
this calculation to proposed applications of codimension-two 6D models to
solutions of the hierarchy and cosmological constant problems.Comment: 49 pages + appendices. This is the final version to appear in JHE
Session 1 : Political and economic alternative paradigms : Network of rurban republics
On Day 1 (13 June 2018), in the session of “Political and Economic Alternative Paradigms”, M. P. PARAMESWARAN (Kerala Sastra Sahitya Parishad, India) delivered a lecture on Network of Rurban Republics.
The video is produced by Global University for Sustainability, 2018
Comprehensive review of various corrosion behaviours on 316 stainless steel
Corrosion is a destructive process that converts the pure metal into a chemically stabled form by hydroxide or sulphide and it is a slow process of destruction on the material by the chemical or electrochemical reaction in the environmental space. This kind of destruction has been typically produced from oxides or salt content on the material and it results in distinctive orange coloration. The classifications of corrosion act on atmospheric air and liquids as well as on contact of two solids. To resist the corrosion rate, stainless steel 316 has been chosen because of the presence of 2-3% molybdenum content and the presence of molybdenum plays a vital role in corrosion resistance. In this study, literature related to various works has been reviewed to explain the corrosion behaviour on cavitation, crevice, electrochemical, erosion, fatigue, galvanic, uniform, pitting, and stress corrosion which act on 316 stainless steel. In the present work, several coating processes and the additives, that have been added to SS 316 to enhance the outcomes according to various corrosion causes, are discussed
Experimental determination of the Compton profile of C60 through binary encounter electron spectroscopy
The method of 0° electron spectroscopy was used to study binary encounter electrons resulting from hard collisions between 1.5 MeV/u C6+ ions and the electrons in a C60 vapor target. The Compton profile of C60 was then extracted from the electron spectra using an impulse approximation treatment. The experimental results are in excellent agreement with theoretical Compton profiles of C60. The C60 Compton profile is compared with that of atomic carbon, as well as those for graphite and diamond.Peer reviewe
Bulk Axions, Brane Back-reaction and Fluxes
Extra-dimensional models can involve bulk pseudo-Goldstone bosons (pGBs)
whose shift symmetry is explicitly broken only by physics localized on branes.
Reliable calculation of their low-energy potential is often difficult because
it requires details of the stabilization of the extra dimensions. In rugby ball
solutions, for which two compact extra dimensions are stabilized in the
presence of only positive-tension brane sources, the effects of brane
back-reaction can be computed explicitly. This allows the calculation of the
shape of the low-energy pGB potential and response of the extra dimensional
geometry as a function of the perturbing brane properties. If the
pGB-dependence is a small part of the total brane tension a very general
analysis is possible, permitting an exploration of how the system responds to
frustration when the two branes disagree on what the proper scalar vacuum
should be. We show how the low-energy potential is given by the sum of brane
tensions (in agreement with common lore) when only the brane tensions couple to
the pGB. We also show how a direct brane coupling to the flux stabilizing the
extra dimensions corrects this result in a way that does not simply amount to
the contribution of the flux to the brane tensions. We calculate the mass of
the would-be zero mode, and briefly describe several potential applications,
including a brane realization of `natural inflation,' and a dynamical mechanism
for suppressing the couplings of the pGB to matter localized on the branes.
Since the scalar can be light enough to be relevant to precision tests of
gravity (in a technically natural way) this mechanism can be relevant to
evading phenomenological bounds.Comment: 36 pages, JHEP styl
Systematics of String Loop Corrections in Type IIB Calabi-Yau Flux Compactifications
We study the behaviour of the string loop corrections to the N=1 4D
supergravity Kaehler potential that occur in flux compactifications of IIB
string theory on general Calabi-Yau three-folds. We give a low energy
interpretation for the conjecture of Berg, Haack and Pajer for the form of the
loop corrections to the Kaehler potential. We check the consistency of this
interpretation in several examples. We show that for arbitrary Calabi-Yaus, the
leading contribution of these corrections to the scalar potential is always
vanishing, giving an "extended no-scale structure". This result holds as long
as the corrections are homogeneous functions of degree -2 in the 2-cycle
volumes. We use the Coleman-Weinberg potential to motivate this cancellation
from the viewpoint of low-energy field theory. Finally we give a simple formula
for the 1-loop correction to the scalar potential in terms of the tree-level
Kaehler metric and the correction to the Kaehler potential. We illustrate our
ideas with several examples. A companion paper will use these results in the
study of Kaehler moduli stabilisation.Comment: 34 pages and 3 figures; typos corrected and references adde
Kicking the Rugby Ball: Perturbations of 6D Gauged Chiral Supergravity
We analyze the axially-symmetric scalar perturbations of 6D chiral gauged
supergravity compactified on the general warped geometries in the presence of
two source branes. We find all of the conical geometries are marginally stable
for normalizable perturbations (in disagreement with some recent calculations)
and the nonconical for regular perturbations, even though none of them are
supersymmetric (apart from the trivial Salam-Sezgin solution, for which there
are no source branes). The marginal direction is the one whose presence is
required by the classical scaling property of the field equations, and all
other modes have positive squared mass. In the special case of the conical
solutions, including (but not restricted to) the unwarped `rugby-ball'
solutions, we find closed-form expressions for the mode functions in terms of
Legendre and Hypergeometric functions. In so doing we show how to match the
asymptotic near-brane form for the solution to the physics of the source
branes, and thereby how to physically interpret perturbations which can be
singular at the brane positions.Comment: 21 pages + appendices, references adde
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