3,730 research outputs found
Regular R-R and NS-NS BPS black holes
We show in a precise group theoretical fashion how the generating solution of
regular BPS black holes of N=8 supergravity, which is known to be a solution
also of a simpler N=2 STU model truncation, can be characterized as NS-NS or
R-R charged according to the way the corresponding STU model is embedded in the
original N=8 theory. Of particular interest is the class of embeddings which
yield regular BPS black hole solutions carrying only R-R charge and whose
microscopic description can possibly be given in terms of bound states of
D-branes only. The microscopic interpretation of the bosonic fields in this
class of STU models relies on the solvable Lie algebra (SLA) method. In the
present article we improve this mathematical technique in order to provide two
distinct descriptions for type IIA and type IIB theories and an algebraic
characterization of S*T--dual embeddings within the N=8,d=4 theory. This
analysis will be applied to the particular example of a four parameter
(dilatonic) solution of which both the full macroscopic and microscopic
descriptions will be worked out.Comment: latex, 30 pages. Final version to appear on Int.J.Mod.Phy
Gauge/gravity duality and the interplay of various fractional branes
We consider different types of fractional branes on a Z_2 orbifold of the
conifold and analyze in detail the corresponding gauge/gravity duality. The
gauge theory possesses a rich and varied dynamics, both in the UV and in the
IR. We find the dual supergravity solution which contains both untwisted and
twisted 3-form fluxes, related to what are known as deformation and N=2
fractional branes respectively. We analyze the resulting RG flow from the
supergravity perspective, by developing an algorithm to easily extract it. We
find hints of a generalization of the familiar cascade of Seiberg dualities due
to a non-trivial interplay between the different types of fractional branes. We
finally consider the IR behavior in several limits, where the dominant
effective dynamics is either confining, in a Coulomb phase or runaway, and
discuss the resolution of singularities in the dual geometric background.Comment: 38 pages + appendices, 15 figures; v2: refs added and typos correcte
Comparison of new metaheuristics, for the solution of an integrated jobs-maintenance scheduling problem
This paper presents and compares new metaheuristics to solve an integrated jobs-maintenance scheduling problem, on a single machine subjected to aging and failures. The problem, introduced by Zammori et al. (2014), was originally solved using the Modified Harmony Search (MHS) metaheuristic. However, an extensive numerical analysis brought to light some structural limits of the MHS, as the analysis revealed that the MHS is outperformed by the simpler Simulated Annealing by Ishibuchi et al. (1995). Aiming to solve the problem in a more effective way, we integrated the MHS with local minima escaping procedures and we also developed a new Cuckoo Search metaheuristic, based on an innovative Levy Flight. A thorough comparison confirmed the superiority of the newly developed Cuckoo Search, which is capable to find better solutions in a smaller amount of time. This an important result, both for academics and practitioners, since the integrated job-maintenance scheduling problem has a high operational relevance, but it is known to be extremely hard to be solved, especially in a reasonable amount of time. Also, the developed Cuckoo Search has been designed in an extremely flexible way and it can be easily readapted and applied to a wide range of combinatorial problems. (C) 2018 Elsevier Ltd. All rights reserved
Feynman Rules in the Type III Natural Flavour-Conserving Two-Higgs Doublet Model
We consider a two Higgs-doublet model with symmetry, which implies a
rather than 0 relative phase between the vacuum expectation
values . The corresponding Feynman rules are derived
accordingly and the transformation of the Higgs fields from the weak to the
mass eigenstates includes not only an angle rotation but also a phase
transformation. In this model, both doublets couple to the same type of
fermions and the flavour-changing neutral currents are naturally suppressed. We
also demonstrate that the Type III natural flavour-conserving model is valid at
tree-level even when an explicit symmetry breaking perturbation is
introduced to get a reasonable CKM matrix. In the special case , as the ratio runs from 0 to ,
the dominant Yukawa coupling will change from the first two generations to the
third generation. In the Feynman rules, we also find that the charged Higgs
currents are explicitly left-right asymmetric. The ratios between the left- and
right-handed currents for the quarks in the same generations are estimated.Comment: 16 pages (figures not included), NCKU-HEP/93-1
A Heavy-Light Chiral Quark Model
We present a new chiral quark model for mesons involving a heavy and a light
(anti-) quark. The model relates various combinations of a quark - meson
coupling constant and loop integrals to physical quantities. Then, some
quantities may be predicted and some used as input. The extension from other
similar models is that the present model includes the lowest order gluon
condensate of the order (300 MeV)^4 determined by the mass splitting of the 0^-
and the 1^- heavy meson states. Within the model, we find a reasonable
description of parameters such as the decay constants f_B and f_D, the
Isgur-Wise function and the axial vector coupling g_A in chiral perturbation
theory for light and heavy mesons.Comment: 31 pages, 13 figures, RevTex4.
New checks and subtleties for AdS/CFT and a-maximization
We provide a cross-check of AdS/CFT and a-charge maximization for a four
dimensional =1 SCFT with irrational R-charges. The gauge theory is the low
energy effective theory of N D3-branes at the tip of the complex cone over the
first del Pezzo surface. By carefully taking into account the subtle issue of
flavor symmetry breaking at the fixed point, we show, using a-maximization,
that this theory has in fact irrational central charge and R-charges. Our
results perfectly match with those inherited from the recently discovered
supergravity dual background. Along analogous lines, we make novel predictions
for the still unknown AdS dual of the quiver theory for the second del Pezzo
surface. This should flow to a SCFT with irrational charges, too. All of our
results differ from previous findings in the literature and outline interesting
subtleties in a-maximization and AdS/CFT techniques overlooked in the past.Comment: Latex, 16 pagex, 2 figures; v2, comments and a reference added; v3,
typos correcte
Trophic cascades and the transient keystone concept
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordApex predator reintroductions are commonly motivated by the imperative to restore populations and wider ecosystem function by precipitating trophic cascades that release basal species. Yet evidence for the existence of such cascades is often equivocal, particularly where consumptive interactions between apex and intermediate predators are weak or absent. Here, using a tri-trophic skate-crab-bivalve study-system, we find that non-consumptive interactions between apex skate and intermediate crabs cascade down to consumptive interactions between crabs and bivalves, significantly reducing bivalve mortality. However, skate only functioned as keystone where crabs foraged for bivalves in the absence of mature bivalve reef: where reef was present, bivalve mortality was not significantly different in the presence or absence of skate. By facilitating the establishment of basal species which, in turn, diminish apex-intermediate effects, the skate's keystone function is subject to negative regulation. Thus, we propose that keystone functionality can be transient with respect to environmental context. Our findings have two central implications for apex predator reintroductions and basic ecology: (i) species hitherto not considered as keystone may have the capacity to act as such transiently, and; (ii) keystones are known to regulate ecosystems, but transience implies that ecosystems can regulate keystone function.Natural Environment Research Council (NERC
Towards Supergravity Duals of Chiral Symmetry Breaking in Sasaki-Einstein Cascading Quiver Theories
We construct a first order deformation of the complex structure of the cone
over Sasaki-Einstein spaces Y^{p,q} and check supersymmetry explicitly. This
space is a central element in the holographic dual of chiral symmetry breaking
for a large class of cascading quiver theories. We discuss a solution
describing a stack of N D3 branes and M fractional D3 branes at the tip of the
deformed spaces.Comment: 28 pages, no figures. v2: typos, references and a note adde
The Non-Perturbative SUSY Yang-Mills Theory from Semiclassical Absorption of Supergravity by Wrapped D Branes
The imaginary part of the two point functions of the superconformal anomalous
currents are extracted from the cross-sections of semiclassical absorption of
dilaton, RR-2 form and gravitino by the wrapped D5 branes. From the central
terms of the two point functions anomalous Ward identity is established which
relates the exact pre-potential of the SUSY Yang-Mills theory with
the vacuum expectation value of the anomaly multiplet. From the Ward identity,
WDVV (Witten-Dijkgraaf-Verlinde-Verlinde) equation can be derived which is
solved for the exact pre-potential.Comment: 11 pages, late
Microphotoluminescence study of disorder in ferromagnetic (Cd,Mn)Te quantum well
Microphotoluminescence mapping experiments were performed on a modulation
doped (Cd,Mn)Te quantum well exhibiting carrier induced ferromagnetism. The
zero field splitting that reveals the presence of a spontaneous magnetization
in the low-temperature phase, is measured locally; its fluctuations are
compared to those of the spin content and of the carrier density, also measured
spectroscopically in the same run. We show that the fluctuations of the carrier
density are the main mechanism responsible for the fluctuations of the
spontaneous magnetization in the ferromagnetic phase, while those of the Mn
spin density have no detectable effect at this scale of observation.Comment: 4 pages, 3 figure
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