11,423 research outputs found
Dilatation operator and the Super Yang-Mills duals of open strings on AdS Giant Gravitons
We study the one-loop anomalous dimensions of the Super Yang-Mills dual
operators to open strings ending on AdS giant gravitons. AdS giant gravitons
have no upper bound for their angular momentum and we represent them by the
contraction of scalar fields, carrying the appropriate R-charge, with a totally
symmetric tensor. We represent the open string motion along AdS directions by
appending to the giant graviton operator a product of fields including
covariant derivatives. We derive a bosonic lattice Hamiltonian that describes
the mixing of these excited AdS giants operators under the action of the
one-loop dilatation operator of N=4 SYM. This Hamiltonian captures several
intuitive differences with respect to the case of sphere giant gravitons. A
semiclassical analysis of the Hamiltonian allows us to give a geometrical
interpretation for the labeling used to describe the fields products appended
to the AdS giant operators. It also allows us to show evidence for the
existence of continuous bands in the Hamiltonian spectrum.Comment: 28 page
Noncommutative fermions and Morita equivalence
We study the Morita equivalence for fermion theories on noncommutative
two-tori. For rational values of the parameter (in appropriate units)
we show the equivalence between an abelian noncommutative fermion theory and a
nonabelian theory of twisted fermions on ordinary space. We study the chiral
anomaly and compute the determinant of the Dirac operator in the dual theories
showing that the Morita equivalence also holds at this level.Comment: 12 pages, LaTex file, no figures. Minor corrections, version to
appear in Phys. Lett.
Ladder exponentiation for generic large symmetric representation Wilson loops
A recent proposal was made for a large representation rank limit for which
the expectation values of N = 4 super Yang-Mills Wilson loops are given by the
exponential of the 1-loop result. We verify the validity of this exponentiation
in the strong coupling limit using the holographic D3-brane description for
straight Wilson loops following an arbitrary internal space trajectory.Comment: 12 pages, 1 figur
Quantum Corrals, Eigenmodes and Quantum Mirages in s-wave Superconductors
We study the electronic structure of magnetic and non-magnetic quantum
corrals embedded in s-wave superconductors. We demonstrate that a quantum
mirage of an impurity bound state peak can be projected from the occupied into
the empty focus of a non-magnetic quantum corral via the excitation of the
corral's eigenmodes. We observe an enhanced coupling between magnetic
impurities inside the corral, which can be varied through oscillations in the
corral's impurity potential. Finally, we discuss the form of eigenmodes in
magnetic quantum corrals.Comment: 4 pages, 4 figure
Predation risk reduces a female preference for heterospecific males in the green swordtail
The presence of a predator can result in the alteration, loss or reversal of a mating preference. Under predation risk, females often change their initial preference for conspicuous males, favouring less flashy males to reduce the risk of being detected by predators. Previous studies on predator-induced plasticity in mate preferences have given females a choice between more and less conspicuous conspecific males. However, in species that naturally hybridize, it is also possible that females might choose an inconspicuous heterospecific male over a conspicuous conspecific male under predation risk. Our study addresses this question using the green swordtail (Xiphophorus helleri) and the southern platyfish (Xiphophorus maculatus), which are sympatric in the wild. We hypothesized that X. helleri females would prefer the sworded conspecific males in the absence of a predator but favour the less conspicuous, swordless, heterospecific males in the presence of a predator. Contrary to our expectation, females associated more with the heterospecific male than the conspecific male in the control (no predator) treatment, and they were non-choosy in the predator treatment. This might reflect that females were attracted to the novel male phenotype when there was no risk of predation but became more neophobic after predator exposure. Regardless of the underlying mechanism, our results suggest that predation pressure may affect female preferences for conspecific versus heterospecific males. We also found striking within-population, between-individual variation in behavioural plasticity: females differed in the strength and direction of their preferences, as well as in the extent to which they altered their preferences in response to changes in perceived predation risk. Such variation in female preferences for heterospecific males could potentially lead to temporal and spatial variation in hybridization rates in the wild
The importance of scalar fields as extradimensional metric components in Kaluza-Klein models
Extradimensional models are achieving their highest popularity nowadays,
among other reasons, because they can plausible explain some standard cosmology
issues, such as the cosmological constant and hierarchy problems. In
extradimensional models, we can infer that the four-dimensional matter rises as
a geometric manifestation of the extra coordinate. In this way, although we
still cannot see the extra dimension, we can relate it to physical quantities
that are able to exert such a mechanism of matter induction in the observable
universe. In this work we propose that scalar fields are those physical
quantities. The models here presented are purely geometrical in the sense that
no matter lagrangian is assumed and even the scalar fields are contained in the
extradimensional metric. The results are capable of describing different
observable cosmic features and yield an alternative to ultimately understand
the extra dimension and the mechanism in which it is responsible for the
creation of matter in the observable universe
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