10,041 research outputs found
Killings, Duality and Characteristic Polynomials
In this paper the complete geometrical setting of (lowest order) abelian
T-duality is explored with the help of some new geometrical tools (the reduced
formalism). In particular, all invariant polynomials (the integrands of the
characteristic classes) can be explicitly computed for the dual model in terms
of quantities pertaining to the original one and with the help of the canonical
connection whose intrinsic characterization is given. Using our formalism the
physically, and T-duality invariant, relevant result that top forms are zero
when there is an isometry without fixed points is easily proved.Comment: 14 pages, Late
Unified formalism for higher-order non-autonomous dynamical systems
This work is devoted to giving a geometric framework for describing
higher-order non-autonomous mechanical systems. The starting point is to extend
the Lagrangian-Hamiltonian unified formalism of Skinner and Rusk for these
kinds of systems, generalizing previous developments for higher-order
autonomous mechanical systems and first-order non-autonomous mechanical
systems. Then, we use this unified formulation to derive the standard
Lagrangian and Hamiltonian formalisms, including the Legendre-Ostrogradsky map
and the Euler-Lagrange and the Hamilton equations, both for regular and
singular systems. As applications of our model, two examples of regular and
singular physical systems are studied.Comment: 43 pp. We have corrected and clarified the statement of Propositions
2 and 3. A remark is added after Proposition
Time-dependent Mechanics and Lagrangian submanifolds of Dirac manifolds
A description of time-dependent Mechanics in terms of Lagrangian submanifolds
of Dirac manifolds (in particular, presymplectic and Poisson manifolds) is
presented. Two new Tulczyjew triples are discussed. The first one is adapted to
the restricted Hamiltonian formalism and the second one is adapted to the
extended Hamiltonian formalism
Highly-efficient noise-assisted energy transport in classical oscillator systems
Photosynthesis is a biological process that involves the highly-efficient
transport of energy captured from the sun to a reaction center, where
conversion into useful biochemical energy takes place. Even though one can
always use a quantum perspective to describe any physical process, since
everything follows the laws of Quantum Mechanics, is the use of quantum theory
imperative to explain this high efficiency? Making use of the quantum-classical
correspondence of electronic energy transfer recently introduced by Eisfeld and
Briggs [Phys. Rev. E 85, 046118 (2012)], we show here that the highly-efficient
noise-assisted energy transport described by Rebentrost et al. [New J. Phys.
11, 033003 (2009)], and Plenio and Huelga [New J. Phys. 10, 113019 (2008)], as
the result of the interplay between the quantum coherent evolution of the
photosynthetic system and noise introduced by its surrounding environment, it
can be found as well in purely classical systems. The wider scope of
applicability of the enhancement of energy transfer assisted by noise might
open new ways for developing new technologies aimed at enhancing the efficiency
of a myriad of energy transfer systems, from information channels in
micro-electronic circuits to long-distance high-voltage electrical lines.Comment: 4 pages, 3 figure
Inflation including collapse of the wave function: The quasi-de Sitter case
The precise physical mechanism describing the emergence of the seeds of
cosmic structure from a perfect isotropic and homogeneous universe has not been
fully explained by the standard version of inflationary models. To handle this
shortcoming, D. Sudarsky and collaborators have developed a proposal: the
self-induced collapse hypothesis. In this scheme, the objective collapse of the
inflaton wave function is responsible for the emergence of inhomogeneity and
anisotropy at all scales. In previous papers, the proposal was developed with
an almost exact de Sitter space-time approximation for the background that led
to a perfect scale-invariant power spectrum. In the present article, we
consider a full quasi-de Sitter expansion and calculate the primordial power
spectrum for three different choices of the self-induced collapse. The
consideration of a quasi-de Sitter background allow us to distinguish
departures from an exact scale-invariant power spectrum that are due to the
inclusion of the collapse hypothesis. These deviations are also different from
the prediction of standard inflationary models with running spectral index.
Comparison with the primordial power spectrum and the CMB temperature
fluctuation spectrum preferred by the latest observational data is also
discussed. From the analysis performed in this work, it follows that most of
the collapse schemes analysed in this paper are viable candidates to explain
present observations of the CMB fluctuation spectrum.Comment: 24 pages, 12 figures. Replaced to match published versio
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