24,180 research outputs found
Time and Tachyon
Recent analysis suggests that the classical dynamics of a tachyon on an
unstable D-brane is described by a scalar Born-Infeld type action with a
runaway potential. The classical configurations in this theory at late time are
in one to one correspondence with the configuration of a system of
non-interacting (incoherent), non-rotating dust. We discuss some aspects of
canonical quantization of this field theory coupled to gravity, and explore,
following earlier work on this subject, the possibility of using the scalar
field (tachyon) as the definition of time in quantum cosmology. At late `time'
we can identify a subsector in which the scalar field decouples from gravity
and we recover the usual Wheeler - de Witt equation of quantum gravity.Comment: LaTeX file, 24 page
Federalism and fiscal reform in India.
This paper attempts to analyse the experience of incentivising economic reforms at the state level through central transfers to states. It reviews the experiences of the central government introducing incentives for reform directly through various specific purpose transfers as well as the incentive schemes recommended by various Finance Commissions. The incentive schemes directly introduced by the central government include, accelerated irrigation benefit programme, accelerated power development and reform programme, Jawaharlal Nehru Urban Renewal Mission, education and health sector reforms. The reforms recommended by the Finance Commissions include incentivising tax reforms and fiscal restructuring and consolidation. The review of the experiences of Indian fiscal federalism shows that the incentivising reforms have neither been an unqualified success nor have they been a total failure. There are interesting lessons to be learnt from the experiences for both designing the incentive schemes and implementing them. The paper summarises the lessons of experience. While incorporating these in designing and implementing incentive schemes can be useful in the short and medium term, what matters in the long run is the political incentive for reforms.
Geometry versus Entanglement in Resonating Valence Bond Liquids
We investigate the behavior of bipartite as well as genuine multipartite
entanglement of a resonating valence bond state on a ladder. We show that the
system possesses significant amounts of bipartite entanglement in the steps of
the ladder while no substantial bipartite entanglement is present in the rails.
Genuine multipartite entanglement present in the system is negligible. The
results are in stark contrast with the entanglement properties of the same
state on isotropic lattices in two and higher dimensions, indicating that the
geometry of the lattice can have important implications on the quality of
quantum information and other tasks that can be performed by using multiparty
states on that lattice.Comment: 6 pages, 8 figures, RevTeX
Remark about Non-BPS D-Brane in Type IIA Theory
In this paper we would like to show simple mechanisms how from the action for
non-BPS D-brane we can obtain action describing BPS D(p-1)-brane in Type IIA
theory.Comment: 13 pages, completely rewritten pape
Entanglement production due to quench dynamics of an anisotropic XY chain in a transverse field
We compute concurrence and negativity as measures of two-site entanglement
generated by a power-law quench (characterized by a rate 1/tau and an exponent
alpha) which takes an anisotropic XY chain in a transverse field through a
quantum critical point (QCP). We show that only the even-neighbor pairs of
sites get entangled in such a process. Moreover, there is a critical rate of
quench, 1/tau_c, above which no two-site entanglement is generated; the entire
entanglement is multipartite. The ratio of the two-site entanglements between
consecutive even neighbors can be tuned by changing the quench rate. We also
show that for large tau, the concurrence (negativity) scales as sqrt{alpha/tau}
(alpha/tau), and we relate this scaling behavior to defect production by the
quench through a QCP.Comment: 5 pages including 4 figures; added a figure on multipartite
entanglement and some references -- this is the published versio
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Investigation of Shallow Sedimentary Structure of the Anchorage Basin, Alaska, Using Simulated Annealing Inversion of Site Response
This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this purpose, inversion of site response [SR(f)] data in the frequency range 0.5-11.0 Hz from various sites of the basin has been performed using the simulated annealing method to compute subsurface layer thickness, shear-wave velocity (beta), density, and shear-wave quality factor. The one-dimensional (1D) models for the aforementioned parameters were obtained with preset bounds on the basis of available geological information such that the L-2 norm error between the observed and computed site response attained a global minimum. Next, the spatial distribution of the important parameter beta was obtained by interpolating values yielded by the 1D models. The results indicate the presence of three distinct velocity zones as the source of spatial variation of SR(f) in the Anchorage basin. In the uppermost part of the basin, the beta values of fine-grain Quaternary sediments mainly lie in the range of 180-500 m/sec with thickness varying from 15 to 50 m. This formation overlies relatively thick (80-200 m) coarse-grain Quaternary sediments with beta values in the range of 600-900 m/sec. These two Quaternary units are, in turn, overlain on Tertiary sediments with beta > 1000 m/sec located at depths of 100 and 250 m, respectively, in the central and western side along the Knik Arm parts of the basin. The important implication of the result is that the sources of spatial variation of SR(f) in the Anchorage basin for the frequency band 0.5-11 Hz, besides in the uppermost 30 m, are found to be deeper than this depth. Thus, use of commonly considered geological formations in the depth intervals from 0 to 30 m for the ground-motion interpretation will likely yield erroneous results in the Anchorage basin.GIEnvironment and Natural Resources InstituteSchool of Engineering of the University of Alaska, AnchorageGeological Science
Cylindrical thin-shell wormholes and energy conditions
We prove the impossibility of cylindrical thin-shell wormholes supported by
matter satisfying the energy conditions everywhere, under reasonable
assumptions about the asymptotic behaviour of the - in general different -
metrics at each side of the throat. In particular, we reproduce for singular
sources previous results corresponding to flat and conical asymptotics, and
extend them to a more general asymptotic behaviour. Besides, we establish
necessary conditions for the possibility of non exotic cylindrical thin-shell
wormholes.Comment: 9 pages; slightly improved version of the article accepted in Int. J.
Mod. Phys.
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