41,608 research outputs found
Second central extension in Galilean covariant field theory
The second central extension of the planar Galilei group has been alleged to
have its origin in the spin variable. This idea is explored here by considering
local Galilean covariant field theory for free fields of arbitrary spin. It is
shown that such systems generally display only a trivial realization of the
second central extension. While it is possible to realize any desired value of
the extension parameter by suitable redefinition of the boost operator, such an
approach has no necessary connection to the spin of the basic underlying field.Comment: 6 pgs., late
Comment on Gauge-Independent Analysis of Chern-Simons Theory with Matter Coupling
It is shown that a recently proposed relativistic field theory of anyons is
mathematically flawed and also does not satisfy reasonable criteria for such a
theory.Comment: 4 page
Vanguard Concentration
The design, manufacture, and performance of a solar parabolic dish/stirling engine system are investigated. The commercialization of the system is discussed based on ease of fabrication, assembly, and cost effectiveness. The various components contributed from government and related industries are evaluated
Soluble field theory with a massless gauge invariant limit
It is shown that there exists a soluble four parameter model in (1+1)
dimensions all of whose propagators can be determined in terms of the
corresponding known propagators of the vector coupling theory. Unlike the
latter case, however, the limit of zero bare mass is nonsingular and yields a
nontrivial theory with a rigorously unbroken gauge invariance.Comment: 7 pages, revtex, no figure
The functions of postpartum depression
Evolutionary approaches to parental care suggest that parents will not automatically invest in all offspring, and should reduce or eliminate investment in their children if the costs outweigh the benefits. Lack of paternal or social support will increase the costs born by mothers, whereas infant health problems will reduce the evolutionary benefits to be gained. Numerous studies support the correlation between postpartum depression (PPD) and lack of social support or indicators of possible infant health and development problems. PPD may be an adaptation that informs mothers that they are suffering or have suffered a fitness cost, that motivates them to reduce or eliminate investment in offspring under certain circumstances, and that may help them negotiate greater levels of investment from others. PPD also appears to be a good model for depression in general
Supersymmetric branes on curved spaces and fluxes
We discuss general supersymmetric brane configurations in flux backgrounds of
string and M-theory and derive a necessary condition for the worldvolume theory
to be supersymmetric on a given curved manifold. This condition resembles very
much the conditions found from coupling a supersymmetric field theory to
off-shell supergravity but can be derived in any dimension and for up to
sixteen supercharges. Apart from the topological twist, all couplings appearing
in the supersymmetry condition are linked to fluxes in the bulk. We explicitly
derive the condition for D3-, M2- and M5-branes, in which case the results are
also useful for constructing holographic duals to the corresponding field
theories. In setups we compare the supersymmetry conditions to those that
arise by coupling the field theory to off-shell supergravity. We find that the
couplings of both old and new minimal supergravity are simultaneously realized,
indicating that off-shell supergravity should be coupled via the S-multiplet of
16/16 supergravity in order to describe all supersymmetric brane theories on
curved spaces.Comment: 18 pages; v2: Added discussion refering to 16/16 supergravity for the
N=1 case and added reference
Casimir effect for the sphere revisited
In a recent work Brevik \emph{et al.} have offered formal proofs of two
results which figure prominently in calculations of the Casimir pressure on a
sphere. It is shown by means of simple counterexamples that each of those
proofs is necessarily incorrect.Comment: 4 pages, no figures, to be published in Physics Letters
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