12,557 research outputs found
Two-dimensional topological field theories as taffy
In this paper we use trivial defects to define global taffy-like operations
on string worldsheets, which preserve the field theory. We fold open and closed
strings on a space X into open strings on products of multiple copies of X, and
perform checks that the "taffy-folded" worldsheets have the same massless
spectra and other properties as the original worldsheets. Such folding tricks
are a standard method in the defects community; the novelty of this paper lies
in deriving mathematical identities to check that e.g. massless spectra are
invariant in topological field theories. We discuss the case of the B model
extensively, and also derive the same identities for string topology, where
they become statements of homotopy invariance. We outline analogous results in
the A model, B-twisted Landau-Ginzburg models, and physical strings. We also
discuss the understanding of the closed string states as the Hochschild
homology of the open string algebra, and outline possible applications to
elliptic genera.Comment: 61 pages, LaTeX; v2: typos fixe
Physical Results from Unphysical Simulations
We calculate various properties of pseudoscalar mesons in partially quenched
QCD using chiral perturbation theory through next-to-leading order. Our results
can be used to extrapolate to QCD from partially quenched simulations, as long
as the latter use three light dynamical quarks. In other words, one can use
unphysical simulations to extract physical quantities - in this case the quark
masses, meson decay constants, and the Gasser-Leutwyler parameters L_4-L_8. Our
proposal for determining L_7 makes explicit use of an unphysical (yet
measurable) effect of partially quenched theories, namely the double-pole that
appears in certain two-point correlation functions. Most of our calculations
are done for sea quarks having up to three different masses, except for our
result for L_7, which is derived for degenerate sea quarks.Comment: 26 pages, 12 figures (discussion on discretization errors at end of
sec. IV clarified; minor improvements in presentation; results unchanged
Unphysical Operators in Partially Quenched QCD
We point out that the chiral Lagrangian describing pseudo-Goldstone bosons in
partially quenched QCD has one more four-derivative operator than that for
unquenched QCD with three flavors. The new operator can be chosen to vanish in
the unquenched sector of the partially quenched theory. Its contributions begin
at next-to-leading order in the chiral expansion. At this order it contributes
only to unphysical scattering processes, and we work out some examples. Its
contributions to pseudo-Goldstone properties begin at next-to-next-to-leading
order, and we determine their form. We also determine all the zero and two
derivative operators in the partially quenched chiral Lagrangian,
finding three more than in unquenched QCD, and use these to give the general
form of the analytic next-to-next-to-leading order contributions to the
pseudo-Goldstone mass and decay constant. We discuss the general implications
of such additional operators for the utility of partially quenched simulationsComment: 13 pages, 11 figures Version 2: Additional footnote and parenthesis
in section
Partially quenched chiral perturbation theory without
This paper completes the argument that lattice simulations of partially
quenched QCD can provide quantitative information about QCD itself, with the
aid of partially quenched chiral perturbation theory. A barrier to doing this
has been the inclusion of , the partially quenched generalization of
the , in previous calculations in the partially quenched effective
theory. This invalidates the low energy perturbative expansion, gives rise to
many new unknown parameters, and makes it impossible to reliably calculate the
relation between the partially quenched theory and low energy QCD. We show that
it is straightforward and natural to formulate partially quenched chiral
perturbation theory without , and that the resulting theory contains
the effective theory for QCD without the . We also show that previous
results, obtained including , can be reinterpreted as applying to the
theory without . We contrast the situation with that in the quenched
effective theory, where we explain why it is necessary to include .
We also compare the derivation of chiral perturbation theory in partially
quenched QCD with the standard derivation in unquenched QCD. We find that the
former cannot be justified as rigorously as the latter, because of the absence
of a physical Hilbert space. Finally, we present an encouraging result:
unphysical double poles in certain correlation functions in partially quenched
chiral perturbation theory can be shown to be a property of the underlying
theory, given only the symmetries and some plausible assumptions.Comment: 45 pages, no figure
Recommended from our members
Sex-related differences in chromatic sensitivity
Generally women are believed to be more discriminating than men in the use of colour names and this is often taken to imply superior colour vision. However, if both X-chromosome linked colour deficient males (~8%) and females (<1%) as well as heterozygote female carriers (~15%) are excluded from comparisons, then differences between men and women in red-green colour discrimination have been reported as not being significant (e.g., Pickford, 1944; Hood et al., 2006). We re-examined this question by assessing the performance of 150 males and 150 females on the Colour Assessment and Diagnosis (CAD) test (Rodriguez-Carmona, 2005). This is a sensitive test that yields small colour detection thresholds. The test employs direction-specific, moving, chromatic stimuli embedded in a background of random, dynamic, luminance contrast noise. A four-alternative, forced-choice procedure is employed to measure the subject’s thresholds for detection of colour signals in 16 directions in colour space, while ensuring that the subject cannot make use of any residual luminance contrast signals. In addition, we measured the Rayleigh anomaloscope matches in a subgroup of 111 males and 114 females. All the age-matched males (30.8 ± 9.7) and females (26.7 ± 8.8) had normal colour vision as diagnosed by a battery of conventional colour vision tests. Females with known colour deficient relatives were excluded from the study. Comparisons between the male and female groups revealed no significant differences in anomaloscope midpoints (p=0.709), but a significant difference in matching ranges (p=0.040); females on average tended to have a larger mean range (4.11) than males (3.75). Females also had significantly higher CAD thresholds than males along the red-green (p=0.0004), but not along the yellow-blue discrimination axis. The differences between males and females in red-green discrimination may be related to the heterozygosity in X-linked cone photopigment expression common among females
Thermodynamics of Coarse Grained Models of Super-Cooled Liquids
In recent papers, we have argued that kinetically constrained coarse grained
models can be applied to understand dynamic properties of glass forming
materials, and we have used this approach in various applications that appear
to validate this view. In one such paper [J.P. Garrahan and D. Chandler, Proc.
Nat. Acad. Sci. USA 100, 9710 (2003)], among other things we argued that this
approach also explains why the heat capacity discontinuity at the glass
transition is generally larger for fragile materials than for strong materials.
In the preceding article, Biroli, Bouchaud and Tarjus (BB&T) [cond-mat/0412024]
have objected to our explanation on this point, arguing that the class of
models we apply is inconsistent with both the absolute size and temperature
dependence of the experimental specific heat. Their argument, however, neglects
parameters associated with the coarse graining. Accounting for these
parameters, we show here that our treatment of dynamics is not inconsistent
with heat capacity discontinuities.Comment: 5 pages, 2 figures. Revised version to appear in J. Chem. Phy
Aluminium or copper substrate panel for selective absorption of solar energy
A method for making panels which selectively absorb solar energy is disclosed. The panels are comprised of an aluminum substrate, a layer of zinc thereon, a layer of nickel over the zinc layer and an outer layer of solar energy absorbing nickel oxide or a copper substrate with a layer of nickel thereon and a layer of solar energy absorbing nickel oxide distal from the copper substrate
Cork-resin ablative insulation for complex surfaces and method for applying the same
A method of applying cork-resin ablative insulation material to complex curved surfaces is disclosed. The material is prepared by mixing finely divided cork with a B-stage curable thermosetting resin, forming the resulting mixture into a block, B-stage curing the resin-containing block, and slicing the block into sheets. The B-stage cured sheet is shaped to conform to the surface being insulated, and further curing is then performed. Curing of the resins only to B-stage before shaping enables application of sheet material to complex curved surfaces and avoids limitations and disadvantages presented in handling of fully cured sheet material
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