78,647 research outputs found
Some notes on degree spectra of the structures
In the paper the problem of existence of an algebraic structure with the degree spectra {x: x ≮ b} is studied for arbitrary degree b. © Springer-Verlag Berlin Heidelberg 2007
Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
The Standard Model of particle physics assumes that the so-called fundamental
constants are universal and unchanging. Absorption lines arising in molecular
clouds along quasar sightlines offer a precise test for variations in the
proton-to-electron mass ratio, mu, over cosmological time and distance scales.
The inversion transitions of ammonia are particularly sensitive to mu compared
to molecular rotational transitions. Comparing the available ammonia spectra
observed towards the quasar B0218+357 with new, high-quality rotational
spectra, we present the first detailed measurement of mu with this technique,
limiting relative deviations from the laboratory value to |dmu/mu| <
1.8x10^{-6} (95% confidence level) at approximately half the Universe's current
age - the strongest astrophysical constraint to date. Higher-quality ammonia
observations will reduce both the statistical and systematic uncertainties in
these measurements.Comment: Science, 20th June 2008. 22 pages, 5 figures (12 EPS files), 2
tables, including Supporting Online Material; v2: Corrected reference for
laboratory mu-variation bound
On differential graded categories
Differential graded categories enhance our understanding of triangulated
categories appearing in algebra and geometry. In this survey, we review their
foundations and report on recent work by Drinfeld, Dugger-Shipley, ..., Toen
and Toen-Vaquie.Comment: 30 pages, correction at the end of 3.9, corrections and added
references in 5.
A lower bound for coherences on the Brown-Peterson spectrum
We provide a lower bound for the coherence of the homotopy commutativity of
the Brown-Peterson spectrum, BP, at a given prime p and prove that it is at
least (2p^2 + 2p - 2)-homotopy commutative. We give a proof based on
Dyer-Lashof operations that BP cannot be a Thom spectrum associated to n-fold
loop maps to BSF for n=4 at 2 and n=2p+4 at odd primes. Other examples where we
obtain estimates for coherence are the Johnson-Wilson spectra, localized away
from the maximal ideal and unlocalized. We close with a negative result on
Morava-K-theory.Comment: This is the version published by Algebraic & Geometric Topology on 26
February 200
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