349 research outputs found
Louse (Insecta : Phthiraptera) mitochondrial 12S rRNA secondary structure is highly variable
Lice are ectoparasitic insects hosted by birds and mammals. Mitochondrial 12S rRNA sequences obtained from lice show considerable length variation and are very difficult to align. We show that the louse 12S rRNA domain III secondary structure displays considerable variation compared to other insects, in both the shape and number of stems and loops. Phylogenetic trees constructed from tree edit distances between louse 12S rRNA structures do not closely resemble trees constructed from sequence data, suggesting that at least some of this structural variation has arisen independently in different louse lineages. Taken together with previous work on mitochondrial gene order and elevated rates of substitution in louse mitochondrial sequences, the structural variation in louse 12S rRNA confirms the highly distinctive nature of molecular evolution in these insects
Technically natural dark energy from Lorentz breaking
We construct a model of dark energy with a technically natural small
contribution to cosmic acceleration, i.e. this contribution does not receive
corrections from other scales in the theory. The proposed acceleration
mechanism appears generically in the low-energy limit of gravity theories with
violation of Lorentz invariance that contain a derivatively coupled scalar
field Theta. The latter may be the Goldstone field of a broken global symmetry.
The model, that we call Theta-CDM, is a valid effective field theory up to a
high cutoff just a few orders of magnitude below the Planck scale. Furthermore,
it can be ultraviolet-completed in the context of Horava gravity. We discuss
the observational predictions of the model. Even in the absence of a
cosmological constant term, the expansion history of the Universe is
essentially indistinguishable from that of Lambda-CDM. The difference between
the two theories appears at the level of cosmological perturbations. We find
that in Theta-CDM the matter power spectrum is enhanced at subhorizon scales
compared to Lambda-CDM. This property can be used to discriminate the model
from Lambda-CDM with current cosmological data.Comment: A few equations in the Appendix correcte
Constraints on diffuse neutrino background from primordial black holes
We calculated the energy spectra and the fluxes of electron neutrino emitted
in the process of evaporation of primordial black holes (PBHs) in the early
universe. It was assumed that PBHs are formed by a blue power-law spectrum of
primordial density fluctuations. We obtained the bounds on the spectral index
of density fluctuations assuming validity of the standard picture of
gravitational collapse and using the available data of several experiments with
atmospheric and solar neutrinos. The comparison of our results with the
previous constraints (which had been obtained using diffuse photon background
data) shows that such bounds are quite sensitive to an assumed form of the
initial PBH mass function.Comment: 18 pages,(with 7 figures
Parity Violation in Proton-Proton Scattering at 221 MeV
TRIUMF experiment 497 has measured the parity violating longitudinal
analyzing power, A_z, in pp elastic scattering at 221.3 MeV incident proton
energy. This paper includes details of the corrections, some of magnitude
comparable to A_z itself, required to arrive at the final result. The largest
correction was for the effects of first moments of transverse polarization. The
addition of the result, A_z=(0.84 \pm 0.29 (stat.) \pm 0.17 (syst.)) \times
10^{-7}, to the pp parity violation experimental data base greatly improves the
experimental constraints on the weak meson-nucleon coupling constants
h^{pp}_\rho and h^{pp}_\omega, and has implications for the interpretation of
electron parity violation experiments.Comment: 17 pages RevTeX, 14 PostScript figures. Revised version with
additions suggested by Phys. Rev.
Photo-production of Nucleon Resonances and Nucleon Spin Structure Function in the Resonance Region
The photo-production of nucleon resonances is calculated based on a chiral
constituent quark model including both relativistic corrections H{rel} and
two-body exchange currents, and it is shown that these effects play an
important role. We also calculate the first moment of the nucleon spin
structure function g1 (x,Q^2) in the resonance region, and obtain a
sign-changing point around Q^2 ~ 0.27 {GeV}^2 for the proton.Comment: 23 pages, 5 figure
Logarithmic correction to BH entropy as Noether charge
We consider the role of the type-A trace anomaly in static black hole
solutions to semiclassical Einstein equation in four dimensions. Via Wald's
Noether charge formalism, we compute the contribution to the entropy coming
from the anomaly induced effective action and unveil a logarithmic correction
to the Bekenstein-Hawking area law.
The corrected entropy is given by a seemingly universal formula involving the
coefficient of the type-A trace anomaly, the Euler characteristic of the
horizon and the value at the horizon of the solution to the uniformization
problem for Q-curvature. Two instances are examined in detail: Schwarzschild
and a four-dimensional massless topological black hole. We also find agreement
with the logarithmic correction due to one-loop contribution of conformal
fields in the Schwarzschild background.Comment: 14 pages, JHEP styl
On the formation of a Hawking-radiation photosphere around microscopic black holes
We show that once a black hole surpasses some critical temperature
, the emitted Hawking radiation interacts with itself and forms a
nearly thermal photosphere. Using QED, we show that the dominant interactions
are bremsstrahlung and electron-photon pair production, and we estimate
, which when calculated more precisely is
found to be 45 GeV. The formation of the photosphere is
purely a particle physics effect, and not a general relativistic effect, since
the the photosphere forms roughly Schwarzschild radii away from
the black hole. The temperature of the photosphere decreases with distance
from the black hole, and the outer surface is determined by the constraint
(for the QED case), since this is the point at which electrons
and positrons annihilate, and the remaining photons free stream to infinity.
Observational consequences are discussed, and it is found that, although the
QED photosphere will not affect the Page-Hawking limits on primordial black
holes, which is most important for 100MeV black holes, the inclusion of QCD
interactions may significantly effect this limit, since for QCD we estimate
. The photosphere greatly reduces possibility of
observing individual black holes with temperatures greater than ,
since the high energy particles emitted from the black hole are processed
through the photosphere to a lower energy, where the gamma ray background is
much higher. The temperature of the plasma in the photosphere can be extremely
high, and this offers interesting possibilities for processes such as symmetry
restoration.Comment: Latex, 16 pages, 3 postscript figures, submitted to PRD. Also
available at http://fnas08.fnal.gov
Recommended from our members
Solar wind channels for MeV particles
Plasma, magnetic field and charged particle data from the Ulysses spacecraft is used to demonstrate that MeV particles follow channels defined by solar wind flow regimes
The Refederalization of American Health Care
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69090/2/10.1177_107755878704400103.pd
Negative Parity 70-plet Baryon Masses in the 1/Nc Expansion
The masses of the negative parity SU(6) 70-plet baryons are analyzed in the
1/Nc expansion to order 1/Nc and to first order in SU(3) breaking. At this
level of precision there are twenty predictions. Among them there are the well
known Gell-Mann Okubo and equal spacing relations, and four new relations
involving SU(3) breaking splittings in different SU(3) multiplets. Although the
breaking of SU(6) symmetry occurs at zeroth order in 1/Nc, it turns out to be
small. The dominant source of the breaking is the hyperfine interaction which
is of order 1/Nc. The spin-orbit interaction, of zeroth order in 1/Nc, is
entirely fixed by the splitting between the singlet states Lambda(1405) and
Lambda(1520), and the spin-orbit puzzle is solved by the presence of other
zeroth order operators involving flavor exchange.Comment: 31 pages, 3 figure
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