7,351 research outputs found
Constraining neutrino masses with the ISW-galaxy correlation function
Temperature anisotropies in the Cosmic Microwave Background (CMB) are
affected by the late Integrated Sachs-Wolfe (lISW) effect caused by any
time-variation of the gravitational potential on linear scales. Dark energy is
not the only source of lISW, since massive neutrinos induce a small decay of
the potential on small scales during both matter and dark energy domination. In
this work, we study the prospect of using the cross-correlation between CMB and
galaxy density maps as a tool for constraining the neutrino mass. On the one
hand massive neutrinos reduce the cross-correlation spectrum because
free-streaming slows down structure formation; on the other hand, they enhance
it through their change in the effective linear growth. We show that in the
observable range of scales and redshifts, the first effect dominates, but the
second one is not negligible. We carry out an error forecast analysis by
fitting some mock data inspired by the Planck satellite, Dark Energy Survey
(DES) and Large Synoptic Survey Telescope (LSST). The inclusion of the
cross-correlation data from Planck and LSST increases the sensitivity to the
neutrino mass m_nu by 38% (and to the dark energy equation of state w by 83%)
with respect to Planck alone. The correlation between Planck and DES brings a
far less significant improvement. This method is not potentially as good for
detecting m_nu as the measurement of galaxy, cluster or cosmic shear power
spectra, but since it is independent and affected by different systematics, it
remains potentially interesting if the total neutrino mass is of the order of
0.2 eV; if instead it is close to the lower bound from atmospheric
oscillations, m_nu ~ 0.05 eV, we do not expect the ISW-galaxy correlation to be
ever sensitive to m_nu.Comment: 10 pages, 8 figures. References added. Accepted for publication in
Phys.Rev.
How to distinguish between interacting and noninteracting molecules in tunnel junctions
Recent experiments demonstrate a temperature control of the electric
conduction through a ferrocene-based molecular junction. Here we examine the
results in view of determining means to distinguish between transport through
single-particle molecular levels or via transport channels split by Coulomb
repulsion. Both transport mechanisms are similar in molecular junctions given
the similarities between molecular intralevel energies and the charging energy.
We propose an experimentally testable way to identify the main transport
process. By applying a magnetic field to the molecule, we observe that an
interacting theory predicts a shift of the conductance resonances of the
molecule whereas in the noninteracting case each resonance is split into two
peaks. The interaction model works well in explaining our experimental results
obtained in a ferrocene-based single-molecule junction, where the charge
degeneracy peaks shift (but do not split) under the action of an applied
7-Tesla magnetic field. This method is useful for a proper characterization of
the transport properties of molecular tunnel junctions.Comment: Main text: 7 pages, 5 figures; SI: 2 pages, 2 figures. Accepted to
RSC Nanoscal
Renormalisation group determination of the order of the DNA denaturation transition
We report on the nature of the thermal denaturation transition of homogeneous
DNA as determined from a renormalisation group analysis of the
Peyrard-Bishop-Dauxois model. Our approach is based on an analogy with the
phenomenon of critical wetting that goes further than previous qualitative
comparisons, and shows that the transition is continuous for the average
base-pair separation. However, since the range of universal critical behaviour
appears to be very narrow, numerically observed denaturation transitions may
look first-order, as it has been reported in the literature.Comment: 6 pages; no figures; to appear in Europhysics Letter
Non-locality and short-range wetting phenomena
We propose a non-local interfacial model for 3D short-range wetting at planar
and non-planar walls. The model is characterized by a binding potential
\emph{functional} depending only on the bulk Ornstein-Zernike correlation
function, which arises from different classes of tube-like fluctuations that
connect the interface and the substrate. The theory provides a physical
explanation for the origin of the effective position-dependent stiffness and
binding potential in approximate local theories, and also obeys the necessary
classical wedge covariance relationship between wetting and wedge filling.
Renormalization group and computer simulation studies reveal the strong
non-perturbative influence of non-locality at critical wetting, throwing light
on long-standing theoretical problems regarding the order of the phase
transition.Comment: 4 pages, 2 figures, accepted for publication in Phys. Rev. Let
Lensing Corrections to Features in the Angular Two-Point Correlation Function and Power Spectrum
It is well known that magnification bias, the modulation of galaxy or quasar
source counts by gravitational lensing, can change the observed angular
correlation function. We investigate magnification-induced changes to the shape
of the observed correlation function w(\theta) and the angular power spectrum
C_{\ell}, paying special attention to the matter-radiation equality peak and
the baryon wiggles. Lensing mixes the correlation function of the source
galaxies with the matter correlation at the lower redshifts of the lenses.
Since the lenses probe structure nearer to the observer, the angular scale
dependence of the lensing terms is different from that of the sources, thus the
observed correlation function is distorted. We quantify how the lensing
corrections depend on the width of the selection function, the galaxy bias b,
and the number count slope s. The correction increases with redshift and larger
corrections are present for sources with steep number count slopes and/or broad
redshift distributions. The most drastic changes to C_{\ell} occur for
measurements at z >~1.5 and \ell <~ 100. For the source distributions we
consider, magnification bias can shift the matter-radiation equality scale by
1-6% at z ~ 1.5 and by z ~ 3.5 the shift can be as large as 30%. The baryon
bump in \theta^2w(\theta) is shifted by <~ 1% and the width is typically
increased by ~10%. Shifts of >~ 0.5% and broadening of >~ 20% occur only for
very broad selection functions and/or galaxies with (5s-2)/b>~2. However, near
the baryon bump the magnification correction is not constant but a gently
varying function which depends on the source population. Depending on how the
w(\theta) data is fitted, this correction may need to be accounted for when
using the baryon acoustic scale for precision cosmology.Comment: v2: 8 pages, 5 figures, text and figures condensed, references adde
Pion transition form factor in the Regge approach and incomplete vector-meson dominance
The concept of incomplete vector-meson dominance and Regge models is applied
to the transition form factor of the pion. First, we argue that variants of the
chiral quark model fulfilling the chiral anomaly may violate the Terazawa-West
unitarity bounds, as these bounds are based on unverified assumptions for the
real parts of the amplitudes, precluding a possible presence of polynomial
terms. A direct consequence is that the transition form factor need not
necessarily vanish at large values of the photon virtuality. Moreover, in the
range of the BaBar experiment, the Terazawa-West bound is an order of magnitude
above the data, thus is of formal rather than practical interest. Then we
demonstrate how the experimental data may be properly explained with incomplete
vector-meson dominance in a simple model with one state, as well as in more
sophisticated Regge models. Generalizations of the simple Regge model along the
lines of Dominguez result in a proper description of the data, where one may
adjust the parameters in such a way that the Terazawa-West bound is satisfied
or violated. We also impose the experimental constraint from the Z -> pi0 gamma
decay. Finally, we point out that the photon momentum asymmetry parameter may
noticeably influence the precision analysis.Comment: 11 pages, 7 figure
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