3,481 research outputs found
Rational curves on fibered Calabi-Yau manifolds
We show that a smooth projective complex manifold of dimension greater than
two endowed with an elliptic fiber space structure and with finite fundamental
group always contains a rational curve, provided its canonical bundle is
relatively trivial. As an application of this result, we prove that any
Calabi-Yau manifold that admits a fibration onto a curve whose general fibers
are abelian varieties always contains a rational curve
Latest evidence for a late time vacuum -- geodesic CDM interaction
We perform a reconstruction of the coupling function between vacuum energy
and geodesic cold dark matter using the latest observational data. We bin the
interaction in seventeen redshift bins but use a correlation prior to prevent
rapid, unphysical oscillations in the coupling function. This prior also serves
to eliminate any dependence of the reconstruction on the binning method. We use
two different forms of the correlation prior, finding that both give similar
results for the reconstruction of the dark matter -- dark energy interaction.
Calculating the Bayes factor for each case, we find no meaningful evidence for
deviation from the null interacting case, i.e. CDM, in our
reconstruction.Comment: 14 pages, 7 figures. Version 2 matches published version in Physics
of the Dark Universe (Figure 2 updated to better show H0 and sigma 8
tensions, additional discussion of results added in section 4.1
Short and highly efficient synthetic promoters for melanoma-specific gene expression.
Here, we report the construction and functional analysis of synthetic promoters designed for gene therapy applications requiring strong and specific gene expression in melanoma cell lines. We have analysed the transcriptional activity of different combinations of two transcriptional regulatory modules, a melanocyte-specific element from the human tyrosinase promoter and a cell-cycle-specific element from the human alpha-fetoprotein promoter. Transient expression assays in different cell lines show that several of these composite synthetic promoters can drive a strong and selective expression of a reporter gene in melanoma cell, providing us with a new powerful tool for gene therapy of melanomas
Semileptonic Form Factors
I report the current status of the heavy-light decay constants, the bag
parameters and the semileptonic form factors. I compare the heavy-light decay
constants with Wilson-Wilson and clover-clover fermions. Systematic errors such
as scale setting and renormalization factors are also discussed. 1/M
dependences for the heavy-light semileptonic form factors near
with clover-clover and NRQCD-Wilson fermions are found to be small.Comment: 12 pgs. 15 figures. Talk presented at LATTICE9
Renormalization of the effective theory for heavy quarks at small velocity
The slope of the Isgur-Wise function at the normalization point,
,is one of the basic parameters for the extraction of the
matrix element from exclusive semileptonic decay data. A method for
measuring this parameter on the lattice is the effective theory for heavy
quarks at small velocity . This theory is a variant of the heavy quark
effective theory in which the motion of the quark is treated as a perturbation.
In this work we study the lattice renormalization of the slow heavy quark
effective theory. We show that the renormalization of is not
affected by ultraviolet power divergences, implying no need of difficult
non-perturbative subtractions. A lattice computation of with
this method is therefore feasible in principle. The one-loop renormalization
constants of the effective theory for slow heavy quarks are computed to order
together with the lattice-continuum renormalization constant of
. We demonstrate that the expansion in the heavy-quark velocity
reproduces correctly the infrared structure of the original (non-expanded)
theory to every order. We compute also the one-loop renormalization constants
of the slow heavy quark effective theory to higher orders in and the
lattice-continuum renormalization constants of the higher derivatives of the
function. Unfortunately, the renormalization constants of the higher
derivatives are affected by ultraviolet power divergences, implying the
necessity of numerical non-perturbative subtractions. The lattice computation
of higher derivatives of the Isgur-Wise function seems therefore problematic.Comment: Latex, 43 pages, 5 figures available by fax upon request. To be
published in Nucl. Phys
Constraints on the interacting vacuum -- geodesic CDM scenario
We investigate an interacting dark sector scenario in which the vacuum energy
is free to interact with cold dark matter (CDM), which itself is assumed to
cluster under the sole action of gravity, i.e. it is in free fall (geodesic),
as in CDM. The interaction is characterised by a dimensionless
coupling that we constrain using cosmic microwave background data
from the Planck 2015 data release, along with baryon acoustic oscillation,
redshift space distortion and Type Ia supernova measurements. We present the
full linear perturbation theory of this interacting scenario and use MCMC
sampling to study five different cases: two cases in which we have CDM
evolution in the distant past, until a set redshift , below
which the interaction switches on and is the single sampled
parameter, with fixed at and respectively; a case where we allow this transition redshift to
vary along with ; a case in which the vacuum energy is zero for
and then begins to grow once the interaction switches on; and
the final case in which we bin in four redshift bins to
investigate the possibility of a dynamical interaction, reconstructing the
redshift evolution of the function using Gaussian processes. We find that, in
all cases where the high redshift evolution is not modified, the results are
compatible with a vanishing coupling, thus finding no significant deviation
from CDM.Comment: 17 pages, 14 figures. Version 2 aligns with the published MNRAS
article (some model comparison discussion added with respect to version 1
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