5,718 research outputs found
Emulsions stabilised with pectin-based microgels: investigations into the effect of pH and ionic strength on emulsion stability
A clean signal for a top-like isosinglet fermion at the Large Hadron Collider
We predict a clean signal at the Large Hadron Collider (=14 TeV for
a scenario where there is a top-like, charge +2/3 vectorlike isosinglet
fermion. Such a quark, via mixing with the standard model top, can undergo
decays via both flavour-changing Z-boson coupling and flavour-changing Yukawa
interactions. We concentrate on the latter channel, and study the situation
where, following its pair-production, the heavy quark pair gives rise to two
tops and two Higgs boson. We show that the case where each Higgs decays in the
channel, there can be a rather distinct and background-free signal
that can unveil the existence of the vectorlike isosinglet quark of this kind.Comment: 14 pages, 5 figures, 4 table
Quantitative reconstruction of primary productivity in low latitudes during the last glacial maximum and the mid-to-late Holocene from a global Florisphaera profunda calibration dataset
[EN]Ocean net primary productivity (Npp) is a key component of the marine carbon cycle. Multi-model Npp projections based on a few decades of satellite data show large uncertainties, in particular at low latitudes (30°N−30°S). Calibration of sedimentary proxies with satellite-based Npp estimates allows for the quantitative reconstruction of this variable at longer time-scales. Relative abundance of deep-photic zone coccolithophore species Florisphaera profunda in the fossil record can potentially be used as a quantitative proxy for Npp. However, the robustness of this proxy calibration has been tested in very specific oceanographic settings using surface sediment samples. Here, we use a global dataset of surface sediment (n = 1258) and sediment trap (n = 26) samples with relative abundance data of F. profunda (%) to test the robustness of this proxy as a quantitative indicator of Npp. We study the modern and paleo-ecology of this species and the main factors affecting its latitudinal distribution. Results show that F. profunda % is a strong indicator of Npp at latitudes between 30°N and 30°S, while at higher latitudes temperature-related variables are more important. We develop a global calibration model between satellite Npp estimates and F. profunda for the latitudinal range between 30°N and 30°S, and we apply it to several low-latitude sediment cores with available F. profunda counts covering the Late Glacial Maximum (LGM; 24–19 ka) and the Mid-to-Late Holocene period (MLH; <6 ka). Reconstructed Npp during the LGM is 15% higher than during the MLHdue to the intensification of trade winds that enhanced oceanic upwelling at low latitudes
Mesoscopic circuits with charge discreteness:quantum transmission lines
We propose a quantum Hamiltonian for a transmission line with charge
discreteness. The periodic line is composed of an inductance and a capacitance
per cell. In every cell the charge operator satisfies a nonlinear equation of
motion because of the discreteness of the charge. In the basis of one-energy
per site, the spectrum can be calculated explicitly. We consider briefly the
incorporation of electrical resistance in the line.Comment: 11 pages. 0 figures. Will be published in Phys.Rev.
Supersymmetry, quark confinement and the harmonic oscillator
We study some quantum systems described by noncanonical commutation relations
formally expressed as [q,p]=ihbar(I + chi H), where H is the associated
(harmonic oscillator-like) Hamiltonian of the system, and chi is a Hermitian
(constant) operator, i.e. [H,chi]=0 . In passing, we also consider a simple
(chi=0 canonical) model, in the framework of a relativistic Klein-Gordon-like
wave equation.Comment: To be published in Journal of Physics A: Mathematical and Theoretical
(2007
Top pair Asymmetries at Hadron colliders with general couplings
Recently it has been shown that measurement of charge asymmetry of top pair
production at LHC excludes any flavor violating vector gauge boson that
could explain Tevatron forward-backward asymmetry (FBA). We consider the
general form of a gauge boson including left-handed, right-handed vector
and tensor couplings to examine FBA and charge asymmetry. To evaluate top pair
asymmetries at Tevatron and LHC, we consider mixing constraints on
flavor changing couplings and show that this model still explain
forward-backward asymmetry at Tevatron and charge asymmetry can not exclude it
in part of parameters space.Comment: 18 pages, 7 figure
Ground State Correlations in 16O and 40Ca
We study the ground state properties of doubly closed shell nuclei O
and Ca in the framework of Correlated Basis Function theory using state
dependent correlations, with central and tensor components. The realistic
Argonne and two-nucleon potentials and three-nucleon
potentials of the Urbana class have been adopted. By means of the Fermi
Hypernetted Chain integral equations, in conjunction with the Single Operator
Chain approximation, we evaluate the ground state energy, one- and two-body
densities and electromagnetic and spin static responses for both nuclei. In
O we compare our results with the available Monte Carlo and Coupled
Cluster ones and find a satisfying agreement. As in the nuclear matter case
with similar interactions and wave functions, the nuclei result under-bound by
2--3 MeV/A.Comment: 33 RevTeX pages + 8 figures, to appear in Phys.Rev.
Is there life inside black holes?
Bound inside rotating or charged black holes, there are stable periodic
planetary orbits, which neither come out nor terminate at the central
singularity. Stable periodic orbits inside black holes exist even for photons.
These bound orbits may be defined as orbits of the third kind, following the
Chandrasekhar classification of particle orbits in the black hole gravitational
field. The existence domain for the third kind orbits is rather spacious, and
thus there is place for life inside supermassive black holes in the galactic
nuclei. Interiors of the supermassive black holes may be inhabited by
civilizations, being invisible from the outside. In principle, one can get
information from the interiors of black holes by observing their white hole
counterparts.Comment: 11 pages, 5 figures; references adde
Correlation effects in single-particle overlap functions and one-nucleon removal reactions
Single-particle overlap functions and spectroscopic factors are calculated on
the basis of the one-body density matrices (ODM) obtained for the nucleus
employing different approaches to account for the effects of
correlations. The calculations use the relationship between the overlap
functions related to bound states of the (A-1)-particle system and the ODM for
the ground state of the A-particle system. The resulting bound-state overlap
functions are compared and tested in the description of the experimental data
from (p,d) reactions for which the shape of the overlap function is important.Comment: 11 pages, 4 figures include
Effects of Short-Range Correlations in (e,e'p) reactions and nuclear overlap functions
A study of the effects of short-range correlations over the (e,e'p) reaction
for low missing energy in closed shell nuclei is presented. We use correlated,
quasi-hole overlap functions extracted from the asymptotic behavior of the
one-body density matrix, containing central correlations of Jastrow type, up to
first-order in a cluster expansion, and computed in the very high asymptotic
region, up to 100 fm. The method to extract the overlap functions is checked in
a simple shell model, where the exact results are known. We find that the
single-particle wave functions of the valence shells are shifted to the right
due to the short-range repulsion by the nuclear core. The corresponding
spectroscopic factors are reduced only a few percent with respect to the shell
model. However, the (e,e'p) response functions and cross sections are enhanced
in the region of the maximum of the missing momentum distribution due to
short-range correlations.Comment: 45 pages, 15 figure
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