7,926 research outputs found
Attosecond Control of Ionization Dynamics
Attosecond pulses can be used to initiate and control electron dynamics on a
sub-femtosecond time scale. The first step in this process occurs when an atom
absorbs an ultraviolet photon leading to the formation of an attosecond
electron wave packet (EWP). Until now, attosecond pulses have been used to
create free EWPs in the continuum, where they quickly disperse. In this paper
we use a train of attosecond pulses, synchronized to an infrared (IR) laser
field, to create a series of EWPs that are below the ionization threshold in
helium. We show that the ionization probability then becomes a function of the
delay between the IR and attosecond fields. Calculations that reproduce the
experimental results demonstrate that this ionization control results from
interference between transiently bound EWPs created by different pulses in the
train. In this way, we are able to observe, for the first time, wave packet
interference in a strongly driven atomic system.Comment: 8 pages, 4 figure
The Ginzburg-Landau Free Energy Functional of Color Superconductivity at Weak Coupling
We derive the Ginzburg-Landau free energy functional of color
superconductivity in terms of the thermal diagrams of QCD in its perturbative
region. The zero mode of the quadratic term coefficient yields the same
transition temperature, including the pre-exponential factor, as the one
obtained previously from the Fredholm determinant of the two quark scattering
amplitude. All coefficients of the free energy can be made identical to those
of a BCS model by setting the Fermi velocity of the latter equal to the speed
of light. We also calculate the induced symmetric color condensate near
and find that it scales as the cubic power of the dominant antisymmetric color
component. We show that in the presence of an inhomogeneity and a nonzero gauge
potential, while the color-flavor locked condensate dominates in the bulk, the
unlocked condensate, the octet, emerges as a result of a simultaneous
color-flavor rotation in the core region of a vortex filament or at the
junction of super and normal phases.Comment: 32 pages, Plain Tex, 3 figure
Neutrino processes in the condensed phase of color flavor locked quark matter
We study weak interactions involving Goldstone bosons in the neutral kaon
condensed phase of color flavor locked quark matter. We calculate the rates for
the dominant processes that contribute to the neutrino mean free p ath and to
neutrino production. A light state, with a mass , where and are the quark
chemical potential and superconducting gap respectively, is shown to play an
important role. We identify unique characteristics of weak interaction rates in
this novel phase and discuss how they might influence neutrino emission in core
collapse supernova and neutron stars.Comment: 21 pages, 4 figure
Short distance current correlators: Comparing lattice simulations to the instanton liquid
Point to point correlators of currents are computed in quenched QCD using a
chiral lattice fermion action, the overlap action. I compare correlators made
of exact quark propagators with correlators restricted to low (less than 500
MeV) eigenvalue eigenmodes of the Dirac operator. In many cases they show
qualitative resemblence (typically at small values of the quark mass and
distances larger than 0.4 fm) and they differ qualitatively at larger quark
masses or at very short distance. Lattice results are in qualitative agreement
(and in the difference of vector and axial vector channels, quantitative
agreement) with the expectations of instanton liquid models. The scalar channel
shows the effects of a quenched finite volume zero mode artifact, a negative
correlator.Comment: 18 pages, Revtex, 11 postscript figures. Some changes. Version to
appear in Phys. Rev.
Above threshold ionization by few-cycle spatially inhomogeneous fields
We present theoretical studies of above threshold ionization (ATI) produced
by spatially inhomogeneous fields. This kind of field appears as a result of
the illumination of plasmonic nanostructures and metal nanoparticles with a
short laser pulse. We use the time-dependent Schr\"odinger equation (TDSE) in
reduced dimensions to understand and characterize the ATI features in these
fields. It is demonstrated that the inhomogeneity of the laser electric field
plays an important role in the ATI process and it produces appreciable
modifications to the energy-resolved photoelectron spectra. In fact, our
numerical simulations reveal that high energy electrons can be generated.
Specifically, using a linear approximation for the spatial dependence of the
enhanced plasmonic field and with a near infrared laser with intensities in the
mid- 10^{14} W/cm^{2} range, we show it is possible to drive electrons with
energies in the near-keV regime. Furthermore, we study how the carrier envelope
phase influences the emission of ATI photoelectrons for few-cycle pulses. Our
quantum mechanical calculations are supported by their classical counterparts
Approach to the Continuum Limit of the Quenched Hermitian Wilson-Dirac Operator
We investigate the approach to the continuum limit of the spectrum of the
Hermitian Wilson-Dirac operator in the supercritical mass region for pure gauge
SU(2) and SU(3) backgrounds. For this we study the spectral flow of the
Hermitian Wilson-Dirac operator in the range . We find that the
spectrum has a gap for and that the spectral density at zero,
, is non-zero for . We find that and, for
(exponential in the lattice spacing) as one goes to
the continuum limit. We also compute the topological susceptibility and the
size distribution of the zero modes. The topological susceptibility scales well
in the lattice spacing for both SU(2) and SU(3). The size distribution of the
zero modes does not appear to show a peak at a physical scale.Comment: 19 pages revtex with 9 postscript figures included by eps
Effects of maternal subnutrition during early pregnancy on cow hematological profiles and offspring physiology and vitality in two beef breeds
This experiment evaluated the effects of subnutrition during early gestation on hematology in cows (Bos Taurus) and on hematological, metabolic, endocrine, and vitality parameters in their calves. Parda de Montaña and Pirenaica dams were inseminated and assigned to either a control (CONTROL, 100% requirements) or a nutrientârestricted group (SUBNUT, 65%) during the first third of gestation. Dam blood samples were collected on days 20 and 253 of gestation, and calf samples were obtained during the first days of life. Pirenaica dams presented higher red series parameters than Parda de Montaña dams, both in the first and the last months of gestation. During early pregnancy, granulocyte numbers and mean corpuscular hemoglobin were lower in PirenaicaâSUBNUT than in PirenaicaâCONTROL cows. Calves from the SUBNUT cows did not show a physiological reduction in red series values in early life, suggesting later maturation of the hematopoietic system. Poor maternal nutrition affected calf endocrine parameters. Newborns from dystocic parturitions showed lower NEFA concentrations and weaker vitality responses. In conclusion, maternal nutrition had shortâterm effects on cow hematology, Pirenaica cows showing a higher susceptibility to undernutrition; and a longâterm effect on their offspring endocrinology, SUBNUT newborns showing lower levels of IGFâ1 and higher levels of cortisol.This work was supported by the Spanish Ministry of Economy and Business and the European Union Regional Development Funds (INIA RTA 2013â00059âC02 and INIA RZP 2015â001) and the Government of Aragon under the Grant Research Group Funds (A14_17R). A. Noya received a PhD grant from INIAâGovernment of Aragon
Implications of the ALEPH tau-Lepton Decay Data for Perturbative and Non-Perturbative QCD
We use ALEPH data on hadronic decays in order to calculate Euclidean
coordinate space correlation functions in the vector and axial-vector channels.
The linear combination receives no perturbative contribution and is
quantitatively reproduced by the instanton liquid model. In the case of
the instanton calculation is in good agreement with the data once perturbative
corrections are included. These corrections clearly show the evolution of
. We also analyze the range of validity of the Operator Product
Expansion (OPE). In the channel we find a dimension contribution
which is comparable to the original SVZ estimate, but the instanton model
provides a different non-singular term of the same magnitude. In the case
both the OPE and the instanton model predict the same power correction
induced by the gluon condensate, but it is masked by much larger perturbative
contributions. We conclude that the range of validity of the OPE is limited to
x\lsim0.3 fm, whereas the instanton model describes the data over the entire
range.Comment: 4 pages, 6 figure
- âŠ