241 research outputs found
Threshold photoelectron photoion coincidence spectroscopy of trichloroethene and tetrachloroethene
The threshold photoelectron, the threshold photoelectron photoion coincidence and ion breakdown spectra of trichloroethene and tetrachloroethene have been recorded from 9 – 22 eV. Comparisons with the equivalent data for the three dichloroethene molecules and theoretical calculations highlight the nature of the orbitals involved during photoionisation in this energy range. The ground electronic state of CHCl (CCl) is bound, with excited valence states dissociating to CHCl (CCl) and CHCl (CCl). Appearance energies suggest that CHCl forms from CHCl by loss of two chlorine atoms, whereas CCl forms from CCl by loss of a Cl molecule. The translational kinetic energy release into CHCl (CCl) + Cl is determined as a function of energy. In both cases, the fraction of the available energy released into translational energy of the two products decreases as the photon energy increases
Radiative Mechanism to Light Fermion Masses in the MSSM
In a previous work we have showed that the Symmetry,
imply that the light fermions, the electron and the quarks, and , get
their masses only at one loop level. Here, we considere the more general
hypothesis for flavour mixing in the sfermion sector in the MSSM. Then, we
present our results to the masses of these light fermions and as a final result
we can explain why the quark is heavier than the quarks. This
mechanism is in agrement with the experimental constraint on the sfermion's
masses values.Comment: 22 pages, 8 figures, TeX mistakes corrected, accepted for publication
in JHE
Connecting LHC, ILC, and Quintessence
If the cold dark matter consists of weakly interacting massive particles
(WIMPs), anticipated measurements of the WIMP properties at the Large Hadron
Collider (LHC) and the International Linear Collider (ILC) will provide an
unprecedented experimental probe of cosmology at temperatures of order 1 GeV.
It is worth emphasizing that the expected outcome of these tests may or may not
be consistent with the picture of standard cosmology. For example, in
kination-dominated quintessence models of dark energy, the dark matter relic
abundance can be significantly enhanced compared to that obtained from freeze
out in a radiation-dominated universe. Collider measurements then will
simultaneously probe both dark matter and dark energy. In this article, we
investigate the precision to which the LHC and ILC can determine the dark
matter and dark energy parameters under those circumstances. We use an
illustrative set of four benchmark points in minimal supergravity in analogy
with the four LCC benchmark points. The precision achievable together at the
LHC and ILC is sufficient to discover kination-dominated quintessence, under
the assumption that the WIMPs are the only dark matter component. The LHC and
ILC can thus play important roles as alternative probes of both dark matter and
dark energy.Comment: 38 pages, 9 figure
Squeezing based on nondegenerate frequency doubling internal to a realistic laser
We investigate theoretically the quantum fluctuations of the fundamental
field in the output of a nondegenerate second harmonic generation process
occuring inside a laser cavity. Due to the nondegenerate character of the
nonlinear medium, a field orthogonal to the laser field is for some operating
conditions indepedent of the fluctuations produced by the laser medium. We show
that this fact may lead to perfect squeezing for a certain polarization mode of
the fundamental field. The experimental feasibility of the system is also
discussed.Comment: 6 pages, 5 figure
CP asymmetries in the supersymmetric trilepton signal at the LHC
In the CP-violating Minimal Supersymmetric Standard Model, we study the
production of a neutralino-chargino pair at the LHC. For their decays into
three leptons, we analyze CP asymmetries which are sensitive to the CP phases
of the neutralino and chargino sector. We present analytical formulas for the
entire production and decay process, and identify the CP-violating
contributions in the spin correlation terms. This allows us to define the
optimal CP asymmetries. We present a detailed numerical analysis of the cross
sections, branching ratios, and the CP observables. For light neutralinos,
charginos, and squarks, the asymmetries can reach several 10%. We estimate the
discovery potential for the LHC to observe CP violation in the trilepton
channel.Comment: 39 pages, 8 figures, version to appear in EPJC, discussion(s) added,
typo in (D.79), (D.118) corrected, new Fig. 7; The European Physical Journal
C, Volume 72, Issue 3, 201
Effects of sea temperature and stratification changes on seabird breeding success
As apex predators in marine ecosystems, seabirds may primarily experience climate change impacts indirectly, via changes to their food webs. Observed seabird population declines have been linked to climate-driven oceanographic and food web changes. However, relationships have often been derived from relatively few colonies and consider only sea surface temperature (SST), so important drivers, and spatial variation in drivers, could remain undetected. Further, explicit climate change projections have rarely been made, so longer-term risks remain unclear. Here, we use tracking data to estimate foraging areas for eleven black-legged kittiwake (Rissa tridactyla) colonies in the UK and Ireland, thus reducing reliance on single colonies and allowing calculation of colony-specific oceanographic conditions. We use mixed models to consider how SST, the potential energy anomaly (indicating density stratification strength) and the timing of seasonal stratification influence kittiwake productivity. Across all colonies, higher breeding success was associated with weaker stratification before breeding and lower SSTs during the breeding season. Eight colonies with sufficient data were modelled individually: higher productivity was associated with later stratification at three colonies, weaker stratification at two, and lower SSTs at one, whilst two colonies showed no significant relationships. Hence, key drivers of productivity varied among colonies. Climate change projections, made using fitted models, indicated that breeding success could decline by 21 – 43% between 1961-90 and 2070-99. Climate change therefore poses a longer-term threat to kittiwakes, but as this will be mediated via availability of key prey species, other marine apex predators could also face similar threats
Electronic structure of the strongly hybridized ferromagnet CeFe2
We report on results from high-energy spectroscopic measurements on CeFe2, a
system of particular interest due to its anomalous ferromagnetism with an
unusually low Curie temperature and small magnetization compared to the other
rare earth-iron Laves phase compounds. Our experimental results indicate very
strong hybridization of the Ce 4f states with the delocalized band states,
mainly the Fe 3d states. In the interpretation and analysis of our measured
spectra, we have made use of two different theoretical approaches: The first
one is based on the Anderson impurity model, with surface contributions
explicitly taken into account. The second method consists of band-structure
calculations for bulk CeFe2. The analysis based on the Anderson impurity model
gives calculated spectra in good agreement with the whole range of measured
spectra, and reveals that the Ce 4f -- Fe 3d hybridization is considerably
reduced at the surface, resulting in even stronger hybridization in the bulk
than previously thought. The band-structure calculations are ab initio
full-potential linear muffin-tin orbital calculations within the
local-spin-density approximation of the density functional. The Ce 4f electrons
were treated as itinerant band electrons. Interestingly, the Ce 4f partial
density of states obtained from the band-structure calculations also agree well
with the experimental spectra concerning both the 4f peak position and the 4f
bandwidth, if the surface effects are properly taken into account. In addition,
results, notably the partial spin magnetic moments, from the band-structure
calculations are discussed in some detail and compared to experimental findings
and earlier calculations.Comment: 10 pages, 8 figures, to appear in Phys. Rev. B in December 200
CDMS, Supersymmetry and Extra Dimensions
The CDMS experiment aims to directly detect massive, cold dark matter
particles originating from the Milky Way halo. Charge and lattice excitations
are detected after a particle scatters in a Ge or Si crystal kept at ~30 mK,
allowing to separate nuclear recoils from the dominating electromagnetic
background. The operation of 12 detectors in the Soudan mine for 75 live days
in 2004 delivered no evidence for a signal, yielding stringent limits on dark
matter candidates from supersymmetry and universal extra dimensions. Thirty Ge
and Si detectors are presently installed in the Soudan cryostat, and operating
at base temperature. The run scheduled to start in 2006 is expected to yield a
one order of magnitude increase in dark matter sensitivity.Comment: To be published in the proceedings of the 7th UCLA symposium on
sources and detection of dark matter and dark energy in the universe, Marina
del Rey, Feb 22-24, 200
Determination of Fundamental Supersymmetry Parameters from Chargino Production at Lepii
If accessible at LEP II, chargino production is likely to be one of the few
available supersymmetric signals for many years. We consider the prospects for
the determination of fundamental supersymmetry parameters in such a scenario.
The study is complicated by the dependence of observables on a large number of
these parameters. We propose a straightforward procedure for disentangling
these dependences and demonstrate its effectiveness by presenting a number of
case studies at representative points in parameter space. Working in the
context of the minimal supersymmetric standard model, we find that chargino
production by itself is a fairly sensitive probe of the supersymmetry-breaking
sector. For significant regions of parameter space, it is possible to test the
gaugino mass unification hypothesis and to measure the gaugino contents of the
charginos and neutralinos, thereby testing the predictions of grand unification
and the viability of the lightest supersymmetric particle as a dark matter
candidate. For much of the parameter space, it is also possible to set limits
on the mass of the electron sneutrino, which provide a valuable guide for
future particle searches.Comment: 52pp, Revtex, 30 figures available upon request, SLAC-PUB-6497,
RU-94-67 (text and figures available in ps form by anonymous ftp from
preprint.slac.stanford.edu, directory pub/preprints/hep-ph/9408
Muon anomalous magnetic moment, lepton flavor violation, and flavor changing neutral current processes in SUSY GUT with right-handed neutrino
Motivated by the large mixing angle solutions for the atmospheric and solar
neutrino anomalies, flavor changing neutral current processes and lepton flavor
violating processes as well as the muon anomalous magnetic moment are analyzed
in the framework of SU(5) SUSY GUT with right-handed neutrino. In order to
explain realistic mass relations for quarks and leptons, we take into account
effects of higher dimensional operators above the GUT scale. It is shown that
the supersymmetric (SUSY) contributions to the CP violation parameter in
mixing, , the branching ratio,
and the muon anomalous magnetic moment become large in a wide range of
parameter space. We also investigate correlations among these quantities.
Within the current experimental bound of , large
SUSY contributions are possible either in the muon anomalous magnetic moment or
in . In the former case, the favorable value of the recent muon
anomalous magnetic moment measurement at the BNL E821 experiment can be
accommodated. In the latter case, the allowed region of the Kobayashi-Maskawa
phase can be different from the prediction within the Standard Model (SM) and
therefore the measurements of the CP asymmetry of mode and
could discriminate this case from the SM. We also show that
the branching ratio can be close to the current
experimental upperbound and the mixing induced CP asymmetry of the radiative B
decay can be enhanced in the case where the neutrino parameters correspond to
the Mikheyev-Smirnov-Wolfenstein small mixing angle solution.Comment: 70 pages, 14 figure
- …