118,891 research outputs found
Helium 2 3S - 2 1S metrology at 1557 nm
An experiment is proposed to excite the 'forbidden' 1s2s 3S1 - 1s2s 1S0
magnetic dipole (M1) transition at 1557 nm in a collimated and slow atomic beam
of metastable helium atoms. It is demonstrated that an excitation rate of 5000
/s can be realised with the beam of a 2W narrowband telecom fiber laser
intersecting the atomic beam perpendicularly. A Doppler-limited sub-MHz
spectroscopic linewidth is anticipated. Doppler-free excitation of 2% of
trapped and cooled atoms may be realised in a one-dimensional optical lattice
geometry, using the 2W laser both for trapping and spectroscopy. The very small
(8 Hz) natural linewidth of this transition presents an opportunity for
accurate tests of atomic structure calculations of the helium atom. A
measurement of the 3He - 4He isotope shift allows for accurate determination of
the difference in nuclear charge radius of both isotopes.Comment: accepted for publication in Europhysics Letter
BE Ursae Majoris: A detached binary with a unique reprocessing spectrum
New infrared photometry, optical and UV spectrophotometry, and a photographic ephemeris are presented for the detached binary BE UMa. Results show the primary to be a DO white dwarf with an effective temperature of 80,000 + or - 15,000 K and a mass of 0.6 + or - 0.1 solar masses. No evidence is found for variability of the primary. The main sequence secondary star is shown to be of early M spectral type, with a formal range of M1 to M5 being possible. A reflection effect in reprocessed line and continuum radiation is produced by EUV radiation from the primary incident on the secondary atmosphere. It is suggested that the temperature of the reprocessed component of the secondary's atmosphere is in the 5000 to 8500 K range, and that emission lines of decreasing ionization form deeper in the irradiated envelope. Relatively narrow He II and high excitation metal lines are formed from recombination and continuum fluorescence processes
Acute effects of transcranial direct current stimulation (tDCS) on peak torque and 5000 m running performance: a randomized controlled trial
The benefits of transcranial direct current stimulation (tDCS) on brain function, cognitive response, and motor ability are well described in scientific literature. Nevertheless, the effects of tDCS on athletes’ performance remain unclear. To compare the acute effects of tDCS on the running performance of 5000 m (m) runners. Eighteen athletes were randomized into Anodal (n = 9) groups that received tDCS for 20 min and 2 mA, and Sham (n = 9), in the motor cortex region (M1). Running time in 5000 m, speed, perceived exertion (RPE), internal load and peak torque (Pt) were evaluated. The Shapiro–Wilk test followed by a paired Student’s t-test was used to compare Pt and total time to complete the run between the groups. The running time and speed of the Anodal group (p = 0.02; 95% CI 0.11–2.32; d = 1.24) was lower than the Sham group (p = 0.02, 95% CI 0.05–2.20; d = 1.15). However, no difference was found in Pt (p = 0.70; 95% CI − 0.75 to 1.11; d = 0.18), RPE (p = 0.23; 95% CI − 1.55 to 0.39; d = 0.60) and internal charge (p = 0.73; 95% CI − 0.77 to 1.09; d = 0.17). Our data indicate that tDCS can acutely optimize the time and speed of 5000 m runners. However, no alterations were found for Pt and RPE
On SUSY GUTs with a degenerate Higgs mass matrix
Certain supersymmetric grand unified models predict that the coefficients of
the quadratic terms in the MSSM Higgs potential should be degenerate at the GUT
scale. We discuss some examples for such models, and we analyse the
implications of this peculiar condition of a GUT-scale degenerate Higgs mass
matrix for low-scale MSSM phenomenology. To this end we explore the parameter
space which is consistent with existing experimental constraints by means of a
Markov Chain Monte Carlo analysis.Comment: 31 pages, 27 figures; v2: typos correcte
Dynamics of Ordering of Heisenberg Spins with Torque --- Nonconserved Case. I
We study the dynamics of ordering of a nonconserved Heisenberg magnet. The
dynamics consists of two parts --- an irreversible dissipation into a heat bath
and a reversible precession induced by a torque due to the local molecular
field. For quenches to zero temperature, we provide convincing arguments, both
numerically (Langevin simulation) and analytically (approximate closure scheme
due to Mazenko), that the torque is irrelevant at late times. We subject the
Mazenko closure scheme to systematic numerical tests. Such an analysis, carried
out for the first time on a vector order parameter, shows that the closure
scheme performs respectably well. For quenches to , we show, to , that the torque is irrelevant at the Wilson-Fisher fixed
point.Comment: 13 pages, REVTEX, and 19 .eps figures, compressed, Submitted to Phys.
Rev.
Effects of Sfermion Mixing induced by RGE Running in the Minimal Flavor Violating CMSSM
Within the Constrained Minimal Supersymmetric Standard Model (CMSSM) with
Minimal Flavor Violation (MFV) for scalar quarks we study the effects of
intergenerational squark mixing on -physics observables, electroweak
precision observables (EWPO) and the Higgs boson mass predictions. Squark
mixing is generated through the Renormalization Group Equations (RGE) running
from the GUT scale to the electroweak scale due to presence of non diagonal
Yukawa matrices in the RGE's, e.g. due to the CKM matrix. We find that the
-Physics observables as well as the Higgs mass predictions do not receive
sizable corrections. On the other hand, the EWPO such as the boson mass can
receive corrections by far exceeding the current experimental precision. These
contributions can place new upper bounds on the CMSSM parameter space. We
extend our analysis to the CMSSM extended with a mechanism to explain neutrino
masses (CMSSM-seesaw I), which induces flavor violation in the scalar lepton
sector. Effects from slepton mixing on the analyzed observables are in general
smaller than from squark mixing, but can reach the level of the current
experimenal uncertainty for the EWPO
Constraining Supersymmetry using the relic density and the Higgs boson
Recent measurements by Planck, LHC experiments, and Xenon100 have significant
impact on supersymmetric models and their parameters. We first illustrate the
constraints in the mSUGRA plane and then perform a detailed analysis of the
general MSSM with 13 free parameters. Using SFitter, Bayesian and Profile
Likelihood approaches are applied and their results compared. The allowed
structures in the parameter spaces are largely defined by different mechanisms
of dark matter annihilation in combination with the light Higgs mass
prediction. In mSUGRA the pseudoscalar Higgs funnel and stau co-annihilation
processes are still avoiding experimental pressure. In the MSSM stau
co-annihilation, the light Higgs funnel, a mixed bino--higgsino region
including the heavy Higgs funnel, and a large higgsino region predict the
correct relic density. Volume effects and changes in the model parameters
impact the extracted mSUGRA and MSSM parameter regions in the Bayesian
analysis
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