13,203 research outputs found
Comparing Instanton Contributions with Exact Results in N=2 Supersymmetric Scale Invariant Theories
We discuss the general issues and ambiguities involved in matching the exact
results for the low energy effective action of scale invariant N=2
supersymmetric QCD to those obtained by instanton methods. We resolve the
reported disagreements and verify agreement between an infinite series of
coefficients in the low energy effective actions calculated in the two
approaches. In particular, we show that the exact low-energy effective
couplings for SU(N) for all N with 2N fundamental hypermultiplets agree at a
special vacuum on the Coulomb branch where a large unbroken discrete global
symmetry makes the matching of parameters relatively straightforward.Comment: 26 pages, 1 figure; report-no. correcte
Cosmic microwave background constraints on coupled dark matter
We study CMB constraints on a model with a cosmological constant and a
fraction of dark matter non-minimally coupled to a massless scalar field. In
this scenario, there is an extra gravity-like fifth force which can affect the
evolution of the Universe enough to have a discernible effect on measurements
of cosmological parameters. Using Planck and WMAP polarisation data, we find
that up to half of the dark matter can be coupled. The coupling can also be
several times larger than in models with a single species of cold dark matter
coupled to a quintessence scalar field, as the scalar field does not play the
role of dark energy and is therefore less constrained by the data.Comment: 5 pages, 4 figure
The role of the right tempoparietal junction in the elicitation of vicarious experiences and detection accuracy while observing pain and touch
This study investigated the effects of observing pain and touch in others upon vicarious somatosensory experiences and the detection of subtle somatosensory stimuli. Furthermore, transcranial direct current stimulation (tDCS) was used to assess the role of the right temporoparietal junction (rTPJ), as this brain region has been suggested to be involved in perspective taking and self-other distinction. Undergraduates (N = 22) viewed videos depicting hands being touched, hands being pricked, and control scenes (same approaching movement as in the other video categories but without the painful/touching object), while experiencing vibrotactile stimuli themselves on the left, right, or both hands. Participants reported the location at which they felt a somatosensory stimulus. Vibrotactile stimuli and visual scenes were applied in a congruent or incongruent way. During three separate testing sessions, excitability of the rTPJ was modulated with tDCS (cathodal, anodal, or sham). We calculated the proportion of correct responses and false alarms (i.e., number of trials in which a vicarious somatosensory experience was reported congruent to the site of the visual information). Pain-related scenes facilitated the correct detection of tactile stimuli and augmented the number of vicarious somatosensory experiences compared with observing touch or control videos. Stimulation of the rTPJ had no reliable influence upon detection accuracy or the number of vicarious errors. This study indicates that the observation of pain-related scenes compared to the observation of touch or control videos increases the likelihood that a somatosensory stimulus is detected. Contrary to our expectations, the rTPJ did not modulate detection accuracy
Probing the Upper Limit of Nonclassical Rotational Inertia
We study the effect of confinement on solid 4-He's nonclassical rotational
inertia (NCRI) in a torsional oscillator by constraining it to narrow annular
cells of various widths. The NCRI exhibits a broad maximum value of 20% for
annuli of approximately 100 micrometer width. Samples constrained to porous
media or to larger geometries both have smaller NCRI, mostly below about 1%. In
addition, we extend Kim and Chan's blocked annulus experiment to solid samples
with large supersolid fractions. Blocking the annulus suppresses the
nonclassical decoupling from 17.1% below the limit of our detection of 0.8%.
This result demonstrates the nonlocal nature of the supersolid phenomena. At 20
mK, NCRI depends on velocity history showing a closed hysteresis loop in
different thin annular cells.Comment: 5 pages, 4 figure
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