803 research outputs found
Post-Wick theorems for symbolic manipulation of second-quantized expressions in atomic many-body perturbation theory
Manipulating expressions in many-body perturbation theory becomes unwieldily
with increasing order of the perturbation theory. Here I derive a set of
theorems for efficient simplification of such expressions. The derived rules
are specifically designed for implementing with symbolic algebra tools. As an
illustration, we count the numbers of Brueckner-Goldstone diagrams in the first
several orders of many-body perturbation theory for matrix elements between two
states of a mono-valent system.Comment: J. Phys. B. (in press); Mathematica packages available from
http://wolfweb.unr.edu/homepage/andrei/WWW-tap/mathematica.htm
Closing the Symmetry at Electroweak Scale
We show that some models with gauge
symmetry can be realized at the electroweak scale and that this is a
consequence of an approximate global symmetry. This symmetry
implies a condition among the vacuum expectation value of one of the neutral
Higgs scalars, the 's coupling constant, , the sine of the weak
mixing angle , and the mass of the boson, . In the limit
in which this symmetry is valid it avoids the tree level mixing of the
boson of the Standard Model with the extra boson. We have verified
that the oblique parameter is within the allowed range indicating that the
radiative corrections that induce such a mixing at the 1-loop level are small.
We also show that a custodial symmetry implies that in some of
the models we have to include sterile (singlets of the 3-3-1 symmetry)
right-handed neutrinos with Majorana masses, being the see-saw mechanism
mandatory to obtain light active neutrinos. Moreover, the approximate
symmetry implies that the extra non-standard
particles of these 3-3-1 models can be considerably lighter than it had been
thought before so that new physics can be really just around the corner.Comment: 32 pages, no figure, RevTeX. Some typos correcte
Cooperation in one machine scheduling
Contains fulltext :
172966.pdf (publisher's version ) (Open Access
Transverse Polarization of Top Quarks Produced at a Photon-Photon Collider
At future colliders copious production of pairs
is possible. This would allow a detailed investigation of the interactions
involving the top quark. We propose some orrelations which are sensitive to final state interactions and we compute the QCD and standard model
Higgs boson contributions to these correlations. QCD induced transverse
polarization of top quarks is found to be sizeable and measurable at a
high-energy collider with an integrated luminosity of 10 which is converted into a photon collider by backscattering of laser
photons.Comment: 8 pages. No fig. Preprint UM-P-94/25 and PITHA 94/1
Trust and the city: Linking urban upbringing to neural mechanisms of trust in psychosis
Objective: Elevated prevalence of non-affective psychotic disorders is often found in densely populated areas. This functional magnetic resonance imaging study investigates if reduced trust, a component of impaired social functioning in patients with psychotic disorder, is associated with urban upbringing.
Methods: In total, 39 patients (22 first episode and 17 clinical high risk) and 30 healthy controls, aged 16â29, performed two multi-round trust games, with a cooperative and unfair partner during functional magnetic resonance imaging scan-ning. Baseline trust was operationalized as the first investment made, and changes of trust as changes in investments made over the 20 trials during the games. Urban exposure during upbringing (0â15 years) was defined as higher urban (â„2500 inhabitants/km2) or lower urban (<2500 inhabitants/km2).
Results: Patients displayed lower baseline trust (first investment) than controls, regardless of urbanicity exposure. During cooperative interactions, lower-urban patients showed increasing investments. In addition, during cooperative interactions, group-by-developmental urbanicity interactions were found in the right and left amygdalae, although for the latter only at trend level. Higher urbanicity was associated with decreased activation of the left amygdala in patients and controls during investments and with increased activation of the right and left amygdalae in patients only, during repayments. During unfair interactions, no associations of urbanicity with behavior or brain activation were found.
Conclusion: Urban upbringing was unrelated to baseline trust. Associations with urbanicity were stronger for patients compared to controls, suggesting greater susceptibility to urbanicity effects during the developmental period. Higher-urban patients failed to compensate for the initial distrust specifically during repeated cooperative interactions. This finding highlights potential implications for social functioning. Urban upbringing was linked to dif-ferential amygdala activation, suggesting altered mechanisms of feedback learning, but this was not associated with trust game behavio
Natural New Inflation in Broken Supergravity
We consider a natural new inflationary model in broken supergravity based on
an R symmetry. The model predicts a concrete relation between the amplitude of
primordial density fluctuations and the scale of supersymmetry breaking. The
observed value of the density fluctuations is obtained for the gravitino mass
of order the weak scale along with a power-law spectral index considerably less
than one, which may be tested in future observations.Comment: 12 pages, late
Black Holes with a Generalized Gravitational Action
Microscopic black holes are sensitive to higher dimension operators in the
gravitational action. We compute the influence of these operators on the
Schwarzschild solution using perturbation theory. All (time reversal invariant)
operators of dimension six are included (dimension four operators don't alter
the Schwarzschild solution). Corrections to the relation between the Hawking
temperature and the black hole mass are found. The entropy is calculated using
the Gibbons-Hawking prescription for the Euclidean path integral and using
naive thermodynamic reasoning. These two methods agree, however, the entropy is
not equal to 1/4 the area of the horizon.Comment: plain tex(uses phyzzx.tex), 8 pages, CALT-68-185
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