10,650 research outputs found
Conformal and non Conformal Dilaton Gravity
The quantum dynamics of the gravitational field non-minimally coupled to an
(also dynamical) scalar field is studied in the {\em broken phase}. For a
particular value of the coupling the system is classically conformal, and can
actually be understood as the group averaging of Einstein-Hilbert's action
under conformal transformations. Conformal invariance implies a simple Ward
identity asserting that the trace of the equation of motion for the graviton is
the equation of motion of the scalar field. We perform an explicit one-loop
computation to show that the DeWitt effective action is not UV divergent {\em
on shell} and to find that the Weyl symmetry Ward identity is preserved {\em on
shell} at that level. We also discuss the fate of this Ward identity at the
two-loop level --under the assumption that the two-loop UV divergent part of
the effective action can be retrieved from the Goroff-Sagnotti counterterm--
and show that its preservation in the renormalized theory requires the
introduction of counterterms which exhibit a logarithmic dependence on the
dilaton field.Comment: LateX, 50 pages. Several points clarified; references added. New
section on Weyl invariant renormalisation adde
A Renormalization Group Analysis of the NCG constraints m_{top} = 2\,m_W},
We study the evolution under the renormalization group of the restrictions on
the parameters of the standard model coming from Non-Commutative Geometry,
namely and . We adopt the point of
view that these relations are to be interpreted as {\it tree level} constraints
and, as such, can be implemented in a mass independent renormalization scheme
only at a given energy scale . We show that the physical predictions on
the top and Higgs masses depend weakly on .Comment: 7 pages, FTUAM-94/2, uses harvma
The U(1)A anomaly in noncommutative SU(N) theories
We work out the one-loop anomaly for noncommutative SU(N) gauge
theories up to second order in the noncommutative parameter .
We set and conclude that there is no breaking of the classical
symmetry of the theory coming from the contributions that are either
linear or quadratic in . Of course, the ordinary anomalous
contributions will be still with us. We also show that the one-loop
conservation of the nonsinglet currents holds at least up to second order in
. We adapt our results to noncommutative gauge theories with
SO(N) and U(1) gauge groups.Comment: 50 pages, 5 figures in eps files. Some comments and references adde
Yukawa terms in noncommutative SO(10) and E6 GUTs
We propose a method for constructing Yukawa terms for noncommutative SO(10)
and E6 GUTs, when these GUTs are formulated within the enveloping-algebra
formalism. The most general noncommutative Yukawa term that we propose
contains, at first order in thetamunu, the most general BRS invariant Yukawa
contribution whose only dimensionful parameter is the noncommutativity
parameter. This noncommutative Yukawa interaction is thus renormalisable at
first order in thetamunu.Comment: 14 pages, no figure
Hokupa'a-Gemini Discovery of Two Ultracool Companions to the Young Star HD 130948
We report the discovery of two faint ultracool companions to the nearby
(d~17.9 pc) young G2V star HD 130948 (HR 5534, HIP 72567) using the Hokupa'a
adaptive optics instrument mounted on the Gemini North 8-meter telescope. Both
objects have the same common proper motion as the primary star as seen over a 7
month baseline and have near-IR photometric colors that are consistent with an
early-L classification. Near-IR spectra taken with the NIRSPEC AO instrument on
the Keck II telescope reveal K I lines, FeH, and water bandheads. Based on
these spectra, we determine that both objects have spectral type dL2 with an
uncertainty of 2 spectral subclasses. The position of the new companions on the
H-R diagram in comparison with theoretical models is consistent with the young
age of the primary star (<0.8 Gyr) estimated on the basis of X-ray activity,
lithium abundance and fast rotation. HD 130948 B and C likely constitute a pair
of young contracting brown dwarfs with an orbital period of about 10 years, and
will yield dynamical masses for L dwarfs in the near future.Comment: 10 pages, 3 figures, (13 total pages
Operation speed of polariton condensate switches gated by excitons
We present a time-resolved photoluminescence (PL) study in real- and
momentum-space of a polariton condensate switch in a quasi-1D semiconductor
microcavity. The polariton flow across the ridge is gated by excitons inducing
a barrier potential due to repulsive interactions. A study of the device
operation dependence on the power of the pulsed gate beam obtains a
satisfactory compromise for the ON/OFF-signal ratio and -switching time of the
order of 0.3 and ps, respectively. The opposite transition is
governed by the long-lived gate excitons, consequently the OFF/ON-switching
time is ps, limiting the overall operation speed of the device
to GHz. The experimental results are compared to numerical
simulations based on a generalized Gross-Pitaevskii equation, taking into
account incoherent pumping, decay and energy relaxation within the condensate.Comment: 11 pages, 11 figure
Attitude towards gender equality and coeducation among Secondary School teachers: a case study in Madrid, Spain
Introduction. In spite of the education reform and the introduction of mixed schools, there are still obstacles to gender equality in Spain. Sexist attitudes and values continue to influence personal development and career choices, limiting women''s participation in many spheres. The opinions, beliefs, ideas, conceptions, expectations and personal attitude of teaching professionals exert a great influence on the students who perceive them, which calls for up-to-date information on teaching staff’s perceptions towards gender equality and coeducation. Method. In this work, results from a survey distributed to 105 teachers in three Secondary Schools in the Autonomous Community of Madrid are presented. The retrieved data was analyzed by using parametric (ANOVA) and non-parametric (Kruskal-Wallis) tests. Results. Significant differences were found among the respondents in terms of their views on gender equality for the gender and gender*age factors, and for the gender and years of teaching experience factors in the case of their perceptions about coeducation. Discussion and Conclusion. Although the tendency toward a true status of equality was more pronounced in women than in men, an adequate predisposition of the majority of teachers of both sexes towards the achievement of a social equality model based on the promotion of peer roles and coeducational practices was found. Teaching staff appears to be aware of the importance of adopting policies and laws that favor effective and real equality between men and women. © 2021. Universidad de Almería and Ilustre Colegio Oficial de la Psicología de Andalucía Oriental (Spain). All Rights Reserved
Spin Selective Filtering of Polariton Condensate Flow
Spin-selective spatial filtering of propagating polariton condensates, using
a controllable spin-dependent gating barrier, in a one-dimensional
semiconductor microcavity ridge waveguide is reported. A nonresonant laser beam
provides the source of propagating polaritons while a second circularly
polarized weak beam imprints a spin dependent potential barrier, which gates
the polariton flow and generates polariton spin currents. A complete spin-based
control over the blocked and transmitted polaritons is obtained by varying the
gate polarization.Comment: 5 pages, 4 figure
Universal Conductance Distributions in the Crossover between Diffusive and Localization Regimes
The full distribution of the conductance in quasi-one-dimensional
wires with rough surfaces is analyzed from the diffusive to the localization
regime. In the crossover region, where the statistics is dominated by only one
or two eigenchannels, the numerically obtained P(G) is found to be independent
of the details of the system with the average conductance as the only
scaling parameter. For < e^2/h, P(G) is given by an essentially
``one-sided'' log-normal distribution. In contrast, for e^2/h <= 2e^2/h,
the shape of P(G) remarkable agrees with those predicted by random matrix
theory for two fluctuating transmission eigenchannels.Comment: Accepted for publication in Phys. Rev. Let
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