556 research outputs found
Experimental test of magnetic photons
A "magnetic" photon hypothesis associated with magnetic monopoles is tested
experimentally. These photons are predicted to easily penetrate metal.
Experimentally the optical transmittance T of a metal foil was less than 2 x
10^-17. The hypothesis is not supported since it predicts T = 2 x 10^-12
The Minimal Moose for a Little Higgs
Recently a new class of theories of electroweak symmetry breaking have been
constructed. These models, based on deconstruction and the physics of theory
space, provide the first alternative to weak-scale supersymmetry with naturally
light Higgs fields and perturbative new physics at the TeV scale. The Higgs is
light because it is a pseudo-Goldstone boson, and the quadratically divergent
contributions to the Higgs mass are cancelled by new TeV scale ``partners'' of
the {\em same} statistics. In this paper we present the minimal theory space
model of electroweak symmetry breaking, with two sites and four link fields,
and the minimal set of fermions. There are very few parameters and degrees of
freedom beyond the Standard Model. Below a TeV, we have the Standard Model with
two light Higgs doublets, and an additional complex scalar weak triplet and
singlet. At the TeV scale, the new particles that cancel the 1-loop quadratic
divergences in the Higgs mass are revealed. The entire Higgs potential needed
for electroweak symmetry breaking--the quartic couplings as well as the
familiar negative mass squared--can be generated by the top Yukawa coupling,
providing a novel link between the physics of flavor and electroweak symmetry
breaking.Comment: 15 pages. References added. Included clarifying comments on the
origin of quartic couplings, and on power-counting. More elegant model for
generating Higgs potential from top Yukawa coupling presente
The Littlest Higgs
We present an economical theory of natural electroweak symmetry breaking,
generalizing an approach based on deconstruction. This theory is the smallest
extension of the Standard Model to date that stabilizes the electroweak scale
with a naturally light Higgs and weakly coupled new physics at TeV energies.
The Higgs is one of a set of pseudo Goldstone bosons in an
nonlinear sigma model. The symmetry breaking scale is around a TeV, with
the cutoff \Lambda \lsim 4\pi f \sim 10 TeV. A single electroweak doublet,
the ``little Higgs'', is automatically much lighter than the other pseudo
Goldstone bosons. The quartic self-coupling for the little Higgs is generated
by the gauge and Yukawa interactions with a natural size ,
while the top Yukawa coupling generates a negative mass squared triggering
electroweak symmetry breaking. Beneath the TeV scale the effective theory is
simply the minimal Standard Model. The new particle content at TeV energies
consists of one set of spin one bosons with the same quantum numbers as the
electroweak gauge bosons, an electroweak singlet quark with charge 2/3, and an
electroweak triplet scalar. One loop quadratically divergent corrections to the
Higgs mass are cancelled by interactions with these additional particles.Comment: 15 pages. References added. Corrected typos in the discussion of the
top Yukawa couplin
Strengthening Web Based Learning through Software Quality Analysis
The Web is changing the way people access & exchange information. Specifically in the teaching & learning environment, we are witnessing that the traditional model of presence based magisterial classes is shifting towards Web Based Learning. This new model draws on remote access systems, knowledge sharing, and student mobility. In this context, pedagogical strategies are also changing, and for instance, Project- Based Learning (PBL) is seen as a potential driver for growth and development in this arena. This study is focused on a PBL oriented course with a Distributed Remote ACcess (DRAC) system. The objective is to analyze how quantitative methods can be leveraged to design and evaluate automatic diagnosis and feedback tools to assist students on quality-related pedagogical issues in DRAC enabled PBL courses. Main conclusions derived from this study are correlation-based and reveal that the development of automatic quality assessment and feedback requires further research
A Composite Little Higgs Model
We describe a natural UV complete theory with a composite little Higgs. Below
a TeV we have the minimal Standard Model with a light Higgs, and an extra
neutral scalar. At the TeV scale there are additional scalars, gauge bosons,
and vector-like charge 2/3 quarks, whose couplings to the Higgs greatly reduce
the UV sensitivity of the Higgs potential. Stabilization of the Higgs mass
squared parameter, without finetuning, occurs due to a softly broken shift
symmetry--the Higgs is a pseudo Nambu-Goldstone boson. Above the 10 TeV scale
the theory has new strongly coupled interactions. A perturbatively
renormalizable UV completion, with softly broken supersymmetry at 10 TeV is
explicitly worked out. Our theory contains new particles which are odd under an
exact "dark matter parity", (-1)^{(2S+3B+L)}. We argue that such a parity is
likely to be a feature of many theories of new TeV scale physics. The lightest
parity odd particle, or "LPOP", is most likely a neutral fermion, and may make
a good dark matter candidate, with similar experimental signatures to the
neutralino of the MSSM. We give a general effective field theory analysis of
the calculation of corrections to precision electroweak observables.Comment: 28 page
Can the Pioneer anomaly be of gravitational origin? A phenomenological answer
In order to satisfy the equivalence principle, any non-conventional mechanism
proposed to gravitationally explain the Pioneer anomaly, in the form in which
it is presently known from the so-far analyzed Pioneer 10/11 data, cannot leave
out of consideration its impact on the motion of the planets of the Solar
System as well, especially those orbiting in the regions in which the anomalous
behavior of the Pioneer probes manifested itself. In this paper we, first,
discuss the residuals of the right ascension \alpha and declination \delta of
Uranus, Neptune and Pluto obtained by processing various data sets with
different, well established dynamical theories (JPL DE, IAA EPM, VSOP). Second,
we use the latest determinations of the perihelion secular advances of some
planets in order to put on the test two gravitational mechanisms recently
proposed to accommodate the Pioneer anomaly based on two models of modified
gravity. Finally, we adopt the ranging data to Voyager 2 when it encountered
Uranus and Neptune to perform a further, independent test of the hypothesis
that a Pioneer-like acceleration can also affect the motion of the outer
planets of the Solar System. The obtained answers are negative.Comment: Latex2e, 26 pages, 6 tables, 2 figure, 47 references. It is the
merging of gr-qc/0608127, gr-qc/0608068, gr-qc/0608101 and gr-qc/0611081.
Final version to appear in Foundations of Physic
Statistics of the gravitational force in various dimensions of space: from Gaussian to Levy laws
We discuss the distribution of the gravitational force created by a
Poissonian distribution of field sources (stars, galaxies,...) in different
dimensions of space d. In d=3, it is given by a Levy law called the Holtsmark
distribution. It presents an algebraic tail for large fluctuations due to the
contribution of the nearest neighbor. In d=2, it is given by a marginal
Gaussian distribution intermediate between Gaussian and Levy laws. In d=1, it
is exactly given by the Bernouilli distribution (for any particle number N)
which becomes Gaussian for N>>1. Therefore, the dimension d=2 is critical
regarding the statistics of the gravitational force. We generalize these
results for inhomogeneous systems with arbitrary power-law density profile and
arbitrary power-law force in a d-dimensional universe
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
Using job strain and organizational justice models to predict multiple forms of employee performance behaviours among Australian policing personnel
The overall purpose of this investigation was to examine the relationship between stress-related working conditions and three forms of employee performance behaviours: in-role behaviours, citizenship behaviours directed at other individuals and citizenship behaviours directed at the organization. The potentially stressful working conditions were based on the job strain model (incorporating job demands, job control and social support) as well as organizational justice theory. A sample of Australian-based police officers (n = 640) took part in this study and the data were collected via a mail-out survey. Multiple regression analyses were undertaken to assess both the strength and the nature of the relationships between the working conditions and employee performance and these analyses included tests for additive, interactional and curvilinear effects. The overall results indicated that a significant proportion of the explained variance in all three outcome measures was attributed to the additive effects of demand, control and support. The level of variance associated with the organizational justice dimensions was relatively small, although there were signs that specific dimensions of justice may provide unique insights into the relationship between job stressors and employee performance. The implications of these and other notable findings are discussed.<br /
Electron Dynamics in NdCeCuO: Evidence for the Pseudogap State and Unconventional c-axis Response
Infrared reflectance measurements were made with light polarized along the a-
and c-axis of both superconducting and antiferromagnetic phases of electron
doped NdCeCuO. The results are compared to
characteristic features of the electromagnetic response in hole doped cuprates.
Within the CuO planes the frequency dependent scattering rate,
1/, is depressed below 650 cm; this behavior is a
hallmark of the pseudogap state. While in several hole doped compounds the
energy scales associated with the pseudogap and superconducting states are
quite close, we are able to show that in NdCeCuO
the two scales differ by more than one order of magnitude. Another feature of
the in-plane charge response is a peak in the real part of the conductivity,
, at 50-110 cm which is in sharp contrast with the
Drude-like response where is centered at . This
latter effect is similar to what is found in disordered hole doped cuprates and
is discussed in the context of carrier localization. Examination of the c-axis
conductivity gives evidence for an anomalously broad frequency range from which
the interlayer superfluid is accumulated. Compelling evidence for the pseudogap
state as well as other characteristics of the charge dynamics in
NdCeCuO signal global similarities of the cuprate
phase diagram with respect to electron and hole doping.Comment: Submitted to PR
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