3,796 research outputs found
Introducing the concept of infinite series: Preliminary analyses of curriculum content and pedagogical practice
Introducing the concept of infinite series: preliminary analyses of curriculum content and pedagogical practice
Leptogenesis, Z' bosons, and the reheating temperature of the Universe
We study the impact for leptogenesis of new U(1) gauge bosons coupled to the
heavy Majorana neutrinos. They can significantly enhance the efficiency of
thermal scenarios in the weak washout regime as long as the Z' masses are not
much larger than the reheating temperature (), with the
highest efficiencies obtained for Z' bosons considerably heavier than the heavy
neutrinos (). We show how the allowed region of the parameter
space is modified in the presence of a Z' and we also obtain the minimum
reheating temperature that is required for these models to be successful.Comment: 14 pages, 6 figures; One figure added, discussion on the reheating
temperature extende
Identifying Unconventional E Models at Colliders
Recently it was shown that, in the framework of superstring inspired \E
models, the presence of generation dependent discrete symmetries allows us to
construct a phenomenologically viable class of models in which the three
generations of fermions do not have the same embedding within the fundamental
{\bf 27} dimensional representation of E. In this scenario, these different
embeddings of the conventional fermions imply that the left-handed charged
leptons and the right-handed -type quarks are coupled in a non--universal
way to the new neutral gauge bosons present in these models. It
was also shown that a unique signature for this scenario, would be a deviation
from unity for the ratio of cross sections for the production of two different
lepton species in annihilation. However, several different scenarios
are possible, depending on the particular assignment chosen for ,
and and for the right-handed -type quarks, as well as on the type
of boson. Such scenarios can not be disentangled from one another by
means of cross section measurements alone. In this paper we examine the
possibility of identifying the pattern of embeddings through measurements of
polarized and unpolarized asymmetries for fermion pair-production at the 500
GeV Next Linear Collider (NLC). We show that it will be possible to
identify the different patterns of unconventional assignments for the
left-handed leptons and for the quark, for masses as large as
TeV.Comment: Plain Tex, 15 pages, + 9 figure available upon request
([email protected] or [email protected]), UM-TH 93--1
A Comparison Between Different Cycle Decompositions for Metropolis Dynamics
In the last decades the problem of metastability has been attacked on
rigorous grounds via many different approaches and techniques which are briefly reviewed in this paper.
It is then useful to understand connections between different
point of views. In view of this
we consider irreducible, aperiodic and
reversible Markov chains with exponentially
small transition probabilities in the framework of Metropolis dynamics.
We compare two different cycle decompositions and prove their equivalence
Intersection of reality and fiction in art perception: pictorial space, body sway and mental imagery
Background The thesis of embodied cognition claims that perception of the environment entails a complex set of multisensory processes which forms a basis for the agent’s potential and immediate actions. However, in the case of artworks, an agent becomes an observer and action turns into a reaction. This raises questions about the presence of embodied or situated cognition involved in art reception.
Aims The study aimed to assess the bodily correlates of perceiving fictional pictorial spaces in the absence of a possibility of an actual physical immersion or manipulation of represented forms.
Method The subjects were presented with paintings by Vermeer and De Hooch, whilst their body sway and eye movements were recorded. Moreover, test and questionnaires on mental imagery (MRT, VVIQ and OSIQ) were administered.
Results Three major results were obtained: (1) the degree of pictorial depth did not influence body sway; (2) fixations to distant elements in paintings (i.e. backgrounds) were accompanied by an increase in body sway; and (3) mental rotation test scores correlated positively with body sway.
Conclusions Our results suggest that in certain cases— despite the fictional character of art—observers’ reactions resemble reactions to real stimuli. It is proposed that these reactions are mediated by mental imagery (e.g. mental rotation) that contributes to the act of representing alternative to real artistic spaces
Z', new fermions and flavor changing processes, constraints on E models from --> eee
We study a new class of flavor changing interactions, which can arise in
models based on extended gauge groups (rank 4) when new charged fermions are
present together with a new neutral gauge boson. We discuss the cases in which
the flavor changing couplings in the new neutral current coupled to the
are theoretically expected to be large, implying that the observed
suppression of neutral flavor changing transitions must be provided by heavy
masses together with small - mixing angles.
Concentrating on E models, we show how the tight experimental limit on implies serious constraints on the mass and mixing
angle. We conclude that if the value of the flavor changing parameters is
assumed to lie in a theoretically natural range, in most cases the presence of
a much lighter than 1 TeV is unlikely.Comment: plain tex, 22 pages + 2 pages figures in PostScript (appended after
`\bye'), UM-TH 92-1
Projected U.S. demographics and social security
Without policy reforms, the aging of the U.S. population is likely to increase the burden of the currently unfunded social security and medicare systems. In this paper we build an applied general equilibrium model and incorporate the population projections made by the Social Security Administration (SSA) to evaluate the macroeconomic and welfare implications of alternative fiscal responses to the retirement of the baby- boomers. Our calculation suggest that it will be costly to maintain the benefits at the levels now promised because the increases in distortionary taxes required to finance those benefits will reduce private saving and labor supply. We also find that the “accounting calculations” made by SSA underestimate the required fiscal adjustments. Finally, our results confirm that policies with similar long-run characteristics have very different transitional implications about the distribution of welfare across generations.Demography ; Social security
Supersymmetric Leptogenesis
We study leptogenesis in the supersymmetric standard model plus the seesaw.
We identify important qualitative differences that characterize supersymmetric
leptogenesis with respect to the non-supersymmetric case. The lepton number
asymmetries in fermions and scalars do not equilibrate, and are related via a
non-vanishing gaugino chemical potential. Due to the presence of new anomalous
symmetries, electroweak sphalerons couple to winos and higgsinos, and QCD
sphalerons couple to gluinos, thus modifying the corresponding chemical
equilibrium conditions. A new constraint on particles chemical potentials
corresponding to an exactly conserved -charge, that also involves the number
density asymmetry of the heavy sneutrinos, appears. These new ingredients
determine the matrices that mix up the density asymmetries of the
lepton flavours and of the heavy sneutrinos. We explain why in all temperature
ranges the particle thermodynamic system is characterized by the same number of
independent quantities. Numerical differences with respect to usual treatment
remain at the level.Comment: 30 pages, 2 figures. Typos corrected, one reference added. Version
published in JCA
Review of High Towers and Strong Places: A Political History of Middle- earth
A review of Timothy R. Furnish, High Towers and Strong Places: A Political History of Middle- earth (Toronto: Oloris Publishing, 2016). 166 pages. $35.00. ISBN 9781940992518
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