2,414 research outputs found
Nuclear Coherent versus Incoherent Effects in Peripheral RHI Collisions
We derive simple and physically transparent expressions for the contribution
of the strong interaction to one nucleon removal processes in peripheral
relativistic heavy ion collisions. The coherent contribution,i.e, the
excitation of a giant dipole resonance via meson exchange is shown to be
negligible as well as interference between coulomb and nuclear excitation.
Incoherent nucleon knock out contribution is also derived suggesting the nature
of the nuclear interaction in this class of processes. We also justify the
simple formulae used to fit the data of the E814 Collaboration.Comment: LATEX, 20 pags, Submited to Nucl. Phys. C, NUCPHA 176
Fractal Theory Space: Spacetime of Noninteger Dimensionality
We construct matter field theories in ``theory space'' that are fractal, and
invariant under geometrical renormalization group (RG) transformations. We
treat in detail complex scalars, and discuss issues related to fermions,
chirality, and Yang-Mills gauge fields. In the continuum limit these models
describe physics in a noninteger spatial dimension which appears above a RG
invariant ``compactification scale,'' M. The energy distribution of KK modes
above M is controlled by an exponent in a scaling relation of the vacuum energy
(Coleman-Weinberg potential), and corresponds to the dimensionality. For
truncated-s-simplex lattices with coordination number s the spacetime
dimensionality is 1+(3+2ln(s)/ln(s+2)). The computations in theory space
involve subtleties, owing to the 1+3 kinetic terms, yet the resulting
dimensionalites are equivalent to thermal spin systems. Physical implications
are discussed.Comment: 28 pages, 6 figures; Paper has been amplified with a more detailed
discussion of a number of technical issue
Flavour Universal Dynamical Electroweak Symmetry Breaking
The top condensate see-saw mechanism of Dobrescu and Hill allows electroweak
symmetry to be broken while deferring the problem of flavour to an electroweak
singlet, massive sector. We provide an extended version of the singlet sector
that naturally accommodates realistic masses for all the standard model
fermions, which play an equal role in breaking electroweak symmetry. The models
result in a relatively light composite Higgs sector with masses typically in
the range of (400-700)~GeV. In more complete models the dynamics will
presumably be driven by a broken gauged family or flavour symmetry group. As an
example of the higher scale dynamics a fully dynamical model of the quark
sector with a GIM mechanism is presented, based on an earlier top condensation
model of King using broken family gauge symmetry interactions (that model was
itself based on a technicolour model of Georgi). The crucial extra ingredient
is a reinterpretation of the condensates that form when several gauge groups
become strong close to the same scale. A related technicolour model of Randall
which naturally includes the leptons too may also be adapted to this scenario.
We discuss the low energy constraints on the massive gauge bosons and scalars
of these models as well as their phenomenology at the TeV scale.Comment: 22 pages, 3 fig
Closure of two dimensional turbulence: the role of pressure gradients
Inverse energy cascade regime of two dimensional turbulence is investigated
by means of high resolution numerical simulations. Numerical computations of
conditional averages of transverse pressure gradient increments are found to be
compatible with a recently proposed self-consistent Gaussian model. An
analogous low order closure model for the longitudinal pressure gradient is
proposed and its validity is numerically examined. In this case numerical
evidence for the presence of higher order terms in the closure is found. The
fundamental role of conditional statistics between longitudinal and transverse
components is highlighted.Comment: 4 pages, 2 figures, in press on PR
Probing Heavy Higgs Boson Models with a TeV Linear Collider
The last years have seen a great development in our understanding of particle
physics at the weak scale. Precision electroweak observables have played a key
role in this process and their values are consistent, within the Standard Model
interpretation, with a light Higgs boson with mass lower than about 200 GeV. If
new physics were responsible for the mechanism of electroweak symmetry
breaking, there would, quite generally, be modifications to this prediction
induced by the non-standard contributions to the precision electroweak
observables. In this article, we analyze the experimental signatures of a heavy
Higgs boson at linear colliders. We show that a linear collider, with center of
mass energy \sqrt{s} <= 1 TeV, would be very useful to probe the basic
ingredients of well motivated heavy Higgs boson models: a relatively heavy
SM-like Higgs, together with either extra scalar or fermionic degrees of
freedom, or with the mixing of the third generation quarks with non-standard
heavy quark modes.Comment: 21 page
Beautiful Mirrors and Precision Electroweak Data
The Standard Model (SM) with a light Higgs boson provides a very good
description of the precision electroweak observable data coming from the LEP,
SLD and Tevatron experiments. Most of the observables, with the notable
exception of the forward-backward asymmetry of the bottom quark, point towards
a Higgs mass far below its current experimental bound. The disagreement, within
the SM, between the values for the weak mixing angle as obtained from the
measurement of the leptonic and hadronic asymmetries at lepton colliders, may
be taken to indicate new physics contributions to the precision electroweak
observables. In this article we investigate the possibility that the inclusion
of additional bottom-like quarks could help resolve this discrepancy. Two
inequivalent assignments for these new quarks are analysed. The resultant fits
to the electroweak data show a significant improvement when compared to that
obtained in the SM. While in one of the examples analyzed, the exotic quarks
are predicted to be light, with masses below 300 GeV, and the Higgs tends to be
heavy, in the second one the Higgs is predicted to be light, with a mass below
250 GeV, while the quarks tend to be heavy, with masses of about 800 GeV. The
collider signatures associated with the new exotic quarks, as well as the
question of unification of couplings within these models and a possible
cosmological implication of the new physical degrees of freedom at the weak
scale are also discussed.Comment: 21 pages, 4 embedded postscript figures, LaTeX. Two minor corrections
performe
Assessment, evaluation and quality assurance: implications for integrity in reporting academic achievement in higher education
The terms assessment, evaluation and quality assurance have various interpretations in higher education. The first two, assessment and evaluation, share considerable conceptual ground and interconnected histories. Quality assurance, on the other hand, is a more recent development. The issue of academic achievement standards in particular has significant implications for quality assurance. The first half of this article provides a selective broad-brush outline of the topics just described. The second half is about an emerging concept, grade integrity, which is focused on the trustworthiness of course grades recorded on student academic transcripts. This focus serves as a platform to illustrate: how difficult issues can be analysed; why established conventions and assumptions need to be challenged; and how ways forward can be sought out and thought through. The context for the paper is higher education but the principles also apply to other educational sectors
Little Higgses from an Antisymmetric Condensate
We construct an SU(6)/Sp(6) non-linear sigma model in which the Higgses arise
as pseudo-Goldstone bosons. There are two Higgs doublets whose masses have no
one-loop quadratic sensitivity to the cutoff of the effective theory, which can
be at around 10 TeV. The Higgs potential is generated by gauge and Yukawa
interactions, and is distinctly different from that of the minimal
supersymmetric standard model. At the TeV scale, the new bosonic degrees of
freedom are a single neutral complex scalar and a second copy of SU(2)xU(1)
gauge bosons. Additional vector-like pairs of colored fermions are also
present.Comment: 13 page
On Power Suppressed Operators and Gauge Invariance in SCET
The form of collinear gauge invariance for power suppressed operators in the
soft-collinear effective theory is discussed. Using a field redefinition we
show that it is possible to make any power suppressed ultrasoft-collinear
operators invariant under the original leading order gauge transformations. Our
manipulations avoid gauge fixing. The Lagrangians to O(lambda^2) are given in
terms of these new fields. We then give a simple procedure for constructing
power suppressed soft-collinear operators in SCET_II by using an intermediate
theory SCET_I.Comment: 15 pages, journal versio
Asymptotically Free Non-Abelian Gauge Theories With Fermions and Scalars As Alternatives to QCD
In this paper we construct non-Abelian gauge theories with fermions and
scalars that nevertheless possess asymptotic freedom.The scalars are taken to
be in a chiral multiplet transforming as under
and transforming as singlets under the colour SU(3) group. We consider two
distinct scenarios, one in which the additional scalars are light and another
in which they are heavier than half the Z-boson mass. It is shown that
asymptotic freedom is obtained without requiring that all additional couplings
keep fixed ratios with each other. It is also shown that both scenarios can not
be ruled out by what are considered standard tests of QCD like R- parameter,
g-2 for muons or deep inelastic phenomena. The light mass scenario is however
ruled out by high precision Z-width data (and only by that one data).The heavy
mass scenario is still viable and is shown to naturally pass the test of
flavour changing neutral currents. It also is not ruled out by precision
electroweak oblique parameters. Many distinctive experimental signatures of
these models are also discussed.Comment: 37 pages in LATEX with 10 fig
- …