127 research outputs found
Stability of Subsequent-to-Leading-Logarithm Corrections to the Effective Potential for Radiative Electroweak Symmetry Breaking
We demonstrate the stability under subsequent-to-leading logarithm
corrections of the quartic scalar-field coupling constant and the
running Higgs boson mass obtained from the (initially massless) effective
potential for radiatively broken electroweak symmetry in the
single-Higgs-Doublet Standard Model. Such subsequent-to-leading logarithm
contributions are systematically extracted from the renormalization group
equation considered beyond one-loop order. We show to be the dominant
coupling constant of the effective potential for the radiatively broken case of
electroweak symmetry. We demonstrate the stability of and the running
Higgs boson mass through five orders of successively subleading logarithmic
corrections to the scalar-field-theory projection of the effective potential
for which all coupling constants except the dominant coupling constant
are disregarded. We present a full next-to-leading logarithm
potential in the three dominant Standard Model coupling constants
(-quark-Yukawa, , and ) from these coupling constants'
contribution to two loop - and -functions. Finally, we
demonstrate the manifest order-by-order stability of the physical Higgs boson
mass in the 220-231 GeV range. In particular, we obtain a 231 GeV physical
Higgs boson mass inclusive of the -quark-Yukawa and coupling
constants to next-to-leading logarithm order, and inclusive of the smaller
gauge coupling constants to leading logarithm order.Comment: 21 pages, latex2e, 2 eps figures embedded in latex file. Updated
version contains expanded analysis in Section
Renormalization Group Determination of the Five-Loop Effective Potential for Massless Scalar Field Theory
The five-loop effective potential and the associated summation of subleading
logarithms for O(4) globally-symmetric massless field theory in
the Coleman-Weinberg renormalization scheme (where is the renormalization scale) is calculated via
renormalization-group methods. An important aspect of this analysis is
conversion of the known five-loop renormalization-group functions in the
minimal-subtraction (MS) scheme to the Coleman-Weinberg scheme.Comment: 5 pages. Write-up of talk given at Theory Canada III, June 2007,
University of Albert
Optimal Renormalization-Group Improvement of Two Radiatively-Broken Gauge Theories
In the absence of a tree-level scalar-field mass, renormalization-group (RG)
methods permit the explicit summation of leading-logarithm contributions to all
orders of the perturbative series for the effective-potential functions
utilized in radiative symmetry breaking. For scalar-field electrodynamics, such
a summation of leading logarithm contributions leads to upper bounds on the
magnitudes of both gauge and scalar-field coupling constants, and suggests the
possibility of an additional phase of spontaneous symmetry breaking
characterized by a scalar-field mass comparable to that of the theory's gauge
boson. For radiatively-broken electroweak symmetry, the all-orders summation of
leading logarithm terms involving the dominant three couplings (quartic
scalar-field, t-quark Yukawa, and QCD) contributing to standard-model radiative
corrections leads to an RG-improved potential characterized by a 216 GeV Higgs
boson mass. Upon incorporation of electroweak gauge couplants we find that the
predicted Higgs mass increases to 218 GeV. The potential is also characterized
by a quartic scalar-field coupling over five times larger than that anticipated
for an equivalent Higgs mass obtained via conventional spontaneous symmetry
breaking, leading to a concomitant enhancement of processes (such as ) sensitive to this coupling. Moreover, if the QCD coupling constant is
taken to be sufficiently strong, the tree potential's local minimum at is shown to be restored for the summation of leading logarithm corrections.
Thus if QCD exhibits a two-phase structure similar to that of
supersymmetric Yang-Mills theory, the weaker asymptotically-free phase of QCD
may be selected by the large logarithm behaviour of the RG-improved effective
potential for radiatively broken electroweak symmetry.Comment: latex2e using amsmath, 36 pages, 7 eps figures embedded in latex.
Section 8.3 errors asociated with electroweak coupling effects are correcte
Exact One Loop Running Couplings in the Standard Model
Taking the dominant couplings in the standard model to be the quartic scalar
coupling, the Yukawa coupling of the top quark, and the SU(3) gauge coupling,
we consider their associated running couplings to one loop order. Despite the
non-linear nature of the differential equations governing these functions, we
show that they can be solved exactly. The nature of these solutions is
discussed and their singularity structure is examined. It is shown that for a
sufficiently small Higgs mass, the quartic scalar coupling decreases with
increasing energy scale and becomes negative, indicative of vacuum instability.
This behavior changes for a Higgs mass greater than 168 GeV, beyond which this
couplant increases with increasing energy scales and becomes singular prior to
the ultraviolet (UV) pole of the Yukawa coupling. Upper and lower bounds on the
Higgs mass corresponding to new physics at the TeV scale are obtained and
compare favourably with the numerical results of the one-loop and two-loop
analyses with inclusion of electroweak couplings.Comment: 5 pages, LaTeX, additional references and further discussion in this
version. Accepted for publication in Canadian Journal of Physic
Assessing the effects of climate change on arthropod abundance in Azorean pastures: PASTURCLIM project's baseline monitoring data
Background
The data we present are part of the project PASTURCLIM (Impact of climate change on pasture’s productivity and nutritional composition in the Azores). The project aims to assess the consequences of climate change (e.g. temperature increase) on the grass production and its quality for forage, as well as to assess changes in the arthropod communities associated with the Azorean intensive pastures. An in situ experiment was set up using Open Top Chambers (OTCs), in order to simulate an increasing of temperature (average of +1.2ºC) on pastures. In this contribution, we present the data relative to the arthropod sampling.
New information
We provide an inventory of all arthropods recorded inside OTCs and in control plots in three intensively managed pastures dominated by grasses in Terceira Island (Azores): two of them dominated by ryegrass, Lolium multiflorum Lam. (Poaceae), located respectively at 186 m and 301 m above sea level; and one field dominated by common velvetgrass, Holcus lanatus L. (Poaceae), located at an altitude of 385 m.
A total of 41351 specimens were collected. Organisms collected belong to four classes, 15 orders, 60 families and 171 species/morphospecies (including 34 taxa identified only at order, family or genus level). Therefore, for only 137 taxa, we have a scientific name associated (n = 38918). A total of 75% of the species (n = 129 species) are considered introduced (including all the species with indeterminate colonisation status that are possibly also exotic species (n = 7622)), representing 71% of the total abundance (n = 29664 specimens). A total of 19% of the species (n = 33 species) are considered native non-endemic representing 28% of the total abundance (n = 11608 specimens). Only one endemic species was sampled, the wolf spider Pardosa acorensis Simon, 1883 (1% of the species), representing 0.2% of the total abundance (n = 79 specimens). Spiders (5056 specimens) and beetles (18310 specimens) were the dominant taxa representing, respectively, 20 and 78 morphospecies.
Since the main aim of this study was to have a better knowledge on arthropod communities present in Azorean pastures under a simulated temperature increase, the principal novelty of this paper is the contribution with distribution and abundance data to a baseline knowledge on the future consequences of climate changes on arthropod communities in Azorean pastures.info:eu-repo/semantics/publishedVersio
The Renormalization Group with Exact beta-Functions
The perturbative -function is known exactly in a number of
supersymmetric theories and in the 't Hooft renormalization scheme in the
model. It is shown how this allows one to compute the effective
action exactly for certain background field configurations and to relate bare
and renormalized couplings. The relationship between the MS and SUSY
subtraction schemes in super Yang-Mills theory is discussed
Neutron charge form factor at large
The neutron charge form factor is determined from an analysis of
the deuteron quadrupole form factor data. Recent calculations, based
on a variety of different model interactions and currents, indicate that the
contributions associated with the uncertain two-body operators of shorter range
are relatively small for , even at large momentum transfer . Hence,
can be extracted from at large without undue
systematic uncertainties from theory.Comment: 8 pages, 3 figure
Elastic electron deuteron scattering with consistent meson exchange and relativistic contributions of leading order
The influence of relativistic contributions to elastic electron deuteron
scattering is studied systematically at low and intermediate momentum transfers
( fm). In a -expansion, all leading order
relativistic -exchange contributions consistent with the Bonn OBEPQ models
are included. In addition, static heavy meson exchange currents including boost
terms and lowest order -currents are considered. Sizeable
effects from the various relativistic two-body contributions, mainly from
-exchange, have been found in form factors, structure functions and the
tensor polarization . Furthermore, static properties, viz. magnetic
dipole and charge quadrupole moments and the mean square charge radius are
evaluated.Comment: 15 pages Latex including 5 figures, final version accepted for
publication in Phys.Rev.C Details of changes: (i) The notation of the curves
in Figs. 1 and 2 have been clarified with respect to left and right panels.
(ii) In Figs. 3 and 4 an experimental point for T_20 has been added and a
corresponding reference [48] (iii) At the end of the text we have added a
paragraph concerning the quality of the Bonn OBEPQ potential
Global change in microcosms:Environmental and societal predictors of land cover change on the Atlantic Ocean Islands
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