4,830 research outputs found
Isospin Symmetry Breaking within the HLS Model: A Full () Mixing Scheme
We study the way isospin symmetry violation can be generated within the
Hidden Local Symmetry (HLS) Model. We show that isospin symmetry breaking
effects on pseudoscalar mesons naturally induces correspondingly effects within
the physics of vector mesons, through kaon loops. In this way, one recovers all
features traditionally expected from \rho-\omg mixing and one finds support
for the Orsay phase modelling of the e^+e^- \ra \pi^+ \pi^- amplitude. We
then examine an effective procedure which generates mixing in the whole ,
\omg, sector of the HLS Model. The corresponding model allows us to
account for all two body decays of light mesons accessible to the HLS model in
modulus and phase, leaving aside the \rho \ra \pi \pi and K^* \ra K \pi
modes only, which raise a specific problem. Comparison with experimental data
is performed and covers modulus and phase information; this represents 26
physics quantities successfully described with very good fit quality within a
constrained model which accounts for SU(3) breaking, nonet symmetry breaking in
the pseudoscalar sector and, now, isospin symmetry breaking.Comment: 38 pages, version published in Eur. Phys. J.
VMD, the WZW Lagrangian and ChPT: The Third Mixing Angle
We show that the Hidden Local Symmetry Model, supplemented with well-known
procedures for breaking flavor SU(3) and nonet symmetry, provides all the
information contained in the standard Chiral Perturbation Theory (ChPT)
Lagrangian . This allows to rely on radiative
decays of light mesons ( and ) in order to extract
some numerical information of relevance to ChPT: a value for , a quark mass ratio of , and a negligible
departure from the Gell-Mann--Okubo mass formula. The mixing angles are
and . We also give the values of all decay constants. It is shown that
the common mixing pattern with one mixing angle is actually quite
appropriate and algebraically related to the mixing pattern
presently preferred by the ChPT community. For instance the traditional
is functionally related to the ChPT and fulfills
. The vanishing of , supported by all
data on radiative decays, gives a novel relation between mixing angles and the
violation of nonet symmetry in the pseudoscalar sector. Finally, it is shown
that the interplay of nonet symmetry breaking through U(3) \ra SU(3)
U(1) satisfies all requirements of the physics of radiative decays without any
need for additional glueballs.Comment: 31 pages, 1 figur
Constraints on New Physics from Baryogenesis and Large Hadron Collider Data
We demonstrate the power of constraining theories of new physics by insisting
that they lead to electroweak baryogenesis, while agreeing with current data
from the Large Hadron Collider. The general approach is illustrated with a
singlet scalar extension of the Standard Model. Stringent bounds can already be
obtained, which reduce the viable parameter space to a small island.Comment: 4 pages, 2 figures. References added, figures updated. Version to
appear in PR
Colour-Kinematics Duality for One-Loop Rational Amplitudes
Colour-kinematics duality is the conjecture of a group theory-like structure
for the kinematic dependence of scattering amplitudes in gauge theory and
gravity. This structure has been verified at tree level in various ways, but
similar progress has been lacking at loop level, where the power of the duality
would be most significant. Here we explore colour-kinematics duality at one
loop using the self-dual sector as a starting point. The duality is shown to
exist in pure Yang-Mills theory for two infinite classes of amplitudes:
amplitudes with any number of particles either all of the same helicity or with
one particle helicity opposite the rest. We provide a simple Lagrangian-based
argument in favour of the double copy relation between gauge theory and gravity
amplitudes in these classes, and provide some explicit examples. We further
discuss aspects of the duality which persist after integration, leading to
relations among partial amplitudes. Finally, we describe form factors in the
self-dual theory at tree level which also satisfy the duality.Comment: 36 pages, 5 figures; v2: published versio
Understanding Stephen Collins Foster His World and Music
This dissertation is an explanation of the life and music of the American composer Stephen Collins Foster in terms of his historical world. Foster captured the essential dynamics of the antebellum mind and heart, which accounted for the immense popularity of his music even during the composer's lifetime. Consequently, by placing Foster and his music within the historical context of his own antebellum society, culture, and history, I sought explanations for the following: the function of sentimentality in Foster's tear-inducing parlor songs and in his blackface plantation songs; the Copperhead, anti-Lincoln politics of the Foster family; Foster's non-companionate marriage to the high-tempered yet independent "Jeanie;" what the young Foster learned during his stay in the free city of Cincinnati, located just across the river from a slave state; Foster's position on minstrelsy and how he transformed the racially denigrating minstrel song into the refined, sentimental hybrid plantation song that sympathized with the slaves; how and why the piano girls were the major purchasers of Foster's parlor songs; the meaning behind the ghost-like images of the women in Foster's songs; life in Civil War New York along the Bowery where Foster spent his final years and a re-evaluation of his New York songs; and, finally, the curious conditions of his tragic death from an "accident" in his hotel room on the Bowery. Although Foster's association with the minstrel stage is often viewed as a source of embarrassment by twenty-first century Americans, I was able to demonstrate that ivStephen Foster wrote his greatest plantation songs during the years when blackface minstrelsy expressed sympathy for the slaves, and that he abandoned the genre when it did not
RascalC: A Jackknife Approach to Estimating Single and Multi-Tracer Galaxy Covariance Matrices
To make use of clustering statistics from large cosmological surveys,
accurate and precise covariance matrices are needed. We present a new code to
estimate large scale galaxy two-point correlation function (2PCF) covariances
in arbitrary survey geometries that, due to new sampling techniques, runs times faster than previous codes, computing finely-binned covariance
matrices with negligible noise in less than 100 CPU-hours. As in previous
works, non-Gaussianity is approximated via a small rescaling of shot-noise in
the theoretical model, calibrated by comparing jackknife survey covariances to
an associated jackknife model. The flexible code, RascalC, has been publicly
released, and automatically takes care of all necessary pre- and
post-processing, requiring only a single input dataset (without a prior 2PCF
model). Deviations between large scale model covariances from a mock survey and
those from a large suite of mocks are found to be be indistinguishable from
noise. In addition, the choice of input mock are shown to be irrelevant for
desired noise levels below mocks. Coupled with its generalization
to multi-tracer data-sets, this shows the algorithm to be an excellent tool for
analysis, reducing the need for large numbers of mock simulations to be
computed.Comment: 29 pages, 8 figures. Accepted by MNRAS. Code is available at
http://github.com/oliverphilcox/RascalC with documentation at
http://rascalc.readthedocs.io
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