112 research outputs found
Rigid invariance as derived from BRS invariance: The abelian Higgs model
Consequences of a symmetry, e.g.\ relations amongst Green functions, are
renormalization scheme independently expressed in terms of a rigid Ward
identity. The corresponding local version yields information on the respective
current. In the case of spontaneous breakdown one has to define the theory via
the BRS invariance and thus to construct rigid and current Ward identity
non-trivially in accordance with it. We performed this construction to all
orders of perturbation theory in the abelian Higgs model as a prelude to the
standard model. A technical tool of interest in itself is the use of a doublet
of external scalar ``background'' fields. The Callan-Symanzik equation has an
interesting form and follows easily once the rigid invariance is established.Comment: 33 pages, Plain Te
Meson masses in large Nf QCD from the Bethe-Salpeter equation
We solve the homogeneous Bethe-Salpeter (HBS) equation for the scalar,
pseudoscalar, vector, and axial-vector bound states of quark and anti-quark in
large Nf QCD with the improved ladder approximation in the Landau gauge. The
quark mass function in the HBS equation is obtained from the Schwinger-Dyson
(SD) equation in the same approximation for consistency with the chiral
symmetry. Amazingly, due to the fact that the two-loop running coupling of
large Nf QCD is explicitly written in terms of an analytic function, large Nf
QCD turns out to be the first example in which the SD equation can be solved in
the complex plane and hence the HBS equation directly in the time-like region.
We find that approaching the chiral phase transition point from the broken
phase, the scalar, vector, and axial-vector meson masses vanish to zero with
the same scaling behavior, all degenerate with the massless pseudoscalar meson.
This may suggest a new type of manifestation of the chiral symmetry restoration
in large Nf QCD.Comment: 33 pages, 16 figures. Typos are corrected. Minor corrections and
references are added. Version to appear in Phys. Rev.
Note on CKM Matrix Renormalization
A simple inspection of the one loop quark self-energy suggests a prescription
of the CKM matrix renormalization in the standard model. It leads to a CKM
matrix counterterm which is gauge parameter independent and satisfies the
unitarity constraint, and renormalized physical amplitudes which are gauge
parameter independent and smooth in quark mass difference. We make a point that
caution should be practiced when interpreting the CKM martix counterterm in
terms of those of parameters in a given representation due to rephasing effects
from renormalization. We show how this can be done using the degrees of freedom
in the on-shell renormalization scheme.Comment: version 1: 10 pages, no figures; version 2: proofread version for
Phys Rev D with minor revisions: (1) divided into 3 sections; (2) added a
footnote Comment on Ref. [8] as Ref. item [13]; (3) typos fixed and minor
rewordin
Phase transition and critical behaviour of the d=3 Gross-Neveu model
A second order phase transition for the three dimensional Gross-Neveu model
is established for one fermion species N=1. This transition breaks a paritylike
discrete symmetry. It constitutes its peculiar universality class with critical
exponent \nu = 0.63 and scalar and fermionic anomalous dimension \eta_\sigma =
0.31 and \eta_\psi = 0.11, respectively. We also compute critical exponents for
other N. Our results are based on exact renormalization group equations.Comment: 4 pages, 1 figure; v4 corresponds to the published articl
Miniature creep tests using plate specimens bonded by electron beam welding
Many aged thermal power plants restarted to supply sufficient electricity for Japanese industries and daily activities after the seismic earthquake. Reasonable guidelines for assessment of their integrity and estimation of remaining life have been required to operate them with a safety margin. Miniature Creep (MC) test is recognized as a semi-destructive technique to examine the degradation level of aged high temperature components. The MC thin plate specimen of 2.25Cr-1Mo steel and the similar one welded by Electron Beam (EB) for gauge length were employed to evaluate the validity of the EB welded MC thin plate specimen. A series of creep tests using the MC thin plate specimens were conducted in vacuum at 600°C. Then, following conclusions were obtained: (1) Creep rupture lives of the MC thin plate specimens welded by the EB were nearly the same as those of standard ones. (2) Vickers’ hardness in the welded zone decreased in a short time after the test started and reached almost the same as or below that in the base metal. (3) Rupture lives of the EB welded MC thin plate specimen at higher stress levels were longer than those of the standard MC thin plate specimen
Flavour Mixing, Gauge Invariance and Wave-function Renormalisation
We clarify some aspects of the LSZ formalism and wave function
renormalisation for unstable particles in the presence of electroweak
interactions when mixing and CP violation are considered. We also analyse the
renormalisation of the CKM mixing matrix which is closely related to wave
function renormalisation. We critically review earlier attempts to define a set
of "on-shell" wave function renormalisation constants. With the aid of an
extensive use of the Nielsen identities complemented by explicit calculations
we corroborate that the counter term for the CKM mixing matrix must be
explicitly gauge independent and demonstrate that the commonly used
prescription for the wave function renormalisation constants leads to gauge
parameter dependent amplitudes, even if the CKM counter term is gauge invariant
as required. We show that a proper LSZ-compliant prescription leads to gauge
independent amplitudes. The resulting wave function renormalisation constants
necessarily possess absorptive parts, but we verify that they comply with the
expected requirements concerning CP and CPT. The results obtained using this
prescription are different (even at the level of the modulus squared of the
amplitude) from the ones neglecting the absorptive parts in the case of top
decay. The difference is numerically relevant.Comment: 19 pages, plain latex, one ps figur
Exact flow equation for bound states
We develop a formalism to describe the formation of bound states in quantum
field theory using an exact renormalization group flow equation. As a concrete
example we investigate a nonrelativistic field theory with instantaneous
interaction where the flow equations can be solved exactly. However, the
formalism is more general and can be applied to relativistic field theories, as
well. We also discuss expansion schemes that can be used to find approximate
solutions of the flow equations including the essential momentum dependence.Comment: 22 pages, references added, published versio
Deriving Non-decoupling Effects of Heavy Fields from the Path Integral: a Heavy Higgs Field in an SU(2) Gauge Theory
We describe a method to remove non-decoupling heavy fields from a quantized
field theory and to construct a low-energy one-loop effective Lagrangian by
integrating out the heavy degrees of freedom in the path integral. We apply
this method to the Higgs boson in a spontaneously broken SU(2) gauge theory
(gauged linear sigma-model). In this context, the background-field method is
generalized to the non-linear representation of the Higgs sector by applying (a
generalization of) the Stueckelberg formalism. The (background) gauge-invariant
renormalization is discussed. At one loop the log M_H-terms of the heavy-Higgs
limit of this model coincide with the UV-divergent terms of the corresponding
gauged non-linear sigma-model, but vertex functions differ in addition by
finite (constant) terms in both models. These terms are also derived by our
method. Diagrammatic calculations of some vertex functions are presented as
consistency check.Comment: 33 Pages LaTeX, 6 figures uuencoded postscrip
CP Violation and Family Mixing in the Effective Electroweak Lagrangian
We construct the most general effective Lagrangian of the matter sector of
the Standard Model, including mixing and CP violating terms. The Lagrangian
contains the effective operators that give the leading contribution in theories
where the physics beyond the Standard Model shows at a scale .
We perform the diagonalization and passage to the physical basis in full
generality. We determine the contribution to the different observables and
discuss the possible new sources of CP violation, the idea being to be able to
gain some knowledge about new physics beyond the Standard Model from general
considerations, without having to compute model by model. The values of the
coefficients of the effective Lagrangian in some theories, including the
Standard Model, are presented and we try to draw some general conclusions about
the general pattern exhibited by physics beyond the Standard Model in what
concerns CP violation. In the process we have had to deal with two theoretical
problems which are very interesting in their own: the renormalization of the
CKM matrix elements and the wave function renormalization in the on-shell
scheme when mixing is present.Comment: A misplaced sentence was correcte
Mesoscopic interplay of superconductivity and ferromagnetism in ultra-small metallic grains
We review the effects of electron-electron interactions on the ground-state
spin and the transport properties of ultra-small chaotic metallic grains. Our
studies are based on an effective Hamiltonian that combines a superconducting
BCS-like term and a ferromagnetic Stoner-like term. Such terms originate in
pairing and spin exchange correlations, respectively. This description is valid
in the limit of a large dimensionless Thouless conductance. We present the
ground-state phase diagram in the fluctuation-dominated regime where the
single-particle mean level spacing is comparable to the bulk BCS pairing gap.
This phase diagram contains a regime in which pairing and spin exchange
correlations coexist in the ground-state wave function. We discuss the
calculation of the tunneling conductance for an almost-isolated grain in the
Coulomb-blockade regime, and present measurable signatures of the competition
between superconductivity and ferromagnetism in the mesoscopic fluctuations of
the conductance.Comment: 6 pages, 3 figures, To be published in the proceedings of the NATO
Advance Research Workshop "Recent Advances in Nonlinear Dynamics and Complex
System Physics.
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