14,497 research outputs found
One-loop non-renormalization results in EFTs
In Effective Field Theories (EFTs) with higher-dimensional operators many
anomalous dimensions vanish at the one-loop level for no apparent reason. With
the use of supersymmetry, and a classification of the operators according to
their embedding in super-operators, we are able to show why many of these
anomalous dimensions are zero. The key observation is that one-loop
contributions from superpartners trivially vanish in many cases under
consideration, making supersymmetry a powerful tool even for non-supersymmetric
models. We show this in detail in a simple U(1) model with a scalar and
fermions, and explain how to extend this to SM EFTs and the QCD Chiral
Langrangian. This provides an understanding of why most "current-current"
operators do not renormalize "loop" operators at the one-loop level, and allows
to find the few exceptions to this ubiquitous rule.Comment: Corrections made in Sec. 3.2 and Fig.
Self-Gravitational Corrections to the Cardy-Verlinde Formula and the FRW Brane Cosmology in SdS_5 Bulk
The semiclassical corrections to the Cardy-Verlinde entropy of a
five-dimensional Schwarzschild de-Sitter black hole (SdS_5) are explicitly
evaluated. These corrections are considered within the context of KKW analysis
and arise as a result of the self-gravitation effect. In addition, a
four-dimensional spacelike brane is considered as the boundary of the SdS_5
bulk background. It is already known that the induced geometry of the brane is
exactly given by that of a radiation-dominated FRW universe. By exploiting the
CFT/FRW-cosmology relation, we derive the self-gravitational corrections to the
first Friedmann-like equation which is the equation of the brane motion. The
additional term that arises due to the semiclassical analysis can be viewed as
stiff matter where the self-gravitational corrections act as the source for it.
This result is contrary to standard analysis that regards the charge of SdS_5
bulk black hole as the source for stiff matter. Furthermore, we rewrite the
Friedmann-like equation in a such way that it represents the conservation
equation of energy of a point particle moving in a one-dimensional effective
potential. The self-gravitational corrections to the effective potential and,
consequently, to the point particle's motion are obtained. A short analysis on
the asymptotic behavior of the 4-dimensional brane is presented.Comment: 16 pages, LaTeX; (v2) references added and correcte
Renormalization of dimension-six operators relevant for the Higgs decays
The discovery of the Higgs boson has opened a new window to test the SM
through the measurements of its couplings. Of particular interest is the
measured Higgs coupling to photons which arises in the SM at the one-loop
level, and can then be significantly affected by new physics. We calculate the
one-loop renormalization of the dimension-six operators relevant for
, which can be potentially important since
it could, in principle, give log-enhanced contributions from operator mixing.
We find however that there is no mixing from any current-current operator that
could lead to this log-enhanced effect. We show how the right choice of
operator basis can make this calculation simple. We then conclude that
can only be affected by RG mixing from
operators whose Wilson coefficients are expected to be of one-loop size, among
them fermion dipole-moment operators which we have also included.Comment: 21 pages. Improved version with h -> gamma Z results added and
structure of anomalous-dimension matrix determined further. Conclusions
unchange
Joining of thirty three percent by weight random glass fibre reinforced polystyrene using variable frequency microwave
[Abstract]: This paper extends the range of applications for Variable Frequency Microwave (VFM) (2 – 18 GHz) facilities to joining thirty three percent by weight glass fibre reinforced polystyrene composite [PS/GF (33%)]. With a given power level, the composite was exposed to various exposure times to microwave irradiation. The primer or coupling agent used was 5-minute two-part adhesive containing 100% liquid epoxy and 8% amine, i.e. Araldite, which was more readily microwave reactive than the composite itself. Bond strengths of the joints were lap shear tested and results were compared with those obtained using fixed frequency (2.45 GHz) microwave processing. The VFMF was operated under software control, which provided automatic data logging facilities. The maximum lap shear bond strength of joint was 430 N/cm2 using variable frequency microwave facility while that obtained by fixed frequency microwave configuration was only 331 N/cm2. The former is nearly 30% stronger than the latter
Permittivity measurement of thermoplastic composites at elevated temperature
[Abstract]: The material properties of greatest importance in microwave processing of a dielectric are the complex relative permittivity Epsilon = Epsilon' - jEpsilon'', and the loss tangent, tan Delta = Epsilon'/Epsilon''. This paper describes two convenient laboratory based methods to obtain Epsilon', Epsilon'' and hence tan Delta of fibre-reinforced thermoplastic (FRTP) composites. One method employs a microwave network analyser in conjunction with a waveguide transmission technique, chosen because it provides the widest possible frequency range with high accuracy. The values of the dielectric constant and dielectric loss of glass fibre reinforced (33%) low density polyethylene, LDPE/GF (33%), polystyrene, PS/GF (33%), and Nylon 66/GF (33%), were obtained. Results are compared with those obtained by another method using a high-temperature dielectric probe
Improvement of Renormalization-Scale Uncertainties Within Empirical Determinations of the b-Quark Mass
Accurate determinations of the MS-bar b-quark mass from
experimental data currently contain three
comparable sources of uncertainty; the experimental uncertainty from moments of
this cross-section, the uncertainty associated with , and the
theoretical uncertainty associated with the renormalization scale. Through
resummation of all logarithmic terms explicitly determined in the perturbative
series by the renormalization-group (RG) equation, it is shown that the
renormalization-scale dependence is virtually eliminated as a source of
theoretical uncertainty in . This resummation also reduces the
estimated effect of higher-loop perturbative contributions, further reducing
the theoretical uncertainties in . Furthermore, such resummation
techniques improve the agreement between the values of the MS-bar b-quark mass
extracted from the various moments of [], obviating the need to
choose an optimummoment for determining . Resummation techniques are
also shown to reduce renormalization-scale dependence in the relation between
b-quark MS-bar and pole mass and in the relation between the pole and
mass.Comment: 19 pages, latex2e, 6 eps figures contained in latex file. Errors
corrected in equations (20)--(22
Higgs Inflation as a Mirage
We discuss a simple unitarization of Higgs inflation that is genuinely weakly
coupled up to Planckian energies. A large non-minimal coupling between the
Higgs and the Ricci curvature is induced dynamically at intermediate energies,
as a simple ratio of mass scales. Despite not being dominated by the Higgs
field, inflationary dynamics simulates the `Higgs inflation' one would get by
blind extrapolation of the low-energy effective Lagrangian, at least
qualitatively. Hence, Higgs inflation arises as an approximate `mirage' picture
of the true dynamics. We further speculate on the generality of this phenomenon
and show that, if Higgs-inflation arises as an effective description, the
details of the UV completion are necessary to extract robust quantitative
predictions.Comment: 21 pages, 2 figure
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