2,949 research outputs found
Numerical simulation of heavy fermions in an SU(2)_L x SU(2)_R symmetric Yukawa model
An exploratory numerical study of the influence of heavy fermion doublets on
the mass of the Higgs boson is performed in the decoupling limit of a chiral
symmetric Yukawa model with mirror fermions. The
behaviour of fermion and boson masses is investigated at infinite bare quartic
coupling on , and lattices. A first
estimate of the upper bound on the renormalized quartic coupling as a function
of the renormalized Yukawa-coupling is given.Comment: 15 pp + 11 Figures appended as Postscript file
Characterization of new hybrid pixel module concepts for the ATLAS Insertable B-Layer upgrade
The ATLAS Insertable B-Layer (IBL) collaboration plans to insert a fourth
pixel layer inside the present Pixel Detector to recover from eventual failures
in the current pixel system, especially the b-layer. Additionally the IBL will
ensure excellent tracking, vertexing and b-tagging performance during the LHC
phase I and add robustness in tracking with high luminosity pile-up. The
expected peak luminosity for IBL is 2 to 3centerdot1034 cm-2s-1 and IBL is
designed for an integrated luminosity of 700 fb-1. This corresponds to an
expected fluence of 5centerdot1015 1 MeV neqcm-2 and a total ionizing dose of
250 MRad. In order to cope with these requirements, two new module concepts are
under investigation, both based on a new front end IC, called FE-I4. This IC
was designed as readout chip for future ATLAS Pixel Detectors and its first
application will be the IBL. The planar pixel sensor (PPS) based module concept
benefits from its well understood design, which is kept as similar as possible
to the design of the current ATLAS Pixel Detector sensor. The second approach
of the new three dimensional (3D) silicon sensor technology benefits from the
shorter charge carrier drift distance to the electrodes, which completely
penetrate the sensor bulk. Prototype modules of both sensor concepts have been
build and tested in laboratory and test beam environment before and after
irradiation. Both concepts show very high performance even after irradiation to
5centerdot1015 1 MeV neqcm-2 and meet the IBL specifications in terms of hit
efficiency being larger than 97%. Lowest operational threshold studies have
been effected and prove independent of the used sensor concept the excellent
performance of FE-I4 based module concepts in terms of noise hit occupancy at
low thresholds.Comment: Part of 9th International Conference on Position Sensitive Detectors
(PSD9
Quenching Effects in the Hadron Spectrum
Lattice QCD has generated a wealth of data in hadronic physics over the last
two decades. Until relatively recently, most of this information has been
within the "quenched approximation" where virtual quark--anti-quark pairs are
neglected. This review presents a descriptive discussion of the effects of
removing this approximation in the calculation of hadronic masses.Comment: To appear in "Lattice Hadron Physics", ed. A.C. Kalloniatis, D.B.
Leinweber and A.G. William
Mass Spectrum and Bounds on the Couplings in Yukawa Models With Mirror-Fermions
The symmetric Yukawa model with mirror-fermions
in the limit where the mirror-fermion is decoupled is studied both analytically
and numerically. The bare scalar self-coupling is fixed at zero and
infinity. The phase structure is explored and the relevant phase transition is
found to be consistent with a second order one. The fermionic mass spectrum
close to that transition is discussed and a first non-perturbative estimate of
the influence of fermions on the upper and lower bounds on the renormalized
scalar self-coupling is given. Numerical results are confronted with
perturbative predictions.Comment: 7 (Latex) page
Nucleon axial form factors from two-flavour Lattice QCD
We present preliminary results on the axial form factor and the
induced pseudoscalar form factor of the nucleon. A systematic
analysis of the excited-state contributions to form factors is performed on the
CLS ensemble `N6' with and lattice spacing . The relevant three-point functions were computed with
source-sink separations ranging from to $t_s \sim \
1.4 \ \text{fm}$. We observe that the form factors suffer from non-trivial
excited-state contributions at the source-sink separations available to us. It
is noted that naive plateau fits underestimate the excited-state contributions
and that the method of summed operator insertions correctly accounts for these
effects.Comment: 7 pages, 12 figures; talk presented at Lattice 2014 -- 32nd
International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia
University New York, N
Bounds on the renormalized couplings in an SU(2)_L \otimes SU(2)_R symmetric Yukawa model
The vacuum stability lower bound on the mass of the Higgs boson is
numerically investigated in an symmetric Yukawa
model, which describes two heavy degenerate fermion doublets in the limit of
vanishing gauge couplings. Good agreement with perturbation theory is found,
although the couplings are strong. The upper bound on the fermion mass and
renormalized Yukawa coupling is also determined in the part of bare parameter
space where reflection positivity has been proven.Comment: 9 pages + 2 figures (appended as postscript files
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