2,463 research outputs found
Transformations among large c conformal field theories
We show that there is a set of transformations that relates all of the 24
dimensional even self-dual (Niemeier) lattices, and also leads to non-lattice
objects that however cannot be interpreted as a basis for the construction of
holomorphic conformal field theory. In the second part of this paper, we extend
our observations to higher dimensional conformal field theories build on
extremal partition functions, where we generate c=24k theories with spectra
decomposable into the irreducible representations of the Fischer-Griess
Monster. We observe interesting periodicities in the coefficients of extremal
partition functions and characters of the extremal vertex operator algebras.Comment: 14 pages, minor corrections, new references adde
Systematic search for successful lepton mixing patterns with nonzero theta_13
We perform a systematic search for simple but viable lepton mixing patterns.
Our main criterion is that the mixing matrix can be parameterized by three
rotation angles, which are simple fractions of pi. These simple rotation angles
possess exact expressions for their sines and cosines, and often arise in the
flavor symmetry models. All possible parameterizations of the mixing matrix are
taken into account. In total, twenty successful mixing patterns are found to be
consistent with the latest neutrino oscillation data (including the recent T2K
results) in the CP conserving case, whereas fifteen mixing patterns are allowed
in the maximal CP violating case. Potential radiative corrections to the
constant mixing patterns are also calculated by solving the renormalization
group equations.Comment: 10 pages, 4 figures, 2 tables; version to be published in Nuclear
Physics
The calculations of Nucleon Electric Dipole Moment using background field on Lattice QCD
Measurements of nucleon and nuclei Electric Dipole Moments (EDMs) play an
important role in probing CP violation and exploring physics beyond the
Standard Model. We extract the neutron EDM by measuring the energy shift of the
nucleon two-point correlation function in the presence of a background field.
The UV divergence of the topological charge density operator is mitigated using
gradient flow, and the diffusion effect induced by the gradient flow process is
included into the fit ansatz. Our calculations were carried out on two 2+1 DWF
fermion, Iwasaki, gauge field ensembles generated by the RBC/UKQCD
collaborations with inverse lattice spacing 1.73 GeV and pion masses of about
340 and 420 MeV.Comment: 8 pages, 3 figures, Proceedings of the 40th International Symposium
on Lattice Field Theory (Lattice 2023), July 31st - August 4th, 2023, Fermi
National Accelerator Laborator
Dark Scalar Doublets and Neutrino Tribimaximal Mixing from A_4 Symmetry
In the context of A_4 symmetry, neutrino tribimaximal mixing is achieved
through the breaking of A_4 to Z_3 (Z_2) in the charged-lepton (neutrino)
sector respectively. The implied vacuum misalignment of the (1,1,1) and (1,0,0)
directions in A_4 space is a difficult technical problem, and cannot be treated
without many auxiliary fields and symmetries (and perhaps extra dimensions). It
is pointed out here that an alternative scenario exists with A_4 alone and no
redundant fields, if neutrino masses are "scotogenic", i.e. radiatively induced
by dark scalar doublets as recently proposed.Comment: 8 pages, 2 figures, 1 reference and 1 paragraph adde
Non-perturbative Renormalisation of Domain Wall Fermions: Quark Bilinears
We find the renormalisation coefficients of the quark field and the flavour
non-singlet fermion bilinear operators for the domain wall fermion action, in
the regularisation independent (RI) renormalisation scheme. Our results are
from a quenched simulation, on a 16^3x32 lattice, with beta=6.0 and an extent
in the fifth dimension of 16. We also discuss the expected effects of the
residual chiral symmetry breaking inherent in a domain wall fermion simulation
with a finite fifth dimension, and study the evidence for both explicit and
spontaneous chiral symmetry breaking effects in our numerical results. We find
that the relations between different renormalisation factors predicted by
chiral symmetry are, to a good approximation, satisfied by our results and that
systematic effects due to the (low energy) spontaneous chiral symmetry breaking
and zero-modes can be controlled. Our results are compared against the
perturbative predictions for both their absolute value and renormalisation
scale dependence.Comment: 53 pages, 21 figures, revte
A Supersymmetric D4 Model for mu-tau Symmetry
We construct a supersymmeterized version of the model presented by Grimus and
Lavoura (GL) in [1] which predicts theta_{23} maximal and theta_{13}=0 in the
lepton sector. For this purpose, we extend the flavor group, which is D4 x
Z2^{(aux)} in the original model, to D4 x Z5. An additional difference is the
absence of right-handed neutrinos. Despite these changes the model is the same
as the GL model, since theta_{23} maximal and theta_{13}=0 arise through the
same mismatch of D4 subgroups, D2 in the charged lepton and Z2 in the neutrino
sector. In our setup D4 is solely broken by gauge singlets, the flavons. We
show that their vacuum structure, which leads to the prediction of theta_{13}
and theta_{23}, is a natural result of the scalar potential. We find that the
neutrino mass matrix only allows for inverted hierarchy, if we assume a certain
form of spontaneous CP violation. The quantity |m_{ee}|, measured in
neutrinoless double beta decay, is nearly equal to the lightest neutrino mass
m3. The Majorana phases phi1 and phi2 are restricted to a certain range for m3
< 0.06 eV. We discuss the next-to-leading order corrections which give rise to
shifts in the vacuum expectation values of the flavons. These induce deviations
from maximal atmospheric mixing and vanishing theta_{13}. It turns out that
these deviations are smaller for theta_{23} than for theta_{13}.Comment: 19 pages, 4 figure
Influencing the conductance in biphenyl-like molecular junctions with THz radiation
We investigate the torsional vibrations in biphenyl-like molecular junctions
and transport properties in the presence of an external THz field. Ab-initio
calculations including external electric fields show that the torsional angle
{\phi} of a thiolated biphenyl junction exhibits virtually no response.
However, if functional groups are added to the molecule, creating a dipole
moment in each of the rings, an external field becomes more effective for
changing {\phi}. A model based on the cos2{\phi} dependence of the current is
proposed for the biphenyl-like molecular junctions in presence of an external
THz field including 2,2'-bipyridine, 3,3'-bipyridine and 2,2',4,4'-
tetramethyl-3,3'-bipyridine. The current through these molecules is shown to
change if the THz frequency gets in resonance to the torsional vibration mode.Comment: 9 pages, 10 figures, submitted to PSS
Multimodality Treatment for Early-Stage Hepatocellular Carcinoma: A Bridging Therapy for Liver Transplantation
Purpose: To evaluate the efficiency of a multimodality approach consisting of transcatheter arterial chemoembolization (TACE) and radiofrequency ablation (RFA) as bridging therapy for patients with hepatocellular carcinoma (HCC) awaiting orthotopic liver transplantation (OLT) and to evaluate the histopathological response in explant specimens. Materials and Methods: Between April 2001 and November 2011, 36 patients with 50 HCC nodules (1.4-5.0 cm, median 2.8 cm) on the waiting list for liver transplantation were treated by TACE and RFA. The drop-out rate during the follow-up period was recorded. The local efficacy was evaluated by histopathological examination of the explanted livers. Results: During a median follow-up time of 29 (4.0-95.3) months the cumulative drop-out rate for the patients on the waiting list was 0, 2.8, 5.5, 11.0, 13.9 and 16.7% at 3, 6, 12, 24, 36 and 48 months, respectively. 16 patients (with 26 HCC lesions) out of 36(44.4%) were transplanted by the end of study with a median waiting list time of 13.7 (2.5-37.8) months. The histopathological examination of the explanted specimens revealed a complete necrosis in 20 of 26 HCCs (76.9%), whereas 6 (23.1%) nodules showed viable residual tumor tissue. All transplanted patients are alive at a median time of 29.9 months. Imaging correlation showed 100% specificity and 66.7% sensitivity for the depiction of residual or recurrent tumor. Conclusion: We conclude that TACE.combined with RFA could provide an effective treatment to decrease the drop-out rate from the OLT waiting list for HCC patients. Furthermore, this combination therapy results in high rates of complete tumor necrosis as evaluated in the histopathological analysis of the explanted livers. Further randomized trials are needed to demonstrate if there is a benefit in comparison with a single-treatment approach. copyright (C) 2012 S. Karger AG, Base
Molecular switch controlled by pulsed bias voltages
It was observed in recent experiments that the current-voltage
characteristics (IV) of BPDN-DT (bipyridyl- dinitro- oligophenylene-
ethynylene- dithiol) can be switched in a very controlled manner between "on"
and "off" traces by applying a pulse in a bias voltage, V_bias. We have
calculated the polaron formation energies to check a frequently held belief,
namely, that the polaron formation can explain the observed bistability. Our
results are not consistent with such a mechanism. Instead, we propose a
conformational reorientation. The molecule carries an intrinsic dipole moment
which couples to V_bias. Ramping V_bias exerts a force on the dipole that can
reorient ("rotate") the molecule from the ground state ("off") into a
metastable configuration ("on") and back. By elaborated electronic structure
calculations, we identify a specific path for this rotation through the
molecule's conformational phase space. We show that this path has sufficiently
high barriers to inhibit thermal instability but still the molecule can be
switched in the voltage range of the junction stability. The theoretical IVs
reproduce qualitatively the key experimental observations. We propose, how the
alternative mechanism of conductance switching can be experimentally verified.Comment: LaTEX, 6 Figures, published versio
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