4,651 research outputs found
Coexistence of Haldane gap excitations and long-range order in R_2BaNiO_5 (=rare earth)
( rare earth) quasi-1-D antiferromagnets are structurally
equivalent to the well-studied 1-D S=1 Haldane-gap compound Y_2BaNiO_5. Unlike
the Y-nickelate though, these materials undergo 3-D magnetic ordering at finite
temperatures. Recent inelastic neutron scattering studies of Pr_2BaNiO_5 and
(Nd_{x}Y_{1-x})_2BaNiO_5 revealed purely 1-dimensional gap excitations that
propagate exclusively on the Ni-chains and are strikingly similar to Haldane
gap modes in Y_2BaNiO_5. In the ordered phase these excitations survive and
actually coexist with conventional spin waves. Below the gap energy
increases and scales as the square of the ordered moment on the Ni sites. The
results suggest that the Haldane singlet ground state of the Ni-chains is not
fully destroyed by N\'{e}el ordering.Comment: Invited paper for the International Conference on Neutron Scattering,
Toronto, Canada, August 17-21, 199
Immunophenotype of Atypical Polypoid Adenomyoma of the Uterus: Diagnostic Value and Insight on Pathogenesis
Atypical polypoid adenomyoma (APA) is a rare uterine lesion constituted by atypical endometrioid glands, squamous morules, and myofibromatous stroma. We aimed to assess the immunophenotype of the 3 components of APA, with regard to its pathogenesis and its differential diagnosis. A systematic review was performed by searching electronic databases from their inception to January 2019 for immunohistochemical studies of APA. Thirteen studies with 145 APA cases were included. APA glands appeared analogous to atypical endometrial hyperplasia (endometrioid cytokeratins pattern, Ki67â€50%, common PTEN loss, and occasional mismatch repair deficiency); the prominent expression of hormone receptors and nuclear ÎČ-catenin suggest that APA may be a precursor of "copy number-low," CTNNB1-mutant endometrial cancers. Morules appeared as a peculiar type of hyperdifferentiation (low KI67, nuclear ÎČ-catenin+, CD10+, CDX2+, SATB2+, p63-, and p40-), analogous to morular metaplasia in other lesions and distinguishable immunohistochemically from both conventional squamous metaplasia and solid cancer growth. Stroma immunphenotype (low Ki67, α-smooth-muscle-actin+, h-caldesmon-, CD10-, or weak and patchy) suggested a derivation from a metaplasia of normal endometrial stroma. It was similar to that of nonatypical adenomyoma, and different from adenosarcoma (Ki67 increase and CD10+ in periglandular stroma) and myoinvasive endometrioid carcinoma (h-caldesmon+ in myometrium and periglandular fringe-like CD10 pattern)
Phenomenology of Pseudo Dirac Neutrinos
We formulate general conditions on neutrino mass matrices under
which a degenerate pair of neutrinos at a high scale would split at low scale
by radiative corrections involving only the standard model fields. This
generalizes the original observations of Wolfenstein on pseudo Dirac neutrinos
to three generations. A specific model involving partially broken discrete
symmetry and solving the solar and atmospheric anomalies is proposed. The
symmetry pattern of the model naturally generates two large angles one of which
can account for the large angle MSW solution to the solar neutrino problem.Comment: 15 pages LATE
Perturbation Theory of High-Tc Superconductivity in Iron Pnictides
The high-transition-temperature (high-Tc) superconductivity discovered
recently in iron pnictides is analyzed within a perturbation theory.
Specifically, the probable pairing symmetry, the doping dependence of the
transition temperature and the pairing mechanism are studied by solving the
Eliashberg equation for multi-band (2- and 5-band) Hubbard models with
realistic electronic structures. The effective pairing interaction is expanded
perturbatively in the on-site Coulomb integrals up to third order. Our
perturbative weak-coupling approach shows that sufficiently large eigenvalues
of the Eliashberg equation are obtained to explain the actual high transition
temperatures by taking realistic on-site Coulomb integrals in the 5-band model.
Thus, unconventional (non-phonon-mediated) superconductivity is highly likely
to be realized. The superconducting order parameter does not change its sign on
the Fermi surfaces, but it does change between the electron and hole Fermi
surfaces. Consequently, the probable pairing symmetry is always "a nodeless
extended s-wave symmetry (more specifically, an s_{+-}-wave symmetry)" over the
whole parameter region that we investigated. It is suggested that the 2-band
model is insufficient to explain the high values of Tc.Comment: 24 pages, 9 figure
General Issues Connecting Flavor Symmetry and Supersymmetry
We motivate and construct supersymmetric theories with continuous flavor
symmetry, under which the electroweak Higgs doublets transform non-trivially.
Flavor symmetry is spontaneously broken at a large mass scale in a sector of
gauge-singlet fields; the light Higgs multiplets naturally emerge as special
linear combinations that avoid acquiring the generic large mass. Couplings of
the light Higgs doublets to light moduli fields from the singlet sector could
lead to important effects in the phenomenology of the Higgs sector.Comment: 5 page
Naturalness of nearly degenerate neutrinos
If neutrinos are to play a relevant cosmological role, they must be
essentially degenerate. We study whether radiative corrections can or cannot be
responsible for the small mass splittings, in agreement with all the available
experimental data. We perform an exhaustive exploration of the bimaximal mixing
scenario, finding that (i) the vacuum oscillations solution to the solar
neutrino problem is always excluded; (ii) if the mass matrix is produced by a
see-saw mechanism, there are large regions of the parameter space consistent
with the large angle MSW solution, providing a natural origin for the hierarchy; (iii) the bimaximal structure becomes
then stable under radiative corrections. We also provide analytical expressions
for the mass splittings and mixing angles and present a particularly simple
see-saw ansatz consistent with all observations.Comment: 25 pages, LaTeX, 6 ps figures, psfig.sty. Typos, references and minor
details corrected. Additional condition for the MSW mechanism incorporated.
New viable textures adde
The Interplay between Neutrinos and Charged Leptons in the Minimal SU(3)_LxU(1)_N Gauge Model
In the minimal SU(3)_LxU(1)_N gauge model with a global L_e-L_mu-L_tau (=L')
symmetry and a discrete Z_4 symmetry, it is found that the interplay between
neutrinos and charged leptons contained in triplets of \psi^i=(\nu^i_L,
\ell^i_L, \ell^{ci}_L) (i=1,2,3) naturally leads to the large mixing angle
(LMA) MSW solution. The model includes two (anti)sextet Higgs scalars, S^(0)
with L'=0 and S^(+) with L'=2, which, respectively, couple to \psi^1\psi^{2,3}
for the electron mass and masses of atmospheric neutrinos and to
\psi^{2,3}\psi^{2,3} for the \mu- and \tau-masses and one-loop radiative
neutrino masses relevant to solar neutrinos. This mechanism is realized by
utilizing an additional residual discrete symmetry supplied by explicitly
broken L', which guarantees the absence of tree-level neutrino mass terms of
the \psi^{2,3}\psi^{2,3}-type. Pure rotation effects due to the diagonalization
of neutrino and charged-lepton mass matrices are estimated to yield \Delta
m^2_\odot/\Delta m^2_{atm} \leq (m_e/m_\mu)^{3/2}=O(10^{-4}) but the radiative
effects supersede the rotation effects to yield \Delta m^2_\odot/\Delta
m^2_{atm}=O(10^{-2}) as the LMA solution.Comment: 16 pages, RevTeX, including 2 figures with typos and misprints
corrected and with modifications in sections II-B and V, accepted by Nuclear
Physics
Obtaining the large angle MSW solution to the solar neutrino problem in models
The large mixing angle (LMA) MSW solution to the solar neutrino problem seems
favored by the data at the moment over the small mixing angle (SMA) MSW
solution and the vacuum (VAC) solution. In this paper the various main types of
models of neutrino masses and mixings are studied from the point of view of how
naturally they can give the LMA solution. Special attention is given to a very
simple type of "lopsided" SU(5) model.Comment: 29 pages, 2 Postscript figure
Superconformal Flavor Simplified
A simple explanation of the flavor hierarchies can arise if matter fields
interact with a conformal sector and different generations have different
anomalous dimensions under the CFT. However, in the original study by Nelson
and Strassler many supersymmetric models of this type were considered to be
'incalculable' because the R-charges were not sufficiently constrained by the
superpotential. We point out that nearly all such models are calculable with
the use of a-maximization. Utilizing this, we construct the simplest
vector-like flavor models and discuss their viability. A significant constraint
on these models comes from requiring that the visible gauge couplings remain
perturbative throughout the conformal window needed to generate the
hierarchies. However, we find that there is a small class of simple flavor
models that can evade this bound.Comment: 43 pages, 1 figure; V3: small corrections and clarifications,
references adde
A General Classification of Three-Neutrino Models and U_e3
A classification of models with three light neutrinos is given. This
classification includes virtually all of the three-neutrino models proposed in
the last few years, of which there are approximately one hundred. The essential
ideas, attractive features, and characteristic problems of the different
classes of model are discussed. The classification is based principally on how
the large \nu_{\mu} - \nu_{\tau} mixing is obtained. A general discussion of
the mixing parameter U_{e3} is then given, showing what values are to be
expected for it in each type of model.Comment: 37 pages, LaTex. Several serious typos correcte
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