1,574 research outputs found

### Current-voltage characteristics in donor-acceptor systems: Implications of a spatially varying electric field

We have studied the transport properties of a molecular device composed of
donor and acceptor moieties between two electrodes on either side. The device
is considered to be one-dimensional with different on-site energies and the
non-equilibrium properties are calculated using Landauer's formalism. The
current-voltage characteristics is found to be asymmetric with a sharp Negative
Differential Resistance at a critical bias on one side and very small current
on the other side. The NDR arises primarily due to the bias driven electronic
structure change from one kind of insulating phase to another through a highly
delocalized conducting phase. Our model can be considered to be the simplest to
explain the experimental current-voltage characteristics observed in many
molecular devices.Comment: 5 pages, 4 figures (accepted for publication in Physical Review B

### Neutrinoless double beta decay in SO(10) inspired seesaw models

By requiring the lower limit for the lightest right-handed neutrino mass,
obtained in the baryogenesis from leptogenesis scenario, and a Dirac neutrino
mass matrix similar to the up-quark mass matrix we predict small values for the
$\nu_e$ mass and for the matrix element $m_{ee}$ responsible of the
neutrinoless double beta decay, $m_{\nu_e}$ around $5\cdot10^{-3}$ eV and
$m_{ee}$ smaller than $10^{-3}$ eV, respectively. The allowed range for the
mass of the heaviest right-handed neutrino is centered around the value of the
scale of B - L breaking in the SO(10) gauge theory with Pati-Salam intermediate
symmetry.Comment: 9 pages, RevTex4. Revised, title change

### A Truly Minimal Left-Right Symmetric Extension of the Standard Model

By invoking the existence of a general custodial O(2) symmetry, a minimal
Left-Right symmetric model based on the gauge group G=SU(2)L SU(2)R U(1)BL is
shown to require the existence of only two physical Higgs bosons. The lighter
Higgs is predicted to have a small mass which could be evaluated by standard
perturbation theory. The fermionic mass matrices are recovered by insertion of
ad hoc fermion-Higgs interactions. The model is shown to be undistinguishable
from the standard model at the currently reachable energies.Comment: 1 figure in a separate ps fil

### Signatures of Nucleon Disappearance in Large Underground Detectors

For neutrons bound inside nuclei, baryon instability can manifest itself as a
decay into undetectable particles (e.g., $\it n \to \nu \nu \bar{\nu}$), i.e.,
as a disappearance of a neutron from its nuclear state. If electric charge is
conserved, a similar disappearance is impossible for a proton. The existing
experimental lifetime limit for neutron disappearance is 4-7 orders of
magnitude lower than the lifetime limits with detectable nucleon decay products
in the final state [PDG2000]. In this paper we calculated the spectrum of
nuclear de-excitations that would result from the disappearance of a neutron or
two neutrons from $^{12}$C. We found that some de-excitation modes have
signatures that are advantageous for detection in the modern high-mass,
low-background, and low-threshold underground detectors, where neutron
disappearance would result in a characteristic sequence of time- and
space-correlated events. Thus, in the KamLAND detector [Kamland], a
time-correlated triple coincidence of a prompt signal, a captured neutron, and
a $\beta^{+}$ decay of the residual nucleus, all originating from the same
point in the detector, will be a unique signal of neutron disappearance
allowing searches for baryon instability with sensitivity 3-4 orders of
magnitude beyond the present experimental limits.Comment: 13 pages including 6 figures, revised version, to be published in
Phys.Rev.

### Quantum Lie systems and integrability conditions

The theory of Lie systems has recently been applied to Quantum Mechanics and
additionally some integrability conditions for Lie systems of differential
equations have also recently been analysed from a geometric perspective. In
this paper we use both developments to obtain a geometric theory of
integrability in Quantum Mechanics and we use it to provide a series of
non-trivial integrable quantum mechanical models and to recover some known
results from our unifying point of view

### Dark matter from SU(4) model

The left-right symmetric Pati-Salam model of the unification of quarks and
leptons is based on SU(4) and SU(2)xSU(2) groups. These groups are naturally
extended to include the classification of families of quarks and leptons. We
assume that the family group (the group which unites the families) is also the
SU(4) group. The properties of the 4-th generation of fermions are the same as
that of the ordinary-matter fermions in first three generations except for the
family charge of the SU(4)_F group: F=(1/3,1/3,1/3,-1), where F=1/3 for
fermions of ordinary matter and F=-1 for the 4-th generation. The difference in
F does not allow the mixing between ordinary and fourth-generation fermions.
Because of the conservation of the F charge, the creation of baryons and
leptons in the process of electroweak baryogenesis must be accompanied by the
creation of fermions of the 4-th generation. As a result the excess n_B of
baryons over antibaryons leads to the excess n_{\nu 4}=N-\bar N=n_B of
neutrinos over antineutrinos in the 4-th generation. This massive
fourth-generation neutrino may form the non-baryonic dark matter. In principle
their mass density n_{\nu 4}m_N in the Universe can give the main contribution
to the dark matter, since the lower bound on neutrino mass m_N from the data on
decay of the Z-bosons is m_N > m_Z/2. The straightforward prediction of this
model leads to the amount of cold dark matter relative to baryons, which is an
order of magnitude bigger than allowed by observations. This inconsistency may
be avoided by non-conservation of the F-charge.Comment: 9 pages, 2 figures, version accepted in JETP Letters, corrected after
referee reports, references are adde

### Optimal Controlled Teleportation

We give the analytic expressions of maximal probabilities of successfully
controlled teleportating an unknown qubit via every kind of tripartite states.
Besides, another kind of localizable entanglement is also determined.
Furthermore, we give the sufficient and necessary condition that a three-qubit
state can be collapsed to an EPR pair by a measurement on one qubit, and
characterize the three-qubit states that can be used as quantum channel for
controlled teleporting a qubit of unknown information with unit probability and
with unit fidelity.Comment: 4 page

### Universal quantum Controlled-NOT gate

An investigation of an optimal universal unitary Controlled-NOT gate that
performs a specific operation on two unknown states of qubits taken from a
great circle of the Bloch sphere is presented. The deep analogy between the
optimal universal C-NOT gate and the `equatorial' quantum cloning machine (QCM)
is shown. In addition, possible applications of the universal C-NOT gate are
briefly discussed.Comment: 18 reference

### Non SUSY Unification in Left-Right Models

We explore in a model independent way the possibility of achieving the non
supersymmetric gauge coupling unification within left-right symmetric models,
with the minimal particle content at the left-right mass scale which could be
as low as 1 TeV in a variety of models, and with a unification scale M in the
range $10^5$ GeV $< M< 10^{17.7}$ GeV.Comment: 18 pages, Latex file, uses epsf style, four figures. Submitted for
publication to Phys. Rev. D on Oct. 13, 199

### Implementasi Pembelajaran Kontekstual Model React pada Materi Fluida Dinamis untuk Meningkatkan Motivasi Belajar Siswa SMA Kelas XI

This research aimed to find out the improvement of the students motivation learning physic by applying REACT model of Contextual learning.This pre-experimental research used one group pretest and posttest design. There were 35 students of clas XI IPA I SMA Negeri 7 Pekanbaru have participated in this research. We used modification ARCS question one of motivation as instrument in collecting data, before and after treatment. The data were analyzed descriptive by using N-Gain. From the data, we found that N-Gain score in high category for all indicators. And, we can conclude that REACT model have improved students motivation in learning physis especially for class XI IPA I students of SMA Negeri 7 Pekanbaru

- â€¦