1,584 research outputs found
Neutrino Masses and Heavy Triplet Leptons at the LHC: Testability of Type III Seesaw
We study LHC signatures of Type III seesaw in which SU(2)_L triplet leptons
are introduced to supply the heavy seesaw masses. To detect the signals of
these heavy triplet leptons, one needs to understand their decays to standard
model particles which depend on how light and heavy leptons mix with each
other. We concentrate on the usual solutions with small light and heavy lepton
mixing of order the square root of the ratio of light and heavy masses,
(m_\nu/M_{\nu_R})^{1/2}. This class of solutions can lead to a visible
displaced vertex detectable at the LHC which can be used to distinguish small
mixing and large mixing between light and heavy leptons. We show that, in this
case, the couplings of light and heavy triplet leptons to gauge and Higgs
bosons, which determine the decay widths and branching ratios, can be expressed
in terms of light neutrino masses and their mixing. Using these relations, we
study heavy triplet lepton decay patterns and production cross section at the
LHC. If these heavy triplet leptons are below a TeV or so, they can be easily
produced at the LHC due to their gauge interactions from being non-trivial
representations of SU(2)_L. We consider two ideal production channels, 1)
E^+E^- \to \ell^+\ell^+ \ell^-\ell^- jj (\ell=e,\mu,\tau) and 2) E^\pm N \to
\ell^\pm \ell^\pm jjjj in detail. For case 1), we find that with one or two of
the light leptons being \tau it can also be effectively studied. With judicious
cuts at the LHC, the discovery of the heavy triplet leptons as high as a TeV
can be achieved with 100 fb^{-1} integrated luminosity.Comment: 39 pages, 36 figures, accepted version by PR
Primordial Black Holes from Sound Speed Resonance during Inflation
We report on a novel phenomenon of the resonance effect of primordial density
perturbations arisen from a sound speed parameter with an oscillatory behavior,
which can generically lead to the formation of primordial black holes in the
early Universe. For a general inflaton field, it can seed primordial density
fluctuations and their propagation is governed by a parameter of sound speed
square. Once if this parameter achieves an oscillatory feature for a while
during inflation, a significant non-perturbative resonance effect on the
inflaton field fluctuations takes place around a critical length scale, which
results in significant peaks in the primordial power spectrum. By virtue of
this robust mechanism, primordial black holes with specific mass function can
be produced with a sufficient abundance for dark matter in sizable parameter
ranges.Comment: 6 pages, 4 figures; v2: figures replotted with corrections, analysis
extended, version accepted by Phys.Rev.Let
Entanglement distribution over the subsystems and its invariance
We study the entanglement dynamics of two qubits, each of which is embedded
into its local amplitude-damping reservoir, and the entanglement distribution
among all the bipartite subsystems including qubit-qubit, qubit-reservoir, and
reservoir-reservoir. It is found that the entanglement can be stably
distributed among all components, which is much different to the result
obtained under the Born-Markovian approximation by C. E. L\'{o}pez {\it et al.}
[Phys. Rev. Lett. \textbf{101}, 080503 (2008)], and particularly it also
satisfies an identity. Our unified treatment includes the previous results as
special cases. The result may give help to understand the physical nature of
entanglement under decoherence.Comment: 6 pages, 5 figure
Symmetry, dark matter and LHC phenomenology of the minimal SM
A sterile neutrino with a mass of a few keV can play the role of a warm dark
matter(DM). This can be realized in seesaw models with 3 left- and 3
right-handed neutrinos. It is possible to identify the keV neutrino to be one
of the right-handed neutrinos leaving the other two to be much more heavier,
the SM model. We show that with this realization of keV neutrino DM, the
model has an approximate Friedberg-Lee symmetry providing a natural explanation
for the lightness of the right-handed neutrino. We also find that in this model
the mixing parameters couple light and heavy neutrinos are strongly correlated,
and can be large enough to have testable effects at the LHC for the two heavy
right-handed neutrinos to be in the hundred-GeV range.Comment: 20 pages, 5 figures, discussions expanded, references added, to
appear in PR
Evolutionary structure learning algorithm for Bayesian network and penalized mutual information metric
This paper formulates the problem of learning Bayesian network structures from data as determining the structure that best approximates the probability distribution indicated by the data. A new metric, Penalized Mutual Information metric, is proposed, and a evolutionary algorithm is designed to search for the best structure among alternatives. The experimental results show that this approach is reliable and promising.<br /
Dissecting Quantum Phase Transition in the Transverse Ising Model
Irrespective of the fact that a complete theoretical description of critical
phenomena in connection with phase transition has been well-established through
the renormalization group formalism, the understanding of the phase transition
itself remains incomplete. For example, the questions like why and how the
phase transition happens are still unclear. Here we provide a pattern picture
to dissect the quantum phase transition occurring in the transverse Ising model
for a finite lattice. After the validity of the pattern formulation obtained is
confirmed, the energy contributions of different patterns to the ground state
energy provide a sufficient detail to show why and how the phase transition
takes place. Furthermore, a histogram of patterns' occupancy calculated by the
projections of ground state wavefunction on the patterns also shows the
detailed process of the phase transition. Our results are not only fundamental
in understanding the mechanism of phase transition, but also of practical
interest in quantum simulation platforms.Comment: 6 pages, 4 figure
Spin susceptibility of Anderson impurities in arbitrary conduction bands
Spin susceptibility of Anderson impurities is a key quantity in understanding
the physics of Kondo screening. Traditional numerical renormalization group
(NRG) calculation of the impurity contribution to
susceptibility, defined originally by Wilson in a flat wide band, has been
generalized before to structured conduction bands. The results brought about
non-Fermi-liquid and diamagnetic Kondo behaviors in , even
when the bands are not gapped at the Fermi energy. Here, we use the full
density-matrix (FDM) NRG to present high-quality data for the local
susceptibility and to compare them with
obtained by the traditional NRG. Our results indicate
that those exotic behaviors observed in are unphysical.
Instead, the low-energy excitations of the impurity in arbitrary bands only
without gap at the Fermi energy are still a Fermi liquid and paramagnetic. We
also demonstrate that unlike the traditional NRG yielding
less accurate than , the FDM method allows a
high-precision dynamical calculation of at much reduced
computational cost, with an accuracy at least one order higher than
. Moreover, artifacts in the FDM algorithm to
, and origins of the spurious non-Fermi-liquid and
diamagnetic features are clarified. Our work provides an efficient
high-precision algorithm to calculate the spin susceptibility of impurity for
arbitrary structured bands, while negating the applicability of Wilson's
definition to such cases.Comment: the published versio
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