21,606 research outputs found
Low-coverage heteroepitaxial growth with interfacial mixing
We investigate the influence of intermixing on heteroepitaxial growth
dynamics, using a two-dimensional point island model, expected to be a good
approximation in the early stages of epitaxy. In this model, which we explore
both analytically and numerically, every deposited B atom diffuses on the
surface with diffusion constant , and can exchange with any A atom
of the substrate at constant rate. There is no exchange back, and emerging
atoms diffuse on the surface with diffusion constant . When any two
diffusing atoms meet, they nucleate a point island. The islands neither diffuse
nor break, and grow by capturing other diffusing atoms. The model leads to an
island density governed by the diffusion of one of the species at low
temperature, and by the diffusion of the other at high temperature. We show
that these limit behaviors, as well as intermediate ones, all belong to the
same universality class, described by a scaling law. We also show that the
island-size distribution is self-similarly described by a dynamic scaling law
in the limits where only one diffusion constant is relevant to the dynamics,
and that this law is affected when both and play a
role.Comment: 16 pages, 6 figure
Possible new resonance from - interchannel coupling
We propose and theoretically study a possible new resonance caused by strong
coupling between the Higgs-Higgs and the W_L W_L (Z_L Z_L) scattering channels,
without regard to the intensity of the elastic interaction in either channel at
low energy (that could be weak as in the Standard Model). We expose this
channel-coupling resonance from unitarity and dispersion relations encoded in
the Inverse Amplitude Method, applied to the Electroweak Chiral Lagrangian with
a scalar Higgs.Comment: 4 pages, 7 figure
Unitarity, analyticity, dispersion relations and resonances in strongly interacting , and scattering
If the Electroweak Symmetry Breaking Sector turns out to be strongly
interacting, the actively investigated effective theory for longitudinal gauge
bosons plus Higgs can be efficiently extended to cover the regime of saturation
of unitarity (where the perturbative expansion breaks down). This is achieved
by dispersion relations, whose subtraction constants and left cut contribution
can be approximately obtained in different ways giving rise to different
unitarization procedures. We illustrate the ideas with the Inverse Amplitude
Method, one version of the N/D method and another improved version of the
K-matrix. In the three cases we get partial waves which are unitary, analytical
with the proper left and right cuts and in some cases poles in the second
Riemann sheet that can be understood as dynamically generated resonances. In
addition they reproduce at Next to Leading Order (NLO) the perturbative
expansion for the five partial waves not vanishing (up to J=2) and they are
renormalization scale () independent. Also the unitarization formalisms
are extended to the coupled channel case. Then we apply the results to the
elastic scattering amplitude for the longitudinal components of the gauge
bosons at high energy. We also compute and the
inelastic process which are coupled to the elastic
channel for custodial isospin . We numerically compare the three methods
for various values of the low-energy couplings and explain the reasons for the
differences found in the partial wave. Then we study the resonances
appearing in the different elastic and coupled channels in terms of the
effective Lagrangian parameters.Comment: 45 pages, 28 figure
One-loop and scattering from the Electroweak Chiral Lagrangian with a light Higgs-like scalar
By including the recently discovered Higgs-like scalar in the
Electroweak Chiral Lagrangian, and using the Equivalence Theorem, we carry out
the complete one-loop computation of the elastic scattering amplitude for the
longitudinal components of the gauge bosons at high energy. We also
compute and the inelastic process
, and identify the counterterms needed to cancel
the divergences, namely the well known and chiral parameters plus
three additional ones only superficially treated in the literature because of
their dimension 8. Finally we compute all the partial waves and discuss the
limitations of the one-loop computation due to only approximate unitarity.Comment: 28 pages, 19 plots, 9 Feynman-diagram sets This version revised and
accepted in JHE
Coupling WW, ZZ unitarized amplitudes to in the TeV region
We define and calculate helicity partial-wave amplitudes for processes
linking the Electroweak Symmetry Breaking Sector (EWSBS) to ,
employing (to NLO) the Higgs-EFT (HEFT) extension of the Standard Model and the
Equivalence Theorem, while neglecting all particle masses. The resulting
amplitudes can be useful in the energy regime ().
We also deal with their unitarization so that resonances of the EWSBS can
simultaneously be described in the initial or final states. Our
resulting amplitudes satisfy unitarity, perturbatively in , but for all
values. In this way we improve on the HEFT that fails as interactions
become stronger with growing and provide a natural framework for the decay
of dynamically generated resonances into , and pairs.Comment: 23 pages, 9 figure
Comprehensive theory of the relative phase in atom-field interactions
We explore the role played by the quantum relative phase in a well-known
model of atom-field interaction, namely, the Dicke model. We introduce an
appropriate polar decomposition of the atom-field relative amplitudes that
leads to a truly Hermitian relative-phase operator, whose eigenstates correctly
describe the phase properties, as we demonstrate by studying the positive
operator-valued measure derived from it. We find the probability distribution
for this relative phase and, by resorting to a numerical procedure, we study
its time evolution.Comment: 20 pages, 4 figures, submitted to Phys. Rev.
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