2,775 research outputs found

### CP-odd Phases in Slepton Pair Production

The effects of CP-odd supersymmetric phases on slepton pair production are
considered. It is shown that CP-even observables in $e^+ e^-$ and $e^- e^-$
collisions, such as the total selectron cross section, can depend on CP-odd
supersymmetric phases through interference between different tree level
amplitudes. Left handed selectron pair production in $e^- e^-$ collisions is
particularly sensitive to the relative phase between the bino and wino masses.
This sensitivity is not limited to any kinematic regime and extends over all of
neutralino parameter space. The relative phase between the bino and wino masses
is a renormalization group invariant at one-loop, and as such provides a clean
probe for operators which violate gaugino universality at the messenger scale.Comment: Latex, 12 pages, 3 figures, to appear in the proceedings of the the
Second International Workshop on Electron-Electron Interactions at TeV
Energie

### Vacuum Stability of the $\mathcal{PT}$-Symmetric $\left( -\phi^{4}\right)$ Scalar Field Theory

In this work, we study the vacuum stability of the classical unstable $\left(
-\phi^{4}\right)$ scalar field potential. Regarding this, we obtained the
effective potential, up to second order in the coupling, for the theory in
$1+1$ and $2+1$ space-time dimensions. We found that the obtained effective
potential is bounded from below, which proves the vacuum stability of the
theory in space-time dimensions higher than the previously studied $0+1$ case.
In our calculations, we used the canonical quantization regime in which one
deals with operators rather than classical functions used in the path integral
formulation. Therefore, the non-Hermiticity of the effective field theory is
obvious. Moreover, the method we employ implements the canonical equal-time
commutation relations and the Heisenberg picture for the operators. Thus, the
metric operator is implemented in the calculations of the transition
amplitudes. Accordingly, the method avoids the very complicated calculations
needed in other methods for the metric operator. To test the accuracy of our
results, we obtained the exponential behavior of the vacuum condensate for
small coupling values, which has been obtained in the literature using other
methods. We assert that this work is interesting, as all the studies in the
literature advocate the stability of the $\left( -\phi^{4}\right)$ theory at
the quantum mechanical level while our work extends the argument to the level
of field quantization.Comment: 20 pages, 4 figures, appendix added and more details have been added
to

### A Field Theory Model With a New Lorentz-Invariant Energy Scale

A framework is proposed that allows to write down field theories with a new
energy scale while explicitly preserving Lorentz invariance and without
spoiling the features of standard quantum field theory which allow quick
calculations of scattering amplitudes. If the invariant energy is set to the
Planck scale, these deformed field theories could serve to model quantum
gravity phenomenology. The proposal is based on the idea, appearing for example
in Deformed Special Relativity, that momentum space could be curved rather than
flat. This idea is implemented by introducing a fifth dimension and imposing an
extra constraint on physical field configurations in addition to the mass shell
constraint. It is shown that a deformed interacting scalar field theory is
unitary. Also, a deformed version of QED is argued to give scattering
amplitudes that reproduce the usual ones in the leading order. Possibilities
for experimental signatures are discussed, but more work on the framework's
consistency and interpretation is necessary to make concrete predictions.Comment: 20 page

### Two-photon exchange model for production of neutral meson pairs in e+e- annihilation

A vector-dominance two-photon exchange model is proposed to explain the
recently observed production of $\rho^0\rho^0$ and $\rho^0\phi$ pairs in
$e^+e^-$ annihilation at 10.58 GeV with the BaBar detector. All the observed
features of the data --angular and decay distributions, rates-- are in
agreement with the model. Predictions are made for yet-unobserved final states.Comment: 7 pages, 2 figures, 1 tabl

### Dominant $2\pi\gamma$-exchange nucleon-nucleon interaction: Spin-spin and tensor potentials

We calculate at two-loop order in chiral perturbation theory the
electromagnetic corrections to the two-pion exchange nucleon-nucleon
interaction that is generated by the isovector spin-flip $\pi\pi NN$
contact-vertex proportional to the large low-energy constant $c_4\simeq 3.4$GeV$^{-1}$. We find that the respective $2\pi\gamma$-exchange potentials
contain sizeable isospin-breaking components which reach up to -4% of
corresponding isovector $2\pi$-exchange potentials. The typical values of these
novel charge-independence breaking spin-spin and tensor potentials are $-0.11$MeV and $0.09$MeV, at a nucleon distance of $r=m_\pi^{-1}=1.4$fm. The
charge-symmetry breaking spin-spin and tensor potentials come out a factor of
2.4 smaller. Our analytical results for these presumably dominant
isospin-violating spin-spin and tensor NN-forces are in a form such that they
can be easily implemented into phase-shift analyses and few-body calculations.Comment: 7 pages, 1 figure, 2 tables, to be published in Physical Review C:
Brief report

### Electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon potential

We calculate at two-loop order in chiral perturbation theory the
electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon
interaction that is generated by the isoscalar $\pi N$ contact-vertex
proportional to the large low-energy constant $c_3$. We find that the
respective $2\pi\gamma$-exchange potential contains sizeable isospin-breaking
components which amount to about -1% of the strongly attractive isoscalar
central $2\pi$-exchange potential. The typical value of these novel
charge-independence and charge-symmetry breaking central potentials is $0.3$MeV at a nucleon distance of $r= m_\pi^{-1} = 1.4$fm. Our analytical result
for this presumably dominant $2\pi\gamma$-exchange interaction is in a form
such that it can be easily implemented into phase-shift analyses and few-body
calculations.Comment: 7 pages, 1 figure, to be published in Physical Review C (2006): Brief
Report

### About flavor, spin and color

Chiral symmetry breaking (restoration) for SU(N) gauge theories is a topic of
great interest and not yet fully explained. We consider the phenomenon as a
collective spin effect and determine its behavior in terms of the number of
flavors, N_f.Comment: version to be published in Phys. Rev.

### Theory of quasiparticle interference on the surface of a strong topological insulator

Electrons on the surface of a strong topological insulator, such as Bi2Te3 or
Bi1-xSnx, form a topologically protected helical liquid whose excitation
spectrum contains an odd number of massless Dirac fermions. A theoretical
survey and classification is given of the universal features, observable by the
ordinary and spin-polarized scanning tunneling spectroscopy, in the
interference patterns resulting from the quasiparticle scattering by magnetic
and non-magnetic impurities in such a helical liquid. Our results confirm the
absence of backscattering from non-magnetic impurities observed in recent
experiments and predict new interference features, uniquely characteristic of
the helical liquid, when the scatterers are magnetic.Comment: 4 pages, 2 figures, 1 table. Version to appear in PRB/RC; Typos
correcte

### Effective Field calculations of the Energy Spectrum of the $\mathcal{PT}%$-Symmetric ($-x^{4}$) Potential

In this work, we show that the traditional effective field approach can be
applied to the $\mathcal{PT}$-symmetric wrong sign ($-x^{4}$) quartic
potential. The importance of this work lies in the possibility of its extension
to the more important $\mathcal{PT}$-symmetric quantum field theory while the
other approaches which use complex contours are not willing to be applicable.
We calculated the effective potential of the massless $-x^{4}$ theory as well
as the full spectrum of the theory. Although the calculations are carried out
up to first order in the coupling, the predicted spectrum is very close to the
exact one taken from other works. The most important result of this work is
that the effective potential obtained, which is equivalent to the Gaussian
effective potential, is bounded from below while the classical potential is
bounded from above. This explains the stability of the vacuum of the theory.
The obtained quasi-particle Hamiltonian is non-Hermitian but
$\mathcal{PT}$-symmetric and we showed that the calculation of the metric
operator can go perturbatively. In fact, the calculation of the metric operator
can be done even for higher dimensions (quantum field theory) which, up till
now, can not be calculated in the other approaches either perturbatively or in
a closed form due to the possible appearance of field radicals. Moreover, we
argued that the effective theory is perturbative for the whole range of the
coupling constant and the perturbation series is expected to converge rapidly
(the effective coupling $g_{eff}={1/6}$).Comment: 14 pages, 5 figure

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