25,694 research outputs found
Quantized Faraday effect in (3+1)-dimensional and (2+1)-dimensional systems
We study Faraday rotation in the quantum relativistic limit. Starting from
the photon self-energy in the presence of a constant magnetic field the
rotation of the polarization vector of a plane electromagnetic wave which
travel along the fermion-antifermion gas is studied. The connection between
Faraday Effect and Quantum Hall Effect (QHE) is discussed. The Faraday Effect
is also investigated for a massless relativistic (2D+1)-dimensional fermion
system which is derived by using the compactification along the dimension
parallel to the magnetic field. The Faraday angle shows a quantized behavior as
Hall conductivity in two and three dimensions.Comment: 15 pages, 5 figure
Effect of a Magnetic Field on the Electroweak Symmetry
We discuss the effect of a strong magnetic field in the behavior of the
symmetry of an electrically neutral electroweak plasma. We analyze the case of
a strong field and low temperatures as compared with the W rest energy. If the
magnetic field is large enough, it is self-consistently maintained. Charged
vector bosons play the most important role, leading only to a decrease of the
symmetry breaking parameter, the symmetry restoration not being possible.Comment: Presented in the First International Workshop on Astronomy and
Relativistic Astrophysics (IWARA 2003), Olinda, Brazi
Constraint on the stem cell numbers and division rates posed by the risk of cancer
Compiled data for the stem cell numbers, Ns, and division rates, ms, is
reanalized in order to show that we can distinguish two groups of human
tissues. In the first one, there is a relatively high fraction of maintenance
(stem and transit) cells in the tissue, but the division rates are low. The
second group, on the other hand, is characterized by very high transit cell
division rates, of around one division per day. These groups do not have an
embrionary origin. We argue that their properties arise from a combination of
the needs of tissue homeostasis (in particular turnover rate) and a bound on
cancer risk, which is roughly a linear function of the product Ns ms. The bound
on cancer risk leads to a threshold at ms = 8/year, where the fraction of stem
cells falls down two orders of magnitude
Vacuum pressures and energy in a strong magnetic field
We study vacuum in a strong magnetic field. It shows a nonlinear response, as
a ferromagnetic medium. Anisotropic pressures arise, and a negative pressure is
exerted in the direction perpendicular to the field. The analogy of this effect
with the Casimir effect is analyzed. The vacuum transverse pressure is found to
be of the same order of the statistical pressure for and
. Vacuum interaction with the field is studied
also for and larger, including the electron anomalous magnetic
moment. We estimate quark contribution to vacuum behavior.Comment: Presented in the International Workshop on Strong Magnetic Fields and
Neutron Stars, Havana, Cuba, April 200
The LHCb VELO Upgrade
LHCb is a forward spectrometer experiment dedicated to the study of new
physics in the decays of beauty and charm hadrons produced in proton collisions
at the Large Hadron Collider (LHC) at CERN.
The VErtex LOcator (VELO) is the microstrip silicon detector surrounding the
interaction point, providing tracking and vertexing measurements. The upgrade
of the LHCb experiment, planned for 2018, will increase the luminosity up to
and will perform the readout as a
trigger-less system with an event rate of 40 MHz. Extremely non-uniform
radiation doses will reach up to 1 MeV
in the innermost regions of the VELO sensors, and the output data bandwidth
will be increased by a factor of 40. An upgraded detector is under development
based in a pixel sensor of the Timepix/Medipix family, with 55 x 55 pixels. In addition a microstrip solution with finer pitch, higher
granularity and thinner than the current detector is being developed in
parallel.
The current status of the VELO upgrade program will be described together
with recent testbeam results
The photon magnetic moment has not a perpendicular component and is fully paramagnetic
Our paper Phys. Rev. D \textbf{79}, 093002 (2009), in which it was shown the
paramagnetic behavior of photons propagating in magnetized vacuum, is
criticized in Phys. Rev. D \textbf{81}, 105019, (2010) and even claimed that
the photon has a diamagnetic component. Here it is shown that such criticism is
inadequate and that the alleged "perpendicular component" is due to a mistake
in differentiating a vanishing term with regard to the magnetic field , or
either by mistaking the derivative of a scalar product as that of a dyadic
product. A discussion on the physical side of the problem is also made
Is the photon paramagnetic?
A photon exhibits a tiny anomalous magnetic moment due to its
interaction with an external constant magnetic field in vacuum through the
virtual electron-positron background. It is paramagnetic () in
the whole region of transparency, i.e. below the first threshold energy for
pair creation and has a maximum near this threshold. The photon magnetic moment
is different for eigenmodes polarized along and perpendicular to the magnetic
field. Explicit expressions are given for for the cases of
photon energies smaller and closer to the first pair creation threshold. The
region beyond the first threshold is briefly discussed
Series expansion of the photon self-energy in QED and the photon anomalous magnetic moment
We start from the analytical expression of the eigenvalues of
the photon self-energy tensor in an external constant magnetic field
calculated by Batalin Shabad in the Furry representation, and in the one-loop
approximation. We expand in power series of the external field and in terms of
the squared photon transverse momentum and (minus) transverse energy
, in terms of which are expressed . A general
expression is given for the photon anomalous magnetic moment
in the region of transparency, below the first threshold for pair creation, and
it is shown that it is positive, i.e. paramagnetic. The results of the
numerical calculation for are displayed in a region close to
the threshold
Magnetic Fields in Quantum Degenerate Systems and in Vacuum
We consider self-magnetization of charged and neutral vector bosons bearing a
magnetic moment in a gas and in vacuum. For charged vector bosons (W bosons) a
divergence of the magnetization in both the medium and the electroweak vacuum
occurs for the critical field B=B_{wc}=m_{w}^{2}/e. For B>B_{wc} the system is
unstable. This behavior suggests the occurrence of a phase transition at
B=B_{c}, where the field is self-consistently maintained. This mechanism
actually prevents from reaching the critical value B_{c}. For virtual
neutral vector bosons bearing an anomalous magnetic moment, the ground state
has a similar behavior for B=B_{nbc}=m_{nb}^{2}/q . The magnetization in the
medium is associated to a Bose-Einstein condensate and we conjecture a similar
condensate occurs also in the case of vacuum.
The model is applied to virtual electron-positron pairs bosonization in a
magnetic field B \sim B_{pc}\lesssim 2m_{e}^{2}/e, where m_e is the electron
mass. This would lead also to vacuum self-magnetization in QED, where in both
cases the symmetry breaking is due to a condensate of quasi-massless particles
The paramagnetic photon. Absence of perpendicular component and decay in large fields
Previous results from the authors concerning the arising a tiny photon
anomalous paramagnetic moment due to its interaction with a
magnetized virtual electron-positron background are complemented and discussed.
It is argued that such magnetic moment it cannot be a linear function of the
angular momentum and that there is no room for the existence of an hypothetical
perpendicular component, as recently claimed in the literature. It is discussed
that in the region beyond the first threshold, where photons may decay in
electron-positron pairs, the photon magnetic moment cannot be defined
independently of the magnetic moment of the created pairs. It is shown that for
magnetic fields large enough, the vacuum becomes unstable and decays also in
electron-positron pairs.Comment: Most of this paper is based on a talk presented at the International
Workshop on Astronomy and Relativistic Astrophysics 2009 (IWARA09
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