38 research outputs found
Bose-Einstein condensation in the presence of an impurity
It is shown that Bose-Einstein condensation occurs for an ideal gas in two
spatial dimensions in the presence of one impurity which is described quantum
mechanically in terms of a point-like vortex and a contact interaction. This
model is exactly solvable and embodies as a special case the analogous problem
in three spatial dimensions.Comment: 6 pages, LaTeX, no figures. Misprints correcte
On the mystery of the missing pie in graphene
We investigate in some detail the structure of the electromagnetic current
density for the pseudo-relativistic massless spinor effective model for
graphene. It is shown that the pseudo-relativistic massless Dirac field theory
in {\em 2+1} space-time dimensions and in the presence of a constant
homogeneous electric field actually leads to the measured current density and
to the minimum quantum conductivity.Comment: 10 pages, no figures, substantial changes and added reference
Exact Solution of the one-impurity quantum Hall problem
The problem of a non-relativistic electron in the presence of a uniform
electromagnetic field and of one impurity, described by means of an
Aharonov-Bohm point-like vortex, is studied. The exact solution is found and
the quantum Hall's conductance turns out to be the same as in the impurity-free
case. This exactly solvable model seems to give indications, concerning the
possible microscopic mechanisms underlying the integer quantum Hall effect,
which sensibly deviate from some proposals available in the literature.Comment: 25 pages, TeX, to appear in J. Phys.
The quantum Hall effect in graphene samples and the relativistic Dirac effective action
We study the Euclidean effective action per unit area and the charge density
for a Dirac field in a two--dimensional spatial region, in the presence of a
uniform magnetic field perpendicular to the 2D--plane, at finite temperature
and density. In the limit of zero temperature we reproduce, after performing an
adequate Lorentz boost, the Hall conductivity measured for different kinds of
graphene samples, depending upon the phase choice in the fermionic determinant.Comment: Conclusions extended. References added. 9 pages. 1 figur
The quantum Hall effect in graphene samples and the relativistic Dirac effective action
We study the Euclidean effective action per unit area and the charge density for a Dirac field in a two--dimensional spatial region, in the presence of a uniform magnetic field perpendicular to the 2D--plane, at finite temperature and density. In the limit of zero temperature we reproduce, after performing an adequate Lorentz boost, the Hall conductivity measured for different kinds of graphene samples, depending upon the phase choice in the fermionic determinant.Instituto de Física La Plat
Planar QED at finite temperature and density: Hall conductivity, Berry's phases and minimal conductivity of graphene
We study 1-loop effects for massless Dirac fields in two spatial dimensions, coupled to homogeneous electromagnetic backgrounds, both at zero and at finite temperature and density. In the case of a purely magnetic field, we analyze the relationship between the invariance of the theory under large gauge transformations, the appearance of Chern-Simons terms and of different Berry's phases. In the case of a purely electric background field, we show that the effective Lagrangian is independent of the chemical potential and of the temperature. More interesting: we show that the minimal conductivity, as predicted by the quantum field theory, is the right multiple of the conductivity quantum and is, thus, consistent with the value measured for graphene, with no extra factor of pi in the denominator.Instituto de Física La Plat
On the scattering amplitude in the Aharonov-Bohm gauge field
A general expression for the scattering amplitude of nonrelativistic spinless
particles in the Aharonov-Bohm gauge potential is obtained within the time
independent formalism. The result is valid also in the backward and forward
directions as well as for any choice of the boundary conditions on the wave
function at the flux tube position.Comment: 18 pages, plain TE
Planar QED at finite temperature and density: Hall conductivity, Berry's phases and minimal conductivity of graphene
We study 1-loop effects for massless Dirac fields in two spatial dimensions,
coupled to homogeneous electromagnetic backgrounds, both at zero and at finite
temperature and density. In the case of a purely magnetic field, we analyze the
relationship between the invariance of the theory under large gauge
transformations, the appearance of Chern-Simons terms and of different Berry's
phases. In the case of a purely electric background field, we show that the
effective Lagrangian is independent of the chemical potential and of the
temperature. More interesting: we show that the minimal conductivity, as
predicted by the quantum field theory, is the right multiple of the
conductivity quantum and is, thus, consistent with the value measured for
graphene, with no extra factor of pi in the denominator.Comment: 27 pages, no figures. Minor misprints corrected. Final version, to
appear in J. Phys. A: Math. Ge
Domain wall generation by fermion self-interaction and light particles
A possible explanation for the appearance of light fermions and Higgs bosons
on the four-dimensional domain wall is proposed. The mechanism of light
particle trapping is accounted for by a strong self-interaction of
five-dimensional pre-quarks. We obtain the low-energy effective action which
exhibits the invariance under the so called \tau-symmetry. Then we find a set
of vacuum solutions which break that symmetry and the five-dimensional
translational invariance. One type of those vacuum solutions gives rise to the
domain wall formation with consequent trapping of light massive fermions and
Higgs-like bosons as well as massless sterile scalars, the so-called branons.
The induced relations between low-energy couplings for Yukawa and scalar field
interactions allow to make certain predictions for light particle masses and
couplings themselves, which might provide a signature of the higher dimensional
origin of particle physics at future experiments. The manifest translational
symmetry breaking, eventually due to some gravitational and/or matter fields in
five dimensions, is effectively realized with the help of background scalar
defects. As a result the branons acquire masses, whereas the ratio of Higgs and
fermion (presumably top-quark) masses can be reduced towards the values
compatible with the present-day phenomenology. Since the branons do not couple
to fermions and the Higgs bosons do not decay into branons, the latter ones are
essentially sterile and stable, what makes them the natural candidates for the
dark matter in the Universe.Comment: 34 pages, 2 figures, JHEP style,few important refs. adde