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Yuichi Hoshino

Publications and source records attributed to Yuichi Hoshino.

12 recordsLinked to original sources
arXiv2016

Vortex driven phase transition in Topologically Massive QED

There is chiral like symmetry for 4-component massless fermion in (2+1)-dimensional gauge theory.Since QED$_{3}$ with Chern-Simons term contains vortex solution for vector potential,one may expect vortex driven phase transition as Kosterlitz-Thouless type where chiral condensate is washed away at zero temperature.To study this possibility,we evaluate the fermion propagator by Dyson-Schwinger equation numerically and spectral function analytically in the Landau gauge.For quenched case we adopt Ball-Chiu vertex to keep gauge invariance of the results.The critical value of topological mass,above which chiral condensate washed away, turned out to be $O(10^{-2})e^{2}$ at least for weak coupling in both cases.

hep-th↗
arXiv2014

Gauge covariant solution for the Schwinger-Dyson equation in three-dimensional QED with Chern-Simons term

An Abelian gauge theory with Chern-Simons term is investigated for a four-component Dirac fermion in 1+2 dimensions. The Ball-Chiu (BC) vertex function is employed to modify the rainbow-ladder approximation for the Schwinger-Dyson (SD) equation. We numerically solve the SD equation and show the gauge dependence for the resulting phase boundary for the parity and the chiral symmetry.

hep-ph↗
arXiv2014

Soft-photon exponentiation beyond the quenched approximation in QED$_{2+1}$

We discuss the infrared and ultraviolet behavior of the fermion propagator in (2+1)-dimensional QED based on spectral representation.If we choose soft-photon exponentiation to include all orders of soft-photon emission by electron,its spectral function may be written as $e^{F}$,where $F$ is a model independent spectral function of the lowest order in the coupling constant.We evaluate the function $F$ in an analytic way and show its short and long distance behavior with an infrared cut-off $μ$.At short distance function $F$ has linear and logarithmic infrared divergence.However in the long distance limit function $F$ vanishes.So that only short distance part of $e^{F}$ is modified from unity.We may avoid the linear divergence by the choice of the gauge $d=-1$,where $d$ is a covariant gauge fixing parameter.In this gauge the spectral function vanishes in the limit of zero bare photon mass $μ$.We overcome this difficulty by adding continuous spectrum of massive fermion loop to photon spectral function $ρ(μ^{2})$,where $μ$ has the role of invariant mass for fermion-antifermion pair and is larger than $2m.$So that unquenched fermion spectral function survibes.For the application of chiral symmetry breaking we carefully studied the position space propagator $S_{F}(0)$.At least for weak coupling these values agree quite well with that obtained in Dyson-Schwinger equation with proper vertex correction.We also study these parameter as a function of the flavour number $N$ and t'Hooft coupling $α=e^{2}N/8π$ for strong coupling case.

hep-th↗
arXiv2010

Phase structure of Topologically massive gauge theory with fermion

Using Bloch-Nordsieck approximation fermion propagator in 3-dimensional gauge theory with topological mass is studied. Infrared divergence of Chern-Simon term is soft,which modifies anomalous dimension. In unquenched QCD with 2-component spinor anomalous dimension has fractional value,where order parmeter is divergent.

hep-th↗
arXiv2009

Structure of the fermion propagator in QED3

Minkowski structure of the Fermion propagator in QED$_{2+1}$ is evaluated using dispersion like method Including massive fermion loop to the photon spectral function there is no infrared divergences in the gauge d=-1.Screening effects suppress the chiral order parmeter for small numbers of fermion flavour N.We evaluate the order parameter as a function of coupling constant c and N.There exsists a critical region where the chiral symmetry is dynamically broken.

hep-th↗
arXiv2007

Solutions of Bethe-Salpter equations in QED3

To understand the mechanism of the fermion pair and fermion-antifermion pair condensation,the solutions of Bethe-Salpeter equation in QED$_{3}$ is examined.In the ladder appoximation our solution for the axial-scalar is consistent with Ward-Takahashi-identity for the axial vector currents.Since the massless scalar-vector sector is described by a coupled integral equation,it is difficult to solve explicitly.We approximate the equation for large and small momentum region separately and convert them into differential equations in position space.These equation can be solved easily.Boundary condition at the origin leads the eigenvalue for dimensionless coupling constant $λ=e^{2}/m$.There exists solutions for massless scalar-vector fermion-antifermion (fa) system with discrete spectrum. In our approximation massless-scalar-vector ff systemes does not seem to exist.

hep-th↗
arXiv2007

Determination of the propagator in QED3 by spectral function

To study the infrared behaviour of the propagator, exponentiation of the lowest order spectral function has been known.We show this method is helpful in super renormalizable theory with dimension-full coupling constant.In the 1/N approximation anomalous dimension is independent of $N$,which plays an important role for confinement and pair condensation.

hep-th↗
arXiv2006

Spectral function in QED3

We discuss the structure of the dressed fermion propagator in unquenched QED3 based on spectral function of photon.In this approximation infrared divergences that appeared in quenched case turns out to be soft.The dimension full coupling constant naturally appears as an infrared mass scale in this case.We find the reliable results for the effects of vacuum polarization for the dressed fermion propagator.The lowest order fermion spectral function has logarithmically divergent Coulomb energy as well as self-energy,whch plays the role of confinement and dynamical mass generation.In our model finiteness condition of vacuum expectation value is equivalent to choose the scale of physical mass which is expected in the 1/N approximation.

hep-th↗
arXiv2005

Mass singularity and confinement

Infrared behaviour of the fermion propagator is examined by spectral representation.Assuming asymptotic states and using LSZ reduction formula we evaluate the the lowest order spectral function by definition.After exponentiation of it we derive the non perturbative propagator.It shows confinement and dynamical mass generation explicitly.

hep-th↗
arXiv2004

Mass singularity and confining property in $QED_3$

We discuss the properties of the position space fermion propagator in three dimensional QED which has been found previouly based on Ward-Takahashi-identity for soft-photon emission vertex and spectral representation.There is a new type of mass singularity which governs the long distance behaviour.It leads the propagator vanish at large distance.This term corresponds to dynamical mass in position space.Our model shows confining property and dynamical mass generation for arbitrary coupling constant.Since we used dispersion retation in deriving spectral function there is a physical mass which sets a mass scale.For finite cut off we obtain the full propagator in the dispersion integral as a superposition of different massses.Low energy behaviour of the proagator is modified to decrease by position dependent mass.In the limit of zero infrared cut-off the propagator vanishes with a new kind of infrared behaviour.

hep-th↗