406 research outputs found
Meson current in the CFL phase
We study the stability of the color-flavor locked (CFL) phase of dense quark
matter with regard to the formation of a non-zero Goldstone boson current. We
show that an instability appears in the vicinity of the point
which marks the appearance of gapless fermion modes in the CFL phase. Here,
is the shift in chemical potential due to the strange
quark mass and is the gap in the chiral limit. We show that in the
Goldstone boson current phase all components of the magnetic screening mass are
real. In this work we do not take into account homogeneous kaon condensation.
We study the effects of an instanton induced interaction of the magnitude
required to suppress kaon condensation.Comment: 15 pages, 5 figures, v2: minor improvements, results unchange
Goldstone boson currents in a kaon condensed CFL phase
We study the stability of the kaon condensed color-flavor locked (CFL) phase
of dense quark matter with regard to the formation of a non-zero Goldstone
boson current. In the kaon condensed phase there is an electrically charged
fermion which becomes gapless near \mu_s^(1) \simeq 1.35\Delta and a neutral
fermion which becomes gapless near \mu_s^(2)\simeq 1.61\Delta. Here,
\mu_s=m_s^2/(2p_F) is the shift in the Fermi energy due to the strange quark
mass m_s and \Delta is the gap in the chiral limit. The transition to the
gapless phase is continuous at \mu_s^(1) and first order at \mu_s^(2). We find
that the magnetic screening masses are real in the regime \mu_s< \mu_s^(2), but
some screening masses are imaginary for \mu_s> \mu_s^(2). We show that there is
a very weak current instability for \mu_s>\mu_s^(1) and a more robust
instability in a small window near \mu_s^(2). We also show that in the
Goldstone boson current phase all components of the magnetic screening mass are
real. There is a range of values of \mu_s below 2\Delta in which the magnetic
gluon screening masses are imaginary but the phase is stable with respect to
electrically neutral fluctuations of the gauge field.Comment: 16 page
Lattice chirality and the decoupling of mirror fermions
We show, using exact lattice chirality, that partition functions of lattice
gauge theories with vectorlike fermion representations can be split into
"light" and "mirror" parts, such that the "light" and "mirror" representations
are chiral. The splitting of the full partition function into "light" and
"mirror" is well defined only if the two sectors are separately anomaly free.
We show that only then is the generating functional, and hence the spectrum, of
the mirror theory a smooth function of the gauge field background. This
explains how ideas to use additional non-gauge, high-scale mirror-sector
dynamics to decouple the mirror fermions without breaking the gauge
symmetry--for example, in symmetric phases at strong mirror Yukawa
coupling--are forced to respect the anomaly-free condition when combined with
the exact lattice chiral symmetry. Our results also explain a paradox posed by
a recent numerical study of the mirror-fermion spectrum in a toy
would-be-anomalous two-dimensional theory. In passing, we prove some general
properties of the partition functions of arbitrary chiral theories on the
lattice that should be of interest for further studies in this field.Comment: 29 pages, 2 figures; published version, new addendu
Chiral Lattice Gauge Theories and The Strong Coupling Dynamics of a Yukawa-Higgs Model with Ginsparg-Wilson Fermions
The Yukawa-Higgs/Ginsparg-Wilson-fermion construction of chiral lattice gauge
theories described in hep-lat/0605003 uses exact lattice chirality to decouple
the massless chiral fermions from a mirror sector, whose strong dynamics is
conjectured to give cutoff-scale mass to the mirror fermions without breaking
the chiral gauge symmetry. In this paper, we study the mirror sector dynamics
of a two-dimensional chiral gauge theory in the limitof strong Yukawa and
vanishing gauge couplings, in which case it reduces to an XY model coupled to
Ginsparg-Wilson fermions. For the mirror fermions to acquire cutoff-scale mass
it is believed to be important that the XY model remain in its "high
temperature" phase, where there is no algebraic ordering--a conjecture
supported by the results of our work. We use analytic and Monte-Carlo methods
with dynamical fermions to study the scalar and fermion susceptibilities, and
the mirror fermion spectrum. Our results provide convincing evidence that the
strong dynamics does not "break" the chiral symmetry (more precisely, that the
mirror fermions do not induce algebraic ordering in two-dimensions), and that
the mirror fermions decouple from the infrared physics.Comment: 44 pages, 18 figures; v2: clarification of fermion operators,
discussion of recent related work
Evaluation of rapid product development technologies for production of prosthesis in developing communities
The production of prostheses using conventional methods or advanced technologies makes it unaffordable for people living in developing communities. Since the Fablab revolution and due to the collaborative open source movement, numerous rapid product development technologies were invented. The idea of these movements is to provide widespread access to modern means for sustainable invention and to ensure distributed value creation. This research study was to evaluate suitable rapid product technologies for value creation in developing communities, primarily for the production of prostheses. Open source technologies were used to fabricate prosthetic ears. These prototypes were evaluated in terms of cost, time and material consumption. The accuracy of these more affordable open source technologies were also critically analysed, after developing the ears in a few hours. The results revealed that open source technologies can be used for distributed prosthesis production
Non-Fermi-liquid effect in magnetic susceptibility
Taking into account the anomalous self-energy for quarks due to the dynamic
screening effect for the transverse gluon propagator, we study the temperature
dependence of the magnetic susceptibility in detail. It is shown that there
does not exist the term in the susceptibility, different from the
specific heat, but an anomalous term arises instead as a novel
non-Fermi-liquid effect.Comment: 10 pages, 1 figur
A construction of the Glashow-Weinberg-Salam model on the lattice with exact gauge invariance
We present a gauge-invariant and non-perturbative construction of the
Glashow-Weinberg-Salam model on the lattice, based on the lattice Dirac
operator satisfying the Ginsparg-Wilson relation. Our construction covers all
SU(2) topological sectors with vanishing U(1) magnetic flux and would be usable
for a description of the baryon number non-conservation. In infinite volume, it
provides a gauge-invariant regularization of the electroweak theory to all
orders of perturbation theory. First we formulate the reconstruction theorem
which asserts that if there exists a set of local currents satisfying cetain
properties, it is possible to reconstruct the fermion measure which depends
smoothly on the gauge fields and fulfills the fundamental requirements such as
locality, gauge-invariance and lattice symmetries. Then we give a closed
formula of the local currents required for the reconstruction theorem.Comment: 32 pages, uses JHEP3.cls, the version to appear in JHE
Chiral Lattice Gauge Theories Via Mirror-Fermion Decoupling: A Mission (im)Possible?
This is a review of the status and outstanding issues in attempts to
construct chiral lattice gauge theories by decoupling the mirror fermions from
a vectorlike theory. In the first half, we explain why studying nonperturbative
chiral gauge dynamics may be of interest, enumerate the problems that a lattice
formulation of chiral gauge theories must overcome, and briefly review our
current knowledge. We then discuss the motivation and idea of mirror-fermion
decoupling and illustrate the desired features of the decoupling dynamics by a
simple solvable toy model. The role of exact chiral symmetries and matching of
't Hooft anomalies on the lattice is also explained. The second, more
technical, half of the article is devoted to a discussion of the known and
unknown features of mirror-decoupling dynamics formulated with Ginsparg-Wilson
fermions. We end by pointing out possible directions for future studies.Comment: 53 pp; 6 figs; added table of contents, references, fixed typo
Spontaneous magnetization in QCD and non-Fermi-liquid effects
Magnetic properties of quark matter at finite temperature are discussed by
evaluating the magnetic susceptibility. Combining the microscopic calculation
of the self-energy for quarks as well as the screening effects for gluons with
Fermi-liquid theory in a consistent way, we study the temperature dependence of
the magnetic susceptibility. The longitudinal gluons have the static screening
given by the Debye mass, and have a standard temperature dependence of
. An anomalous term arises in the magnetic susceptibility as
a novel non-Fermi-liquid effect due to the anomalous self-energy for quarks
given by the dynamic screening for transverse gluons. We then extract the
critical(Curie) temperature and present the magnetic phase diagram on the
density-temperature plane.Comment: 14 pages, 6 figures; Secs. 1 and 5 have been revise
Magnetic susceptibility of quark matter within Fermi-liquid theory
Possibility of spontaneous magnetization in QCD and magnetic properties of
quark matter is discussed by evaluating the magnetic susceptibility within
Fermi-liquid theory. The screening effects for gluons are taken into account to
figure out the specific properties of the magnetic transition in gauge
theories. It is shown that the static screening effect in terms of the Debye
mass does not necessarily work against the magnetic instability; it promotes
the instability, depending on the coupling constant and the number of flavors.Comment: 10 pages, 2 figure
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