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 $\mu_s=\Delta$ which marks the appearance of gapless fermion modes in the CFL phase. Here, $\mu_s=m_s^2/(2\mu)$ is the shift in chemical potential due to the strange quark mass and $\Delta$ 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 $T\ln T$ term in the susceptibility, different from the specific heat, but an anomalous $T^2\ln T$ 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 $O(T^2)$. An anomalous $T^2\ln T$ 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