Search results for "CHIRAL SYMMETRY"
showing 10 items of 75 documents
Textures in hexatic films of nonchiral liquid crystals: Symmetry breaking and modulated phases
1994
Novel modulated textures, such as stripes and multiarmed star defects, have been observed in freely suspended films of nonchiral liquid crystals just below the smectic-$C$ to hexatic phase transition. Detailed studies using depolarized reflection microscopy suggest that the stripes are locally chiral surface splay domains of the smectic-$L$ phase, a tilted hexatic not previously identified in thermotropic liquid crystals. Line defects which form additional domain walls in the hexatic lattice lead to characteristic modulations of the basic one-dimensional stripe pattern. Inside thick circular islands, for example, stripes form circumferentially and the lines form centered 12-armed stars, res…
Electromagnetic mass difference of pions at low temperature
1999
We compute low temperature corrections to the electromagnetic mass difference of pions in the chiral limit. The computation is done in a model independent way in the framework of chiral perturbation theory, using the background field method and the hard thermal loop approximation. We also generalize at low temperature the sum rule of Das et al. We find that the mass difference between the charged and neutral pions decreases at low temperature $T$ with respect to the T=0 value. This is so in spite of the fact that charged particles always get a thermal correction to their masses of order $\sim eT$, where $e$ is the gauge coupling constant. Our result can be understood as a consequence of the…
Determination of the axial coupling constant $g_{A}$ in the linear representations of chiral symmetry
2001
If a baryon field belongs to a certain linear representation of chiral symmetry of $SU(2) \otimes SU(2)$, the axial coupling constant $g_{A}$ can be determined algebraically from the commutation relations derived from the superconvergence property of pion-nucleon scattering amplitudes. This establishes an algebraic explanation for the values of $g_{A}$ of such as the non-relativistic quark model, large-$N_{c}$ limit and the mirror assignment for two chiral partner nucleons. For the mirror assignment, the axial charges of the positive and negative parity nucleons have opposite signs. Experiments of eta and pion productions are proposed in which the sign difference of the axial charges can be…
Mixing-induced spontaneous supersymmetry breaking
2010
It is conjectured that flavor mixing furnishes a universal mechanism for the spontaneous breaking of supersymmetry. The conjecture is proved explicitly for the mixing of two Wess--Zumino $\mathcal{N}=1$ supermultiplets and arguments for its general validity are given. The mechanism relies on the fact that, despite mixing treats fermions and bosons symmetrically, both the fermionic and the bosonic zero point energies are shifted by a positive amount and this kind of shift does not respect supersymmetry.
Domain walls in supersymmetric QCD: The taming of the zoo
2000
We provide a unified picture of the domain wall spectrum in supersymmetric QCD with Nc colors and Nf flavors of quarks in the (anti-) fundamental representation. Within the framework of the Veneziano-Yankielowicz-Taylor effective Lagrangian, we consider domain walls connecting chiral symmetry breaking vacua, and we take the quark masses to be degenerate. For Nf/Ncm** there is no domain wall. We numerically determine m* and m** as a function of Nf/Nc, and we find that m** approaches a constant value in the limit that this ratio goes to one.
Chiral symmetry breaking with lattice propagators
2010
We study chiral symmetry breaking using the standard gap equation, supplemented with the infrared-finite gluon propagator and ghost dressing function obtained from large-volume lattice simulations. One of the most important ingredients of this analysis is the non-abelian quark-gluon vertex, which controls the way the ghost sector enters into the gap equation. Specifically, this vertex introduces a numerically crucial dependence on the ghost dressing function and the quark-ghost scattering amplitude. This latter quantity satisfies its own, previously unexplored, dynamical equation, which may be decomposed into individual integral equations for its various form factors. In particular, the sca…
Infrared enhanced analytic coupling and chiral symmetry breaking in QCD
2005
We study the impact on chiral symmetry breaking of a recently developed model for the QCD analytic invariant charge. This charge contains no adjustable parameters, other than the QCD mass scale $\Lambda$, and embodies asymptotic freedom and infrared enhancement into a single expression. Its incorporation into the standard form of the quark gap equation gives rise to solutions for the dynamically generated mass that display a singular confining behaviour at the origin. Using the Pagels-Stokar method we relate the obtained solutions to the pion decay constant $f_{\pi}$, and estimate the scale parameter $\Lambda$, in the presence of four active quarks, to be about 880 MeV.
Diquark correlations in hadron physics: Origin, impact and evidence
2020
The last decade has seen a marked shift in how the internal structure of hadrons is understood. Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and progress with lattice-regularised QCD have provided strong indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in the flavour-separation of the proton's elect…
Generalized Polarizabilities and the Chiral Structure of the Nucleon
1997
We are studying the electron scattering process e p to e' p' gamma in order to obtain information on the genuine virtual Compton scattering (VCS) process gamma^* N to gamma N. In addition to the two kinematical variables of real Compton scattering, e.g. the scattering angle theta and the energy omega' of the outgoing photon, the invariant amplitude for VCS depends on a third kinematical variable, which we choose as the absolute value of the three-momentum transfer to the nucleon. The structure-dependent coefficients in the VCS amplitude therefore acquire a momentum dependence and are termed ``generalized polarizabilities'' of the nucleon in analogy to real Compton scattering. Utilizing the …
Chiral Symmetry of Baryons
2001
We study chiral symmetry aspects of the positive and negative parity baryons by identifying them with linear representations of the chiral group $SU(N_{f}) \otimes SU(N_{f})$. It is shown that there are two distinctive schemes: naive and mirror assignments. We construct linear sigma models for baryons in the two assignments and examine their physical implications. Then we investigate properties of the naive and mirror nucleons microscopically by using QCD interpolating fields. Finally, we propose experiments to distinguish the two chiral assignments for the nucleon.