Structure of a thermal quasifermion in the QCD/QED Medium

In this paper we carried out a nonperturbative analysis of a thermal quasifermion in the chiral symmetric thermal QCD/QED medium by studying its self-energy function through the Dyson-Schwinger equation with the hard-thermal-loop resummed improved ladder kernel. Our analysis reveals several interesting results, two in some of which may force us to change the image of thermal quasifermions: (1) The thermal mass of a quasifermion begins to decrease as the strength of the coupling gets stronger and finally disappears in the strong coupling region, thus showing a property of a massless particle, and (2) its imaginary part (i.e., the decay width) persists to have $O(g^2T \log(1/g))$ behavior. These results suggest that in the recently produced strongly coupled quark-gluon plasma, the thermal mass of a quasiquark should vanish. Taking into account the largeness of the imaginary part, it seems very hard for a quark to exist as a qausiparticle in the strongly coupled quark-gluon plasma phase. Other important findings are as follows: (3) The collective plasmino mode disappears also in the strongly coupled system, and (4) there exists an ultrasoft third peak in the quasifermion spectral density at least in the weakly coupled QED/QCD plasma, indicating the existence of the ultrasoft fermionic mode.Comment: 20 pages, 28 figure

Bose-enhanced chemistry: Amplification of selectivity in the dissociation of molecular Bose-Einstein condensates

We study the photodissociation chemistry of a quantum degenerate gas of bosonic triatomic $ABC$ molecules, assuming two open rearrangement channels ($AB+C$ or $A+BC$). The equations of motion are equivalent to those of a parametric multimode laser, resulting in an exponential buildup of macroscopic mode populations. By exponentially amplifying a small differential in the single-particle rate-coefficients, Bose stimulation leads to a nearly complete selectivity of the collective $N$-body process, indicating a novel type of ultra-selective quantum degenerate chemistry.Comment: 5 pages, 3 figure

The role of energy-momentum conservation in emission of Cherenkov gluons

The famous formula for the emission angle of Cherenkov radiation should be modified when applied to hadronic reactions because of recoil effects. They impose the upper limit on the energy of the gluon emitted at a given angle. Also, it leads to essential corrections to the nuclear refractive index value as determined from the angular position of Cherenkov rings.Comment: 6

Uraltsev Sum Rule in Bakamjian-Thomas Quark Models

We show that the sum rule recently proved by Uraltsev in the heavy quark limit of QCD holds in relativistic quark models \`a la Bakamjian and Thomas, that were already shown to satisfy Isgur-Wise scaling and Bjorken sum rule. This new sum rule provides a {\it rationale} for the lower bound of the slope of the elastic IW function $\rho^2 \geq {3 \over 4}$ obtained within the BT formalism some years ago. Uraltsev sum rule suggests an inequality $|\tau_{3/2}(1)| > |\tau_{1/2}(1)|$. This difference is interpreted in the BT formalism as due to the Wigner rotation of the light quark spin, independently of a possible LS force. In BT models, the sum rule convergence is very fast, the $n = 0$ state giving the essential contribution in most of the phenomenological potential models. We underline that there is a serious problem, in the heavy quark limit of QCD, between theory and experiment for the decays $B \to D^*_{0,1}(broad) \ell \nu$, independently of any model calculation.Comment: 16 pages, Late

Learning together: Lessons from a collaborative curriculum design project

Based on an action research project implemented at two South African universities, we argue that content and language integration (ICL) collaborative partnerships benefit not only from collaboration between language and content specialists, but in addition, from collaboration between language specialists, general education specialists and content specialists from a variety of disciplines. However, as we illustrate below, these benefits may be accompanied by substantial challenges. We make a further claim, for the value of a transformative approach towards collaboration for content and language integration, in which the teacher/researchers engage in their practice in a critical and reflexive manner, and by so doing, foster their own deep learning, as well as the deep learning of the students

Remarks on sum rules in the heavy quark limit of QCD

We underline a problem existing in the heavy quark limit of QCD concerning the rates of semileptonic B decays into P-wave $D_J(j)$ mesons, where $j = {1 \over 2}$ (wide states) or $j = {3 \over 2}$ (narrow states). The leading order sum rules of Bjorken and Uraltsev suggest $\Gamma [ \bar{B} \to D_{0,1} ({1 \over 2}) \ell \nu ] \ll \Gamma [ \bar{B} \to D_{1,2} ({3 \over 2}) \ell \nu ]$, in contradiction with experiment. The same trend follows also from a sum rule for the subleading $1/m_Q$ curent matrix element correction $\xi_3(1)$. The problem is made explicit in relativistic quarks models \`a la Bakamjian and Thomas, that give a transparent physical interpretation of the latter as due, not to a $L \cdot S$ force, but to the Wigner rotation of the light quark spin. We point out moreover that the selection rule for decay constants of $j = {3 \over 2}$ states, $f_{3/2} = 0$, predicts, assuming the model of factorization, the opposite hierarchy $\Gamma [ \bar{B} \to \bar{D}_{s_{1,2}} ({3 \over 2}) D^{(*)} ] \ll \Gamma [ \bar{B} \to \bar{D}_{s_{0,1}} ({1 \over 2}) D^{(*)} ]$.Comment: Contribution to the International Europhysics Conference on HEP, Budapest, July 2001 (presented by L. Oliver); 5 page

On P-wave meson decay constants in the heavy quark limit of QCD

In previous work it has been shown that, either from a sum rule for the subleading Isgur-Wise function $\xi_3(1)$ or from a combination of Uraltsev and Bjorken SR, one infers for $P$-wave states $|\tau_{1/2}(1)| \ll |\tau_{3/2}(1)|$. This implies, in the heavy quark limit of QCD, a hierarchy for the {\it production} rates of $P$-states $\Gamma(\bar{B}_d \to D ({1 \over 2}) \ell \nu) \ll \Gamma(\bar{B}_d \to D ({3 \over 2}) \ell \nu)$ that seems at present to be contradicted by experiment. It was also shown that the decay constants of $j = {3 \over 2}$ $P$-states vanish in the heavy quark limit of QCD, $f_{3/2}^{(n)} = 0$. Assuming the {\it model} of factorization in the decays $\bar{B}_d \to \bar{D}_s^{**}D$, one expects the opposite hierarchy for the {\it emission} rates $\Gamma(\bar{B}_d \to \bar{D}_s ({3 \over 2}) D) \ll \Gamma(\bar{B}_d \to \bar{D}_s ({1 \over 2}) D)$, since $j = {1 \over 2}$ $P$-states are coupled to vacuum. Moreover, using Bjorken SR and previously discovered SR involving heavy-light meson decay constants and IW functions, one can prove that the sums $\sum\limits_n ({f^{(n)} \over f^{(0)}})^2$, $\sum\limits_n ({f_{1/2}^{(n)} \over f^{(0)}})^2$ (where $f^{(n)}$ and $f_{1/2}^{(n)}$ are the decay constants of $S$-states and $j = {1\over 2}$ $P$-states) are divergent. This situation seems to be realized in the relativistic quark models \`a la Bakamjian and Thomas, that satisfy HQET and predict decays constants $f^{(n)}$ and $f_{1/2}^{(n)}$ that do not decrease with the radial quantum number $n$.Comment: 7 pages, Late