اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTime-delay in a multi-channel formalism
93
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We reexamine the time-delay formalism of Wigner, Eisenbud and Smith, which was developed to analyze both elastic and inelastic resonances. An error in the paper of Smith has propagated through the literature. We correct this error and show how the results of Eisenbud and Smith are related. We also comment on some recent time-delay studies, based on Smiths erroneous interpretation of the Eisenbud result.
قيم البحث
اقرأ أيضاً
Multiple high precision $beta$-decay measurements are being carried out these days on various nuclei, in search of beyond the Standard Model signatures. These measurements necessitate accurate standard model theoretical predictions to be compared wit
h. Motivated by the experimental surge, we present a formalism for such a calculation of $beta$-decay observables, with controlled accuracy, based on a perturbative analysis of the theoretical observables related to the phenomena, including high order nuclear recoil and shape corrections. The accuracy of the corrections is analyzed by identifying a hierarchy of small parameters, related to the low momentum transfer characterizing $beta$-decays. Furthermore, we show that the sub-percent uncertainties, targeted by on-going and planned experiments, entail an accuracy of the order of 10% for the solution of the nuclear many body problem, which is well within the reach of modern nuclear theory for light to medium mass nuclei.
We consider a model of relativistic three-body scattering with a bound state in the two-body sub-channel. We show that the naive K-matrix type parametrization, here referred to as the B-matrix, has nonphysical singularities near the physical region.
We show how to eliminate such singularities by using dispersion relations and also show how to reproduce unitarity relations by taking into account all relevant open channels.
This review represents a detailed and comprehensive discussion of the Thermal Field Theory (TFT) concepts and key results in Yukawa-type theories. We start with a general pedagogical introduction into the TFT in the imaginary- and real-time formulati
on. As phenomenologically relevant implications, we present a compendium of thermal decay rates for several typical reactions calculated within the framework of the real-time formalism and compared to the imaginary-time results found in the literature. Processes considered here are those of a neutral (pseudo)scalar decaying into two distinct (pseudo)scalars or into a fermion-antifermion pair. These processes are extended from earlier works to include chemical potentials and distinct species in the final state. In addition, a (pseudo)scalar emission off a fermion line is also discussed. These results demonstrate the importance of thermal effects in particle decay observables relevant in many phenomenological applications in systems at high temperatures and densities.
We present a coupled-channel Lagrangian approach (GiM) to describe the $pi N to pi N$, $2pi N$ scattering in the resonance energy region. The $2pi N$ production has been significantly improved by using the isobar approximation with $sigma N$ and $pi
Delta(1232)$ in the intermediate state. The three-body unitarity is maintained up to interference pattern between the isobar subchannels. The scattering amplitudes are obtained as a solution of the Bethe-Salpeter equation in the $K$ matrix approximation. As a first application we perform a partial wave analysis of the $pi N to pi N$, $pi^0pi^0 N$ reactions in the Roper resonance region. We obtain $R_{sigma N}(1440)=27^{+4}_{-9}$,% and $R_{sigma N}(1440)=12^{+5}_{-3}$,% for the $sigma N$ and $pi Delta$ decay branching ratios of $N^*(1440)$ respectively. The extracted $pi N$ inelasticities and reaction amplitudes are consistent with the results from other groups.
We formulate singular classical theories without involving constraints. Applying the action principle for the action (27) we develop a partial (in the sense that not all velocities are transformed to momenta) Hamiltonian formalism in the initially re
duced phase space (with the canonical coordinates $q_{i},p_{i}$, where the number $n_{p}$ of momenta $p_{i}$, $i=1,...,n_{p}$ (17) is arbitrary $n_{p}leq n$, where $n$ is the dimension of the configuration space), in terms of the partial Hamiltonian $H_{0}$ (18) and $(n-n_{p})$ additional Hamiltonians $H_{alpha}$, $alpha=n_{p}+1,...,n$ (20). We obtain $(n-n_{p}+1)$ Hamilton-Jacobi equations (25)-(26). The equations of motion are first order differential equations (33)-(34) with respect to $q_{i},p_{i}$ and second order differential equations (35) for $q_{alpha}$. If $H_{0}$, $H_{alpha}$ do not depend on $dot{q}_{alpha}$ (42), then the second order differential equations (35) become algebraic equations (43) with respect to $dot{q}_{alpha}$. We interpret $q_{alpha}$ as additional times by (45), and arrive at a multi-time dynamics. The above independence is satisfied in singular theories and $r_{W}leq n_{p}$ (58), where $r_{W}$ is the Hessian rank. If $n_{p}=r_{W}$, then there are no constraints. A classification of the singular theories is given by analyzing system (62) in terms of $F_{alphabeta}$ (63). If its rank is full, then we can solve the system (62); if not, some of $dot{q}_{alpha}$ remain arbitrary (sign of a gauge theory). We define new antisymmetric brackets (69) and (80) and present the equations of motion in the Hamilton-like form, (67)-(68) and (81)-(82) respectively. The origin of the Dirac constraints in our framework is shown: if we define extra momenta $p_{alpha}$ by (86), then we obtain the standard primary constraints (87), and the new brackets transform to the Dirac bracket. Quantization is discussed.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
