An Algorithm to Construct Groebner Bases for Solving Integration by Parts Relations

This paper is a detailed description of an algorithm based on a generalized Buchberger algorithm for constructing Groebner-type bases associated with polynomials of shift operators. The algorithm is used for calculating Feynman integrals and has proven itself efficient in several complicated cases.Comment: LaTeX, 9 page

Correlation Functions Along a Massless Flow

A non-perturbative method based on the Form Factor bootstrap approach is proposed for the analysis of correlation functions of 2-D massless integrable theories and applied to the massless flow between the Tricritical and the Critical Ising Models.Comment: 11 pages (two figures not included in the text), Latex file, ISAS/EP/94/15

Studies of light liner compression dynamics in plasma focus

The study is devoted to the investigation of plasma focus systems as a driver for magnetic compression of liners. The experiments on the comparative analyse of the foam and multiwired liners compression were done on the Filippov-type plasma focus facility PF-3. The compression of the light (linear mass 0.3-0.6 mg/cm) liners with velocity (2-3).10⁶ cm/s was obtained. It is shown that under conditions of considerable radiation fluxes at the usage of strongly-radiating working gases a preliminary heating of the target can be attained. This results in acceleration of the transition of initially – condensed substance into plasma state, that assists in overcoming “cool start” problem.Робота присвячена дослідженню плазмового фокусу (ПФ) в ролі драйверa для магнітного обтиснення лайнерів. Проведено експерименти з порівняльного аналізу стиснення пінних й багатодротових лайнерів на установці типу Філіппова ПФ-3. Отримано стиснення лайнерів з погонною масою 0.3-0.6 мг/см зі швидкостями (2-3).10⁶ см/с при амплітуді розрядного струму 2 МА. Показано, що в умовах значних радіаційних потоків при використанні сильновипромінюючих робочих газів може бути здійснений попередній нагрів мішені. Це призводить до прискорення переходу первісно конденсованої речовини у плазмовий стан, що дає змогу подолати проблему «холодного старту».Работа посвящена исследованию плазменного фокуса (ПФ) в качестве драйвера для магнитного обжатия лайнеров. Проведены эксперименты по сравнительному анализу сжатия пенных и многопроволочных лайнеров на установке типа Филиппова ПФ-3. Получено сжатие лайнеров с погонной массой 0.3-0.6 мг/см со скоростями (2-3).10⁶ см/с при амплитуде разрядного тока 2 МА. Показано, что в условиях значительных радиационных потоков при использовании сильноизлучающих рабочих газов может быть осуществлен предварительный нагрев мишени. Это приводит к ускорению перехода первоначально конденсированного вещества в плазменное состояние, что способствует преодолению проблемы “холодного старта ”

Search for light pseudoscalar sgoldstino in K- decays

A search for the light pseudoscalar sgoldstino production in the three body K- decay K-->pipi0P has been performed with the ISTRA+ detector exposed to the 25 GeV negative secondary beam of the U70 proton synchrotron. No signal is seen. An upper limit for the branching ratio Br(K->pipi0P), at 90% confidence level, is found to be around 9*10**-6 in the effective mass m(P) range from 0 till 200 MeV, excluding the region near m(pi0) where it degrades to 3.5*10**-5.Comment: 10 pages, LATEX, 8 EPS figures, revised version, to be published in Phys.Lett.

High statistic measurement of the K- -> pi0 e- nu decay form-factors

The decay K- -> pi0 e- nu is studied using in-flight decays detected with the ISTRA+ spectrometer. About 920K events are collected for the analysis. The lambda+ slope parameter of the decay form-factor f+(t) in the linear approximation (average slope) is measured: lambda+(lin)= 0.02774 +- 0.00047(stat) +- 0.00032(syst). The quadratic contribution to the form-factor was estimated to be lambda'+ = 0.00084 +- 0.00027(stat) +- 0.00031(syst). The linear slope, which has a meaning of df+(t)/dt|_{t=0} for this fit, is lambda+ = 0.02324 +- 0.00152(stat) +- 0.00032(syst). The limits on possible tensor and scalar couplings are derived: f_{T}/f_{+}(0)=-0.012 +- 0.021(stat) +- 0.011$(syst), f_{S}/f_{+}(0)=-0.0037^{+0.0066}_{-0.0056}(stat) +- 0.0041(syst).Comment: 11 pages, 8 figures. Accepted by Phys.Lett.

Measurement of the Dalitz plot slope parameters for K- -> pi0 pi0 pi- decay using ISTRA+ detector

The Dalitz plot slope parameters g, h and k for the K- -> pi0 pi0 pi- decay have been measured using in-flight decays detected with the ISTRA+ setup operating in the 25 GeV negative secondary beam of the U-70 PS. About 252 K events with four-momenta measured for the pi- and four involved photons were used for the analysis. The values obtained g=0.627+/-0.004(stat)+/-0.010(syst), h=0.046+/-0.004(stat)+/-0.012(syst), k=0.001+/-0.001(stat)+/-0.002(syst) are consistent with the world averages dominated by K+ data, but have significantly smaller errors.Comment: LaTeX, 10 pages, 8 eps-figures, update of IHEP 2002-1

On the 3-particle scattering continuum in quasi one dimensional integer spin Heisenberg magnets

We analyse the three-particle scattering continuum in quasi one dimensional integer spin Heisenberg antiferromagnets within a low-energy effective field theory framework. We exactly determine the zero temperature dynamical structure factor in the O(3) nonlinear sigma model and in Tsvelik's Majorana fermion theory. We study the effects of interchain coupling in a Random Phase Approximation. We discuss the application of our results to recent neutron-scattering experiments on the Haldane-gap material ${\rm CsNiCl_3}$.Comment: 8 pages of revtex, 5 figures, small changes, to appear in PR

Integrable Structure of Conformal Field Theory, Quantum KdV Theory and Thermodynamic Bethe Ansatz

We construct the quantum versions of the monodromy matrices of KdV theory. The traces of these quantum monodromy matrices, which will be called as ``${\bf T}$-operators'', act in highest weight Virasoro modules. The ${\bf T}$-operators depend on the spectral parameter $\lambda$ and their expansion around $\lambda = \infty$ generates an infinite set of commuting Hamiltonians of the quantum KdV system. The ${\bf T}$-operators can be viewed as the continuous field theory versions of the commuting transfer-matrices of integrable lattice theory. In particular, we show that for the values $c=1-3{{(2n+1)^2}\over {2n+3}} , n=1,2,3,...$of the Virasoro central charge the eigenvalues of the ${\bf T}$-operators satisfy a closed system of functional equations sufficient for determining the spectrum. For the ground-state eigenvalue these functional equations are equivalent to those of massless Thermodynamic Bethe Ansatz for the minimal conformal field theory ${\cal M}_{2,2n+3}$; in general they provide a way to generalize the technique of Thermodynamic Bethe Ansatz to the excited states. We discuss a generalization of our approach to the cases of massive field theories obtained by perturbing these Conformal Field Theories with the operator $\Phi_{1,3}$. The relation of these ${\bf T}$-operators to the boundary states is also briefly described.Comment: 24 page

High statistic study of the K- -> pi0 mu- nu decay

The decay K- -> pi0 mu- nu has been studied using in-flight decays detected with the "ISTRA+" spectrometer. About 540K events were collected for the analysis. The lambda+ and lambda0 slope parameters of the decay form-factors f+(t), f0(t) have been measured : lambda+ = 0.0277+-0.0013 (stat)+-0.0009 (syst), lambda0 = 0.0183+-0.0011(stat)+-0.0006(syst), and d(lambda0)/d(lambda+)=-0.348. The limits on the possible tensor and scalar couplings have been derived: fT/f+(0)=-0.0007 +- 0.0071, fS/f+(0)=0.0017 +- 0.0014. No visible non-linearity in the form-factors have been observed.Comment: 11 pages, 8 EPS figures, accepted by Physics Letters