arXiv subjects

M. Dasgupta

Publications and source records attributed to M. Dasgupta.

59 records · Page 4Linked to original sources

arXiv1997

Power Corrections to Event Shapes in Deep Inelastic Scattering

We investigate the power-suppressed corrections to the mean values of various quantities that characterise the shapes of final states in deep inelastic lepton scattering. Our method is based on an analysis of one-loop Feynman graphs containing a massive gluon, which is equivalent to the evaluation of leading infrared renormalon contributions. As in $\ee$ annihilation, we find that the leading corrections are proportional to $1/Q$. We give quantitative estimates based on the hypothesis of a universal low-energy effective coupling.

hep-ph↗

arXiv1997

Adiabatic quantum tunneling in heavy-ion sub-barrier fusion

High precision measurements of the fusion excitation functions for the reactions ^{40}Ca + ^{194}Pt, ^{192}Os clearly demonstrate that projectile excitation significantly modifies the potential barrier distribution. In sharp contrast, fusion of ^{16}O + ^{144}Sm appears to show no influence of the projectile excitation on the shape of the barrier distribution. These apparently conflicting conclusions are reconciled in this work, using realistic coupled--channels calculations, which show that high energy states produce an adiabatic potential renormalisation. This result indicates that adiabatic effects restrict, in a natural way, the states which influence the shape of a fusion barrier distribution. The analysis of barrier distributions thus offers a criterion for the relevance of the `counter term' prescription in the Caldeira-Leggett approach.

nucl-th↗

arXiv1996

Power Corrections and Renormalons in $e^+e^-$ Fragmentation Functions

We estimate the power corrections (infrared renormalon contributions) to the coefficient functions for the transverse, longitudinal and asymmetric fragmentation functions in $e^+e^-$ annihilation, using a method based on the analysis of one-loop Feynman graphs containing a massive gluon. The leading corrections have the expected $1/Q^2$ behaviour, but the gluonic coefficients of the longitudinal and transverse contributions separately have strong singularities at small $x$, which cancel in their sum. This leads to $1/Q$ corrections to the longitudinal and transverse parts of the annihilation cross section, which cancel in the total cross section.

hep-ph↗

arXiv1996

Validity of the linear coupling approximation in heavy-ion fusion reactions at sub barrier energies

The role of higher order coupling of surface vibrations to the relative motion in heavy-ion fusion reactions at near-barrier energies is investigated. The coupled channels equations are solved to all orders, and also in the linear and the quadratic coupling approximations. Taking $^{64}$Ni + $^{92,96}$Zr reactions as examples, it is shown that all order couplings lead to considerably improved agreement with the experimentally measured fusion cross sections and average angular momenta of the compound nucleus for such heavy nearly symmetric systems. The importance of higher order coupling is also examined for asymmetric systems like $^{16}$O + $^{112}$Cd, $^{144}$Sm, for which previous calculations of the fusion cross section seemed to indicate that the linear coupling approximation was adequate. It is shown that the shape of the barrier distributions and the energy dependence of the average angular momentum can change significantly when the higher order couplings are included, even for systems where measured fusion cross sections may seem to be well reproduced by the linear coupling approximation.

nucl-th↗

arXiv1996

Power Corrections and Renormalons in Deep Inelastic Structure Functions

We study the power corrections (infrared renormalon contributions) to the coefficient functions for non-singlet deep inelastic structure functions due to gluon vacuum polarization insertions in one-loop graphs. Remarkably, for all the structure functions $F_1$, $F_2$, $F_3$ and $g_1$, there are only two such contributions, corresponding to $1/Q^2$ and $1/Q^4$ power corrections. We compute their dependence on Bjorken $x$. The results could be used to model the dominant higher-twist contributions.

hep-ph↗