Unified treatment of A+Bto 0 and A+Ato 0 chemical reactions through Thompson's approach

In this work we propose an action to describe diffusion limited chemical reactions belonging to various classes of universality. This action is treated through Thompson's approach and can encompass both cases where we have segregation as in the $A+B\to 0$ reaction, as well the simplest one, namely the $A+A\to 0$ reaction .Our results for long time and long wavelength behaviors of the species concentrations and reaction rates agree with exact results of Peliti for $A+A\to 0$ reaction and rigorous results of Bramson and Lebowitz for $A+B\to 0$ reaction, with equal initial concentrations.The different classes of universality are reflected by the obtained upper critical dimensions varying continuously from $d_{c}=2$ in the first case to $d_{c}=4$ in the last one. Just at the upper critical dimensions we find universal logarithmic corrections to the mean field behavior.