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The action for a (3+1)-dimensional particle in very special relativity is studied. It is proved that massless particles only travel in effective (2 + 1)-dimensional space-time. It is remarkable that this action can be written as an action for a relativistic particle in a background gauge field and it is shown that this field causes the dimensional reduction. A new symmetry for this system is found. Furthermore, a general action with restored Lorentz symmetry is proposed for this system. It is shown that this new action contains very special relativity and two-time physics.

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In this work we explicitly calculate the thermal conductivity for a general bidimensional dilute gas of neutral molecules by solving Boltzmann's equation. Chapman-Enskog's method is used in order to analytically obtain this transport coefficient to first approximation in terms of a collision integral for an unspecified molecular interaction model. In the particular case of hard disks interactions, the result is shown to be consistent with previous work by J. V. Sengers [1], yielding the expected T 1/2 dependence with the temperature. This dependence is widely used for dense gases as the low density limit in the Enskog expansion. The case of Maxwellian molecules is also explored where a linear dependence with the temperature is obtained.