Spectral energy distribution and generalized Wien's law for photons and cosmic string loops

Physical objects with energy u (l) ∼ l? 3w, with l a characteristic length and w a dimensionless constant, lead to an equation of state p = w?, with p the pressure and ? the energy density. Special entities with this property are, for instance, photons (u = hc l, with l the wavelength) with w = 1 3, and some models of cosmic string loops (u = (c4 aG)l, with l the length of the loop and a a numerical constant), with w = ?1 3. Here, we discuss some features of the spectral energy distribution of these systems and the corresponding generalization of Wien's law, which in terms of l has the form Tl = constant mp 3w , being lmp the most probable size of the mentioned entities. © 2014 The Royal Swedish Academy of Sciences.