with a 90% C.L. Other limits on the mixing angle φ reported in the literature are given in Refs. [26, 28, 38, 39]. In Figure 1 we show the emissivity as a function of the degeneration parameter β for several values representative of the mixing angle φ = − 0 . 0016 , 0 , 0 . 0011. We observe that emissivity decreases when β increases, which is due to the reduction in the number of positrons available necessary to cause the collision. Also we see that the emissivity is affected by the φ parameter. There are other effects which may change the emissivity, for example, the radiative corrections at one-loop level. To analyze the effects of the φ parameter of the left-right symmetric model on the emissiv- ity Q LRSM ν ¯ ν ( φ, β ) of the neutrinos, in Fig. 2 we show the ratio Q LRSM ν ¯ ν ( φ,β ) Q SM ν ¯ ν ( β ) (ratio of emissivity calculated in the LRSM to the emissivity calculated in the SM [34]), as a function of the φ parameter for several values representative of degeneration parameter β = 0 , 5 , 12. According to collapse theories, the full energy loss in a stellar collapse is L$_{ν}$$_{¯}$ ν = Q$_{ν}$$_{¯}$ ν · V$_{star}$ · t$_{col}$ ≈ 10 53 erg , where V$_{star}$ is the volume of a star and t$_{col}$ the collapse time. Therefore, if we assume that t$_{col}$ ∼ 1 − 10 s , the stellar collapse temperature T$_{col}$ ∼ (1 . 1 − 1 . 4) × 10 11 $^{o}$K will be obtained. On the contrary, if we know the exact stellar collapse temperature, the collapse time can be obtained. For instance, the value T$_{col}$ ∼ × 10 12 $^{o}$K corresponds to t$_{col}$ ∼ 10 − 7 s . In summary, we have analyzed the effects of the mixing angle φ of a left-right symmetric model on the emissivity of the neutrinos via the process e $^{+}$e − → ν ¯ ν . We find that the emissivity is dependent of the mixing angle φ of the model in the allowed range for this parameter. As expected, in the limit of vanishing φ we recover the expression for the emissivity Q SM ν ¯ ν ( β ) for the SM previously obtained in the literature [29–33]. In addition, the analytical and numerical results for the emissivity have never been reported in the literature before and could be of relevance for the scientific community. This work was supported by CONACyT, SNI and PROMEP (M´ exico). Acknowledgments 10