^{1,2}

^{3,4}

^{1}

^{2}

^{3}

^{4}

^{3}.

The Hawking radiation spectrum of Kerr-Sen axion-dilaton black holes is derived, in the context of dark spinors tunnelling across the horizon. Since a black hole has a well defined temperature, it should radiate in principle all the standard model particles, similar to a black body at that temperature. We investigate the tunnelling of mass dimension one spin-1/2 dark fermions, which are beyond the standard model and are prime candidates to the dark matter. Their interactions with the standard model matter and gauge fields are suppressed by at least one power of unification scale, being restricted just to the Higgs field and to the graviton likewise. The tunnelling method for the emission and absorption of mass dimension one particles across the event horizon of Kerr-Sen axion-dilaton black holes is shown here to provide further evidence for the universality of black hole radiation, further encompassing particles beyond the standard model.

Black hole tunnelling procedures have been placed as prominent methods to calculate the temperature of black holes [

The tunnelling method was employed to provide Hawking radiation due to dark spinors for black strings [

Our approach here is to employ an exact classical solution in the low energy effective field theory describing heterotic string theory: the Kerr-Sen axion-dilaton black holes [

We shall study similar methods for spin-1/2 fermions of mass dimension one, different from the procedure for standard mass dimension 3/2 fermions. Elko dark spinors, namely, the dual-helicity eigenspinors of the charge conjugation operator [

This paper is presented as follows: the Kerr-Sen axion-dilaton black hole is briefly revisited in the next section, together with the dark spinors framework. We thus shall calculate in Section

String theory has solutions describing extra-dimensional extended objects surrounded by event horizons, presenting a causal structure associated with singularities in string theory. The low energy effective action of the heterotic string theory is ruled by an action that, up to higher derivative terms and other fields which are set to zero for the particular class of backgrounds considered [

The Kerr-Sen dilaton-axion black hole metric is a solution of the field equations derived from (

Metric (

By performing the transformation

A mass dimension one quantum field can be thus constructed as [

Hawking radiation from general black holes encompasses distinguished charged and uncharged particles. Tunnelling methods can be employed for Elko dark particles across the horizon of Kerr-Sen black holes. From (

Elko dark spinors can be written as

In the above system the equations for

Combining either (

In compliance with the WKB approximation, the tunnelling rate reads

We derived the Hawking radiation for spin-1/2 fermions of mass dimension one, represented by dark spinors tunnelling across a Kerr-Sen dilaton-axion black hole horizon. The temperature of these solutions was computed and demonstrated to confirm the universal character of the Hawking effect, even for mass dimension one fermions of spin-1/2 that are beyond the standard model. The mass dimension one feature of such spinor fields sharply suppresses the couplings to other fields of the standard model. Indeed, by power counting arguments, Elko spinor fields can self-interact and further interact with a scalar (Higgs) field, providing a renormalizable framework. This type of interaction means an unsuppressed quartic self-interaction. The quartic self-interaction is essential to dark matter observations [

The authors declare that there is no conflict of interests regarding the publication of this paper.

R. T. Cavalcanti thanks CAPES and UFABC. Roldão da Rocha is grateful to CNPq Grants no. 303027/2012-6, no. 451682/2015-7, and no. 473326/2013-2, for partial financial support, and to FAPESP Grant no. 2015/10270-0.