Ultralight $(L_mu-L_tau)$ vector dark matter interpretation of NANOGrav observations. (arXiv:2311.10148v1 [hep-ph])

Ultralight $(L_mu-L_tau)$ vector dark matter interpretation of NANOGrav observations. (arXiv:2311.10148v1 [hep-ph])
<a href="http://arxiv.org/find/hep-ph/1/au:+Chowdhury_D/0/1/0/all/0/1">Debtosh Chowdhury</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Hait_A/0/1/0/all/0/1">Arpan Hait</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Mohanty_S/0/1/0/all/0/1">Subhendra Mohanty</a>, <a href="http://arxiv.org/find/hep-ph/1/au:+Prakash_S/0/1/0/all/0/1">Suraj Prakash</a>

The angular correlation of pulsar residuals observed by NANOGrav and other
pulsar timing array (PTA) collaborations show evidence in support of the
Hellings-Downs correlation expected from stochastic gravitational waves (SGW).
In this paper, we offer a non-gravitational wave explanation of the observed
pulsar timing correlations as caused by an ultra-light $L_{mu} – L_{tau}$
gauge boson dark matter (ULDM). ULDM can affect the pulsar correlations in two
ways. The gravitational potential of vector ULDM gives rise to a Shapiro
time-delay of the pulsar signals and a non-trivial angular correlation (as
compared to the scalar ULDM case). In addition, if the pulsars have a non-zero
charge of the dark matter gauge group then the electric field of the local dark
matter causes an oscillation of the pulsar and a corresponding Doppler shift of
the pulsar signal. We point out that pulsars carry a significant charge of
muons and thus the $L_{mu} – L_{tau}$ vector dark matter contributes to both
the Doppler oscillations and the time-delay of the pulsar signals. Our analysis
shows that the NANOGrav data has a better fit to the $L_{mu} – L_{tau}$ ULDM
scenario compared to the SGW or the SGW with Shapiro time-delay hypotheses.

The angular correlation of pulsar residuals observed by NANOGrav and other
pulsar timing array (PTA) collaborations show evidence in support of the
Hellings-Downs correlation expected from stochastic gravitational waves (SGW).
In this paper, we offer a non-gravitational wave explanation of the observed
pulsar timing correlations as caused by an ultra-light $L_{mu} – L_{tau}$
gauge boson dark matter (ULDM). ULDM can affect the pulsar correlations in two
ways. The gravitational potential of vector ULDM gives rise to a Shapiro
time-delay of the pulsar signals and a non-trivial angular correlation (as
compared to the scalar ULDM case). In addition, if the pulsars have a non-zero
charge of the dark matter gauge group then the electric field of the local dark
matter causes an oscillation of the pulsar and a corresponding Doppler shift of
the pulsar signal. We point out that pulsars carry a significant charge of
muons and thus the $L_{mu} – L_{tau}$ vector dark matter contributes to both
the Doppler oscillations and the time-delay of the pulsar signals. Our analysis
shows that the NANOGrav data has a better fit to the $L_{mu} – L_{tau}$ ULDM
scenario compared to the SGW or the SGW with Shapiro time-delay hypotheses.

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