Light Dirac neutrino portal dark matter with gauged $U(1{)}_{B-L}$ symmetry

We propose a gauged $U(1{)}_{B-L}$ version of the light Dirac neutrino portal dark matter. The $U(1{)}_{B-L}$ symmetry provides a UV completion by naturally accommodating three right-handed neutrinos from anomaly cancellation requirements which, in combination with the left-handed neutrinos, form the sub-eV Dirac neutrinos after electroweak symmetry breaking. The particle content and the gauge charges are chosen in such a way that light neutrinos remain purely Dirac and dark matter, a gauge singlet Dirac fermion, remain stable. We consider both thermal and nonthermal production possibilities of dark matter and correlate the corresponding parameter space with the one within reach of future cosmic microwave background (CMB) experiments sensitive to enhanced relativistic degrees of freedom $\mathrm{\Delta }{N}_{\mathrm{eff}}$. The interplay of dark matter, CMB, structure formation and other terrestrial constraints keep the scenario very predictive leading the $U(1{)}_{B-L}$ parameter space into tight corners.

Figure 1

$\mathrm{\Delta }{N}_{\mathrm{eff}}^{\mathrm{th}}$ as a function of $m_{Z^{\prime }}$ and $g_{BL}$.

Figure 2

Evolution of comoving number density of ${\varphi }_1$, $\psi$ and comoving energy density of ${\nu }_R$. The left (right) panel shows the variation with respect to $g_{BL}$ ($y_{{\varphi }_1}$).

Figure 3

Scan plot showing the total $\mathrm{\Delta }{N}_{\mathrm{eff}}$ versus $m_{Z^{\prime }}$ for different ${\lambda }_{H{\varphi }_1}$, $g_{BL}$ and $m_{\psi }$. The magenta colored region is excluded by Planck 2018 bounds at $2\sigma$ CL The region in gray color is within the reach of future experiments.

Figure 4

Thermal average velocity of FIMP dark matter as a function of temperature for four different benchmark points.

Figure 5

Parameter space in $m_{Z^{\prime }}$ versus $g_{BL}$ plane for the FIMP scenario considering three different values of DM mass. The other parameters are kept fixed as $m_{{\varphi }_1}=500\mathrm{GeV}$, ${\lambda }_{H{\varphi }_1}={10}^{-5}$, $y_{{\varphi }_1}={10}^{-9}$.

Figure 6

Evolution of comoving number densities of ${\varphi }_1$ and $\psi$ and comoving energy density of ${\nu }_R$ for two different values of $y_{{\varphi }_1}$ (left panel) and $m_{{\varphi }_1}$ (right panel).

Figure 7

Interaction rate as a function of temperature for processes responsible for keeping dark sector in equilibrium with the SM bath. The benchmark parameters chosen are ${\lambda }_{H{\varphi }_1}=10^{-2}(\text{left panel}),10^{-4}(\text{right panel})$, $m_{{\varphi }_1}=100\mathrm{GeV}$, $m_{Z^{\prime }}=100\mathrm{GeV}$, $g_{BL}={10}^{-4}$.

Figure 8

Evolution of dark sector temperature after its decoupling from SM bath ($T<T_{\mathrm{dec}}$) for different values of $m_{Z^{\prime }}$ (left panel), dark sector Yukawa coupling $y_{{\varphi }_1}$ (middle panel) and dark matter mass $m_{\psi }$ (right panel). The rest of the parameters are kept fixed and are shown in respective plots.

Figure 9

Scan plot showing $\mathrm{\Delta }{N}_{\mathrm{eff}}$ vs $m_{{\varphi }_1}$ for different dark matter mass $m_{\psi }$ and different $m_{Z^{\prime }}$ and $g_{BL}$.

Figure 10

Bound on $m_{Z^{\prime }}$ vs $g_{BL}$ for the WIMP scenario with different values of ${\lambda }_{H{\varphi }_1}$. The solid black line separates regime 1 (below the solid black line) and regime 2 (above the solid black line). In all the plots, $m_{{\varphi }_1}=60\mathrm{GeV}$, $m_{\psi }=15\mathrm{GeV}$, $y_{{\varphi }_1}=0.28$.

Figure 11

Left panel: $\frac{\sigma (pp\to Z^{\prime })\mathrm{BR}(Z^{\prime }\to l^{-}{l}^{+})}{g_{BL}^2}$ vs $m_{Z^{\prime }}$. Right panel: bound on $g_{BL}$ vs $m_{Z^{\prime }}$ plane.

Figure 12

The DM-nucleon cross section vs DM mass as a function of effective number of relativistic species. The blue color region shows the sensitivity of DARWIN experiment [82].