Interplay between the muon $g-2$ anomaly and the PTA nHZ gravitational waves from domain walls in the next-to-minimal supersymmetric standard model

With some explicitly $Z_3$ breaking terms in the NMSSM (next-to-minimal supersymmetric standard model) effective superpotential and scalar potential, domain walls (DWs) from spontaneously breaking of the discrete symmetry in approximate $Z_3$-invariant NMSSM can collapse and lead to observable stochastic gravitational wave (GW) background signals. In the presence of a hidden sector, such terms may originate from the geometric superconformal breaking with holomorphic quadratic correction to frame function when the global scale-invariant superpotential is naturally embedded into the canonical superconformal supergravity models. The smallness of such mass parameters in the NMSSM may be traced back to the original superconformal invariance. Naive estimations indicate that a SUSY explanation to muon $g-2$ anomaly can have tension with the constraints on SUSY by pulsar timing arrays data, because large SUSY contributions to $\mathrm{\Delta }{a}_{\mu }$ in general needs relatively light superpartners while present ${\mathrm{\Omega }}_{gw}^0$ can set the lower bounds for $m_{\mathrm{soft}}$. We calculate numerically the signatures of GWs produced from the collapse of DWs and find that the observed nHZ stochastic GW background by NANOGrav, etc., can indeed be explained with proper tiny values of $\chi m_{3/2}\sim {10}^{-14}\mathrm{eV}$ for $\chi S^2$ case (and $\chi m_{3/2}\sim {10}^{-10}\mathrm{eV}$ for $\chi H_u{H}_d$ case), respectively. Besides, there are still some parameter points, whose GW spectra intersect with the NANOGrav signal region, that can explain the muon $g-2$ anomaly to $1\sigma$ range.

Figure 1

The upper panel shows the present-day peak amplitude of stochastic GW background ${\mathrm{\Omega }}_{\mathrm{gw}}{h}^2$ versus the peak frequency $f_{\mathrm{peak}}$ for the parameter points of $\chi S^2$ case. The corresponding GW spectra (with the NANOGrav observation data denoted by the red contour) are shown in the lower panel. Each parameter point satisfies the experimental constraints (i)–(v).

Figure 2

The tensions of the DWs versus their collapse time for the parameter points of $\chi S^2$ case are shown in the upper panel. The parameter points that can account for the NANOGrav GW background observations are marked with blue color. Each parameter point satisfies the experimental constraints (i)–(v). The values of $\chi m_{3/2}$ versus the peak frequencies are shown in the lower panel.

Figure 3

The tensions of the DWs versus their collapse time for the parameter points of $\chi S^2$ case are shown in the upper panel. The parameter points that can account for the NANOGrav GW background observations are marked with the color blue. Each parameter point satisfies the experimental constraints (i)–(v). The values of $\chi m_{3/2}$ versus the peak frequencies are shown in the lower panel.

Figure 4

The upper panel shows the present-day peak amplitude of stochastic GW background ${\mathrm{\Omega }}_{\mathrm{gw}}{h}^2$ versus the peak frequency $f_{\mathrm{peak}}$ for the parameter points of $\chi H_u{H}_d$ case. The corresponding GW spectra (with the NANOGrav observation data denoted by the red contour) are shown in the lower panel. Each parameter point satisfies the experimental constraints (i)–(v).

Figure 5

The tensions of the DWs versus their collapse time for the parameter points of $\chi H_u{H}_d$ case are shown in the upper panel. The parameter points that can account for the NANOGrav GW background observations are marked with the color blue. Each parameter point satisfies the experimental constraints (i)–(v). The values of $\chi m_{3/2}$ versus the peak frequencies are shown in the lower panel.

Figure 6

The tensions of the DWs versus their collapse time for the parameter points of $\chi H_u{H}_d$ case are shown in the upper panel. The parameter points that can account for the NANOGrav GW background observations are marked with the color blue. Each parameter point satisfies the experimental constraints (i)–(v). The values of $\chi m_{3/2}$ versus the peak frequencies are shown in the lower panel.