LISA as a probe for particle physics: electroweak scale tests in synergy with ground-based experiments

TL;DR

This work assesses whether a stochastic gravitational-wave background from cosmological first-order phase transitions can be detected by LISA, including synergy with ground-based detectors and pulsar timing arrays. It adopts a minimal regime with negligible plasma effects and substantial supercooling, derives the SGWB spectrum with peak parameters dependent on $H_\star$, $\beta/H_\star$, $v_w$, $T_\star$, and $g_\star$, and analyzes detectability across a network of detectors. It shows that by the end of the LISA era, a wide region of the FOPT parameter space could be tested, with many scenarios allowing multi-detector confirmation; crucially, LISA could reconstruct the signal shape, locate the peak, and infer the phase transition energy scale, informing particle physics beyond the SM. This work therefore provides a bridge between GW observations and collider guidance for electroweak- and beyond-electroweak-scale physics.

Abstract

We forecast the prospective of detection for a stochastic gravitational wave background sourced by cosmological first-order phase transitions. We focus on first-order phase transitions with negligible plasma effects, and consider the experimental infrastructures built by the end of the LISA mission. We make manifest the synergy among LISA, pulsar time array experiments, and ground-based interferometers. For phase transitions above the TeV scale or below the electroweak scale, LISA can detect the corresponding gravitational wave signal together with Einstein Telescope, SKA or even aLIGO-aVIRGO-KAGRA. For phase transitions at the electroweak scale, instead, LISA can be the only experiment observing the gravitational wave signal. In case of detection, by using a parameter reconstruction method that we anticipate in this work, we show that LISA on its own has the potential to determine when the phase transition occurs and, consequently, the energy scale above which the standard model of particle physics needs to be modified. The result may likely guide the collider community in the post-LHC era.

Figures (3)

• Figure 1: Left panel: The value of the frequency peak $f_p$ in the parameter space $T_\star$--$\beta/H_\star$ for bubble velocities $v_w=0.99$. On the background (colored bands) the frequencies the forthcoming GW detectors are sensitive to; the stronger the color, the better the sensitivity. The blue area is excluded by the BBN bound. Right panel: Sensitivity curves of the current and forthcoming GW experiments and the SGWB signals (dotted curves) sourced by the FOPT benchmark scenarios with $g_\star = 106$, $\beta/H_\star=3$, and $T_\star/\,$GeV and $v_w$ being respectively 3 and 0.99 (dotted purple line), 3 and 0.05 (dotted gray line), 120 and 0.99 (dotted magenta line), 120 and 0.05 (dotted orange line), 10$^4$ and 0.99 (dotted blue line), and 10$^4$ and 0.05 (dotted green line). The dotted-dashed lines correspond to the power-law sensitivity curves of PPTA & EPTA & NANOGRAV (at frequencies $f\sim$ nHz) and aLIGO O1 (at frequencies $f\sim$ 100 Hz); the solid lines correspond to the sensitivity curves $\Omega_{\rm sens}(f)$ of SKA observing 100 milli-second pulsars (dark red), SKA observing 2000 milli-second pulsars (light red), LISA (orange), ET (yellow), and aLIGO-aVirgo-KAGRA network at its final design (green). The BBN bound rules out the FOPT SGWB signals touching the blue area.
• Figure 2: The parameter reach of the future GW experiment network for $v_w=0.99$ (left panel) and $v_w=0.05$ (right panel). In each area the corresponding experiment (see labels) detect the FOPT with SNR $> 10$. The BBN bound rules out the blue region. The bullet points correspond to the benchmark SGWB signals appearing with the same color in the right panel of Fig. \ref{['fig:sens']}.
• Figure 3: Reconstruction of the FOPT SGWB signals (blue lines) displayed in the left panel of Fig. \ref{['fig:sens']} by means of the "multi-bin" procedure assuming a good knowledge on the LISA instrumental noise (red curves). The power-law fit is performed inside several intervals indicated by vertical yellow dashed lines. The 1-$\sigma$ uncertainties are represented by the light blue band. The signal reconstruct is performed only where the error bands are displayed.