Abstract
Abstract Particle production at the end of a first-order electroweak phase transition may be rather generic in theories beyond the standard model. Dark matter may then be abundantly produced by this mechanism if it has a sizable coupling to the Higgs field. For an electroweak phase transition occuring at a temperature T EW ~ 50–100 GeV, non- thermally generated dark matter with mass M X > TeV will survive thermalization after the phase transition, and could then potentially account for the observed dark matter relic density in scenarios where a thermal dark matter component is either too small or absent. Dark matter in these scenarios could then either be multi-TeV WIMPs whose relic abundace is mostly generated at the electroweak phase transition, or “Baby-Zillas” with mass M GUT ≫ M X ≫ ${v_{\mathrm{EW}}}$ that never reach thermal equilibrium in the early universe.
Highlights
Recognize a wider range of possible collider and astrophysical signals of dark matter than what would result from the thermal WIMP scenario
Dark matter in these scenarios could either be multi-TeV WIMPs whose relic abundace is mostly generated at the electroweak phase transition, or “Baby-Zillas” with mass MGUT ≫ MX ≫ vEW that never reach thermal equilibrium in the early universe
The red lines in figure 9 show the values of λV yielding the correct “non-thermal” annihilation cross section (4.13) for several values of TEW. This analysis shows that non-thermal production of multi-TeV vector boson dark matter at the EW phase transition (in (MV, λV ) parameter space in which the amount of dark matter yielded by thermal freeze-out is not enough to account for the observed dark matter relic density) is efficient as to generate a dark matter amount much larger than the observed relic density
Summary
If the early Universe was hotter than TEW ∼ 100 GeV it must have undergone an EW phase transition at some point in its history. For “runaway” bubbles this will correspond to a very large portion of the energy budget of the phase transition, and this process can be very important Under certain circumstances, this may hold true for highly relativistic bubble walls (γw ≫ 1) that reach a stationary state long before bubble collisions start (meaning that γw ≪ γwmax), in which case the amount of energy stored in the bubble walls will be very small compared to the available energy of the transition, but still important when released into the plasma at the end of the transition. Following [14], we compute the numerical solution for the field profile h(z, t) corresponding to the collision of two bubble walls, obtained from solving (2.4) with a toy potential V (h) of the form Both in the case of nearly degenerate minima (figure 1 - Left) and very non-degenerate minima (figure 1 - Right). The analysis for the dynamics of bubble collisions presented here may be extended to phase transitions involving multiple fields (see for example [31]), in this case the analysis of the field evolution after the bubble collision becomes much more complicated (since the scalar potential is multidimensional and the field “excursion” at the moment of the bubble collision will involve several fields), and we will not attempt it here
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