Scenario Of Electroweak Baryogenesis Research Articles

Embedded domain walls and electroweak baryogenesis

Embedded walls are domain wall solutions which are unstable in the vacuum but stabilized in a plasma of the early Universe. We show how embedded walls in which the electroweak symmetry is restored can lead to an efficient scenario of electroweak baryogenesis. We construct an extension of the Standard Model of particle physics in which embedded walls exist and are stabilized in an electromagnetic plasma. Published by the American Physical Society 2024

Electroweak baryogenesis via top-charm mixing

We investigate a scenario of electroweak baryogenesis in the two Higgs doublet model with quark flavor mixing. In general, off-diagonal components of quark Yukawa interactions with additional Higgs bosons are strongly constrained by the data for flavor changing neutral currents. However, top-charm quark mixing is not the case, so that a large off-diagonal element can be taken, which can contribute to generating baryon asymmetry of the universe. It turns out that CP violating phases of the off-diagonal element in the source term in the Boltzmann equation are eliminated by the rephasing. This result is somewhat different from previous works on electroweak baryogenesis by flavor off-diagonal Yukawa couplings. Instead, we find that the absolute value of the top-charm off-diagonal element enhances CP violating phases in the Higgs potential, by which sufficient amount of the baryon number can be generated to explain the observed baryon asymmetry of the universe. We find that such a scenario is viable under the current experimental data. The model can be tested by the current and future measurements of various flavor experiments like Kaon rare decays, in addition to high energy collider experiments as well as gravitational wave observations. Characteristic predictions of our model would be deviations in Kaon rare decays. Branching ratios of K+→π+νν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {K}^{+}\ o {\\pi}^{+}\ u \\overline{\ u} $$\\end{document} and KL→π0νν¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {K}_L\ o {\\pi}^0\ u \\overline{\ u} $$\\end{document} can deviate by the order of 10% and 1%, respectively, which may be tested at future Kaon experiments such as NA62 and KOTO step-2.

Electroweak baryogenesis in the three-loop neutrino mass model with dark matter

Baryon asymmetry of the Universe is evaluated in the model originally proposed in Phys. Rev. Lett. 102 (2009) 051805, where Majorana masses of neutrinos are generated via three-loop diagrams composed of additional scalar bosons including the dark matter candidate which is odd under an unbroken $Z_2$ symmetry. In order for the model to include multiple CP-violating phases, we do not impose the softly broken $Z_2$ symmetry imposed in the original model to avoid the flavor-changing neutral current at tree level. Instead, for simplicity, we assume the flavor alignment structure in the Yukawa interactions. We also simply assume the alignment structure in the Higgs potential so that the Higgs couplings coincide with those in the SM at tree level. Under these phenomenological simplifications, the model still contains multiple CP-violating phases. By using destructive interferences among them, it is compatible with the stringent constraint from the electric dipole moment measurements to generate the observed baryon asymmetry along with the scenario of electroweak baryogenesis. We show a benchmark scenario which can explain neutrino mass, dark matter and baryon asymmetry of the universe simultaneously and can satisfy all the other available experimental data. Some phenomenological predictions of the model are also discussed.

Asymmetric dark matter may not be light

It is often said that asymmetric dark matter is light compared to typical weakly interacting massive particles. Here we point out a simple scheme with a neutrino portal and $\mathcal{O}(60 \text{ GeV})$ asymmetric dark matter which may be ''added'' to any standard baryogenesis scenario. The dark sector contains a copy of the Standard Model gauge group, as well as (at least) one matter family, Higgs, and right-handed neutrino. After baryogenesis, some lepton asymmetry is transferred to the dark sector through the neutrino portal where dark sphalerons convert it into a dark baryon asymmetry. Dark hadrons form asymmetric dark matter and may be directly detected due to the vector portal. Surprisingly, even dark anti-neutrons may be directly detected if they have a sizeable electric dipole moment. The dark photons visibly decay at current and future experiments which probe complementary parameter space to dark matter direct detection searches. Exotic Higgs decays are excellent signals at future $e^+ e^-$ Higgs factories.

Higgs boson coupling as a probe of the sphaleron property

Sphaleron is a non-perturbative solution of electroweak gauge theories, which is crucially important for the scenario of electroweak baryogenesis. The sphaleron energy depends on details of the mechanism for the electroweak symmetry breaking. We find that in many of new physics models the deviation of the sphaleron energy from the prediction in the standard model is proportional to that of the triple Higgs boson coupling with opposite signs. This interesting relation would be useful to determine the sphaleron energy by measuring this couplings at future collider experiments.

Adiabatic electroweak baryogenesis driven by an axionlike particle

An axion-like particle (ALP) offers a new direction in electroweak baryogenesis because the periodic nature enables it to trigger a strong first-order phase transition insensitively to the decay constant $f$. For $f$ much above TeV, the ALP-induced electroweak phase transition is approximately described by adiabatic processes, distinguishing our scenario for electroweak baryogenesis from the conventional ones. We show that, coupled to the electroweak anomaly, the ALP can naturally realize spontaneous electroweak baryogenesis to solve the matter-antimatter asymmetry problem for $f$ in the range between about $10^5$ GeV and $10^7$ GeV. In such an ALP window, the $CP$ violation for baryogenesis is totally free from the experimental constraints, especially from the recently improved limit on the electron electric dipole moment. Future searches for ALPs could probe our scenario while revealing the connection between electroweak symmetry breaking and baryogenesis.

Primordial black holes and the origin of the matter-antimatter asymmetry.

We review here a new scenario of hot spot electroweak baryogenesis where the local energy released in the gravitational collapse to form primordial black holes (PBHs) at the quark-hadron (QCD) epoch drives over-the-barrier sphaleron transitions in a far from equilibrium environment with just the standard model CP violation. Baryons are efficiently produced in relativistic collisions around the black holes and soon redistribute to the rest of the universe, generating the observed matter-antimatter asymmetry well before primordial nucleosynthesis. Therefore, in this scenario there is a common origin of both the dark matter to baryon ratio and the photon to baryon ratio. Moreover, the sudden drop in radiation pressure of relativistic matter at H0/W±/Z0 decoupling, the QCD transition and e+e- annihilation enhances the probability of PBH formation, inducing a multi-modal broad mass distribution with characteristic peaks at 10-6, 1, 30 and 106 M⊙, rapidly falling at smaller and larger masses, which may explain the LIGO-Virgo black hole mergers as well as the OGLE-GAIA microlensing events, while constituting all of the cold dark matter today. We predict the future detection of binary black hole (BBH) mergers in LIGO with masses between 1 and 5 M⊙, as well as above 80 M⊙, with very large mass ratios. Next generation gravitational wave and microlensing experiments will be able to test this scenario thoroughly. This article is part of a discussion meeting issue 'Topological avatars of new physics'.

Revisiting electroweak phase transition with varying Yukawa coupling constants

We revisited the scenario of electroweak baryogenesis in the presence of large Yukawa couplings, in which it was found previously that a strongly first order electroweak phase transition can occur with the Higgs mass at its observed value of 125 GeV. Given the sensitivity of the running of the Higgs quartic coupling on the Yukawa coupling constants, we find that the addition of order one Yukawa couplings beyond the top quark drastically lowers the scale at which the Higgs potential becomes unstable. Specifically, even with only one additional order one Yukawa coupling, the scalar potential becomes unstable already at the TeV scale, assuming the Standard Model values for the Higgs sector parameters at the electroweak scale. Furthermore, by assuming the Standard Model values for the Higgs sector parameters at the TeV scale, the quartic coupling constant is driven to be larger than its Standard Model value at the electroweak scale. This in turn predicts a much lighter Higgs mass than the measured value of 125 GeV. In this scenario, the strength of the electroweak phase transition is also significantly weakened.

High scale electroweak phase transition: baryogenesis & symmetry non-restoration

We explore the possibility that the electroweak phase transition happens at a scale much higher than the electroweak scale today. In this context, high scale CP-violating sources for electroweak baryogenesis are not constrained by low-energy experiments. We propose a scenario of high-scale electroweak baryogenesis linked to flavour physics. This scenario allows for a period of enhanced Yukawa couplings during the evolution of the universe, which source time-dependent CP violation. The electroweak symmetry is never restored after the high-scale phase transition due to negative contributions to the Higgs thermal mass squared from a large number of additional electroweak-scale neutral scalars coupling to the Higgs. As a result, the washout of the baryon asymmetry is avoided.

Gravitational waves from the first order electroweak phase transition in the Z3 symmetric singlet scalar model

Among various scenarios of baryon asymmetry of the Universe, electroweak baryogenesis is directly connected with physics of the Higgs sector. We discuss spectra of gravitational waves which are originated by the strongly first order phase transition at the electroweak symmetry breaking, which is required for a successful scenario of electroweak baryogenesis. In the Z3 symmetric singlet scalar model, the significant gravitational waves are caused by the multi-step phase transition. We show that the model can be tested by measuring the characteristic spectra of the gravitational waves at future interferometers such as LISA and DECIGO.

Simulations of Cold Electroweak Baryogenesis: quench from portal coupling to new singlet field

We compute the baryon asymmetry generated from Cold Electroweak Baryogenesis, when a dynamical Beyond-the-Standard-Model scalar singlet field triggers the spinodal transition. Using a simple potential for this additional field, we match the speed of the quench to earlier simulations with a “by-hand” mass flip. We find that for the parameter subspace most similar to a by-hand transition, the final baryon asymmetry shows a similar dependence on quench time and is of the same magnitude. For more general parameter choices the Higgs-singlet dynamics can be very complicated, resulting in an enhancement of the final baryon asymmetry. Our results validate and generalise results of simulations in the literature and open up the Cold Electroweak Baryogenesis scenario to further model building.

Electroweak Phase Transitions in Einstein’s Static Universe

We suggest using Einstein’s static universe metric for the metastable state after reheating, instead of the Friedman-Robertson-Walker spacetime. In this case, strong static gravitational potential leads to the effective reduction of the Higgs vacuum expectation value, which is found to be compatible with the Standard Model first-order electroweak phase transition conditions. Gravity could also increase the CP-violating effects for particles that cross the new phase bubble walls and thus is able to lead to the successful electroweak baryogenesis scenario.

Synergy between measurements of gravitational waves and the triple-Higgs coupling in probing the first-order electroweak phase transition

Probing the Higgs potential and new physics behind the electroweak symmetry breaking is one of the most important issues of particle physics. In particular, nature of electroweak phase transition is essential for understanding physics at the early Universe, such that the strongly first order phase transition is required for a successful scenario of electroweak baryogenesis. The strongly first order phase transition is expected to be tested by precisely measuring the triple Higgs boson coupling at future colliders like the International Linear Collider. It can also be explored via the spectrum of stochastic gravitational waves to be measured at future space-based interferometers such as eLISA and DECIGO. We discuss complementarity of both the methods in testing the strongly first order phase transition of the electroweak symmetry in models with additional isospin singlet scalar fields with and without classical scale invariance. We find that they are synergetic in identifying specific models of electroweak symmetry breaking in more details.

Gravitational waves as a probe of extended scalar sectors with the first order electroweak phase transition

We discuss spectra of gravitational waves which are originated by the strongly first order phase transition at the electroweak symmetry breaking, which is required for a successful scenario of electroweak baryogenesis. Such spectra are numerically evaluated without high temperature expansion in a set of extended scalar sectors with additional N isospin-singlet fields as a concrete example of renormalizable theories. We find that the produced gravitational waves can be significant, so that they are detectable at future gravitational wave interferometers such as DECIGO and BBO. Furthermore, since the spectra strongly depend on N and the mass of the singlet fields, our results indicate that future detailed observation of gravitational waves can be in general a useful probe of extended scalar sectors with the first order phase transition.

Stop-catalyzed baryogenesis beyond the MSSM

Non-minimal supersymmetric models that predict a tree-level Higgs mass above the Minimal Supersymmetric Standard Model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. We also introduce a gauge-invariant analysis framework that may generalize to other scenarios in which interactions outside the gauge sector drive the electroweak phase transition.

Towards a scale free electroweak baryogenesis

We propose a new electroweak baryogenesis scenario in high-scale supersymmetric (SUSY) models. We consider a singlet extension of the minimal SUSY standard model introducing additional vectorlike multiplets. We show that the strongly first-order phase transition can occur at a high temperature comparable to the soft SUSY breaking scale. In addition, the proper amount of the baryon asymmetry of the Universe can be generated via the lepton number violating process in the vectorlike multiplet sector. The typical scale of our scenario, the soft SUSY breaking scale, can be any value. Thus our new electroweak baryogenesis scenario can be realized at arbitrary scales, and we call this scenario scale free electroweak baryogenesis. This soft SUSY breaking scale is determined by other requirements. If the soft SUSY breaking scale is $\mathcal{O}(10)\text{ }\text{ }\mathrm{TeV}$, our scenario is compatible with the observed mass of the Higgs boson and the constraints by electric dipole moment measurements and flavor experiments. Furthermore, the singlino can be a good candidate for dark matter.

Lower bound on the electroweak wall velocity from hydrodynamic instability

The subsonic expansion of bubbles in a strongly first-order electroweak phase transition is a convenient scenario for electroweak baryogenesis. For most extensions of the Standard Model, stationary subsonic solutions (i.e., deflagrations) exist for the propagation of phase transition fronts. However, deflagrations are known to be hydrodynamically unstable for wall velocities below a certain critical value. We calculate this critical velocity for several extensions of the Standard Model and compare with an estimation of the wall velocity. In general, we find a region in parameter space which gives stable deflagrations as well as favorable conditions for electroweak baryogenesis.

CP violation and electroweak baryogenesis in the Standard Model

One of the major unresolved problems in current physics is understanding the origin of the observed asymmetry between matter and antimatter in the Universe. It has become a common lore to claim that the Standard Model of particle physics cannot produce sufficient asymmetry to explain the observation. Our results suggest that this conclusion can be alleviated in the so-called cold electroweak baryogenesis scenario. On the Standard Model side, we continue the program initiated by Smit eight years ago; one derives the effective CP-violating action for the Standard Model bosons and uses the resulting effective theory in numerical simulations. We address a disagreement between two previous computations performed effectively at zero temperature, and demonstrate that it is very important to include temperature effects properly. Our conclusion is that the cold electroweak baryogenesis scenario within the Standard Model is tightly constrained, yet producing enough baryon asymmetry using just known physics still seems possible.

Electroweak phase transition in the reduced minimal 3-3-1 model

The electroweak phase transition is considered in the framework of the reduced minimal 3-3-1 model. The structure of the phase transition in this model is divided into two parts. The first part is the phase transition $\mathrm{SU}(3)\ensuremath{\rightarrow}\mathrm{SU}(2)$ at the TeV scale, and the second is $\mathrm{SU}(2)\ensuremath{\rightarrow}\mathrm{U}(1)$, which is like the standard model electroweak phase transition. When the mass of the neutral Higgs boson (${h}_{1}$) is taken to be equal to the LHC value, ${m}_{{h}_{1}}=125\text{ }\text{ }\mathrm{GeV}$, these phase transitions are first-order transitions; the mass of ${Z}_{2}$ is about 4.8 TeV, and we find the region of parameter space with the first-order phase transition at the ${v}_{{\ensuremath{\rho}}_{0}}=246\text{ }\text{ }\mathrm{GeV}$ scale, leading to an effective potential where the mass of the charged Higgs boson is in the range $3.258\text{ }\text{ }\mathrm{TeV}<{m}_{{h}_{++}}<19.549\text{ }\text{ }\mathrm{TeV}$. Therefore, with this approach new bosons are the triggers of the first-order electroweak phase transition, which provides significant implications for the viability of electroweak baryogenesis scenarios.

Electroweak phase transition, Higgs diphoton rate, and new heavy fermions

We show that weak scale vector-like fermions with order one couplings to the Higgs can lead to a novel mechanism for a strongly first-order electroweak phase transition (EWPhT), through their tendency to drive the Higgs quartic coupling negative. These same fermions could also enhance the loop-induced branching fraction of the Higgs into two photons, as suggested by the recent discovery of a ~125 GeV Higgs-like state at the CERN Large Hadron Collider (LHC). Our results suggest that measurements of the diphoton decay rate of the Higgs and its self coupling, at the LHC or perhaps at a future lepton collider, could probe the EWPhT in the early Universe, with significant implications for the viability of electroweak baryogenesis scenarios.