Late Time Phase Transition Research Articles

Axion–neutrino couplings, late-time phase transitions and the far infrared physics

The far infrared physics is a fascinating topic for theoretical physics, since the foundation of quantum field theory and neutrinos seem to be strongly related with the far infrared physics of our Universe. In this work we shall explore the possibility of a late-time thermal phase transition caused by the axion–neutrino interactions. The axion is assumed to be the misalignment axion which is coupled primordially to a chiral symmetric neutrino. The chiral symmetry is supposed to be broken either spontaneously or explicitly, and two distinct phenomenological models of axion–neutrinos are constructed. The axion behaves as cold dark matter during all its evolution eras, however if we assume that the axion and the neutrino fields interact coherently in a classical way as fields, or as ensembles, then we consider thermal effects in the axion sector, due to the values of operators ϕ for the axion and ν̄ν due to the neutrinos. The thermal equilibrium between the two has no effect to the axion effective potential for a wide temperature range. As we show, contrary to the existing literature, the axion never becomes destabilized due to the finite temperature effects, however if axion-Higgs higher order non-renormalizable operators are present in the Lagrangian, the axion potential is destabilized in the temperature range T∼0.1MeV down to T∼0.01eV and a first order phase transition takes place. The initial axion vacuum decays to the energetically more favorable axion vacuum, and the latter decays to the Higgs vacuum which is more preferable. This late-time phase transition might take place in the redshift range z∼385−37 and thus it may cause density fluctuations in the post-recombination era. This might be the source of large scale matter structure at high redshifts z≥9. Following the literature, we qualitatively discuss the implications of such a late-time phase transition at the astrophysical and cosmological level.

Scalar Co-SIMP dark matter: models and sensitivities

In this work, we present UV completions of the recently proposed number-changing Co-SIMP freeze-out mechanism. In contrast to the standard cannibalistic-type dark matter picture that occurs entirely in the dark sector, the 3 → 2 process setting the relic abundance in this case requires one Standard Model particle in the initial and final states. This prevents the dark sector from overheating and leads to rich experimental signatures. We generate the Co-SIMP interaction with a dark sector consisting of two scalars, with the mediator coupling to either nucleons or electrons. In either case, the dark matter candidate is naturally light : nucleophilic interactions favor the sub-GeV mass range and leptophilic interactions favor the sub-MeV mass range. Viable thermal models in these lighter mass regimes are particularly intriguing to study at this time, as new developments in low-threshold detector technologies will begin probing this region of parameter space. While particles in the sub-MeV regime can potentially impact light element formation and CMB decoupling, we show that a late-time phase transition opens up large fractions of parameter space. These thermal light dark matter models can instead be tested with dedicated experiments. We discuss the viable parameter space in each scenario in light of the current sensitivity of various experimental probes and projected future reach.

Probing sterile neutrino dark matter in the PTOLEMY-like experiment

We study the prospect to detect the cosmic background of sterile neutrinos in the tritium β-decay, such as the PTOLEMY-like experiments. The sterile neutrino with mass between 1 eV–10 keV may contribute to the local density as warm or cold dark matter component. In this study, we investigate the possibility for searching them in the models with different production in the early Universe, without assuming sterile neutrino as full dark matter component.In these models, especially with low-reheating temperature and late-time phase transition, the capture rate per year can be greatly enhanced to be \U0001d4aa(10) around the mass range 10–100 eV without violating other astrophysical and cosmological observations.

The cosmic web crystal: Ising model for large-scale structures

If Dark Matter halos possess the gravitational equivalent of an intrinsic magnetic spin, a formal analogy exists between the low redshift behavior of the Cosmic Web in a flat FLRW background and a crystal of spins submerged in a thermal reservoir with temperature [Formula: see text]. We argue that, within the use of the Bianchi type IX geometry to describe the gravitational collapse of matter inhomogeneities, the spins are nothing but the heritage of its underlying SU(2) symmetry. Therefore, just like electrons in quantum mechanics, these structures may have spin independently from their orbital angular momentum. We explore the phenomenological implications on cosmological scales of a possible late-time phase transition of the Cosmic Web towards (the gravitational equivalent of) a ferromagnetic state, described qualitatively using the Ising model in the mean field approximation.

Runaway relaxion from finite density

Finite density effects can destabilize the metastable vacua in relaxion models. Focusing on stars as nucleation seeds, we derive the conditions that lead to the formation and runaway of a relaxion bubble of a lower energy minimum than in vacuum. The resulting late-time phase transition in the universe allows us to set new constraints on the parameter space of relaxion models. We also find that similar instabilities can be triggered by the large electromagnetic fields around rotating neutron stars.

QCD axion dark matter from a late time phase transition

We investigate the possibility that the Peccei-Quinn phase transition occurs at a temperature far below the symmetry breaking scale. Low phase transition temperatures are typical in supersymmetric theories, where symmetry breaking fields have small masses. We find that QCD axions are abundantly produced just after the phase transition. The observed dark matter abundance is reproduced even if the decay constant is much lower than 1011 GeV. The produced axions tend to be warm. For some range of the decay constant, the effect of the predicted warmness on structure formation can be confirmed by future observations of 21 cm lines. A portion of parameter space requires a mixing between the Peccei-Quinn symmetry breaking field and the Standard Model Higgs, and predicts an observable rate of rare Kaon decays.

Models of baryogenesis via spontaneous Lorentz violation

In the presence of background fields that spontaneously violate Lorentz invariance, a matter-antimatter asymmetry can be generated even in thermal equilibrium. In this paper we systematically investigate models of this type, showing that either high-energy or electroweak versions of baryogenesis are possible, depending on the dynamics of the Lorentz-violating fields. In addition to the previously-studied models of spontaneous baryogenesis and quintessential baryogenesis, we identify two scenarios of interest: baryogenesis from a pseudo-Nambu-Goldstone boson with weak-scale mass and intermediate-scale baryon-number violation, and sphaleron-induced baryogenesis driven by a constant-magnitude vector with a late-time phase transition.

Light sterile neutrinos in the supersymmetricU(1)′models and axion models

We propose the minimal supersymmetric sterile neutrino model (MSSNM) where the sterile neutrino masses are about 1 eV, while the active neutrino masses and the mixings among the active and sterile neutrinos are generated during late time phase transition. All the current experimental neutrino data include the LSND can be explained simultaneously, and the constraints on the sterile neutrinos from the big bang nucleosynthesis and large scale structure can be evaded. To realize the MSSNM naturally, we consider the supersymmetric intermediate-scale $U(1{)}^{\ensuremath{'}}$ model, the low-energy $U(1{)}^{\ensuremath{'}}$ model with a secluded $U(1{)}^{\ensuremath{'}}$-breaking sector, and the DFSZ and KSVZ axion models. In these models, the $\ensuremath{\mu}$ problem can be solved elegantly, and the 1 eV sterile neutrino masses can be generated via high-dimensional operators. For the low-energy $U(1{)}^{\ensuremath{'}}$ model with a secluded $U(1{)}^{\ensuremath{'}}$-breaking sector, we also present a scenario in which the masses and mixings for the active and sterile neutrinos are all generated during late time phase transition.

Avoiding BBN constraints on mirror models for sterile neutrinos

We point out that in models that explain the Los Alamos neutrino scintillation detector result for neutrino oscillations using the mirror neutrinos, the big bang nucleosynthesis constraints on the number of sterile neutrinos can be avoided by using the late time phase transition that only helps to mix the active and the sterile neutrinos. The main idea is to have a standard model singlet scalar field that mixes the visible and the mirror sector and has a low vacuum expectation value ($\ensuremath{\sim}100\text{ }\text{ }\mathrm{k}\mathrm{e}\mathrm{V}$) so that the active and sterile neutrinos remain unmixed at the big bang nucleosynthesis epoch. The model predicts different effective number of neutrinos at the epoch of recombination compared to the standard model and is therefore testable in experiments that measure cosmic microwave spectrum with a higher precision.

Late time phase transition as dark energy

We show that the dark energy field can naturally be described by the scalar condensates of a non-abelian gauge group. This gauge group is unified with the standard model gauge groups and it has a late time phase transition. The small phase transition explains why the positive acceleration of the universe is occurring only recently. The model hasno free parameters but for the matter content of the group. The initial energy density at the unification scale and at the condensation scale are fixed by the number of degrees of freedom of the gauge group.

Implications to the CMB from a model independent evolution ofwand a late time phase transition

We present model independent determination of the CMB from any kind of fluid that has an equation of state taking four different values. The first region has $w=1/3$, the second $w=1$, the third $w=-1$ while the last one has $-1<w=cte<-2/3$. This kind of dynamical $w$ contains as a limit the cosmological constant and tracker models. We derive the model independent evolution of $\wp$, for scalar fields, and we see that it remains most of the time in either of its three extremal values given by $\wp=1,-1,w_{tr}$. This varying $w$ is the generic behavior of scalar fields, quintessence, and we determine the size of the different regions by solving the dynamical equations in a model independent way. The dynamical $w$ models have a better fit to CMB data then the cosmological constant and the tracker models. We determine the effect of having the first two regions $w=1/3,1$ and depending on the size of these periods they can be observed in the CMB. In general, the CMB spectrum sets a lower limit to $\D N_T$ and to the phase transition scale $\Lm_c$. For smaller $\D N_T$ the CMB peaks are moved to the right of the spectrum and the hight increases considerably. For $\Ompi=0.1$ the CMB sets a lower limit to the phase transition scale $\Lm_c\geq 0.2 eV$.

Late-time phase transition and the galactic halo as a Bose liquid. II. The effect of visible matter.

In the previous work, we investigated the rotation curves of galaxies assuming that the dark matter consists of ultra light boson appearing in $'$late time phase transition' theory. Generalizing this work, we consider the effect of visible matter and classify the types of rotation curves as we vary the fraction of the mass and extention of visible matter. We show that visible matter, in galaxies with flat rotation curves, has mass fraction $ 2\% \sim 10\% $ and it is confined within the distance fraction $ 10\% \sim 20\%$.

Late-time phase transition and the galactic halo as a Bose liquid.

We consider the ultralight pseudo Nambu-Goldstone boson appearing in the late-time cosmological phase tansition theories as a major dark matter candidate. Since it is almost massless, its nature is more wavelike than particlelike. We study quantum mechanically how they from a galactic halo. Three predictions are made: (i) the mass profile \ensuremath{\rho}\ensuremath{\sim}${\mathit{r}}^{\mathrm{\ensuremath{-}}1.6}$; (ii) there are ripplelike fine structures in the rotation curve; (iii) the rotation velocity multiplied by the ripple's wavelength is galaxy independent.

The phenomenological status of late time phase transition models after cosmic background radiation anisotropy measurements

Some relatively model-independent results for structure formation via late time phase transitions (LTPT) are discussed. In particular, generic LTPT power spectra are presented. The implication of the recent Cosmic Background Explorer (COBE) detection of the cosmic background radiation (CBR) anisotropy at large angular scales (greater than or approximately equal to 7 deg) and the tight upper limits from small angular scales (approximately 1 deg) to LTPT models are discussed. Special attention is focused on the observational constraints and possible non-Gaussian signatures of CBR temperature anisotropies from LTPT and other non-Gaussian models. It is shown that while LTPT have been seriously constrained by the recent data, viable models do remain which provide more power on the 100-200 Mpc scales than do more traditional primordial Gaussian density fluctuation models. Tests for such models are presented, including possible anisotropies on angular scales less than 8 min.

Cosmological limits on deviations from phi2 potentials in oscillating scalar cold dark matter models.

We consider the consequences for oscillating scalar cold dark matter models of a scalar field phi which oscillates in a potential which deviates slightly from a phi2 potential. We consider a correction to the phi2 potential of the form Kphi2ln(phi2) + lambda(phi)phi4. Upper bounds on \K and \lambda)phi) are obtained as a function of the phi mass by requiring that the effects of the pressure introduced by the correction to the potential do not disrupt the conventional cold dark matter scenario for structure formation. The results are applied to some cosmological models of recent interest. In particular, it is shown that a scalar identified with the pseudo Goldstone boson of a U(1) symmetry explicitly broken by neutrino masses (suggested iri connection with late-time phase transitions) is inconsistent with the MSW solution of the solar neutrino problem if it is to account for dark matter. In addition it is shown that a cold dark matter model in which the Compton wavelength of a very light scalar particle accounts for the large-scale structure of the Universe is also ruled out by the effects of pressure on structure formation.

Domain walls, percolation theory, and Abell clusters.

We consider theories with late-time phase transitions that lead to the formation of energetically soft domain wall effects. These transitions occur in the vacuum state of a weakly coupled scalar field which is not in thermal equilibrium. The spatial properties and distribution of these domain walls are computed using percolation theory. Assuming spherical collapse of matter, the percolation results are used to accurately predict the richness distribution of Abell clusters.

Domain wall formation in the post-inflationary universe

We consider the evolution of the probability distribution P(χ, χ, t) , associated with an inhomogenous light scalar field χ in the Robertson-Walker Universe, where the inhomogeneties are produced by quantum fluctuations during an earlier inflationary epoch. For a specific choice of scalar potential which occurs in models of so-called late-time phase transitions in which domain walls are produced, P is shown to evolve from a gaussian to a non-gaussian distribution. The structure of the latter justifies the recent use of three-dimensional percolation theory to describe the initial distribution of domain walls in these models.

Non-Abelian soft boson phase transitions and large-scale structure.

A new class of models with Pseudo-Nambu-Goldstone bosons (PNGB`s) is constructed using a non-Abelian symmetry in the right handed Majorana neutrino sector of see-saw neutrino mass models. The phase structure of these models is examined both at zero and non-zero temperatures, with particular emphasis on their phase transition characteristics. We find that the vacuum manifold of these models exhibits a rich structure in terms of possible topological defects, and we argue that these models may have applications to late time phase transition theories of structure formation.

Late-time cosmological phase transitions: Particle-physics models and cosmic evolution.

We describe a natural particle-physics basis for late-time phase transitions in the Universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultralight pseudo Nambu-Goldstone boson with an astronomically large (\ensuremath{\sim}kpc-Mpc) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultralight bosons may also provide unclustered dark matter in a spatially flat universe, ${\ensuremath{\Omega}}_{\ensuremath{\varphi}}\ensuremath{\simeq}1$.

Domain-wall formation in late-time phase transitions.

We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building.