arXiv subjects

Mattia Dubbini

Publications and source records attributed to Mattia Dubbini.

5 recordsLinked to original sources

arXiv2026

Impact of spectator fields and non-minimal couplings in spontaneous baryogenesis

We investigate the model of spontaneous baryogenesis, considering two extensions to the background paradigm. Firstly, we introduce a non-minimal coupling between gravity and the inflaton, increasing the effective mass squared of the latter. In this way, the inflaton decays more likely into fermion-antifermion pairs during reheating, through baryon-number violating processes. Accordingly, we obtain an overall baryon asymmetry consistent with cosmological observations. Then, we consider a complex scalar spectator field interacting with the inflaton through a biquadratic coupling and non-minimally with gravity, and analyze the impact in terms of baryon asymmetry production. In this scenario too, the background model results significantly enhanced, but the predicted baryon-to-entropy ratio remains smaller than the experimental data.

hep-ph↗

arXiv2026

Entanglement generation from gravitationally produced massless vector particles during inflation

We study the gravitational production of spectator massless vector particles in a single-field inflationary scenario, and the related entanglement generation across the Hubble horizon. Accordingly, we consider a quasi-de Sitter background evolution, with additional metric inhomogeneities induced by the inflaton quantum fluctuations. Afterwards, we compute the corresponding production amplitude and show that it depends only on the transverse polarizations, appearing \emph{de facto} gauge-invariant, consistently with our interpretation of the vector field as the electromagnetic one. We notice that particle wavelengths turn out to be small compared to the Hubble radius, thus favoring sub-Hubble production relative to super-Hubble one. In particular, highly energetic vector particles are preferentially produced and we show that polarization effects provide a significant contribution to this behavior. Moreover, the production of nearly collinear particle pairs appears as the most probable configuration, due to the background conformal invariance of the theory and the plane-wave (massless particle-like) nature of the metric perturbation. We thus specialize our treatment to super-Hubble scales, confirming their subdominant contribution to the number density of produced particles, albeit setting a corresponding lower bound on the reheating temperature. In this scheme, we explore superhorizon entanglement between sub- and super-Hubble field modes, computing the corresponding von Neumann entropy and discussing the effects of horizon crossing on the generation of primordial entanglement.

gr-qc↗

arXiv2025

Vector-field spontaneous baryogenesis with Lorentz invariance violation

We extend spontaneous baryogenesis by considering the spontaneous breaking of $U(1)_B$ through a complex vector field. This field interacts with baryons and leptons via a vector-current coupling and, by construction, acquires a nonzero vacuum expectation value. Accordingly, the theory also exhibits a spontaneous violation of Lorentz invariance, effectively realizing a Bumblebee model. In this picture, the pseudo-Nambu-Goldstone boson arising from spontaneous breaking of the $U(1)_B$ global symmetry is the global phase of the Bumblebee vector and, in the broken phase, it results minimally coupled with the baryonic current, guaranteeing the violation of the baryon number. Consequently, we assume that the pseudo-Nambu-Goldstone, arising from spontaneous breaking of $U(1)_B$, plays the role of the inflaton, leading to baryogenesis across the entire inflationary stage, up to when the inflaton decays into baryon-antilepton and antibaryon-lepton pairs through a CP-violating interaction that also violates the Lorentz symmetry. Afterwards, we address the issue of flavor oscillations among baryon and lepton fields, including the oscillation probability in the calculation of the baryon asymmetry. Remarkably, our framework predicts a non-null mixing factor even for massless fermions. This mixing acts on the spatial momenta rather than on the masses of the produced fermions, allowing larger values of the coupling constant even guaranteeing the production of light fermions. The net baryon asymmetry results accordingly modified, and may also reproduce the experimental data for allowed values of the coupling constant.

hep-ph↗

arXiv2025

Impact of a complex scalar spectator field on baryon asymmetry within spontaneous baryogenesis

We extend the framework of spontaneous baryogenesis by investigating the generation of baryon asymmetry when the inflaton, $\theta$, is minimally coupled with a complex spectator scalar field $\phi$, as $\theta^2|\phi|^2$. To do so, we also consider $\phi$ non-minimally coupled with the Ricci scalar curvature $R$ through a Yukawa-like interaction. We do not consider further interactions of the spectator field with the fermions of the Standard Model, considering it \emph{de facto} as a dark scalar field. In evaluating the violation of the baryon-number conservation during the reheating epoch, in a perfectly homogeneous and isotropic universe, we follow a semiclassical approach, where $\theta$, $\phi$ and gravity are considered as classical fields, whereas the fermions are quantized. We solve the equations of motion for the inflaton and spectator fields, respectively at first and zero-order in perturbation theory, neglecting at first stage the expansion of the universe. Afterwards, we quantify how the spectator field modifies the inflationary dynamics and thus find the baryon asymmetry produced via the inflaton decays into fermion-antifermion pairs by computing the corresponding decay amplitudes. We therefore obtain small first order correction to standard spontaneous baryogenesis and finally discuss the mass-mixing between fermions. Accordingly, the effects of considering the universe expansion are accounted, showing when the coupling between $\phi$ and $R$ becomes noticeable in altering the overall baryon asymmetry.

gr-qc↗

arXiv2025

Consequences of non-minimal coupling for mass mixing in spontaneous baryogenesis

We investigate the impact of a non-minimal Yukawa-like coupling between curvature and inflaton field within the \emph{spontaneous baryogenesis} background. We demonstrate that this coupling leads to a significant enhancement in particle production, even for small values of the coupling constant $\xi$. Assuming a perfectly homogeneous and isotropic universe during the reheating phase, we study the inflaton decay into fermion-antifermion pairs by means of a semiclassical approach, treating fermions as quantized fields and considering the inflaton and the Ricci scalar as classical quantities. We adopt the simplest approach in which the inflaton is minimally coupled to baryons, and non-minimally with gravity. In particular, we solve the equations of motion for the inflaton to first order in perturbation theory, with $\xi$ serving as perturbative parameter. Afterwards, we compute the difference in the number densities of baryons and antibaryons produced through the inflaton decay into fermion-antifermion pairs. We show that the non-minimal coupling term \emph{de facto} increases inflaton mass, letting fermion-antifermion decays be more probable, and thus enhancing the overall baryogenesis process. As a further outcome, we find that the non-minimal Yukawa coupling also leads to a renormalization of the inflaton mass and weakly influences the bounds over the gravitational constant. Finally, since the fermionic fields appear not to be mass eigenstates, we specialize the mass-mixing between them only. To this end, we thus include the effects of mass-mixing and cosmic expansion into our calculations. Physical consequences of baryon production are therefore explored.

gr-qc↗