arXiv subjects

Tommaso Mengoni

Publications and source records attributed to Tommaso Mengoni.

7 recordsLinked to original sources

arXiv2026

Continuous Bogoliubov formalism for gravitational-wave generation in a unified dark sector warm inflation

In this work, we review gravitational-wave generation in a two-scalar-field cosmological model. The framework relies on a two-field scenario in which warm inflation is unified with the dark sector within a single theoretical description. It has recently been shown that this setup leads to a gravitational-wave spectrum potentially detectable by future experiments. Here we also demonstrate that the resulting spectrum is largely independent of the $\phi$ field initial condition, thereby extending previous findings.

gr-qc↗

arXiv2026

Inflationary magnetogenesis from non-minimal coupling in large- and small-field potentials

We investigate inflationary magnetogenesis in a scenario where conformal invariance of electromagnetism is broken through a \emph{non-minimal Yukawa-like coupling between the inflaton and the Ricci scalar}. We account for electromagnetic backreaction and the Schwinger effect, analyzing both standard single-field inflation and a generalized K-essence framework, \emph{dubbed quasi-quintessence}. We consider inflationary potentials compatible with Planck satellite constraints, including Starobinsky and $\alpha$-attractor models for large fields, as well as hilltop scenarios for small fields. Moreover, we explore very different functional electromagnetic couplings, introducing a novel ansatz modeled for small-fields. We show that the non-minimal coupling plays a central role in controlling the dynamics, \emph{acting as a timing parameter that regulates the onset of electric backreaction and the Schwinger regime}. This leads to a deep modification of the magnetogenesis process. Indeed, the amplitude of the generated magnetic fields can be enhanced by several orders of magnitude with respect to the minimally coupled case, reaching present-day values up to $B_0 \sim 10^{-13}\,\mathrm{G}$ in large-field scenarios, \emph{which appear as the only ones compatible with observational bounds}. Conversely, small-field models yield negligible magnetic amplitudes and appear non-predictive within our non-minimal framework.

astro-ph.CO↗

arXiv2026

Gravitational waves from warm inflation in the weak dissipative regime

Previous work on the gravitational-wave background generated in a two-scalar-field cosmological model, in which warm inflation and the dark sector are unified within a single framework, has shown that the resulting spectrum could be potentially detectable by planned next-generation gravitational-wave observatories. In this work, we extend this analysis to the weak dissipation regime of warm inflation, highlighting how the features of the inflationary scenario play a crucial role in the production of gravitational waves. The full gravitational-wave energy spectrum is calculated using the formalism of continuous Bogoliubov coefficients. By comparing our results with those obtained in the strong dissipation regime and with the sensitivity curves of future detectors, we find that the weak dissipation regime improves the prospects for observational detection.

gr-qc↗

arXiv2025

Constraints on Chiral-Quintom dark energy after DESI DR2 and impact on unifying dark energy with inflation

The recent data release DR2 from the Dark Energy Spectroscopic Instrument (DESI) has reinforced compelling evidence supporting the dynamical nature of dark energy. In this respect, we here explore a two-scalar field cosmological model, dubbed Chiral-Quintom paradigm, that allows for a unified description of early- and late-time cosmic accelerations, namely inflation and dark energy, respectively. Moreover, we show that it provides a mechanism to cross the phantom divide without instabilities. To do so, we first focus on scenarios where the scalar fields evolve under an exponential potential, leading to distinct cosmological behaviors, including tracking solutions and slow-roll or hyperbolic inflation. Afterwards, by considering a nonlinear potential and a mixing in the kinetic sector, we show that the model can also describe the matter-dominated era, offering a potential unification of the dark sector. Accordingly, we place bounds on this double-field paradigm by employing recent low-redshift observational data, including supernovae from the Pantheon+ and Union3.0 compilations, observational Hubble parameter measurements, and baryon acoustic oscillation data from the latest DESI release. By means of the Akaike information criterion, the standard $\Lambda$CDM scenario and the $w_0w_a$CDM model are thus compared with the Chiral-Quintom approach, showing that, in principle, multiple-field dynamics does not seem to be ruled out, ultimately providing a flexible framework for describing late-time dynamics.

astro-ph.CO↗

arXiv2025

Gravitational waves from two scalar fields unifying the dark sector with inflation

We investigate the gravitational-wave background predicted by a two-scalar-field cosmological model that aims to unify primordial inflation with the dark sector, namely late-time dark energy and dark matter, in a single and self-consistent theoretical framework. The model is constructed from an action inspired by several extensions of general relativity and string-inspired scenarios and features a non-minimal interaction between the two scalar fields, while both remain minimally coupled to gravity. In this context, we derive the gravitational-wave energy spectrum over wavelengths ranging from today's Hubble horizon to those at the end of inflation. We employ the continuous Bogoliubov coefficient formalism, originally introduced to describe particle creation in an expanding Universe, in analogy to the well-established mechanism of gravitational particle production and, in particular, generalized to gravitons. Using this method, which enables an accurate description of graviton creation across all cosmological epochs, we find that inflation provides the dominant gravitational-wave contribution, while subdominant features arise at the inflation-radiation, radiation-matter, and matter-dark energy transitions, i.e., epochs naturally encoded inside our scalar field picture. The resulting energy density spectrum is thus compared with the sensitivity curves of the planned next-generation ground- and space-based gravitational-wave observatories. The comparison identifies frequency bands where the predicted signal could be probed, providing those windows associated with potentially detectable signals, bounded by our analyses. Consequences of our recipe are thus compared with numerical outcomes and the corresponding physical properties discussed in detail.

gr-qc↗

arXiv2024

Comparing geometric and gravitational particle production in Jordan and Einstein frames

We explore cosmological particle production associated with inflationary fluctuations by comparing gravitational and geometric mechanisms, within a non-minimal Yukawa-like coupling between a inflaton and spacetime curvature. We show under which circumstances the number of geometric particles is comparable to the purely gravitational contribution by introducing the S-matrix formalism and approximating the inflationary potentials through power series. Despite the geometric production is a second-order effect, we show that it cannot be neglected \emph{a priori}, emphasizing that throughout inflation we do expect geometric particles to form as well as in the reheating phase. This result is investigated in both the Jordan and Einstein frames, selecting inflationary potentials supported by the Planck Satellite outcomes, \textit{i.e.}, the Starobinsky, hilltop, $\alpha$-attractor, and natural inflationary paradigms. We notice that, for large field approaches, the only feasible coupling may occur in case of extremely small field-curvature coupling constants, while the small field frameworks, namely the hilltop and $\alpha$-attractor models with quartic behavior, are essentially ruled out since they do not appear dynamically viable. We then point out that, while dynamically there exists a net equivalence between the Jordan and Einstein frames, the number of particles appears quite different passing from a representation to another one, thus pointing out the existence of a possible \emph{quantum frame issue}. In summary, while the classical inflationary dynamics is equivalently described in the Jordan and Einstein frames, a viable physical description of particle production valid in both the frames may be hindered by the absence of a complete quantum gravity. The latter could therefore be seen as missing puzzle to address the longstanding challenge of consistently passing between the two frames.

gr-qc↗

arXiv2023

Quasi-quintessence inflation with non-minimal coupling to curvature in the Jordan and Einstein frames

We here explore a specific class of scalar field, dubbed quasi-quintessence which exhibits characteristics akin to ordinary matter. Specifically, we investigate under which conditions this fluid can mitigate the classical cosmological constant problem. We remark that, assuming a phase transition, it is possible to predict inflationary dynamics within the metastable phase triggered by the symmetry breaking mechanism. During this phase, we study inflationary models incorporating this cancellation mechanism for vacuum energy within the context of quasi-quintessence. There, we introduce four novel potentials, categorized into two main groups, \emph{i.e.}, the Starobinsky-like and symmetry breaking paradigms. Afterwards, we consider two distinct cases, the first without coupling with the curvature, while the second exhibiting a Yukawa-like interacting term. Hence, we compute the inflationary dynamics within both the Jordan and Einstein frames and discuss the objective to unify old with chaotic inflation into a single scheme. We therefore find the tensor-to-scalar ratio and the spectral terms and conclude that the most suited approach involves the Starobinsky-like class of solution. Indeed, our findings show that small field inflationary scenarios appear disfavored and propose \emph{de facto} a novel technique to reobtain the Starobinsky potential without passing through generalizations of Einstein's gravity. Last but not least, we conjecture that vacuum energy may be converted into particles by virtue of the geometric interacting term and speculate about the physics associated with the Jordan and Einstein frames.

gr-qc↗