arXiv subjects

Carlo Ungarelli

Publications and source records attributed to Carlo Ungarelli.

12 recordsLinked to original sources

arXiv2008

The "Quantum Mousetrap": Entangled States and Gravitational Waves

We propose a "thought technique" for detecting Gravitational Waves using Einstein-Podolski-Rosen photon Entangled States. GWs decohere the entangled photon pairs, introduce a relative rotation and de-synchronize Alice and Bob's reference frames thus reducing the measured non-locality of correlated quanta described by Bell's inequalities. Gravitational Waves, distorting quantum encryption key statistics away from a pure white noise, act then as shadow eavesdroppers. The deviation from the intrinsic white-noise randomness of a Quantum Key Distribution process can reveal the presence of a gravitational wave by analyzing the emerging color distortions in the key. Photon entangled states provide the key advantage of revealing the polarization rotation introduced by GWs without the need of previously fixed reference frames

gr-qc↗

arXiv2005

Gravitational waves, inflation and the cosmic microwave background: towards testing the slow-roll paradigm

One of the fundamental and yet untested predictions of inflationary models is the generation of a very weak cosmic background of gravitational radiation. We investigate the sensitivity required for a space-based gravitational wave laser interferometer with peak sensitivity at $\sim 1$ Hz to observe such signal as a function of the model parameters and compare it with indirect limits that can be set with data from present and future cosmic microwave background missions. We concentrate on signals predicted by slow-roll single field inflationary models and instrumental configurations such as those proposed for the LISA follow-on mission: Big Bang Observer.

astro-ph↗

arXiv2003

A family of filters to search for frequency dependent gravitational wave stochastic backgrounds

We consider a three dimensional family of filters based on broken power law spectra to search for gravitational wave stochastic backgrounds in the data from Earth-based laser interferometers. We show that such templates produce the necessary fitting factor for a wide class of cosmological backgrounds and astrophysical foregrounds and that the total number of filters required to search for those signals in the data from first generation laser interferometers operating at the design sensitivity is fairly small

gr-qc↗

arXiv2003

Condensate cosmology -- dark energy from dark matter

Imagine a scenario in which the dark energy forms via the condensation of dark matter at some low redshift. The Compton wavelength therefore changes from small to very large at the transition, unlike quintessence or metamorphosis. We study CMB, large scale structure, supernova and radio galaxy constraints on condensation by performing a 4 parameter likelihood analysis over the Hubble constant and the three parameters associated with Q, the condensate field: Omega_Q, w_f and z_t (energy density and equation of state today, and redshift of transition). Condensation roughly interpolates between Lambda CDM (for large z_t) and sCDM (low z_t) and provides a slightly better fit to the data than Lambda CDM. We confirm that there is no degeneracy in the CMB between H and z_t and discuss the implications of late-time transitions for the Lyman-alpha forest. Finally we discuss the nonlinear phase of both condensation and metamorphosis, which is much more interesting than in standard quintessence models.

astro-ph↗

arXiv2003

Large-scale curvature and entropy perturbations for multiple interacting fluids

We present a gauge-invariant formalism to study the evolution of curvature perturbations in a Friedmann-Robertson-Walker universe filled by multiple interacting fluids. We resolve arbitrary perturbations into adiabatic and entropy components and derive their coupled evolution equations. We demonstrate that perturbations obeying a generalised adiabatic condition remain adiabatic in the large-scale limit, even when one includes energy transfer between fluids. As a specific application we study the recently proposed curvaton model, in which the curvaton decays into radiation. We use the coupled evolution equations to show how an initial isocurvature perturbation in the curvaton gives rise to an adiabatic curvature perturbation after the curvaton decays.

astro-ph↗

arXiv2002

Did the dark energy always have a large Compton wavelength?

Until now all well-studied dark energy models proposed have very large Compton wavelengths, $λ_c > 100 Mpc$ at all time and hence show no clustering on small scales. Evidence against this would disfavour both $Λ$CDM and quintessence. We show however, that large $λ_c$ is actually favoured by current CMB, LSS and SN1a data by comparing quintessence with a condensate scenario with the same background dynamics. The condensate scenario has a very small $λ_c$ before making a transition to negative pressure and large $λ_c$ and therefore exhibits a rich CMB phenomenology which roughly interpolates between $Λ$CDM and flat CDM models.

astro-ph↗

arXiv2002

The primordial density perturbation in the curvaton scenario

We analyse the primordial density perturbation when it is generated by a `curvaton' field different from the inflaton. In some cases this perturbation may have large isocurvature components, fully correlated or anti-correlated with the adiabatic component. It may also have a significant non-Gaussian component. All of these effects are calculated in a form which will enable direct comparison with current and forthcoming observational data.

astro-ph↗

arXiv2002

A late-time transition in the cosmic dark energy?

We study constraints from the latest CMB, large scale structure (2dF, Abell/ACO, PSCz) and SN1a data on dark energy models with a sharp transition in their equation of state, w(z). Such a transition is motivated by models like vacuum metamorphosis where non-perturbative quantum effects are important at late times. We allow the transition to occur at a specific redshift, z_t, to a final negative pressure -1 < w_f < -1/3. We find that the CMB and supernovae data, in particular, prefer a late-time transition due to the associated delay in cosmic acceleration. The best fits (with 1 sigma errors) to all the data are z_t = 2.0^{+2.2}_{-0.76}, Ω_Q = 0.73^{+0.02}_{-0.04} and w_f = -1^{+0.2}.

astro-ph↗

arXiv2001

Magnetized gravitational waves

We investigate the influence of cosmic magnetic fields on gravitational wave perturbations, and find exact solutions on large scales. We show that a large-scale magnetic field can generate large-scale non-decaying gravitational waves. In the general case where gravitational waves are generated by other mechanisms, a large-scale magnetic field introduces a new decaying tensor mode and modifies the non-decaying mode. The direct effect of the magnetic field is to damp the gravitational waves, while an indirect magneto-curvature effect can either damp or boost the waves. A magnetic field also leads to a breaking of statistical isotropy, and the magnetic imprint on the tensor spectrum in principle provides a means of detecting a primordial field.

astro-ph↗

arXiv2000

Detection of gravitational waves with quantum encryption technology

We propose a new technique for detecting gravitational waves using Quantum Entangled STate (QUEST) technology. Gravitational waves reduce the non-locality of correlated quanta controlled by Bell's inequalities, distorting quantum encryption key statistics away from a pure white noise. Gravitational waves therefore act as shadow eavesdroppers. The resulting colour distortions can, at least in principle, be separated from noise and can differentiate both deterministic and stochastic sources.

gr-qc↗

arXiv1999

Quantum gravity corrections to the Schwarzschild mass

Vacuum spherically symmetric Einstein gravity in $N\ge 4$ dimensions can be cast in a two-dimensional conformal nonlinear sigma model form by first integrating on the $(N-2)$-dimensional (hyper)sphere and then performing a canonical transformation. The conformal sigma model is described by two fields which are related to the Arnowitt-Deser-Misner mass and to the radius of the $(N-2)$-dimensional (hyper)sphere, respectively. By quantizing perturbatively the theory we estimate the quantum corrections to the ADM mass of a black hole.

hep-th↗

arXiv1999

Canonical and path integral quantisation of string cosmology models

We discuss the quantisation of a class of string cosmology models that are characterized by scale factor duality invariance. We compute the amplitudes for the full set of classically allowed and forbidden transitions by applying the reduce phase space and the path integral methods. We show that these approaches are consistent. The path integral calculation clarifies the meaning of the instanton-like behaviour of the transition amplitudes that has been first pointed out in previous investigations.

gr-qc↗