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Gaetano Lambiase

Publications and source records attributed to Gaetano Lambiase.

At least 55 records · Page 3Linked to original sources

Spacetime-curvature induced uncertainty principle: linking the large-structure global effects to the local black hole physics

This paper links the advanced formulation of the Generalized Uncertainty Principle, termed the Asymptotic Generalized Extended Uncertainty Principle (AGEUP), to the corpuscular framework to derive the AGEUP-inspired black hole metric. The former incorporates spacetime curvature effects to explore black hole dynamics under quantum gravitational corrections, while the latter is a view that black holes are Bose-Einstein condensates of weakly interacting gravitons. In a particular case, the phenomenological union between the AGEUP with cosmological constant $Λ$ to the corpuscular framework enabled a black hole metric that has a scaled mass, which depends on $Λ$ and the Planck length $l_{\rm Pl}$. Interesting implications occur, such as the maximum limit for mass $M$ where $Λ$ ceases to influence the black hole. Another is the derived value of the modulation factor of the EUP term, $α$, if the large-scale fundamental length is defined solely as the cosmological horizon. Additional analyses were done through the shadow and deflection angle phenomena, deriving constraints on the quantum gravity modulation parameter $β$. Constraints from the Event Horizon Telescope (EHT) and Very Long Baseline Interferometry (VLBI) are discussed as avenues for verifying AGEUP-related deviations in black hole shadow radius and deflection angles, offering potential observational evidence of quantum gravitational effects at astrophysical scales. The findings suggest that AGEUP could be instrumental in providing hints on the quantum gravity nature of black holes, particularly in high-energy astrophysical contexts. By linking local black hole physics with large-scale curvature effects, AGEUP paves the way for further research at the intersection of quantum gravity and cosmology, with implications for observational astrophysics and the fundamental structure of spacetime.

gr-qc↗

Non-locality in Quadrupolar Gravitational Radiation

General Relativity suffers for two main problems which have not yet been overcome: it predicts spacetime singularities and cannot be formulated as a perturbative renormalizable theory. In particular, many attempts have been made for avoiding singularities, such as considering higher order or infinite derivative theories. The price to pay in both cases is to give up locality and therefore they are known altogether as non-local theories of gravity. In this paper, we investigate how to recognize the presence of non-local effects by exploiting the power emitted by gravitational waves in a binary system in presence of non-local corrections as $R\Box^{-1}R$ to the Hilbert-Einstein action. After solving the field equations in terms of the source stress-energy tensor $T_{μν}$ and obtaining the gravitational wave stress-energy pseudo-tensor, $τ_{μν}$, we find that the General Relativity quadrupole formula is modified in a non-trivial way, making it feasible to find a possible signature of non-locality. Our final results on the gravitational wave stress-energy pseudo-tensor could also be applied to several astrophysical scenarios involving energy or momentum loss, potentially providing multiple tests for non-local deviations from General Relativity. We finally discuss the detectability of the massless transverse scalar mode, discovering that, although this radiation is extremely weak, in a small range around the model divergence, its amplitude could fall within the low-frequency Einstein Telescope sensitivity.

gr-qc↗

Quantum coherence in neutrino spin-flavor oscillations

Coherence, which represents the superposition of orthogonal states, is a fundamental concept in quantum mechanics and can also be precisely defined within quantum resource theory. Thus exploring quantum coherence in neutrino oscillations can not only help in examining the intrinsic quantum nature but can also explore their potential applications in quantum information technologies. Previous studies on quantum coherence have focused on neutrino flavor oscillations (FO). However, FO imply that neutrinos have mass and this can lead to the generation of a tiny but finite magnetic dipole moment of neutrinos through quantum loop diagrams at higher orders of perturbative expansion of the interaction. This electromagnetic property of neutrinos can induce spin flavor oscillations (SFO) in the presence of an external magnetic field and hence is expected to enrich the study of coherence. In this work, we investigate quantum coherence in neutrino SFO with three flavor mixing within the interstellar as well as intergalactic magnetic fields, quantified by the $l_1$ norm and the relative entropy of coherence, and express these measures in terms of neutrino SFO probabilities. For FO, coherence measures can sustain higher values (say, within 50% of the maximum) over distances of several kilometers, which are relevant for terrestrial experiments like reactor and accelerator neutrinos. However, for SFO, we find that the coherence scale can extend to astrophysical distances, spanning from kiloparsecs to gigaparsecs.

hep-ph↗

Limits on dark matter, ultralight scalars, and cosmic neutrinos with gyroscope spin and precision clocks

Dark matter (DM) within the solar system induces deviations in the geodetic drift of gyroscope spin due to its gravitational interaction. Assuming a constant DM density as a minimal scenario, we constrain DM overdensity within the Gravity Probe B (GP-B) orbit and project limits for Earth's and Neptune's orbits around the Sun. The presence of electrons in gravitating sources and test objects introduces a scalar-mediated Yukawa potential, which can be probed using terrestrial and space--based precision clocks. We derive projected DM overdensity $(η)$ limits from Sagnac time measurements using onboard satellite clocks, highlighting their dependence on the source mass and orbital radius. The strongest limit, $η\lesssim 4.45\times 10^3$, is achieved at Neptune's orbit ($\sim 30~\mathrm{AU}$), exceeding existing constraints. Correspondingly, the cosmic neutrino overdensity is bounded as $ξ\lesssim 5.34\times 10^{10}$, surpassing results from KATRIN and cosmic ray studies. The best limit on electrophilic scalar coupling is $g\lesssim 7.09\times 10^{-24}$ for scalar mass $m_φ\lesssim 1.32\times 10^{-18}~\mathrm{eV}$ competitive with existing fifth-force bounds. These precision measurements offer a robust framework for testing gravity at solar system scales and probing DM in scenarios inaccessible to direct detection experiments.

hep-ph↗

Constraints on electrophilic scalar coupling from rotating magnetized stars and effects of cosmic neutrino background

An ultralight electrophilic scalar field can produce a long-range Yukawa-like spatial profile around a rotating, magnetized star when coupled to the constant number density of electrons in either the magnetosphere or the star itself. This long-range scalar field generates an effective scalar charge in the star or its magnetosphere, leading to a long-range force between two compact stars in a binary system. The electrophilic scalar can also radiate from isolated pulsars or double pulsar binary systems. Using the Crab pulsar and PSR J0737-3039A/B as test cases, we derive constraints on the scalar-electron coupling by analyzing observations of long-range force, orbital period decay in binary systems, and pulsar spin-down rates. Among these, the most stringent limits on the coupling are obtained from the orbital period decay. However, these constraints can be significantly reduced if the scalar interacts with the pervasive cosmic neutrino background. Enhancing experimental sensitivity and studying compact objects with stronger magnetic fields and higher angular velocities could further strengthen these bounds.

hep-ph↗

Pulsar Kick: Status and Perspective

The high speeds seen in rapidly rotating pulsars after supernova explosions present a longstanding puzzle in astrophysics. Numerous theories have been suggested over the years to explain this sudden "kick" imparted to the neutron star, yet each comes with its own set of challenges and limitations. Key explanations for pulsar kicks include hydrodynamic instabilities in supernovae, anisotropic neutrino emission, asymmetries in the magnetic field, binary system disruption, and physics beyond the Standard Model. Unraveling the origins of pulsar kicks not only enhances our understanding of supernova mechanisms but also opens up possibilities for exploring new physics. In this brief review, we will introduce pulsar kicks, examine the leading hypotheses, and explore future directions for this intriguing phenomenon.

astro-ph.HE↗

Probing chiral and flavored $Z^\prime$ from cosmic bursts through neutrino interactions

The origin of tiny neutrino mass is an unsolved puzzle leading to a variety of phenomenological aspects beyond the Standard Model (BSM). We consider $U(1)$ gauge extension of the Standard Model (SM) where so-called seesaw mechanism is incarnated with the help of thee generations of Majorana type right-handed neutrinos followed by the breaking of $U(1)$ and electroweak gauge symmetries providing anomaly free structure. In this framework, a neutral BSM gauge boson $Z^\prime$ is evolved. To explore the properties of its interactions we consider chiral (flavored) frameworks where $Z^\prime$ interactions depend on the handedness (generations) of the fermions. In this paper we focus on $Z^\prime-$neutrino interactions which could be probed from cosmic explosions. We consider $ν\overlineν \to e^+ e^-$ process which can energize gamma-ray burst (GRB221009A, so far the highest energy) through energy deposition. Hence estimating these rates we constrain $U(1)$ gauge coupling $(g_X)$ and $Z^\prime$ mass $(M_{Z^\prime})$ under Schwarzchild (Sc) and Hartle-Thorne (HT) scenarios. We also study $ν-$DM scattering through $Z^\prime$ to constrain $g_X-M_{Z^\prime}$ plane using IceCube data considering high energy neutrinos from cosmic blazar (TXS0506+056), active galaxy (NGC1068), the Cosmic Microwave Background (CMB) and the Lyman-$α$ data, respectively. Finally highlighting complementarity we compare our results with current and prospective bounds on $g_X-M_{Z^\prime}$ plane from scattering, beam-dump and $g-2$ experiments.

hep-ph↗

Complete complementarity relations in tree level QED processes

We exploit the complete complementarity relations (CCR) to fully characterize various aspects of quantumness in QED scattering processes at tree level. As a paradigmatic example, we consider Bhabha scattering in two different configurations: in the first case, the initial state is factorized in the spin and we study the generation of entanglement due to the scattering. Then we consider the most general case in which the initial state can be entangled: we find that the scattering generates and distributes quantum information in a non-trivial way among the spin degrees of freedom of the particles, with CCR relations being preserved. An important outcome of our analysis is that maximal entanglement is conserved in the scattering process involving only fermions as input and output states, with a more complex situation if photons are present.

quant-ph↗

Gravitational-wave signatures of gravito-electromagnetic couplings

Gravitational waves (GWs) can undoubtedly serve as a messenger from the early Universe acting as well as a novel probe of the underlying gravity theory. In this work, motivated by one-loop vacuum-polarization effects on curved spacetime, we investigate a gravitational theory with non-minimal curvature-electromagnetic coupling terms of the form $ξR F_{μν}F^{μν}$, where $R$ is the scalar curvature and $F_{μν}$ the Faraday tensor, which can be responsible for the generation of primordial electromagnetic fields. We study then the GW signatures of such coupling terms deriving in particular for the first time to the best of our knowledge the modified tensor modes equation of motion. Remarkably, we find a universal infrared (IR) frequency scaling $f^5$ of the electromagnetically induced GW (EMIGW) signal, which, depending on the energy scale of inflation, the duration of inflation and reheating as well as the dynamical behaviour of the gauge coupling function $ξ$, can be well within the detection sensitivity bands of GW experiments such as SKA, LISA, ET and BBO, being thus potentially detectable in the future by GW observatories.

astro-ph.CO↗

Gravitational tensor and scalar modes in $f(Q,B)$ non-metric gravity

We investigate gravitational waves generated in $f(Q,B)$ non-metric gravity, i.e., a theory of gravity described by a non-metric compatible connection, free of torsion and curvature. It is an extension of symmetric teleparallel gravity, equipped with a boundary term $B$. This theory exhibits gravitational waves regardless of the gauge adopted: they are the standard massless tensors plus a massive scalar gravitational wave like in the case of $f(R)$ gravity. It is precisely the boundary term $B$ that generates the massive scalar mode with an effective mass $m_{B}$ associated to a Klein-Gordon equation in the linearized boundary term. As in $f(Q)$ gravity also in $f(Q,B)$ non-metric gravity, a free test particle follows a geodesic motion due to the covariant conservation with respect to the Levi-Civita connection of the energy and momentum densities on shell. Therefore, in $f(Q,B)$ gravity, the proper acceleration between two neighboring worldlines traveled by two free point-like particle is governed by a first-order geodesic deviation equation in the metric perturbation $h_{μν}$. Thanks to this approximate linear equation, $f(Q,B)$ non-metric gravity shows three polarization modes: two massless transverse tensor radiation modes, with helicity equal to 2, reproducing the standard plus and cross modes, exactly as in General Relativity, and an additional massive scalar wave mode with transverse polarization of zero helicity. We obtain the same result both by considering the coincidence gauge and by leaving the gauge free. In summary, three degrees of freedom propagate in the $f(Q,B)$ linearized theory with amplitudes $\tilde{h}^{(+)}$ and $\tilde{h}^{(\times)}$ for tensor modes and amplitude $\tilde{h}^{(s)}$ for the scalar mode. Specifically, both $f(Q,B)$ and $f(R)$ gravity involve the same massive transverse scalar perturbation.

gr-qc↗

Traces of quantum gravitational correction at third-order curvature through the black hole shadow and particle deflection at the weak field limit

This study investigates the impact of the quantum-gravity correction at the third-order curvature ($c_6$) on the black hole's shadow and deflection angle on the weak field regime, both involving finite distances of observers. While the calculation of the photonsphere and shadow radius $R_{\rm sh}$ can easily be achieved by the standard Lagrangian for photons, the deflection angle $α$ employs the finite-distance version of the Gauss-Bonnet theorem (GBT). We find that the photonsphere reduces to the classical expression $r_{\rm ph} = 3M$ for both the Planck mass and the theoretical mass limit for BH, thus concealing the information about the applicability of the metric on the quantum and astrophysical grounds. Our calculation of the shadow, however, revealed that $c_6$ is strictly negative and constrains the applicability of the metric to quantum black holes. For instance, the bounds for the mass is $M/l_{\rm Pl} \in [0.192, 4.315]$. We also derived the analytic formula for the observer-dependent shadow, which confirms $c_6$'s influence on quantum black holes even for observers in the asymptotic regions. The influence of such a parameter also strengthens near the quantum black hole. Our analytic calculation of $α$ is shown to be independent of $c_6$ if the finite distance $u \rightarrow 0$, and $c_6$ is not coupled to any time-like geodesic. Finally, the effect of $c_6$ manifests in two ways: if $M^2$ is large enough to offset the small value of $l_{\rm Pl}$ (which is beyond the theoretical mass limit), or if $b$ is comparable to $l_{\rm Pl}$ for a quantum black hole.

gr-qc↗

Relativistic periastron advance beyond Einstein theory: analytical solution with applications

We find a new solution to calculate the orbital periastron advance of a test body subject to a central gravitational force field, for relativistic theories and models beyond Einstein. This analitycal formula has general validity that includes all the post-Newtonian (PN) contributions to the dynamics and is useful for high-precision gravitational tests. The solution is directly applicable to corrective potentials of various forms, without the need for numerical integration. Later, we apply it to the Scalar Tensor Fourth Order Gravity (STFOG) and NonCommutative Geometry, providing corrections to the Newtonian potential of Yukawa-like form $V(r)=α\frac{e^{-βr}}{r}$, and we conduct the first analysis involving all the PN terms for these theories. The same work is performed with a Schwarzschild geometry perturbed by a Quintessence Field, leading to a power-law potential $V(r)=α_q {r}^q$. Finally, by using astrometric data of the Solar System planetary precessions and those of S2 star around Sgr A*, we infer new theoretical constraints and improvements in the bounds for $β$. The resulting simulated orbits turn out to be compatible with General Relativity.

gr-qc↗

Imprints of Barrow-Tsallis Cosmology in Primordial Gravitational Waves

Both the Barrow and Tsallis $δ$ entropies are one-parameter generalizations of the black-hole entropy, with the same microcanonical functional form. The ensuing deformation is quantified by a dimensionless parameter $Δ$, which in the case of Barrow entropy represents the anomalous dimension, while in Tsallis' case, it describes the deviation of the holographic scaling from extensivity. Here, we utilize the gravity-thermodynamics conjecture with the Barrow--Tsallis entropy to investigate the implications of the related modified Friedmann equations on the spectrum of primordial gravitational waves. We show that, with the experimental sensitivity of the next generation of gravitational wave detectors, such as the Big Bang Observer, it will be possible to discriminate deviations from the $Λ$CDM model up to $Δ\lesssim\mathcal{O}(10^{-3})$.

gr-qc↗

Black hole surrounded by the pseudo-isothermal dark matter halo

The abundance of dark matter in the actual universe motivates us to construct the black hole spacetime enveloped by dark matter. In this paper, we derive a new spherically symmetric black hole surrounded by the pseudo-isothermal dark matter halo, and then explore the effects of the pseudo-isothermal halo profile on a rotating black hole at the M87 galactic center, aiming to achieve a black hole solution that aligns with those found in the real universe. Using the Newman-Janis method, we derive a rotating black hole solution encompassed by the pseudo-isothermal halo, which is consistent with observations of actual black holes that are believed to possess spin. Our investigation focuses on the impact of the pseudo-isothermal halo on the black hole event horizon, time-like and null orbits, as well as the black hole shadow. We find that as the spin parameter $a$ increases, the interval between the inner event horizon and the outer event horizon of the rotating black hole surrounded by the pseudo-isothermal halo in M87 diminishes. This leads to the formation of an extreme black hole. The presence of dark matter, however, has minimal effect on the event horizon. Moreover, in the M87 as the spin parameter $a$ increases, the black hole shadow deviates increasingly from a standard circle, with larger spin parameters causing more pronounced distortion relative to the standard circle. Surprisingly, we observe that the dark matter density has very little influence on the shadow of the black hole surrounded by the pseudo-isothermal halo in the M87. This study contributes to a deeper understanding of black hole structures and the role of dark matter in the universe.

gr-qc↗

Entanglement distribution in Bhabha scattering with entangled spectator particle

We analyze how entanglement is generated and distributed in a Bhabha scattering process $(e^-e^+\rightarrow e^-e^+)$ at tree level. In our setup an electron $A$ scatters with a positron $B$, which is initially entangled with another electron $C$ (spectator), that does not participate directly to the process. We find that the QED scattering generates and distributes entanglement in a non-trivial way among the three particles: the correlations in the output channels $AB$, $AC$ and $BC$ are studied in detail as functions of the scattering parameters and of the initial entanglement weight. Although derived in a specific case, our results exhibit some general features of other similar QED scattering processes, for which the extension of the present analysis is straightforward.

quant-ph↗

Pulsar kicks in ultralight dark matter background induced by neutrino oscillation

The interaction of neutrinos with ultralight scalar and vector dark matter backgrounds induce a modification of the neutrino dispersion relation. The effects of this modification are reviewed in the framework of asymmetric emission of neutrinos from the supernova core, and, in turn, of pulsar kicks. We consider the neutrino oscillations, focusing in particular to active-sterile conversion. The ultralight dark matter induced neutrino dispersion relation contains a term of the form $δ{\bf Ω}\cdot \hat{\bf{p}}$, where $δ{\bf Ω}$ is related to the ultralight dark matter field and $\hat{\bf p}$ is the unit vector along the direction of neutrino momentum. The relative orientation of ${\bf p}$ with respect to $δ{\bf Ω}$ affects the mechanism for the generation of the observed pulsar velocities. We obtain the resonance condition for the active-sterile neutrino oscillation in ultralight dark matter background and calculate the star parameters in the resonance surface so that both ultralight scalar and vector dark matter backgrounds can explain the observed pulsar kicks. The asymmetric emission of neutrinos in presence of ultralight dark matter background results gravitational memory signal which can be probed from the future gravitational wave detectors such as adLIGO (advanced LIGO), adVIRGO (advanced VIRGO), DECIGO (DECi-hertz Interferometer Gravitational wave Observatory), BBO (Big Bang Observer), and ET (Einstein Telescope). We also establish a relation between the ultralight dark matter parameters and the Lorentz and CPT invariance violation parameters.

hep-ph↗

Rotating black hole mimicker surrounded by the string cloud

Traversable wormholes and regular black holes usually represent completely different scenarios. But in the black bounce spacetime they can be described by a same line element, which is very attractive. Furthermore, the black hole photos taken by EHT show that black holes have spin, so spin is an indispensable intrinsic property of black holes in the actual universe. In this work, we derive a rotating black hole mimicker surrounded by the string cloud (SC), which can be interpolated to represent regular black hole spacetime and traversable wormhole spacetime. We investigate the effect of the spin $a$ and SC parameter $L$ on the observables (shadow radius $R_s$ and distortion $δ_s$) and energy emission rate of the black hole mimicker surrounded by the SC. We find that shadow for this spacetime is very sensitive to the $L$, i.e., the SC parameter can significantly increase the boundary of the shadow.

gr-qc↗

Astrophysical neutrino oscillations after pulsar timing array analyses

The pattern of neutrino flavor oscillations could be altered by the influence of noisy perturbations such as those arising from a gravitational wave background (GWB). A stochastic process that is consistent with a GWB has been recently reported by the independent analyses of pulsar timing array (PTA) data sets collected over a decadal timescale by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the European Pulsar Timing Array (EPTA), the Parkes Pulsar Timing Array (PPTA), and the Chinese Pulsar Timing Array (CPTA) collaborations. We investigate the modifications in the neutrino flavor oscillations under the influence of the GWB reported by the PTA collaborations and we discuss how such effects could be potentially revealed in near-future neutrino detectors, possibly helping the discrimination of different models for the GWB below the nHz frequency range.

astro-ph.HE↗