CyberSec Research

The experimental possibility of detecting gravitational waves via their induced time perturbations is explored here, expanding from previous work. The oscillations of the time-time component in the metric are made explicit when working in asynchronous gauges: the desynchronization between a perturbed clock and a reference unperturbed clock constitutes the corresponding observable core target of a detector. To this end we explore the experimental techniques currently available for a preliminary assessment towards a feasibility study. We survey the state of the art in the fields of high precision timing and information preservation, necessary for achieving geodesic non-locality. A synthesis for a feasible prototype detector with the desired characteristics is presented. The optimum point between existing technologies is found around the 1 Hz frequency band, opening the window for the observation of classes of speculated sources of gravitational radiation such as intermediate mass black hole binaries.

In this work we examine the 2025 DESI analysis of dark energy, which suggests that dark energy is evolving in time with an increasing equation of state $w$. We explore a wide range of quintessence models, described by a potential function $V(\varphi)$, including: quadratic potentials, quartic hilltops, double wells, cosine functions, Gaussians, inverse powers. We find that while some provide improvement in fitting to the data, compared to a cosmological constant, the improvement is only modest. We then consider non-minimally coupled scalars which can help fit the data by providing an effective equation of state that temporarily obeys $w<-1$ and then relaxes to $w>-1$. Since the scalar is very light, this leads to a fifth force and to time evolution in the effective gravitational strength, which are both tightly constrained by tests of gravity. For a very narrow range of carefully selected non-minimal couplings we are able to evade these bounds, but not for generic values.

We consider 331 composite Higgs model (CHM3) in which the Lagrangian of the strongly coupled sector is invariant with respect to global SU(3)_C \times SU(3)\times U(1)_6 symmetry that can originate from SU(6) subgroup of E_6 and contains the gauge group of the standard model (SM) as a subgroup. The breakdown of the approximate SU(3)\times U(1)_6 symmetry down to SU(2)_W\times U(1)_Y subgroup around the scale f\sim 10 TeV results in a set of pseudo--Nambu--Goldstone bosons (pNGBs) that, in particular, involves Higgs doublet. The generation of the masses of the SM fermions in the CHM3 is discussed. We argue that an approximate discrete Z_2 symmetry may give rise to tiny masses of the left-handed neutrinos and several composite fermions with masses 1-2 TeV. The lepton and baryon asymmetries can be generated within the CHM3 via the out--of equilibrium decays of extra Majorana particle into the Higgs doublet and these composite fermions.

Detecting unmodeled gravitational wave (GW) bursts presents significant challenges due to the lack of accurate waveform templates required for matched-filtering techniques. A primary difficulty lies in distinguishing genuine signals from transient noise. Machine learning approaches, particularly convolutional neural networks (CNNs), offer promising alternatives for this classification problem. This paper presents a CNN-based pipeline for detecting short GW bursts (duration $< 10~\mathrm{s}$), adapted from an existing framework designed for longer-duration events. The CNN has been trained on core-collapse supernova (CCSN) gravitational waveform models injected into simulated Gaussian noise. The network successfully identifies these signals and generalizes to CCSN waveforms not included in the training set, showing the potential of U-Net architectures for detecting short-duration gravitational wave transients across diverse astrophysical scenarios.

Asymptotic velocity domination (AVD) posits that when back-propagated to the Big Bang generic cosmological spacetimes solve a drastically simplified version of the Einstein field equations, where all dynamical spatial gradients are absent (similar as in the Belinski-Khalatnikov-Lifshitz scenario). Conversely, a solution can in principle be reconstructed from its behavior near the Big Bang. This property has been rigorously proven for the Gowdy class of cosmologies, both polarized and unpolarized. Here we establish for the polarized case a quantum version of the AVD property formulated in terms of two-point functions of (the integrands of) Dirac observables: these correlators approach their much simpler velocity dominated counterparts when the time support is back-propagated to the Big Bang. Conversely, the full correlators can be expressed as a uniformly convergent series in averaged spatial gradients of the velocity dominated ones.

The macroscopic model for a neutron star (NS) as a perfect liquid drop at the equilibrium is extended to rotating systems with a small frequency $\omega$ within the effective-surface (ES) approach. The NS angular momentum $I$ and moment of inertia (MI) for a slow stationary azimuthal rotation around the symmetry axis is calculated by using the Kerr metric approach in the Boyer-Lindquist and Hogan forms for the perfect liquid-drop model of NSs. The gradient surface terms of the NS energy density $\mathcal{E}(\rho)$ [Equation of State] are taken into account along with the volume ones at the leading order of the leptodermic parameter $a/R \ll 1$, where $a$ is the ES crust thickness and $R$ is the mean NS radius. The macroscopic NS angular momentum $I$ at small frequencies $\omega$, up to quadratic terms, can be specified for calculations of the adiabatic MI, $\Theta=d I/d \omega$, by using Hogan's inner gravitational metric, $r\le R$. The NS MI, $\Theta=\tilde{\Theta}/(1-\mathcal{G}_{t\varphi})$, was obtained in terms of the statistically averaged MI, $\tilde{\Theta}$, and its time and azimuthal angle correlation, $\mathcal{G}_{t\varphi}$, as sumes of the volume and surface components. The MI $\Theta$ depends dramatically on its effective radius $R$ because of a strong gravitation. We found the significant shift of the Schwarzschild radius $R_{\rm S}$ to a much smaller position due to the time and azimuthal correlation term $\mathcal{G}_{t\varphi}$. The adiabaticity condition is carried out for several neutron stars in a strong gravitation case.

We construct exact solutions that describe the near horizon region of extremal rotating black holes in Einstein-Born-Infeld theory. Using generalized Komar integrals, we extract the electric charge and angular momentum from the near horizon geometries and study their deviations from the Kerr-Newman solution. We identify two features that are direct consequences of the nonlinearities of Born-Infeld theory. First, we find solutions which have vanishing charge but nontrivial electric and magnetic fields. Second, we find that extremal rotating black holes do not exist for sufficiently small charge and angular momentum. Based on analogy with the static black holes, we argue that it would be particularly interesting to construct the full rotating solutions in these parameter regions as they may provide examples of rotating black holes without Cauchy horizons.

The classification of exact solutions of Maxwell vacuum equations for pseudo-Riemannian spaces with spatial symmetry (homogeneous non-null spaces of Petrov) in the presence of electromagnetic fields invariant with respect to the action of the group of space motions is summarized. A new classification method is used, common to all homogeneous zero spaces of Petrov. The method is based on the use of canonical reper vectors and a on the use a new approach to the systematization of solutions. The classification results are presented in a form more convenient for further use. Using the previously made refinement of the classification of Petrov spaces, the classification of exact solutions of Maxwell vacuum equations for spaces with the group of motions $G_3(VIII )$ is completed.

In this work, our aim is to obtain a Hamiltonian formulation suitable for canonical quantization. Moreover, we assume that the early Universe can be described with fewer initial symmetries, thus we abandon the isotropy assumption and instead explore anisotropic universes, beginning with the simplest one, namely Bianchi I (BI). The presence of small initial fluctuations in the early universe can be well described by perturbations around a homogeneous background. GR is a constrained system, and we apply the so-called Dirac procedure for constrained systems to derive a gauge-invariant Hamiltonian formulation suitable for quantization. In this work, we present how this procedure can be extended to a generic background and its relation to the Kuchar decomposition. Subsequently, we apply this formulation to a BI universe, obtaining new and interesting results on the gauge-invariant representation of matter and geometry perturbations. Contrary to the FLRW case, in which all the modes decouple, in BI we see that scalar and tensor modes do not decouple. We show that new types of gauge-fixing conditions exit in this case. For instance, a gravitational wave can be encoded into scalar modes, by introducing a new gauge which is not valid in FLRW. Furthermore, we make a first step towards a consistent and unified quantization of the composite system made of a background mode and perturbation modes. Specifically, we study tensor modes in a FLRW universe. We focus on the relation between the choice of internal time of the universe and the quantum evolution it undergoes. Our results indicate that the time reparametrization invariance in general relativity affects the quantum evolution of the background and perturbation modes. However, in the classical limit, i.e. for a large universe, the dynamics becomes unique. Thus, the predictive power of the theory is maintained.

Considering an exact solution of the five-dimensional Einstein equations in vacuum space, which represents a distorted Myers-Perry black hole with a single angular momentum, we investigate how the distortion affects the horizon surface of this black hole. We illustrate a special case where we have a bumpy deformed black hole horizon that feels the presence of the external sources. However, the ergosphere is oblivious to the presence of external sources.

This dissertation focuses on the reconstruction of Equations of State (EoSs) describing the interior of compact stars, using modern machine learning and deep learning methods. The pipeline is based on data from mass-radius (M-R) curves, obtained by numerically solving the Tolman-Oppenheimer-Volkoff equations for a wide range of admissible EoSs. The manuscript is divided into a Theoretical Part (Chs. 1-4) and a Computational Part (Chs. 5-7). The theoretical chapters analyze the properties of neutron and quark stars, the physical constraints of viable EoS models, and introduce regression algorithms (Decision Tree, Random Forest, Gradient Boosting, XGBoost) and neural networks with normalization and dropout techniques. The computational part presents the generation of artificial EoSs for hadronic and quark stars (MIT bag, CFL), the numerical solution of the TOV equations, data preparation, and hyperparameter tuning. Results include training and evaluation of models using MSE/MSLE metrics, learning curves for neural networks, and reconstruction of 21 hadronic and 20 quark star EoSs. Source code and tools for reproducibility and future research are provided. The work aims to establish a reusable and scalable framework, strengthening the connection between theoretical astrophysics and computational science.

The GeV $\gamma$-ray excess observed towards the Galactic Centre remains unexplained. While dark matter annihilation has long been considered a leading interpretation, an alternative scenario involving a large population of millisecond pulsars has not been ruled out. Testing this hypothesis with electromagnetic observations is difficult, as pulsar searches in the bulge are strongly affected by scattering, high sky temperature, and source confusion. We investigate whether gravitational-wave observations with the Laser Interferometer Space Antenna (LISA) could provide an independent probe of the millisecond pulsar binary population in the Galactic bulge. We construct synthetic populations of millisecond pulsar-white dwarf binaries under two illustrative formation scenarios: an accreted scenario, in which systems are deposited by disrupted globular clusters, and an in situ scenario, in which binaries form through isolated binary evolution. In both cases, only $10^{-5}$--$10^{-4}$ of the underlying bulge population is detectable by LISA. Nevertheless, even a few detections would imply tens to hundreds of thousands of unseen systems. Accreted binaries are expected to have lower chirp masses ($\sim$0.4 M$_\odot$), while in situ binaries produce more massive companions ($\sim$0.9 M$_\odot$). LISA will measure binary frequencies with high precision, but chirp masses can only be determined for the most massive or highest-frequency systems. Distinguishing millisecond pulsar binaries from the far more numerous double white dwarfs will be challenging, though LISA detections could provide valuable targets for follow-up with the Square Kilometre Array, enabling a critical test of the millisecond pulsar origin of the $\gamma$-ray excess.

The consideration of timelike boundaries in de Sitter static patches has a broad motivation, such as the formulation of a well-defined canonical ensemble and the realization of a natural framework for static patch holography. In this work we study Jackiw-Teitelboim de Sitter gravity with symmetric timelike reflecting boundaries, which, in the presence of both cosmological and "black hole" horizons, naturally separate the spacetime into a "black hole system" and a "cosmological system". We apply the island formula to compute the entanglement entropy of conformal matter in both systems. In the "black hole system" an island appears, causing the entanglement entropy to saturate at the horizon value and preventing late-time growth. In the "cosmological system" no island appears, and the entanglement entropy can become arbitrarily large depending on the position of the boundaries, indicating a tension with unitarity.

The field of gravitational wave (GW) detection is progressing rapidly, with several next-generation observatories on the horizon, including LISA. GW data is challenging to analyze due to highly variable signals shaped by source properties and the presence of complex noise. These factors emphasize the need for robust, advanced analysis tools. In this context, we have initiated the development of a low-latency GW detection pipeline based on quantum neural networks (QNNs). Previously, we demonstrated that QNNs can recognize GWs simulated using post-Newtonian approximations in the Newtonian limit. We then extended this work using data from the LISA Consortium, training QNNs to distinguish between noisy GW signals and pure noise. Currently, we are evaluating performance on the Sangria LISA Data Challenge dataset and comparing it against classical methods. Our results show that QNNs can reliably distinguish GW signals embedded in noise, achieving classification accuracies above 98\%. Notably, our QNN identified 5 out of 6 mergers in the Sangria blind dataset. The remaining merger, characterized by the lowest amplitude, highlights an area for future improvement in model sensitivity. This can potentially be addressed using additional mock training datasets, which we are preparing, and by testing different QNN architectures and ansatzes.

In this work, we explore a possible application of a machine learning classifier for candidate events in a template-based search for gravitational-wave (GW) signals from various compact system sources. We analyze data from the O3a and O3b data acquisition campaign, during which the sensitivity of ground-based detectors is limited by real non-Gaussian noise transient. The state-of-the-art searches for such signals tipically rely on the signal-to-noise ratio (SNR) and a chi-square test to assess the consistency of the signal with an inspiral template. In addition, a combination of these and other statistical properties are used to build a 're-weighted SNR' statistics. We evaluate a Random Forest classifiers on a set of double-coincidence events identified using the MBTA pipeline. The new classifier achieves a modest but consistent increase in event detection at low false positive rates relative to the standard search. Using the output statistics from the Random Forest classifier, we compute the probability of astrophysical origin for each event, denoted as $p_\mathrm{astro}$. This is then evaluated for the events listed in existing catalogs, with results consistent with those from the standard search. Finally, we search for new possible candidates using this new statistics, with $p_\mathrm{astro} > 0.5$, obtaining a new subthreshold candidate (IFAR =0.05) event at $gps: 1240423628$ .

An interesting class of time dependent backgrounds in $1+1$ dimensional string theory involves worldsheet Liouville walls which move in (target space) time. When a parameter in such a background exceeds a certain critical value, the speed of the Liouville wall exceeds the speed of light, and there is no usual S-Matrix. We examine such backgrounds in the dual $c=1$ matrix model from the point of view of fluctuations of the collective field, and determine the nature of the emergent space-time perceived by these fluctuations. We show that so long as the corresponding Liouville wall remains time-like, the emergent space time is conformal to full Minkowski space with a time-like wall. However, for the cases where the Liouville wall is superluminal, the emergent space-time has a {\em space-like boundary} where the collective field couplings diverge. This appears as a space-like singularity in perturbative collective field theory. We comment on the necessity of incorporating finite $N$, as well as finite (double-scaled) coupling, effects to understand the behavior of the exact theory near this boundary.

Recently, Hou et al. [Astrophys. J. Lett. 988, L51 (2025)] revealed that the EVPA (Electric Vector Position Angle) of polarization vectors in the near-horizon images is governed solely by spacetime geometry and is irrespective of the plasma flows. Here, we generalize the study to the scenario of a rotating hair black hole within Horndeski gravity and probe the effects of the hairy parameter on the EVPA. For a fixed inclination, the hairy parameter enhances the observed EVPA in the slowly rotating case, but decreases it in the rapidly rotating case. For a fixed black hole spin, the influence of the hairy parameter on the observed EVPA under different observer inclinations is further modulated by the azimuthal angle of the observed polarization vector. The hairy parameter's impact is more distinct in the low inclination case as the azimuthal angle lies within a specific range, but is almost independent of the observer inclination as the azimuthal angle is beyond this specific range. Furthermore, the dependence of the hairy parameter's impact on the EVPA is stronger with respect to the black hole spin than to the inclination angle. These results could help to further understand the near-horizon polarized images and Horndeski gravity.

I revisit whether black-hole remnants, from sub-Planckian compact objects to Planck relics and up to (super)massive black holes, can preserve Standard-Model (SM) electric charge. Two exterior-field mechanisms -- Coulomb-focused capture from ambient media and QED Schwinger pair production -- robustly neutralize such objects across cosmic history. I first derive the general capture rate including both Coulomb and gravitational focusing, and sum the stepwise discharge time in closed form via the trigamma function, exhibiting transparent Coulomb- and gravity-dominated limits. I then integrate the Schwinger rate over the near-horizon region to obtain an explicit $\dot Q(Q)$ law: discharge proceeds until the horizon field falls below $E_{\rm crit}$, leaving a residual charge $Q_{\rm stop}^{(e)}\!\propto\! r_h^2$ that is $\ll e$ for Planck radii. Mapping the mass dependence from sub-Planckian to astrophysical scales, I also analyze dark-sector charges with heavy carriers (including kinetic mixing and massive mediators). In a conservative ``no-Schwinger'' limit where vacuum pair creation is absent, cumulative ambient exposures alone force discharge of any integer SM charge. Three possible loopholes remain. (i) A fine-tuned SM corner in which the relic sits arbitrarily close to Reissner-Nordstr\"om extremality so greybody factors suppress charged absorption, while Schwinger pair creation is absent due to Planck-scale physics. (ii) Charge relocated to a hidden $U(1)_D$ with no light opposite carriers, e.g. if the lightest state is very heavy and/or kinetic mixing with $U(1)_{\rm EM}$ is vanishingly small. (iii) Discrete or topological charges rather than ordinary SM electric charge. Outside these cases, the conclusion is robust: within SM electromagnetism, charged black-hole relics neutralize efficiently and cannot retain charge over cosmological times.