Phase modulation (PM) method has been introduced to study periodic variability within variable stars by converting phase shifts into time delays of the traveled light path known as the light time travel effect (LTTE). This method was highly successful in detecting binary companions and in studying Blazhko-type modulation in RR Lyrae and δ Scuti stars. However, both binary motion and intrinsic Blazhko modulation introduce periodic phase variations, which can produce very similar signatures in the PM time-delay curves, particularly when the period ranges of the two effects overlap or when both effects may be present simultaneously. As a result, some stars might be misclassified as Blazhko or Binary type stars. One way to discriminate between the tow effects is to adopt the O-C diagram to test for binarity, although recent studies show the complexity of this approach in the presence of other intrinsic variations. Another approach is to examine the multiplets seen in the Fourier transform . In this work, we investigate an other method to distinguish between intrinsic Blazhko and binary orbital modulations using Wavelet analysis for characterizing the behavior of the modulation over a wide range of time scale, the time series are decomposed into time–frequency space to determine both the dominant modes of variability and how those modes vary in time. By carefully investigating some RR Lyrae stars where the two effects have been confused or simultaneously present, the wavelet analysis turned out to be a powerful tool to separate the two effects and to investigate other types of intrinsic variations present in RR Lyrae stars like period breaks and secular period changes .

We investigate the sub-Chandrasekhar mass double detonation pathway as a viable mechanism for Type Ia supernovae, focusing on systems arising from single degenerate carbon–oxygen (CO) white dwarfs (WDs) that accrete helium. Building upon our previous one-dimensional study of recurrent helium novae (Hillman et al. 2025), we modeled the secular evolution of a 0.7 M⊙​ WD. This WD was evolved through steady helium accretion at a relatively slow rate of 10−8 M⊙​ yr−1 until it reached a critical mass of 1.1 M⊙​. This detailed evolution yielded realistic, time-evolved temperature and composition profiles within the WD and its helium layer.

These time-evolved profiles were then mapped into the multi-dimensional hydrodynamic code FLASH, which incorporates a sophisticated reaction network for nuclear burning in both the helium shell and the CO core. The simulations were initiated by introducing a localized, modest temperature perturbation near the base of the helium shell. This subtle trigger robustly instigated an outward-propagating helium-shell detonation. The resulting inward-propagating shock wave from the helium detonation converged strongly near the center of the CO core, igniting a secondary, catastrophic carbon–oxygen detonation that completely unbinds the star.

We report a total 56Ni yield of ≃0.64M⊙​, an intermediate-mass element (Si-Ca) mass of ≃0.41M⊙​, and maximum ejecta velocities approaching ∼22,000 km s−1. These key characteristic values are consistent with observations of normal, cosmologically useful Type Ia supernovae. Our results compellingly demonstrate that recurrent helium accretors, systems typically characterized by long quiescent timescales, can evolve under subtle, "quiet" conditions to trigger robust double detonations, firmly supporting their role as viable and important progenitors of sub-Chandrasekhar mass Type Ia supernovae.

Polarimetric observations serve as an effective diagnostic tool for studying the interstellar medium and identifying stellar membership of an open star cluster. Starlight becomes linearly polarized due to the dichroic extinction from aligned asymmetric interstellar dust grains. The resulting polarization signatures differ for member and non-member stars of the cluster. This makes polarimetry a valuable tool for separating member stars from the foreground or background field.

The open star clusters NGC 1817 and NGC 7380, representing intermediate-age and young stellar environments, respectively, offer important laboratories for exploring star formation, stellar evolution, and cluster dynamics. However, uncertainties in membership determination continue to affect the accuracy of their derived properties. In this study, I will present a method based on linear polarization of stars that can be used to evaluate and refine the membership probabilities of stars in open star clusters. Using the polarimetric technique, I have calculated the membership probability of stars of the cluster NGC 1817 and NGC 7380. A good correlation is found between my results and previously estimated probabilities of members from the proper motion technique. From this study, one can infer that the polarization property can be used for deriving the membership probability. Additionally, I will discuss some drawbacks of this technique.

Periodic maser flares in high-mass star-forming regions provide a sensitive probe of the physical conditions in these environments. The methanol maser source G9.62+0.20E is a benchmark object, exhibiting multiple long-lived periodicities and a rich variety of flare morphologies, from highly asymmetric to nearly symmetric profiles across different velocity components. In previous work, we showed that the Maxwell-Bloch equations operating in the fast-transient superradiance regime, driven by narrow periodic pump excitations, can reproduce the asymmetric flares in this source while yielding consistent environmental parameters for the masing gas.

We recently extended that framework by demonstrating that the same Maxwell–Bloch equations can also accounts for the symmetric flares observed in maser-hosting regions such as G9.62+0.20E. Using a common set of physical conditions (e.g. temperature, collisional timescales) across components, we fit representative symmetric and assymetric flares and show that modest changes in the pump modulation and coherence history are sufficient to explain the full range of observed light-curve shapes, without invoking distinct environments for each periodicity. This consistent modelling of both symmetric and asymmetric flares in a single benchmark source strengthens the case for superradiance as a general framework for flaring in maser-hosting regions and motivates its application to other flaring systems.

The redshifted 21 cm line signal is a unique probe for the Epoch of Reionisation (EoR)—it enables tomographic studies, which track the evolution of the averaged intergalactic medium (IGM) properties and their fluctuations. Accurate modelling of the 21 cm global and power spectrum signals is crucial for interpreting measurements from current and forthcoming 21 cm experiments. Theoretical predictions usually post-process reionisation simulations with optical depth approximation, which treats local line broadening and peculiar velocities approximately and often leads to divergences due to its velocity gradient term. I will present our cosmological 21 cm line radiative transfer (C21LRT) formulation, which explicitly accounts for local 21 cm line emission and absorption, Doppler shifts by peculiar velocity, broadening of the line, and the radiation transfer effects. We will adopt the IGM properties from reionisation simulations as inputs and assess the accuracy of the optical depth approximation for predicting 21 cm global signals and power spectra. I will demonstrate how our C21LRT delivers robust results for the redshift-space distortion (RSD) effects in the 21 cm power spectrum. I will show where the optical depth approach remains valid (for length scales of 1 -10 cMpc at mid-reionisation) and highlight the need to fully quantify the uncertainties with further exploration across a wider EoR parameter space using our C21LRT code.

Galactic cosmic rays (GCRs) are continuously propagating high-energy charged particles originating outside the Solar System, whose intensity near Earth is significantly modulated by solar activity. One of the most prominent manifestations of this modulation is the transient reduction in GCR intensity known as a Forbush decrease (FD), which typically occurs in association with coronal mass ejections (CMEs), interplanetary shocks, and solar flare activity. This paper provides a comprehensive review of the primary physical mechanisms responsible for the suppression of cosmic ray flux during FD events. These mechanisms include magnetic shielding caused by enhanced interplanetary magnetic fields embedded within CMEs, shock-driven disturbances, and increased turbulence in the heliosphere. Observational data obtained from ground-based neutron monitor networks and space-borne instruments are analyzed to illustrate typical FD temporal profiles, recovery phases, and amplitude variations. The observed decreases in cosmic ray intensity generally range from approximately 3% for weak events to more than 20% for strong solar disturbances. Four illustrative figures are presented, showing characteristic FD events, schematic diagrams of CME–Earth interactions, shock structures, and large-scale heliospheric magnetic field configurations. The results emphasize the dominant role of strengthened interplanetary magnetic fields in deflecting and scattering low-energy GCRs, thereby reducing their access to the inner heliosphere. This study contributes to a deeper understanding of cosmic ray modulation processes and their relevance to space weather forecasting and heliophysical research.

In this contribution, I will present a novel detection technique for low-energy antideuterons in cosmic rays, a promising signature of dark matter annihilation. Sub-GeV antideuterons represent an exceptionally clean channel for dark matter searches: their secondary production through conventional astrophysical processes (inelastic collisions of primary cosmic rays with interstellar medium) is extremely rare at low energies, making the expected background essentially negligible. Consequently, even a few detected events would constitute a significant signal potentially attributable to dark matter annihilation or decay in the Galactic halo. Current dark matter models predict antideuteron fluxes several orders of magnitude above the astrophysical background in the sub-GeV range, motivating the development of novel detection techniques optimized for this energy window.

PLASTICAMI is a segmented plastic tracker designed to identify a distinctive "double pion-star" topology characteristic of antideuteron annihilation: when an antideuteron stops in hydrogen-rich plastic, one antinucleon annihilates promptly, while the second survives with kinetic energy, travels several centimeters, and annihilates after nanoseconds. This spatial separation and timing delay between two annihilation vertices creates a unique double-vertex signature. The detector consists of 30 segmented plastic scintillator layers (3×3 m²) stacked with gaps to resolve these displaced vertices, combined with external Cherenkov veto layers based on the newly characterized FB118 wavelength-shifting plastic for efficient background rejection. Geant4 simulations demonstrate 90% efficiency for identifying antideuterons while rejecting 99% of proton background. Considering atmospheric and geomagnetic effects for Antarctic balloon flights, two missions could achieve sensitivity of ~2×10⁻⁶ (m²sr s GeV/n)⁻¹ in the 100-600 MeV/n range, enabling exploration of theoretically motivated dark matter scenarios. Construction of a prototype detector subsystem is ongoing at INFN-TIFPA, utilizing SiPM photodetectors from FBK and custom front-end electronics.

In this talk, a closed isotropic universe with scalar and spinor fields is considered within the framework of the extended phase space approach. This approach implies the derivation of the Schrödinger equation for the wave function of the universe from the path integral with the Faddeev–Popov effective action, including gauge fixing and ghost terms, instead of the Wheeler–DeWitt equation. In the path integral, we use a mixed representation: a coordinate representation for gravitational variables (the lapse function and scale factor) and the so-called holomorphic representation for scalar and spinor fields. In the first step, the scalar field is assumed to be conformal. It enables us to find exact solutions to the Schrödinger equation for special gauge conditions. We consider a set of supersymmetric multiplets of scalar and spinor fields to cancel vacuum divergences and to determine vacuum energy in a closed universe. In the next step, the scalar field is slightly non-conformal. In a time-dependent gravitational field, it gives rise to scalar particle production. In its turn, it acts as a perturbation and results in transitions between quantum states in the Early Universe. Making use of the perturbation theory technique, it is possible to compute probabilities of transitions between states with different energy values.

We investigate the generation of the matter–antimatter asymmetry in the early Universe, prior to the electroweak phase transition, by extending the Standard Model with three right-handed neutrinos that complete Dirac mass terms and two heavy scalar fields. This constitutes a minimal and well-motivated Beyond-the-Standard-Model framework, since the Standard Model alone cannot account for neutrino masses or produce the observed baryon asymmetry due to insufficient CP violation. Using the Closed Time Path (CTP) formalism, we analyze 2→2 scattering processes mediated by the heavy off-shell scalars. Since these scalars remain off-shell throughout, the post-inflationary temperature of the Universe does not need to be high enough to produce them on-shell.

In this setup, right-handed neutrinos depart from thermal equilibrium, generating a lepton asymmetry that is subsequently converted into the observed baryon asymmetry via sphaleron processes. We compute the resulting baryon-to-photon ratio and compare it with the observational value reported by the Planck mission. We also compare the predicted contribution of the right-handed neutrinos to the effective number of relativistic species N_{eff}​ with current cosmological bounds, confirming the model’s consistency with observations.

The use of the CTP formalism eliminates the need for Real Intermediate State (RIS) subtraction, leading to a more consistent and elegant treatment. Furthermore, by incorporating quantum statistical factors, we demonstrate that viable asymmetry generation is achievable even with only two right-handed neutrino flavours. Consequently, the mechanism is generic and does not rely on specific particle species such as leptoquarks or other particular Standard Model extensions.

Atom interferometry provides a unique platform for testing fundamental physics. Building on the successful realization of the gravitational Aharonov-Bohm (gAB) effect in a large-baseline atom interferometer, I propose a next-generation experiment adapting this precise setup by adding a controllable electric potential. This experiment enables a background-free search for Beyond Standard Model (BSM) physics manifesting as a phenomenological composition-dependent coupling to both a gravitational and an electric potential ($\mathcal{L}_{BSM} \propto q \varphi_g \varphi_e$). I show that the analogous Standard Model (SM) effect, a gravitationally-modified Stark shift, vanishes identically due to parity conservation; as the atomic ground state has even parity, the expectation value of this interaction is zero. To detect the target microradian-scale signal beneath milliradian-scale technical noise and gigaradian-scale inertial backgrounds, the experimental design integrates three crucial solutions: (1) a simultaneous dual-isotope ($^{85}$Rb/$^{87}$Rb) interferometer to reject technical common-mode noise, (2) optimal spin-squeezed states providing N$^{-2/3}$ sensitivity scaling to surpass the Standard Quantum Limit, and (3) a four-point differential quadrature ($\pm V_0, \pm k_{\text{eff}}$) to algebraically cancel the dominant inertial phase and all k-odd systematics. A Monte Carlo analysis validates this complete protocol's robustness against systematics and projects a realistic path to a 5-sigma discovery within a 3-month integration time. This model-independent search, particularly sensitive to neutron-coupled forces like U(1)$_{B-L}$ gauge bosons, constitutes a high-precision null test that further solidifies the Aharonov–Bohm intuition that potentials are more fundamental than fields.