It is still unknown whether the mass terms for neutrinos are of Majorana type or of Dirac type. An interesting possibility, known as pseudo-Dirac scheme, combines these two with a dominant Dirac mass term and a subdominant Majorana one. As a result, the mass eigenstates come in pairs with a maximal mixing and a small splitting determined by the Majorana mass. This will affect the neutrino oscillation pattern for long baselines. We revisit this scenario employing recent solar neutrino data, including the seasonal variation of the ${}^7\mathrm{Be}$ flux recently reported by BOREXINO. We constrain the splitting using these data and find that both the time integrated solar neutrino data and the seasonal variation independently point towards a new pseudo-Dirac solution with nonzero splitting for ${\nu }_2$ of $\mathrm{\Delta }{m}_2^2\simeq 1.5\times {10}^{-11}{\mathrm{eV}}^2$. We propose alternative methods to test this new solution. In particular, we point out the importance of measuring the solar neutrino flux at the intermediate energies $1.5\mathrm{MeV}<E_{\nu }<3.5\mathrm{MeV}$ (below the Super-Kamiokande detection threshold) as well as a more precise measurement of the $pep$ flux.

Atmospheric Carbon Dioxide (CO2), a significant greenhouse gas, drives climate change, influencing temperature, rainfall, and the hydrologic cycle. This alters precipitation patterns, intensifies storms, and changes drought frequency and timing of floods, impacting ecosystems, agriculture, water resources, and societies globally. Understanding how global CO2 fluctuations impact regional atmospheric CO2 levels can inform mitigation strategies and Facilitate water resources management. The study investigates how global CO2 fluctuations affect atmospheric CO2 concentrations (XCO2) in Iran from 2015 to 2020, aiming to inform mitigation strategies against climate change. XCO2 data OCO-2 satellite and CO2 surface flux data from the Copernicus Atmosphere Monitoring Service (CAMS) were analyzed. Over the 6 years, XCO2 in Iran increased steadily by 12.66 ppm, mirroring global rises. However, Iran's CO2 surface flux decreased, with slight increases in anthropogenic emissions but decreased natural and total fluxes. Monthly patterns of XCO2 and surface flux exhibited variations, with XCO2 reaching its zenith in spring and dipping to its lowest point during summer, while surface flux peaked during the summer months. The results reveal a significant discrepancy between Iran's surface CO2 flux and atmospheric XCO2 trends. While Iran's anthropogenic emissions increased barely from 2015–2020, its natural and total CO2 fluxes decreased. However, XCO2 increased steadily over this period, indicating the dominant impact of global rather than local factors on Iran's XCO2. Curbing worldwide greenhouse gas output is imperative to disrupt the current trajectory of climate change. Reporting CO2 levels can inform climate mitigation plans, reducing emissions to combat global warming and minimize global impacts on the hydrologic cycle.

The (g − 2)_μ anomaly indicates that the second generation of leptons should have new interactions beyond the standard model. The high flux of ν_μ and $$ \overline{\nu} $$ν ¯ _μ at the forward experiments such as FASERν and SND@LHC makes them suitable setups to search for new interactions of the second generation leptons. In this paper, we build a model in which the second generation left-handed leptons couple to a new right-handed neutrino, N and a new Higgs doublet which also couples to the quarks. The scattering of high energy ν_μ off nuclei can produce N. We investigate how forward experiments can test this model by looking for the N production vertex followed by the displaced vertex of the N decay. Discovering even a single such event can be a harbinger to look for the spectacular signals of the new Higgs doublet production at the LHC. We discuss the possibility of explaining the (g − 2)_μ anomaly by adding more generations of N which will lead to chain decays of N and multiple leptons with distinct signals both at forward experiments and at the CMS and ATLAS detectors. Finally, we show that by adding a new light singlet scalar mixed with the neutral component of the new Higgs doublet (i.e., 2HDM+S model), the statistics of the data sample can be dramatically increased.

During the run III of the LHC, the forward experiments FASER $$\nu $$ν and SND@LHC will be able to detect the Charged Current (CC) interactions of the high energy neutrinos of all three flavors produced at the ATLAS Interaction Point (IP). This opportunity may unravel the mysteries of the third generation leptons. We build three models that can lead to a tau excess at these detectors through the following Lepton Flavor Violating (LFV) beyond Standard Model (SM) processes: (1) $$\pi ^+ \rightarrow \mu ^+ \nu _\tau $$π + → μ + ν τ ; (2) $$\pi ^+ \rightarrow \mu ^+ \bar{\nu }_\tau $$π + → μ + ν ¯ τ and (3) $$\nu _e+\mathrm{nucleus}\rightarrow \tau +X$$ν e + nucleus → τ + X . We comment on the possibility of solving the $$(g-2)_\mu $$( g - 2 ) μ anomaly and the $$\tau $$τ decay anomalies within these models. We study the potential of the forward experiments to discover the $$\tau $$τ excess or to constrain these models in case of no excess. We then compare the reach of the forward experiments with that of the previous as well as next generation experiments such as DUNE. We also discuss how the upgrade of FASER $$\nu $$ν can distinguish between these models by studying the energy spectrum of the tau.

We quantify the effects of light spin-zero particles with pseudoscalar couplings to leptons and scalar couplings to nucleons on the evolution of solar neutrinos. In this scenario the matter potential sourced by the nucleons in the Sun’s matter gives rise to spin precession of the relativistic neutrino ensemble. As such the effects in the solar observables are different if neutrinos are Dirac or Majorana particles. For Dirac neutrinos the spin-flavour precession results into left-handed neutrino to right-handed neutrino (i.e., active-sterile) oscillations, while for Majorana neutrinos it results into left-handed neutrino to right-handed antineutrino (i.e., active-active) oscillations. In both cases this leads to distortions in the solar neutrino spectrum which we use to derive constraints on the allowed values of the mediator mass and couplings via a global analysis of the solar neutrino data. In addition for Majorana neutrinos spin-flavour precession results into a potentially observable flux of solar electron antineutrinos at the Earth which we quantify and constrain with the existing bounds from Borexino and KamLAND.

The BOREXINO experiment has been collecting solar neutrino data since 2007, providing the opportunity to study the variation of the event rate over a decade. We find that at 96% C.L., the rate of low energy events shows a time modulation favoring a correlation with a flux from Jupiter. We present a new physics model, the Jovian whisper model, based on dark matter of mass $\sim 0.1–4\mathrm{GeV}$ captured by Jupiter that can account for such modulation. We discuss how the Jovian whisper model (JWM) can be tested.