This work treats few-body systems consisting of neutrons interacting with a $^{4}{\mathrm{He}}$ nucleus. The adiabatic hyperspherical representation is utilized to solve the $N$-body Schr$\ddot{\mathrm{o}}$dinger equation for the three- and four-body systems, treating both $^{6}{\mathrm{He}}$ and $^{7}{\mathrm{He}}$ nuclei. A simplified central potential model for the $^{4}{\mathrm{He}}-n$ interaction is used in conjunction with a spin-dependent three-body interaction to reproduce $^{6}{\mathrm{He}}$ bound-state and resonance properties as well as properties for the $^{8}{\mathrm{He}}$ nucleus in its ground-state. With this Hamiltonian, the adiabatic hyperspherical representation is used to compute bound and scattering states for both $^{6}{\mathrm{He}}$ and $^{7}{\mathrm{He}}$ nuclei. For the $^{6}{\mathrm{He}}$ system, the electric quadrupole transition between the $0^{+}$ and $2^{+}$ state is investigated. For the $^{7}{\mathrm{He}}$ system, $^{6}{\mathrm{He}}+n$ elastic scattering is investigated along with the four-body recombination process $^{4}{\mathrm{He}}+n+n+n\rightarrow$$^{6}{\mathrm{He}}+n$ and breakup process $^{6}{\mathrm{He}}+n\rightarrow$$^{4}{\mathrm{He}}+n+n+n$.

Very strong electromagnetic field can be generated in peripheral relativistic heavy ion collisions. This work is devoted to exploring the interplay between the effects of a constant external electric field and confining potential on heavy-flavor mesons. As the corresponding vector potential linearly depends on one spatial coordinate for a constant electric field, it might be able to overcome the linear confining potential of QCD and induce deconfinement. To perform analytic calculations and for comparison, one and two dimensional systems are studied together with the realistic three dimensional systems. The one dimensional Schr$\ddot{\text o}$dinger equation can be solved analytically with the help of Airy functions, and deconfinement is indeed realized when the electric field is larger than the string tension. Focus on the confining case, the two and three dimensional Schr$\ddot{\text o}$dinger equations can be solved analytically in large $r$ limit with the help of elliptic cosine/sine functions, and the wave functions are dominated by the region antiparallel to the electric field. When a more realistic potential is applied, a non-monotonic feature is found for $\Upsilon(2S)$ and $\Upsilon(3S)$-like mesons with increasing electric field.

The production mechanism of light nuclei in heavy-ion collisions is vital to understanding the intricate details of nucleon-nucleon interactions. The coalescence of nucleons is a well-known mechanism that attempts to explain the production mechanism of these light clusters. This work investigates the formation mechanism of these nucleon clusters with a combination of coalescence and femtoscopy of nucleons and nuclei. It is achieved by appending a coalescence and correlation afterburner (\texttt{CRAB}) to the \texttt{SMASH} transport model. To have a proper view of the anisotropy of light nuclei clusters, a mean-field approach to \texttt{SMASH} is applied. The anisotropic coefficients of various light nuclei clusters are calculated and compared to experimental measurements. To incorporate hydrodynamics into the picture, the anisotropic measurements are completed in a hybrid \texttt{SMASH}+\texttt{vHLLE} mode. In both approaches, the femtoscopy of nucleons and light nuclei is performed, reported with CRAB, and compared to the latest experimental measurements. An insight into cluster formation time is drawn by extracting the emission source size with the Lednick\'y-Lyuboshits (LL) model.

The construction of predictive models of atomic nuclei from first principles is a challenging (yet necessary) task towards the systematic generation of theoretical predictions (and associated uncertainties) to support nuclear data evaluation. The consistent description of the rich phenomenology of nuclear systems indeed requires the introduction of reductionist approaches that construct nuclei directly from interacting nucleons by solving the associated quantum many-body problem. In this context, so-called \textit{ab initio} methods offer a promising route by deriving controlled (and systematically improvable) approximations both to the inter-nucleon interaction and to the solutions of the many-body problem. From a technical point of view, approximately solving the many-body Schr\"odinger equation in heavy open-shell systems typically requires the construction and contraction of large mode-4 (mode-6) tensors that need to be stored repeatedly. Recently, a new dimensionality reduction method based on randomized singular value decomposition has been introduced to reduce the numerical cost of many-body perturbation theory. This work applies this lightweight formalism to the study of the Germanium isotopic chain, where standard approaches would be too expansive to run. Inclusion of triaxiality is found to improve the overall agreement with experimental data on differential quantities.

The microscopic description of alpha decay from the nucleons' degree of freedom involves a two-step process. The first consists of the clusterization of neutron and proton pairs; the second involves the tunneling process. A robust protocol for calculating the normalized spectroscopic factor, as defined by Fliessbach, and its error is established and used for calculating the alpha-width for the $0^+$ states of the nucleus $^{44}$Ti. The Gamow Shell Model is used to calculate the structure part of the alpha-decay, while the Gamow wave function determines the reaction part. The conventional and normalized spectroscopic factors are calculated for the ground and excited $0^+$ states of $^{44}$Ti and the alpha-width and half-life of the excited states. A near alpha-threshold state has an alpha half-life of 5 $\mu$sec. The normalization does not appreciably modify the ground-state clusterization, while the excited states do. The non-resonant continuum significantly increases the clustering of some of the excited states, particularly the $T=2$ state. The normalized formation amplitude looks like a single-particle wave function.

The determination of the nuclear spectral function from the measured cross section of the electron-nucleus scattering process $e + A \to e^\prime + p + (A-1)$is discussed, and illustrated for the case of a carbon target. The theoretical model based on the local density approximation, previously employed to derive the spectral function from a combination of accurate theoretical calculations and experimental data, has been developed further by including additional information obtained from measurements performed with high missing energy resolution. The implications for the analysis of $\gamma$-ray emission associated with nuclear deexcitation are considered.

The recent demonstration of laser excitation of the $\approx 8$ eV isomeric state of thorium-229 is a significant step towards a nuclear clock. The low excitation energy likely results from a cancellation between the contributions of the electromagnetic and strong forces. Physics beyond the Standard Model could disrupt this cancellation, highlighting nuclear clocks' sensitivity to new physics. Accurate predictions of the different contributions to nuclear transition energies, and therefore of the quantitative sensitivity of a nuclear clock, are challenging. We improve upon previous sensitivity estimates and assess a ''nightmare scenario'', where all binding energy differences are small and the new physics sensitivity is poor. A classical geometric model of thorium-229 suggests that fine-tuning is needed for such a scenario. We also propose a $d$-wave halo model, inspired by effective field theory. We show that it reproduces observations and suggests the ''nightmare scenario'' is unlikely. We find that the nuclear clock's sensitivity to variations in the effective fine structure constant is enhanced by a factor of order $10^4$. We finally propose auxiliary nuclear measurements to reduce uncertainties and further test the validity of the halo model.

While dynamical tides only become relevant during the last couple of orbits for circular inspirals, orbital eccentricity can increase their impact during earlier phases of the inspiral by exciting tidal oscillations at each close encounter. We investigate the effect of dynamical tides on the orbital evolution of eccentric neutron star binaries using post-Newtonian numerical simulations and constructing an analytic stochastic model. Our study reveals a strong dependence of dynamical tides on the pericenter distance, with the energy transferred to dynamical tides over that dissipated in gravitational waves (GWs) exceeding $\sim1\%$ at separations $r_\mathrm{p}\lesssim50$ km for large eccentricities. We demonstrate that the effect of dynamical tides on orbital evolution can manifest as a phase shift in the GW signal. We show that the signal-to-noise ratio of the GW phase shift can reach the detectability threshold of 8 with a single aLIGO detector at design densitivity for eccentric neutron star binaries at a distance of $40$ Mpc. This requires a pericenter distance of $r_\mathrm{p0}\lesssim68$ km ($r_\mathrm{p0}\lesssim76$ km) at binary formation with eccentricity close to 1 for a reasonable tidal deformability and f-mode frequency of 500 and $1.73$ kHz (700 and $1.61$ kHz), respectively. The observation of the phase shift will enable measuring the f-mode frequency of neutron stars independently from their tidal deformability, providing significant insights into neutron star seismology and the properties of the equation of state. We also explore the potential of distinguishing between equal-radius and twin-star binaries, which could provide an opportunity to reveal strong first-order phase transitions in the nuclear equation of state.

We study incoherent diffractive production of two and three jets in electron-nucleus deep inelastic scattering (DIS) at small $x_{\scriptscriptstyle \rm Bj}$ using the color dipole picture and the effective theory of the Color Glass Condensate (CGC). We consider color fluctuations in the CGC weight-function as the source of the nuclear break-up and the associated momentum transfer $\sqrt{|t|}$. We focus on the regime in which the two jets are almost back-to-back in transverse space and have transverse momenta $P_{\perp}$ much larger than both the momentum transfer and the saturation scale $Q_s$. The cross section for producing such a hard dijet is parametrically dominated by large size fluctuations in the projectile wave-function that scatter strongly and for which a third, semi-hard, jet appears in the final state. The 2 + 1 jets cross section can be written in a factorized form in terms of incoherent quark and gluon diffractive transverse momentum distributions (DTMDs) when the third jet is explicit, or incoherent diffractive parton distribution functions (DPDFs) when the third jet is integrated over. We find that the DPDFs and the corresponding cross section saturate logarithmically when $|t| \ll Q_s^2$, while they fall like $1/|t|^2$ in the regime $Q_s^2 \ll |t| \ll P_{\perp}^2$. We further show that there is no angular correlation between the hard jet momentum and the momentum transfer. For typical EIC kinematics the 2 jets and 2 + 1 jets cross sections are of the same order.

Preliminary data from the Beam-Energy Scan II measurements by the STAR Collaboration at the Relativistic Heavy Ion Collider suggest a dip in the fourth-to-second-order cumulant ratio when plotted vs. beam energy. At the same energy range where the structure appears, a transition from hadrons to quarks is expected, the deconfinement transition. In this paper, the role of quark deconfinement in establishing fluctuaitions in the early stages of the collision is considered. Two models are compared: one with stopping occurring on a baryon-by-baryon basis, and a second where stopping proceeds through quark degrees of freedom. In the latter model, the fluctuation of baryon number is significantly reduced and this signal is found to survive recombination into hadrons and the subsequent diffusion. The transformation from baryon to quark stopping thus produces a dip in the fourth-to-second-order cumulant ratio when plotted vs. beam energy, consistent with observations.

By employing modified Chaplygin fluid prescription for the dark energy, we construct slowly rotating isotropic and anisotropic dark energy stars. The slow rotation is incorporated via general relativistic Hartle-Thorne formalism; whereas the anisotropy is introduced through Bowers-Liang prescription. We consider both the monopole and quadrupole deformations and present a complete analysis of rotating dark energy stars. By numerically solving the rotating stellar structure equations in presence of anisotropy, we analyse and quantify various properties of dark energy stars such as mass ($M$), radius, mass deformation, angular momentum ($J$), moment of inertia, and quadrupole moment ($Q$), for three different equation of state parameters. We find that anisotropic slow rotation results in significant deformation of stellar mass and thereby affects other global properties studied. For the values of angular frequencies considered, the effect of anisotropy on the stellar structure is found to be more prominent than that due to rotation. The dimensionless quadrupole moment $QM/J^2$ measuring deviation from a Kerr metric black hole was obtained for anisotropic dark energy stars. We observe that dark energy stars with higher anisotropic strength tend to approach the Kerr solution more closely. We report that our results have considerable agreement with various astrophysical observational measurements.

In certain kinematic and particle mass configurations, triangle singularities may lead to line-shapes which mimic the effects of resonances. This well-known effect is scrutinized here in the presence of final-state rescattering. The goal is achieved first by utilizing general arguments provided by Landau equations, and second by applying a modern scattering formalism with explicit two- and three-body unitarity.

In present work, we present a couple-channel formalism for the description of tunneling time of a quantum particle through a composite compound with multiple energy levels or a complex structure that can be reduced to a quasi-one-dimensional multiple-channel system.