We derive the one-pion exchange potential (OPEP) in the presence of a homogeneous magnetic field using chiral perturbation theory with nonrelativistic nucleons. Our approach is applicable not only to weak magnetic fields but also to strong ones up to around the pion-mass scale. The Green's function of charged pions is modified by the magnetic field, leading to changes in the nuclear force. By numerically evaluating the modified OPEP incorporating its spin and isospin dependencies, we show that the range of the potential decreases in both directions parallel and perpendicular to the magnetic field as the field strength increases. We also compute the resulting energy shift of the deuteron due to the modified OPEP, which can reach the order of 1 MeV around $|eB| = m_\pi^2$, which is comparable to the deuteron binding energy.

The standard $\Lambda{\rm CDM}$ model has encountered serious challenges and the $H_0$ tension has become more significant with increasingly precise cosmological observation. Meanwhile, inconsistencies in measurements of the curvature parameter $\Omega_\mathrm{K}$ between different datasets also have emerged. In this work, we employ two global and cosmic age-based parameterizations, PAge and MAPAge, to perform model-independent measurements of the Hubble constant $H_0$ and $\Omega_\mathrm{K}$ by utilizing the inverse distance ladder (IDL). To construct the PAge-improved IDL, we utilize the strong gravitational lensing (SGL), cosmic chronometers (CC), and gamma ray bursts (GRB) data to calibrate the latest DESI DR2 baryon acoustic oscillation data and DESY5 type Ia supernova data. Our analysis indicate that DESI+DESY5+SGL+CC+GRB gives $H_0=71.59\pm 0.94\,{\rm km}~{\rm s}^{-1}~{\rm Mpc}^{-1}$ in the MAPAge model, reducing the $H_0$ tension to the $1.0\sigma$ level. Extending to MAPAge$+\Omega_{\rm K}$ model, we obtain $\Omega_\mathrm{K}=0.001\pm 0.038$, which suggests that current late-time data are consistent with a flat universe. Finally, the Bayesian analysis indicates that the present late-universe data provide weak to moderate evidence in favor of PAge and MAPAge relative to $\Lambda{\rm CDM}$.

In this letter, we provide a simple algorithm, anyPUB, to systematically derive the $2 \rightarrow 2$ scattering matrix in the high-energy limit for any kind of models, irrespective of their gauge group or their field representation. After computing the eigenvalues analytically and/or numerically from this matrix, we impose perturbative unitarity bounds on them. We tested our method on various models and validated the results against the literature. Finally, as a concrete application of our approach, we discuss the case of the minimal left-right symmetric model and derive, for the first time, the perturbative unitarity constraints in the Pati-Salam model.

We present a complete one-loop analysis of charged scalar boson pair production in photon-photon collisions, $\gamma\gamma \to H^\pm H^\mp$, within the framework of the Inert Doublet Model (IDM). The calculation is carried out in the on-shell renormalization scheme and incorporates both weak corrections and QED effects, including soft and hard photon radiation. Virtual loop contributions and real emission processes are computed using the Feynman diagrammatic method, ensuring the cancellation of ultraviolet and infrared divergences. To properly account for the Coulomb singularity that arises in the QED sector near threshold, we introduce the resummed cross section based on the Sommerfeld factor. The IDM parameter space is explored under theoretical consistency conditions, collider limits, and dark matter constraints, and three representative scenarios are studied in detail. We find that the magnitude of the quantum corrections is strongly controlled by the absolute value of the trilinear scalar coupling $\lambda_{h^0 H^+ H^-}$, which correlates with the charged scalar mass. When all constraints are applied, the weak corrections are typically in the range of $-12\%$ to $-7\%$ at $\sqrt{s}=250$~GeV, and between $-15\%$ and $6\%$ at $\sqrt{s}=500$~GeV. At higher energies, such as $\sqrt{s}=1$~TeV, the corrections can become very large, ranging from about $-20\%$ up to $+60\%$. Our findings highlight the significant role of higher-order effects in photon-photon collisions and establish $\gamma\gamma \to H^\pm H^\mp$ as a promising process to investigate the charged scalar sector of the IDM at future high-energy photon colliders. Several benchmark points are proposed to facilitate future experimental searches.

We introduce local information flows as a diagnostic tool for characterizing out-of-equilibrium quantum dynamics in lattice gauge theories. We employ the information lattice framework, a local decomposition of total information into spatial- and scale-resolved contributions, to characterize the propagation and buildup of quantum correlations in real-time processes. Focusing on the Schwinger model, a canonical $(1+1)$-dimensional U(1) lattice gauge theory, we apply this framework to two scenarios. First, in the near-threshold scattering of two vector mesons, we demonstrate that the emergence of correlations at a longer length scale in the information lattice marks the production of heavier scalar mesons. Second, in the dynamics of electric field strings, we clearly distinguish between the confining regime, which evolves towards a steady state with a static correlation profile, and the string-breaking sector. The latter is characterized by dynamic correlation patterns that reflect the sequential formation and annihilation of strings. This information-centric approach provides a direct, quantitative, and interpretable visualization of complex many-body phenomena, offering a promising tool for analyzing dynamics in higher-dimensional gauge theories and experiments on quantum hardware.

We analyze a model of quintessence governed by an exponential potential and non-minimally coupled to gravity, in light of recent datasets, including cosmic microwave background, baryon acoustic oscillations, and supernovae distance moduli observations. Mainly focusing on the Palatini formulation of gravity, a phase space analysis reveals the existence of a late-time stable de Sitter attractor as long as the non-minimal coupling constant is negative, regardless of the value of the slope of the exponential. Fitting to CMB+DESI+DESY5 data, we find strong evidence for our model over $\Lambda$CDM, with a Bayes factor $\log B = 5.52$. Furthermore, the data seem to prefer dynamical dark energy at $>3\sigma$ C.L. and a phantom crossing in the barotropic parameter of dark energy at $2-3\sigma$ C.L.. We find that the scalar field dynamics in the Palatini formalism provides marginally better agreement to the data compared to the metric formalism.

Ultralight dark matter may couple quadratically to Standard Model particles. Such quadratic interactions give rise to both coherent and stochastic signals in pulsar timing array (PTA) observations. In this work, we characterize these signals, including the effects of dark matter propagation in a finite-density medium, and assess the sensitivity of current and upcoming PTA observations to their detection. For coherent signals, we find that the sensitivity of current PTA observations competes with and sometimes exceeds that of other probes, such as equivalence principle tests and atomic clocks. For stochastic signals, we find that PTA sensitivities underperform equivalence principle constraints for both existing and upcoming PTA data sets.

Dark matter fermions interacting via attractive fifth forces mediated by a light mediator can form dark matter halos in the very early universe. We show that bound systems composed of these halos are capable of generating gravitational wave (GW) signals detectable today, even when the individual halos are very light. The Yukawa force dominates the dynamics of these halo binaries, rather than gravity. As a result, large GW signals can be produced at initially extremely high frequencies, which are then redshifted to frequency bands accessible to current or future GW observatories. In addition, the resulting GW signals carry distinctive features that enable future observations to distinguish them from conventional ones. Notably, even if only a tiny fraction of dark matter experiences strong fifth-force interactions, such effects provide a new avenue to discover self-interacting dark matter through GW observations.

We investigate the impact of an external magnetic field on the vector charmonium system within the framework of Hilbert moment QCD sum rules. By incorporating magnetic corrections to the perturbative contributions of the QCD sector, we analyze the behavior of the hadronic parameters of the $J/\psi$ resonance -- namely, its continuum threshold $s_0$, decay constant $f_V$, width $\Gamma_V$, and its mass $M_V$, as functions of the magnetic field strength. Our results show that $s_0$ and $f_V$ increase monotonically, while $\Gamma_V$ decreases significantly and $M_V$ remains essentially constant. These behaviors indicate a strengthening of the hadronic state in the presence of a magnetic field, consistent with the phenomenon of magnetic catalysis. Although magnetic catalysis has traditionally been associated with light-quark systems via chiral symmetry breaking, our results demonstrate that similar effects persist in the heavy-quark sector, despite the absence of chiral dynamics.

High-energy physics experiments studying neutrinos rely heavily on simulations of their interactions with atomic nuclei. Limitations in the theoretical understanding of these interactions typically necessitate ad hoc tuning of simulation model parameters to data. Traditional tuning methods for neutrino experiments have largely relied on simple algorithms for numerical optimization. While adequate for the modest goals of initial efforts, the complexity of future neutrino tuning campaigns is expected to increase substantially, and new approaches will be needed to make progress. In this paper, we examine the application of simulation-based inference (SBI) to the neutrino interaction model tuning for the first time. Using a previous tuning study performed by the MicroBooNE experiment as a test case, we find that our SBI algorithm can correctly infer the tuned parameter values when confronted with a mock data set generated according to the MicroBooNE procedure. This initial proof-of-principle illustrates a promising new technique for next-generation simulation tuning campaigns for the neutrino experimental community.

Is the usual treatment of axion dark matter as a classical field reliable? We show that the answer is subtle: the axion field could well be in a quantum state that has no complete classical description, but realistic detectors cannot tell the difference. To see this, we solve a fully quantum model of axion detection using quantum optics techniques. We show that intrinsically quantum effects are washed out by mode averaging or small amounts of noise, and significantly suppressed by the weakness of the axion coupling. Our work exemplifies that there should always be a classical analog for axion dark matter effects, extends to other wave (ultralight) dark-matter candidates, and gives a general method to compute the effects of exotic dark-matter states.

Despite stringent constraints from Big Bang Nucleosynthesis (BBN) and cosmic microwave background (CMB) observations, it is still possible for well-motivated particle physics models to substantially alter the cosmic expansion history between BBN and recombination. In this work we consider two different axion models that can realize a period of first matter domination, then kination, in this epoch. We perform fits to both primordial element abundances as well as CMB data and determine that up to a decade of late axion domination is allowed by these probes of the early universe. We establish the implications of late axion domination for the matter power spectrum on the scales $1/\mathrm{Mpc}\lesssim k \lesssim 10^3/$Mpc. Our 'log' model predicts a relatively modest bump-like feature together with a small suppression relative to the standard $\Lambda$CDM predictions on either side of the enhancement. Our 'two-field' model predicts a larger, plateau-like feature that realizes enhancements to the matter power spectrum of up to two orders of magnitude. These features have interesting implications for structure formation at the forefront of current detection capabilities.

We investigate the unique potential of a high-energy muon collider to probe lepton-flavor-violating signals arising from physics beyond the Standard Model (SM). Low-energy, precision searches for charged lepton-flavor violation (LFV) are projected to dramatically improve their sensitivity in the coming years, and could provide the first evidence of new physics. We interpret the sensitivity of these searches in terms of a set of LFV operators in the SM Effective Field Theory. The same operators are then probed at the TeV scale by evaluating the projected reach of a muon collider while accounting for SM backgrounds and using a parameterized detector simulation. We find that for most operators, a muon collider could confirm signals if they are seen at future low energy experiments, whereas for certain flavor combinations it extends the reach to scales well beyond those accessible at lower energies. We also project the sensitivity of a muon collider to lepton flavor-violating decays of the SM Higgs boson and demonstrate improved sensitivity to $h \to e\tau$ and $h \to \mu\tau$ by an order of magnitude compared to the High-Luminosity LHC. The importance of having multiple, complementary probes is illustrated by considering both various combinations of operators and relative sizes of flavor-violating transitions between generations under various assumptions for the flavor structure of new physics.

The past decade has transformed our ability to observe the Universe. Via gravitational waves, merging black holes and neutron stars can now be directly detected, offering unprecedented opportunities to test General Relativity and explore astrophysics in a new way. Driven by this breakthrough, the next generation of detectors is being developed to observe a wider range of sources with greater precision, ushering in a new era in gravitational-wave astronomy: leveraging black holes as probes of new physics. This thesis investigates how astrophysical environments, such as plasma, dark-matter structures, and clouds of ultralight bosons, affect black holes and their gravitational-wave signatures. After a short overview of gravitational-wave astrophysics, I study three classes of scenarios. (i) Isolated black holes: I examine boson clouds around black holes, their electromagnetic couplings and the role of surrounding plasma. (ii) Ringdown: I show that plasma can strongly modify the ringdown of charged black holes, whereas realistic dark-matter halos produce no detectable deviations even for next-generation detectors. (iii) Inspiral: for extreme-mass-ratio inspirals with boson clouds, I find that orbital resonances typically destroy the cloud unless the orbit is nearly counter-rotating, yielding new and exciting observational signatures. Entering the relativistic regime, I develop a self-consistent perturbative framework to model generic environments in extreme-mass-ratio binaries and apply it to the boson-cloud case. Finally, I construct a model for binaries repeatedly crossing active galactic-nucleus disks and track their long-term orbital evolution. The results of this thesis show how black hole environments shape gravitational-wave signals and open avenues for testing new physics with future observatories such as LISA or the Einstein Telescope.

We study heavy-hadron semileptonic decays proceeding via $b \to c$ transition, such as $B \to D^{(*)}\tau\bar{\nu}_\tau$ and $\Lambda_b \to \Lambda_c\tau\bar{\nu}_\tau$. In the heavy-quark limit, where the heavy-quark symmetry holds, we construct a general heavy-quark sum rule for these decays based on the spin decomposition picture. The relation holds directly for the squared amplitudes without requiring phase-space integration. We then apply this relation to reproduce the sum rule among $B \to D^{(*)}\tau\bar{\nu}_\tau$ and $\Lambda_b \to \Lambda_c\tau\bar{\nu}_\tau$. Furthermore, we extend the analysis to $\Omega_b \to \Omega_c^{(*)}$ transitions and those involving excited states, such as $B \to \{D_0^*,D_1^*\}$ and $B \to \{D_1,D_2^*\}$.

We compute the twist-2 matching of transverse momentum dependent (TMD) helicity parton distribution and fragmentation functions at next-to-next-to-next-to-leading order (N$^3$LO) in QCD. This calculation entails the complete set of next-to-next-to-leading order (NNLO) Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) splitting functions govering the evolution of helicity-dependent parton distribution functions (PDFs) and fragmentation functions (FFs). Within TMD factorization framework, we quantify the impact of radiative corrections by completing the next-to-next-to-next-to-leading logarithmic (N$^3$LL) prediction for lepton-hadron transverse momentum imbalance in semi-inclusive deep inelastic scattering (SIDIS). Our results provide the most precise theoretical input for probing the helicity structure and confined motion of quarks and gluons at future electron-ion collider (EIC).

The precise reconstruction of the mass peak of long-lived heavy neutral leptons (HNLs) helps to improve the sensitivity for sterile neutrino searches in both fixed-target and collider environments (e.g., SHiP and the LHC). We present an analytical framework for reconstructing the HNL mass peak in the semileptonic HNL decay channel $N\rightarrow l\rho$ with $\rho\to\pi\pi^0$, using only the lepton and the charged pion emerging from the decay vertex together with kinematic constraints and the known particle masses. Incorporating mass constraints from intermediate resonances (e.g., the $\rho$ meson) or the parent particle (e.g., the $W$ boson at the collider experiments), we propose two methods, suitable for experiments with displaced vertex tracking capabilities. The particle-level simulation's results demonstrate that the $\rho$-mass constraint method yields promising HNL mass resolution in both beam-dump and collider-based environments. The W-mass constraint method, limited to the HNLs produced via $W$-boson decays at the collider-based experiments, shows better HNL mass resolution than the $\rho$-mass constraint method.

We present a calibratable, jet-free framework that enhances the search significance of the flagship LHC channel $HH \to 4b$ by more than a factor of five compared to existing approaches. The method employs a mass-decorrelated discriminant to identify $h_1 h_2 \to 4b$ with variable $h_{1,2}$ masses and a simultaneous estimator of $(m_{h_1}, m_{h_2})$, both derived from multiclass classification on all-particle inputs. The $HH$ signal response can be calibrated using $ZZ \to 4b$. Using a highly realistic simulation framework validated through multiple tests, we demonstrate the method's robustness and identify two prerequisites essential for achieving this level of sensitivity. Results indicate that with LHC Run 2 and 3 data, observation-level sensitivity to $HH$ appears within reach, enabling constraints on $\kappa_\lambda$ comparable to HL-LHC projections and offering an accelerated path to precision measurements of the Higgs trilinear coupling.

For coupled channels $D^0K^+$, $D^+K^0$, $D_s^+\eta$, and $D_s^+\pi^0$, the $S$-wave scattering amplitudes are constructed taking into account the mixing of the isoscalar resonance $D^*_{s0}(2317)^+$ with nonresonance amplitudes with isospin $I=1$. The phenomenological approach we use allows us to quite simply clear up the general structure of the $D^*_{s0}(2317)^+\to D_s^+\pi^0$ decay amplitude violating isospin. We show that the phase of this amplitude coincides with the phase of the nonresonanct $D_s^+\pi^0$ scattering amplitude in agreement with the Watson theorem. Its modulus squared, as it should be, determines the width of the resonance peak in the $D_s^+\pi^0$ channel. Taking into account the $\pi^0-\eta$ mixing in internal lines up to the second order inclusively ensures that the unitarity condition is fulfilled. The presented analysis complements the description of the $D^*_{s0}(2317 )^+\to D_s^+\pi^0$ decay based on the coupled channel unitarized chiral perturbation theory. The numerical estimates obtained by us for the $D^*_{s0}(2317)^+\to D_s^+\pi^0$ decay width do not contradict those available in the literature.

Axion dark matter or any ultralight bosonic dark matter can go through Bose-Einstein condensation due to the large phase density, leading to the formation of axion stars or solitons in dark matter halo centers. The formation rate is enhanced in the presence of the substructures expected in the post-inflationary scenario for the QCD axion or axion-like particles. An axion star will continue to grow until a critical mass is reached, after which it collapses and then explodes, with the emission of relativistic axions, in a process called an ``axinovae.'' There can also be accompanying photon emission due to the stimulated decay of axions in the coherent compact axion star. In axion models with a modest enhancement ($\kappa\sim \mathcal{O}(10)$) of the axion-photon coupling $g_{a\gamma}= \kappa \alpha/(2\pi f_a)$ axinovae will contain a significant flux of radio photons. We determine the range of parameters over which axinovae can be detectable with radio transient searches.