Papers

Gravitational waves (GWs) can induce effective electromagnetic currents when interacting with external electric and magnetic fields, as described by linearized gravity modifications to Maxwell's equations. This coupling enables a novel detection approach for high-frequency gravitational waves (HFGWs) using axion haloscope experiments. Here we present the MAGnetic Gravitational wave Induction Experiment (MAGGIE), the first lumped-element HFGW detector proposed in Europe, designed to probe HFGWs in the kHz-MHz regime by leveraging a 14 T solenoidal magnet at the University of Hamburg. The GW-induced magnetic flux is captured by a custom-designed pickup loop optimized for the expected symmetry of the effective current. A figure-8-shaped geometry, oriented to break the azimuthal symmetry, is implemented, together with a blind-loop configuration, for real-time noise rejection and calibration. The readout scheme is tailored for continuous signals and time-domain transient searches, using waveform templates for primordial black hole (PBH) mergers. The expected experimental reach in terms of strain spectral noise density at the 40 MHz high-frequency end is projected to reach $\sim 4 \times 10^{-16}/\sqrt{\mathrm{Hz}}$ for transient searches, and in terms of strain, projected to reach $\sim 10^{-19}$ for 1 year of continuous search. This allows MAGGIE to constrain currently unexplored regions of the HFGW parameter space.

We propose a ”stepping stone” realization of the varying Peccei Quinn (PQ) scale solution to the QCD axion isocurvature problem. In conventional implementations, suppressing isocurvature during high scale inflation requires a large inflationary PQ scale, while the subsequent evolution toward the much smaller late time vacuum can induce parametric resonance and nonthermal restoration of the PQ symmetry. We ameliorate this tension by introducing an intermediate PQ-breaking vacuum that is reached before the end of inflation, so that the later evolution to the present day PQ scale spans only a moderate hierarchy. The vacuum structure arises radiatively: a Yukawa coupling between the PQ scalar and PQ-charged fermions drives the quartic coupling negative at high scales while keeping it positive at lower scales. A positive dimension six operator then stabilizes a large field minimum, while the positive low energy quartic together with the quadratic terms generates the intermediate vacuum. We study two mechanisms in which the rolling inflaton removes the large field minimum, either by scanning a hidden non-Abelian gauge coupling or by directly scanning the Yukawa coupling. In both cases the PQ field is released toward the intermediate vacuum during inflation, after CMB modes have exited the horizon. We exhibit benchmark regions with subdominant backreaction on the inflationary sector and suppressed vacuum tunneling, and show that the construction permits substantially less hierarchical quartic and higher-dimensional couplings than conventional realizations that depend on a varying PQ scale. The underlying logic may have analogues for extra-dimensional or string axions, where the effective axion decay constant is controlled by geometric moduli, although realizing the required intermediate vacuum in a controlled modulus potential is nontrivial.

Quantum computing offers a new, orthogonal direction for investigating fundamental physics, extending beyond classical numerical methods and conventional observables. Realizing this potential requires directly confronting the noise limiting currently available quantum computers. Progress rests on advancing algorithms, interpreting their results, and managing their errors together. This thesis presents several advancements in the use of quantum simulation and quantum information to probe fundamental physics. The first is in the use of quantum computers to simulate collisions in quantum field theories. Central to these simulations are new wavepacket preparation, time evolution, and error mitigation techniques, which allow for simulations with some of the largest effective circuit volumes to date. These methods enable the first quantum simulation providing numerical evidence for inelastic particle production, a key process in fundamental physics. The second advancement centers on the role quantum-information-theoretic quantities play in physical processes. Beyond mere correlations with the physics of the process, entanglement and magic are shown to probe the interactions present in scattering and hadronization dynamics. A precision study requires a complete quantification of algorithmic and hardware uncertainties, an outstanding goal as quantum simulations mature. The third advancement in this thesis addresses error management. A framework minimizing the effect of algorithmic errors in analog quantum simulations is presented. In a step toward fault tolerance, error detection in encoded quantum simulations is shown to improve estimation of local observables relative to unencoded runs. Together, the developments in this thesis mark practical progress toward fault-tolerant quantum simulations of fundamental physics capable of scientific discovery.

We show that the inert doublet dark matter can reconcile the purported LZ direct detection signal and IceCube constraints. The preferred dark matter mass is 11.3–20.3~TeV, an order of magnitude heavier than the standard higgsino target. The smaller number density at a high mass can reproduce the LZ event given the exponential sensitivity to the velocity, while suppressing the capture rate in the Sun because of the higher infall velocity. On the other hand, the high mass requires a large coupling between the inert doublet and Higgs boson to have the correct annihilation cross section for the freeze-out. There is about an order of magnitude of validity range below the Landau pole, beyond which a UV completion is needed. Electroweak precision observables are below the experimental limits despite the large coupling.

We present a global HQE analysis of inclusive semileptonic $\bar{B} \to X_c l \bar \nu_\ell$ moments, partial branching fractions, and $B^+$, $B^0$ lifetime observables. Our fit setup follows a new approach where perturbative scales are treated as correlated nuisance parameters, while missing higher-order power corrections are assessed through order-by-order fits up to $O(1/m_b^5)$. In the default scenario, we find $|V_{cb}| = (42.32 \pm 0.28|_{\rm fit} \pm 0.10|_{\rm h.o.})\times 10^{-3} = (42.32 \pm 0.30) \times 10^{-3}$ and $\mathcal{B}(\bar B \to X_c \ell \bar \nu_\ell) = (10.91 \pm 0.11|_{\rm fit} \pm 0.21|_{\rm h.o.})\%$. For the lifetimes we obtain $\tau_{B^+} = 1.89^{+0.04}_{-0.22}$ ps and $\tau_{B^0} = 1.74^{+0.03}_{-0.23}$ ps, where the strongly asymmetric uncertainty is dominated by the perturbative scale variation of the non-leptonic width. Our predictions are in agreement with previous predictions and the corresponding widths lie $1.1$-$1.2,\sigma$ below the measurements. For the lifetime ratio, we find $\tau_{B^+}/\tau_{B^0} = 1.082^{+0.031}_{-0.013}$ which agrees with experiment. For the full dataset of $q^2, E_\ell$ and $M_X$ moments, we obtain a poor fit quality, which we investigate using a leave-one-out study. In light of the persisting $|V_{cb}|$ puzzle, new correlated moment measurements as well as updated branching ratio measurements are highly encouraged.

The Standard Model Higgs quartic coupling runs to zero around $10^9-10^{12}$ GeV at $2\sigma$, suggestive of an ultraviolet boundary condition $\lambda\simeq0$ at this scale. In a well-motivated class of high-scale supersymmetric (SUSY) models, the quartic is automatically set to zero at tree level at the superpartner scale. The Higgsino can naturally emerge as the lightest SUSY particle, with its two neutral Weyl components sufficiently degenerate to form an effectively Dirac fermion with an unsuppressed vector coupling to the $Z$. For such Higgsino dark matter, direct detection requires a mass above $\sim10^{11}$ GeV, leading to a coincidence with the scale independently selected by the vanishing quartic. Such a heavy Higgsino cannot freeze out with the observed relic density. However, if its mass exceeds the reheating temperature, the observed dark matter abundance can be reproduced through Boltzmann suppressed freeze-in. This scenario connects the dark matter mass to the measured Higgs mass, with a parameter space already constrained by LUX-ZEPLIN (LZ) and which will be decisively tested at DARWIN/XLZD. Finally, we consider PeV Higgsinos with Majorana gauginos of order $10^7$ GeV, permitting an inelastic Higgsino interpretation of the tentative LZ event while retaining the connection between the scalar superpartner scale and the vanishing Higgs quartic scale.

We discuss the possible topologies of the mass-radius relation for hybrid stars in light of catastrophe theory. We show that different branches of compact stars emerge or disappear depending on the bifurcation structure of the underlying catastrophe potential function, the mathematical analog of an effective potential. For that we assume a single first-order phase transition between nuclear and quark matter. After a warm up with incompressible fluids, we present a qualitative discussion explaining the (dis)appearance of (un)stable branches for hybrid stars as the control parameters change.

The axion coupling to electromagnetism may leave signatures of uncertain nature in astrophysical spectra; one is thought to be a single line centered at the axion frequency $\omega = \sqrt{\left(m_a c^2/\hbar\right)^2 + c^2 k_a^2}$, with $m_a c^2/\hbar$ the axion Compton frequency and $\hbar k_a$ its momentum. If a parametric plasma instability is excited, this signature is transformed into a set of lines, which may be proportionally spaced and linearly polarized. A Crab pulsar signal at a frequency near recent cosmological predictions for the axion Compton frequency has some qualitative similarity to this signature, though this similarity is not evidence that the signal is caused by axions.

In the dual-superconductor picture, the QCD vacuum behaves like a superconductor for chromoelectric fields, with characteristic penetration and coherence lengths. These scales have so far been studied primarily through lattice calculations of static flux tubes. We show that they are also imprinted on exclusive diffraction, where the transverse profile of a gluonic hotspot reflects the response of the vacuum to a localized color source. Using the Clem vortex profile, we fit all 104 H1 and ZEUS measurements of exclusive $J/\psi$ photoproduction and find $\chi^2/{\rm ndf}=0.72$, the penetration depth $\lambda=0.19(2)~{\rm fm}$, the hotspot core size $\xi_v=0.087(13)~{\rm fm}$, and the Ginzburg–Landau parameter $\kappa=2.7(7)$, placing the effective vacuum description in the type-II regime. The corresponding vector mass $1/\lambda=1.03(11)~{\rm GeV}$ agrees with the lattice gluelump mass, and the extracted parameters reproduce the QCD string tension with no free normalization.

A quantum field-theoretical description of neutrino oscillations in matter in adiabatic approximation is developed. Estimates of the oscillation coherence lengths have been made for several solar neutrino production and detection processes. It has been shown that, within the framework of the developed approach, the results of solar neutrino detection experiments can be correctly described in terms of neutrino mass eigenstates without taking oscillations into account.

Particle shower simulation is a major computational cost in high-energy physics. Monte Carlo methods such as Geant4 are accurate but expensive, while most machine learning surrogates are tied to specific detector geometries and require retraining for each design change. We study cross-geometry transfer learning with CaloClouds II, a generative model that produces point clouds rather than voxels and can project onto arbitrary detector readouts. We pre-train on photon showers in the International Large Detector (ILD) and adapt to electron showers in the cylindrical CaloChallenge Dataset 3. With only 100 target showers, fine-tuning reduces the geometric mean Wasserstein distance to Geant4 by about 51% over training from scratch. Bias-only fine-tuning (BitFit) stays within 5% of full fine-tuning while updating only 17% of the diffusion network parameters. We also examine model collapse in CaloClouds II by retraining its normalising flow and diffusion model on its own generated showers across successive generations.

The cancellation of renormalon ambiguities in the operator product expansion is usually formulated as a matching between perturbative Borel ambiguities and prescription dependence in non-perturbative condensates. We give this cancellation a contour realization in the two-dimensional Gross–Neveu model at large $N$. The exact order-$1/N$ fermion self-energy in the massive vacuum is a finite real integral; ambiguities arise only after its large-momentum behavior is decomposed into products of perturbative Wilson coefficients and the matrix elements of the associated operators. A reduced integral isolates the leading renormalon and reveals a two-dimensional contour geometry in which the perturbative series is generated at the boundary corner where the exchanged momentum reaches the external hard scale, while its Stokes discontinuity is controlled by a distinct boundary critical point at zero exchanged momentum. After renormalizing the ultraviolet divergences of the condensate scale integral, we derive its compensating lateral ambiguity without fixing it by matching to the perturbative sector, distinguish the renormalon saddle from the apparent IR Landau pole, and obtain the reduced contour variables from the large-$N$ auxiliary-field path integral. The renormalon saddle is a boundary critical point of this reduced mode-space integral. The perturbative Wilson coefficient and the renormalized condensate thus define complementary relative cycles of the same reduced integrand whose complex tails cancel, reconstructing the original real integration cycle.

When spatial sections of spacetime are topologically nontrivial, the symmetry arguments usually used to choose the Bunch-Davies vacuum are no longer guaranteed to apply. We study this problem for a scalar field on de Sitter spacetime with toroidal spatial sections. The Hadamard conditions, which ensure the same short-distance structure as in flat space, are local and naturally insensitive to the compactification. By contrast, we find that the infrared sector is affected by the toroidal identifications that break global de Sitter invariance, thereby removing the usual argument for discarding zero-mode contributions. We treat the remaining zero-mode freedom as an effective topology-induced source and analyze its effects on an inflationary de Sitter expansion within a semiclassical setting. We show that, for a massless scalar, the zero-mode sector can contain a contribution to the stress-energy tensor with equation of state $P=-\rho$, behaving as a cosmological constant. Thus, the source driving an early-Universe de Sitter phase need not be determined solely by local terms in the action, but can also depend on the infrared structure of the quantum state. Nontrivial topology, as a concrete realization of de Sitter symmetry violation, turns the otherwise-unfixed infrared freedom in vacuum selection to a contribution directly relevant to the semiclassical expansion. This contribution could potentially be applicable to the current accelerated expansion of the Universe.

We present a tool for the automated generation of Universal Feynman Output (UFO) files, used as input by many event generators, for generic Beyond the Standard Model (BSM) theories and their low-energy Effective Field Theory (EFT) descriptions. Building on the Matchete package, which provides a convenient interface for defining BSM models and deriving their EFTs via matching, our extension obtains the Lagrangian in the broken phase of the electroweak symmetry, performs automatic gauge fixing, computes all Feynman rules, imposes flavor symmetries, and exports the model in the UFO format. This significantly streamlines BSM and EFT analyses, as we illustrate with an EFT validity study for a multi-channel leptoquark search. As an application, we provide a complete UFO implementation of the Standard Model EFT up to dimension eight using the $M_W$ electroweak input scheme.

Given any four-point scattering amplitude, the partial wave expansion resolves its residues into contributions from individual spin-$s$ internal particles, where each coefficient in the expansion must be non-negative due to unitarity. In this paper, we introduce a partial wave expansion tailored to "half-ladder" Feynman diagrams at generic multiplicity $n$ and spacetime dimension $d$, with scalars on the external lines and massive bosons on the internal lines. Derived by enforcing that the half-ladder residue is an eigenvector of each internal particle's angular momentum, each basis element is written as a sum over products of special functions related to the Gegenbauer polynomials, and we give a set of simple graphical rules for explicitly building any of them at generic $n$ and $d$. To put the formalism into action, we apply our technology to deformed "string theory" amplitudes, defined a priori in any dimension and with arbitrary Regge intercept $\alpha_0$. By constructing multi-particle positivity tests for the half-ladder and "twisted" half-ladder diagrams, we show that the only amplitudes consistent with unitarity are those belonging to open bosonic string theory ($\alpha_0 = -1$) below the critical dimension $d \leq 26$. In particular, we confirm the expectation that $Z$-theory ($\alpha_0 = 0$) fails to define a unitary string theory at finite $\alpha'$. Finally, for the open bosonic string, we show how knowledge of the partial wave expansion allows us to resolve the contributions to the half-ladder diagram from individual degenerate states at a given level and spin in a purely on-shell analysis. As an ancillary file, we include a Python script combwaves.py which implements the partial wave expansion given a generic (twisted) half-ladder residue.

We explore a model of sneutrino dark matter in the Minimal R-Symmetric Supersymmetric Standard Model as a possible interpretation of the recent event at LZ with high reconstructed nuclear recoil energy. This model can account for a small mass splitting between neutral states in a technically natural way due to terms which violate lepton number; importantly, this model does not require sending masses of other SUSY particles to an extremely high energy scale. Mixing with additional singlet states suppresses the interaction strength with standard model particles which allows the sneutrino to sneak around bounds obtained from searches for annihilating dark matter captured in the sun and allows the dark matter to remain near the TeV scale and still potentially account for the LZ results. Typically, sneutrinos produce too much dark matter unless they are very light; we consider a minimal scenario where production occurs through co-annihilation as one specific mechanism where the dark matter mass is predicted to be around $360$ GeV.

We analyze the effect of axion contribution on the mass, radius and dimensionless deformability of a neutron star (NS) at finite temperature. Although the cooling of an NS is mainly due to the emission of neutrinos, additional cooling cannot be ruled out due to the emission of axions. The existence of an axion is needed for addressing the strong CP problem within the standard model. The Peccei-Quinn (PQ) symmetry breaking mechanism generates axions. They are pseudo-Nambu-Goldstone bosons. Their mass is extremely small but non-zero. This naturally resolves the fine-tuning problem of the strong CP-violating parameter ${\theta} \lesssim 10^{-10}$. We propose that a finite temperature NS feature a quark core surrounded by a baryonic medium admixed with the axions, which are pseudo scalar Goldstone bosons and are considered as strong candidates for the dark matter (DM). Unlike the original quarkyonic model, we formulate a quarkyonic-inspired smooth crossover equation of state (EoS) at finite temperatures. This smooth crossover avoids thermodynamic instabilities found in sharp first-order constructions. We add the axionic EoS to the finite temperature quarkyonic one and solve the Tolman-Oppenheimer-Volkoff equations to estimate the properties of the NS both with and without taking the axion into account at different temperatures. We find that the production of axions is maximum within a radius of $5-11$ km in the star's interior; however, the impact on the mass is significant, i.e., $\sim 60\%$ of axion mass concentrated in the central region of the star. We also find that the effect of temperature on the mass of NS is marginal unlike the radius. In general, the influence of axions is significant for the observational properties of NS. These results highlight the pivotal role of axion physics in neutron star phenomenology.

We investigate the hyperfine structure of $B$ and $D$ mesons within a QCD-inspired potential model based on the Cornell ansatz. The conventional contact spin–spin term is regularized with a Gaussian smearing to remove the short-distance singularity, and analytic wavefunctions are obtained using the Dalgarno–Lewis perturbative method with the Coulomb part as parent. The numerical study has been extended to include explicit 2S hyperfine predictions and results for the $B_c$ system; these additions probe the stability of the potential parameter space (effective $\alpha_s$, confinement strength and smearing width) for unequal-mass systems and radial excitations. We also present a short sensitivity study of the fixed effective coupling $\alpha_s$ and discuss the physical interpretation of the smearing parameter $\sigma$. The combined analytic and phenomenological framework provides compact, testable benchmarks for upcoming spectroscopy measurements.

The ordinary and dark matter in the Universe may share a common origin in the framework of a minimal extension of the Standard Model by three right-handed neutrinos. A pair of such heavy neutral leptons (HNLs) can give masses to neutrinos, generate the baryon asymmetry at the electroweak scale and produce a large lepton asymmetry at the QCD scale, which is then resonantly transformed into an abundance of the third state that acts as sterile neutrino dark matter. The minimality of this setup, known as Neutrino Minimal Standard Model ($\nu$MSM), makes it highly predictive. Earlier attempts to pin down the properties of the HNLs based on the requirement to simultaneously explain the neutrino masses as well as the baryonic and dark matter abundances were hampered by an incomplete understanding of the quantum kinetic equations describing the HNLs throughout cosmic history. We perform the first parameter scan of the $\nu$MSM in which this shortcoming has been overcome. We find that the $\nu$MSM provides a common explanation for all aforementioned phenomena only within a well-defined parameter space that is limited in all directions, with HNL masses kinematically accessible by the SHiP experiment as well as searches at the LHC and future lepton colliders. Further predictions for the HNL decay branching ratios, CP-violation, and lepton number violation (LNV) make the model highly testable, bringing a discovery of the common origin of neutrino masses and all matter in the Universe within reach of existing and planned experiments.

We study $O(4)$ symmetric Euclidean wormholes in four-dimensional gravity with a massless scalar linearly coupled to the Gauss-Bonnet invariant. At nonzero coupling, the Einstein wormhole becomes a regular complex saddle that satisfies the Kontsevich-Segal-Witten criterion until its branch ends at a finite coupling. In asymptotically flat space, the Gauss-Bonnet term modifies the scalar displacement and the on-shell action for finite wormholes, but the size dependent parts of both corrections vanish in the large throat limit. The original imaginary distance threshold therefore remains unchanged. A negative cosmological constant already lowers the Einstein large throat imaginary distance relative to its flat space value. When the Gauss-Bonnet coupling is also present, the scalar is no longer a modulus as it develops a logarithmic running and its trajectory has infinite length. Subtracting the logarithmic asymptotic behavior leaves a finite regulated displacement. Its large throat value is shifted upward from the Einstein AdS result by the Gauss-Bonnet interaction and determines the leading large charge behavior of the renormalized fixed charge action.

We investigate topological defects produced by a chiral phase transition in a fermionic ultraviolet completion of dynamical Chern-Simons (dCS) gravity. The model contains a complex scalar field with a chiral Yukawa coupling to fermions. Below the chiral symmetry breaking scale, integrating out the gapped bulk modes produces a gravitational Chern-Simons coupling which, we argue, modifies cosmic string solutions from the phase transition. The resulting corrected string metric is supported by a generalization of the Callan-Harvey fermionic zero mode solution, in which the null current generated by these zero modes provides a mechanism for parity violation. In the weak-coupling and weak-gravity regime, we derive the leading order-reduced dCS correction to this exterior metric. We also discuss the effective action description for generic string configurations in dCS gravity. The gravitational Pontryagin term provides the anomaly inflow required to cancel the gravitational anomaly of the chiral worldsheet theory.

At loop level, a dark $U(1)_X^{}$ gauge field for dark photon can naturally acquire a tiny kinetic mixing with the standard model $U(1)_Y^{}$ gauge field for hypercharge after a $Z_2^{}$ discrete symmetry is spontaneously broken for generating a small mass difference between two vector-like fermions carrying the same $U(1)_Y^{}$ charge and the opposite $U(1)_X^{}$ charges of equal magnitude. To avoid an unacceptable relic density with electric charge, these vector-like fermions can decay into the standard model charged leptons with a TeV-scale complex dark scalar. The real and imaginary parts of this dark scalar can elegantly obtain a mass split below the MeV scale after a dark Higgs scalar develops its vacuum expectation value for generating a dark photon mass of the GeV order. Therefore, the dark photon can mediate an exothermic inelastic scattering of dark matter off nucleus to naturally explain the recently reported event in the LUX-ZEPLIN experiment and substantially relax the stringent constraints from the IceCube neutrino searches.

We present a microscopic femtoscopic investigation of the space-time emission source in low-multiplicity (80–90% centrality) $\text{Pb}-\text{Pb}$ collisions at $\sqrt{s_{NN}} = 5.02~\text{TeV}$, using a hybrid transport framework coupling SMASH initial conditions, 3+1D viscous hydrodynamics (vHLLE), and a SMASH hadronic cascade afterburner. Access to the full space-time evolution of the produced particles allows for the direct reconstruction of emission source functions in both the Longitudinally Comoving System and the Pair Rest Frame. We study identical pairs of mesons ($\pi\pi$, $KK$) and baryons ($pp$), as well as cross-species combinations, while explicitly isolating the contributions from primordial particles, hadronic rescattering, and long-lived resonance decays. Our analysis shows that simple Gaussian fits are inadequate for precision source analyses, whereas a combined Gaussian plus exponential parametrization better captures the compact core and the extended tail. Finally, the extracted Gaussian core radii, $R_{\text{core}}$, for our very peripheral collisions demonstrate an approximate $m_T$-scaling behavior rather similar to the one observed in pp reactions.

We investigate how one-loop operator mixing reshapes the flavor sensitivity of lepton-number-violating dimension-7 SMEFT interactions. Using both bottom-up and top-down EFT approaches, we study the interplay of neutrinoless double beta decay ($0\nu\beta\beta$) and neutral current rare meson decays $K\to\pi\nu\nu$, and $B\to K^{(*)}\nu\nu$, which at tree level probe apparently disconnected quark- and lepton-flavor sectors. We show that loop mixing qualitatively changes this picture: flavor structures radiatively feed into one another, substantially extending the sensitivity to higher new-physics scales across operators and flavors. In the bottom-up EFT approach, this can make $0\nu\beta\beta$ highly sensitive even to operators involving heavier-generation quarks, while rare kaon and $B$ decays retain crucial complementary sensitivity to other flavor combinations. A top-down EFT approach example using a ultraviolet model involving scalar-leptoquark illustrates how the same effects can reorder the relative importance of different observables.

Supercooled cosmological first-order phase transitions (FOPTs) generate a large temperature inhomogeneity due to their stochastic reheating process. If a baryon asymmetry production predates the FOPT and is conserved during it, the temperature contrast is transferred onto the baryon-to-photon ratio $\eta$ or the baryon-to-entropy ratio $Y_{B}$, producing an inhomogeneity probed by big bang nucleosynthesis (BBN). We extend a recent formalism for this effect by including the reheating dependence of the induced $Y_{B}$ fluctuations, combining the transition-time power spectrum from finite-bubble statistics with proton and neutron diffusion at the BBN epoch. When the nucleation temperature is in the range $10^{-2}\,{\rm GeV} \lesssim T_{n} \lesssim 10^{2}\,{\rm GeV}$, the precise measurement of deuterium abundances disfavors parameter regions with a sizable latent heat and a long transition duration at the $1 \sigma$ level. The bound weakens towards higher $T_{n}$ as diffusion becomes more efficient. We further show that this bound disfavors FOPT parameter regions compatible with the NANOGrav gravitational wave signal. This conclusion assumes that the baryon asymmetry predates the transition and that the fluctuation spectrum remains valid down to sub-bubble scales. Therefore, in such FOPT explanations of the NANOGrav signal, the baryon asymmetry cannot simply predate the transition. It can instead be generated after reheating or during the transition if the local baryon production tracks the local entropy injection. As a result, the timing of baryogenesis may be constrained by combining gravitational wave observations with light element abundance measurements.

The scotogenic model generates sub-eV neutrino masses radiatively through small Yukawa couplings $\sim\mathcal{O}(10^{-3})$ that also set the decay length of the heavy neutral fermion $\Ntwo$; in the compressed regime a separate, much smaller Yukawa entry $\sim\mathcal{O}(10^{-6})$ additionally renders the charged scalar $\etapm$ long-lived. We study the compressed-spectrum regime of its two-inert-doublet variant ($\DMcomp = \mHpm - \mNtwo \simeq 200\MeV$), in which small Yukawa entries render both the charged scalar $\etapm$ and the heavy neutral fermion $\Ntwo$ long-lived and produce a nested cascade at the High-Luminosity LHC~(HL-LHC): $\etapm$ leaves a disappearing track~(DT), decays to an invisible $\Ntwo$, which travels macroscopically before forming a displaced dilepton vertex~(DV). The two slow flights combine into a 4D time-of-flight delay $\dt\sim200$–$800\ps$ resolvable by the CMS MIP Timing Detector, while the DT-to-DV displacement vector inherits the parent track direction, yielding a spatial back-pointing correlation with no SM analogue. These two handles are expected to suppress the background to $B\sim10^{-5}$–$10^{-3}$ events, and the discovery remains $5\sigma$-significant for any background up to $B\sim10$ events. At the benchmark ($\mNtwo=150\GeV$ and proper decay lengths $\ctauH=300\mm$, $\ctauN=189\mm$) the strategy yields $N_s\approx1212$ signal events at $3000\ifb$ and establishes sensitivity across $15\mm\lesssim\ctauH\lesssim300\mm$, $10\mm\lesssim\ctauN\lesssim1000\mm$, a correlated region left uncovered by any standalone DT or DV search. Because the $\Ntwo$ decay length is controlled by the same Yukawa couplings that generate sub-eV neutrino masses, mapping this nested cascade turns the HL-LHC into a direct collider probe of the interaction responsible for neutrino mass.

We compute contours of the enhanced quark number susceptibility ratio $R_q$, normalized by the free quark gas susceptibility, around the critical end point (CEP) using the on-shell renormalized two-flavor quark-meson (RQM) model and its two Polyakov-loop-extended variants: the Log RPQM and PolyLog-glue RPQM models, employing logarithmic and PolyLog-glue forms of the Polyakov-loop potential without and with quark back-reaction, respectively. These contours are compared with those from the curvature-mass parametrized quark-meson-with-vacuum-term (QMVT) model and its logarithmic Polyakov-loop extension (Log PQMVT) [117], to assess how different treatments of quark one-loop vacuum fluctuations affect the critical region. Although the critical fluctuation regions near the RQM/Log RPQM CEP are reduced in $T$-$\mu$ extent relative to the QMVT/Log PQMVT case, the higher-$T$, lower-$\mu$ CEP location shifts its enhanced-susceptibility domain toward higher $T$ and lower $\mu$. Since the $\sigma$ and $\pi$ curvature and pole masses differ in the RQM/Log RPQM model but coincide in QMVT/Log PQMVT, we also compare contours of the enhanced scalar susceptibility ($\sim 1/m_\sigma^2$) around the respective CEPs. To isolate the roles of strange flavor and the $U_A(1)$ anomaly, we compare $R_q = 2, 3, 5$ contours from our two-flavor RQM/Log RPQM/PolyLog-glue RPQM model calculations with the corresponding 2+1 flavor RQM/RPQM model very recent results in Ref [146].

The exclusive photoproduction of the toponium vector meson ($\psi_t$) is investigated within the color dipole model. The overlap function between the light-cone wave function of the vector toponium state and the photon wave function is estimated using the Boosted Gaussian approach. Considering the dominance of small dipoles, the dipole-proton scattering amplitude is estimated in terms of parton distribution functions, and predictions for the photoproduction cross-section in the energy range of the proposed Large Hadron electron Collider (LHeC) are presented. Moreover, the cross-sections and rapidity distributions for the exclusive $\psi_t$ photoproduction in ultraperipheral proton-proton and proton - nucleus collisions at the Large Hadron Collider (LHC) and Future Circular Collider (FCC) energies are calculated. We find that exclusive $\psi_t$ photoproduction is, in principle, feasible in ultraperipheral $pp$ collisions at the FCC-hh.

Motivated by the LUX-ZEPLIN high-energy nuclear-recoil candidate, we ask whether solar evolution can distinguish dark-matter models that are degenerate in their leading xenon recoil response. We compare a split fermionic electroweak doublet with a specified inert scalar doublet, matching their masses, excitation energy, coherent transition interaction, and leading elastic nuclear response. This matching fixes the same direct-detection signal and the same optically thin first-capture source in the Sun, while leaving post-capture dynamics model dependent. We follow finite-temperature capture, orbital evolution, scattering, excited-state decay, escape, thermal entry, and annihilation. The different excited-state lifetimes generate distinct capture histories, but, for the specified cooling interaction, both retained populations thermalize and reach capture–annihilation equilibrium, yielding only a modest difference in their late annihilation rates. We also derive an analytic protected-capture criterion and test the result against shared halo, solar-composition, and nuclear-response variations. Although the total annihilation rates remain similar, model-dependent gauge-boson branching fractions and polarizations produce distinct neutrino spectra at production. A source-level comparison with published IceCube templates shows that the nominal partial $WW$ sources exceed the corresponding pure-$WW$ template limits, without constituting a detector-level exclusion or model discrimination. Solar evolution therefore provides a complementary probe of particle-model differences hidden by a matched xenon signal.

Gravitational-wave (GW) observations offer a promising probe of new physics associated with a strong first-order electroweak phase transition. Null results from direct searches and constraints from precision measurements, together with the comparatively weak constraints on Higgs self-interactions, motivate scenarios in which non-decoupling effects in the Higgs potential coexist with additional decoupling new physics. Previous Fisher matrix studies within the Standard Model effective field theory (SMEFT) have explored the sensitivity of future GW observations to new physics, focusing on transitions driven by the dimension-six operator $(H^\dagger H)^3$. However, the validity of the truncated EFT expansion can become questionable in the parameter regions relevant to such transitions. We instead consider transitions driven by non-decoupling effects described by the nearly aligned Higgs effective field theory (naHEFT). We investigate whether GW observations can probe small corrections to the Higgs effective potential induced by decoupling effects in interactions other than Higgs self-interactions. As a representative benchmark for additional decoupling effects, we consider the dimension-six SMEFT operator $(H^\dagger H)(\overline{q}_3 t_R\widetilde{H})$ with Wilson coefficient $C_{uH}$. Although we focus on this benchmark, the same framework can be applied to other dimension-six SMEFT operators. We perform two-parameter Fisher matrix analyses for DECIGO and BBO to quantify their expected sensitivity to $C_{uH}$ and the naHEFT mass scale $\Lambda$. For the benchmark configurations considered, the non-decoupling dynamics generates a detectable GW signal. We find that these small corrections can produce potentially measurable changes in the GW spectrum, even after accounting for the correlation between $C_{uH}$ and $\Lambda$.