Ignatios Antoniadis, Alonzo R. Diaz Avalos, Alon E. Faraggi
Abstract We present a construction of a perturbatively stable non-supersymmetric type II closed string model in four dimensions. It is based on a freely acting Scherk-Schwarz ℤ 2-deformation of a supersymmetric construction which is recovered in appropriate decompactification limits. The model exhibits also the so-called misaligned supersymmetry with alternating signs for the number difference between bosons and fermions at successive mass levels. The tree-level spectrum is tachyon free for any value of the radii and moduli. At one loop level, the scalar potential has a non-supersymmetric minimum at the self-dual (free fermionic) point with negative energy, around which all tree-level massless scalars acquire positive masses. The model is thus non-supersymmetric and perturbatively stable.
Nuclear and particle physics. Atomic energy. Radioactivity
PIONEER Collaboration, A. Adelmann, W. Altmannshofer
et al.
PIONEER is a rapidly developing effort aimed to perform a pristine test of lepton flavour universality (LFU) and of the unitarity of the first row of the CKM matrix by significantly improving the measurements of rare decays of the charged pion. In Phase I, PIONEER aims to measure the charged-pion branching ratio to electrons vs.\ muons $R_{e/μ}$ to 1 part in $10^4$, improving the current experimental result $R_{e/μ}\,\text{(exp)} =1.2327(23)\times10^{-4}$ by a factor of 15. This precision on $R_{e/μ}$ will match the theoretical accuracy of the SM prediction allowing for a test of LFU at an unprecedented level, probing non-SM explanations of LFU violation through sensitivity to quantum effects of new particles up to the PeV mass scale. Phase II and III will aim to improve the experimental precision of the branching ratio of pion beta decay, $π^+\to π^0 e^+ ν(γ)$, currently at $1.036(6)\times10^{-8}$, by a factor of three and six, respectively. The improved measurements will be used to extract $V_{ud}$ in a theoretically pristine manner. The ultimate precision of $V_{ud}$ is expected to reach the 0.05\,\% level, allowing for a stringent test of CKM unitarity. The PIONEER experiment will also improve the experimental limits by an order of magnitude or more on a host of exotic decays that probe the effects of heavy neutrinos and dark sector physics. This input to the 2026 update of the European Strategy for Particle Physics Strategy describes the physics motivation and the conceptual design of the PIONEER experiment, and is prepared based on the PIONEER proposal submitted to and approved with high priority by the PSI program advisory committee (PAC). Using intense pion beams, and state-of-the-art instrumentation and computational resources, the PIONEER experiment is aiming to begin data taking by the end of this decade.
Heavy-flavour physics is an essential component of the particle-physics programme, offering critical tests of the Standard Model and far-reaching sensitivity to physics beyond it. Experiments such as LHCb, Belle II, and BESIII drive progress in the field, along with contributions from ATLAS and CMS. The LHCb Upgrade II and upgraded Belle II experiments will provide unique and highly sensitive measurements for decades, playing a key role in the searches for new physics. Future facilities with significant heavy-flavour capabilities will further expand these opportunities. We advocate for a European Strategy that fully supports Upgrade II of LHCb and an upgrade of Belle II, along with their subsequent exploitation. Additionally, we support a long-term plan that fully integrates flavour physics in an $e^+e^-$ collider to run as a $Z$ factory.
We present an analytical model to evaluate the triangularity-shaping effects in accessing the second stable region for the ideal ballooning mode. Our results indicate that if the triangularity is sufficiently negative, the path from the first to the second stable region will be closed. The reason is that negative triangularity can weaken the stabilizing effect of the ‘magnetic well’, and even convert the ‘magnetic well’ into a ‘magnetic hill’, which will destabilize the ballooning mode. We also show that the synergistic effects of elongation, inverse aspect ratio, and safety factor can reopen the path to the second stable region. Through a variational approach, we derive an analytical expression of the critical negative triangularity for closing the access to the second stable region. Furthermore, our analysis reveals that in the second ballooning stable regime, the negative triangularity tends to inhibit the emergence of quasi marginally stable discrete Alfvén eigenmodes. These findings provide a quantitative understanding of how the negative triangularity configuration impacts the confinement of tokamak plasmas.
Nuclear and particle physics. Atomic energy. Radioactivity
Abstract We explore hypothetical vector particles, dark photons γ′, which mix with the Standard Model photons and thus mediate interactions with charged particles into the hidden sector. We study the elastic proton bremsstrahlung of dark photons with masses 0.4–1.8 GeV, relevant for direct searches with proton accelerators. A key feature of our calculation is that it explicitly considers the non-zero momentum transfer between protons in the process pp → ppγ′. We compare the obtained differential and full bremsstrahlung cross sections with the results of other authors. Our calculation agrees well (up to 3–9% corrections) with the Weizsacker-Williams approximation that confirms its applicability for proton beams. Then we refine predictions for the dark photon production with proton beams of energy 30 GeV, 70 GeV, 120 GeV and 400 GeV relevant for past, present and future experiments considered in literature.
Nuclear and particle physics. Atomic energy. Radioactivity
Gamma rays from HESS J1849−000, a middle-aged TeV pulsar wind nebula (PWN), are observed by the Tibet air shower array and the muon detector array. The detection significance of gamma rays reaches 4.0σ and 4.4σ levels above 25 TeV and 100 TeV, respectively, in units of the Gaussian standard deviation σ. The energy spectrum measured between 40 TeV < E < 320 TeV for the first time is described with a simple power-law function of dN/dE=(2.86±1.44)×10−16(E/40TeV)−2.24±0.41TeV−1cm−2s−1 . The gamma-ray energy spectrum from the sub-TeV (E < 1 TeV) to sub-PeV (100 TeV < E < 1 PeV) ranges, including the results of previous studies, can be modeled with the leptonic scenario, i.e., inverse Compton scattering by high-energy electrons accelerated by the PWN of PSR J1849−0001. On the other hand, the gamma-ray energy spectrum can also be modeled with the hadronic scenario in which gamma rays are generated from the decay of neutral pions produced by collisions between accelerated cosmic-ray protons and the ambient molecular cloud found in the gamma-ray-emitting region. The cutoff energy of cosmic-ray protons E p,cut is estimated as log10(Ep,cut/TeV)=3.73−0.66+2.98 , suggesting that protons are accelerated up to the PeV energy range. Our study thus proposes that HESS J1849−000 should be further investigated as a new candidate as a Galactic PeV cosmic-ray accelerator, or “PeVatron.”
Aspects of shock waves and instantly-created folded strings operators in the supersymmetric SL(2)k/U(1) CFT, and their relevance to the near-horizon physics of Schwarzschild black holes in perturbative superstring theory, are presented.
Nuclear and particle physics. Atomic energy. Radioactivity
Mohammad Vahid Takook, Jean-Pierre Gazeau, Eric Huguet
Within the de Sitter ambient space framework, the two different bases of the one-particle Hilbert space of the de Sitter group algebra are presented for the scalar case. Using field operator algebra and its Fock space construction in this formalism, we discuss the existence of asymptotic states in de Sitter QFT under an extension of the adiabatic hypothesis and prove the Fock space completeness theorem for the massive scalar field. We define the quantum state in the limit of future and past infinity on the de Sitter hyperboloid in an observer-independent way. These results allow us to examine the existence of the <i>S</i>-matrix operator for de Sitter QFT in ambient space formalism, a question which is usually obscure in spacetime with a cosmological event horizon for a specific observer. Some similarities and differences between QFT in Minkowski and de Sitter spaces are discussed.
Abstract We extend the analysis of [9] to the 6d (1, 0) SCFTs known as massive E-string theories, which can be engineered in massive Type IIA with 8 − n 0 < 8 D8-branes close to an O8 − (or O8* if n 0 = 8, 9). For each choice of n 0 = 1, …, 9 the massive E 1 + 8 − n 0 $$ {E}_{1+\left(8-{n}_0\right)} $$ -strings (including the more exotic E ~ 1 $$ {\overset{\sim }{E}}_1 $$ and E 0) are classified by constrained E 8 Kac labels, i.e. a subset of Hom(ℤ k , E 8), from which one can read off the flavor subalgebra of E 1 + 8 − n 0 $$ {E}_{1+\left(8-{n}_0\right)} $$ of each SCFT. We construct hierarchies for two types of Higgs branch RG flows: flows between massive theories defined by the same n 0 but different labels; flows between massive theories with different n 0. These latter flows are triggered by T-brane vev’s for the right SU factor of the SCFT global symmetry, whose rank is a function of both k and n 0, a situation which has so far remained vastly unexplored.
Nuclear and particle physics. Atomic energy. Radioactivity
We discuss the possible manifestation of pairing dynamics in nuclear collisions beyond the standard quasi-static treatment of pairing correlations. These involve solitonic excitations induced by pairing phase difference of colliding nuclei and pairing dynamic enhancement in the di-nuclear system formed by merging nuclei.
We report on the effects of transverse spatial misalignment on the performance and stability of x-ray free electron laser oscillators (XFELOs). For this study, we adopt the FEL driven paraxial resonator model in which the transverse profile of the radiation field is represented by Gauss-Hermite mode expansion. Then, we apply Gaussian optics for transporting the radiation field along with the misalignment in the optical cavity. We divide the misalignment into relevant categories of static and periodic types to understand their effects on FEL gain, lasing, and saturation. After that, we associate the first order moments of the radiation field to that of driven simple harmonic oscillator models to identify regions of instability. Throughout this report, we validate our models and analyses via theoretical calculations, analytical approximations, and simulations.
Nuclear and particle physics. Atomic energy. Radioactivity
Abstract Within a covariant perturbative field-theoretical approach, the wave-packet modified neutrino propagator is expressed as an asymptotic expansion in powers of dimensionless Lorentz- and rotation-invariant variables. The expansion is valid at high energies and short but macroscopic space-time distances between the vertices of the proper Feynman macrodiagram. In terms of duality between the propagator and the effective neutrino wave packet, at short times and distances, neutrinos are deeply virtual and move quasi-classically. In the lowest-order approximation, this leads to the classical inverse-square dependence of the modulus squared flavor transition amplitude and related neutrino-induced event rate from distance L between the source and detector, and the above-mentioned asymptotics results in the corrections to the classical behavior represented by powers of $$L^2$$ L 2 . This is very different from the long-baseline regime, where similar corrections are given by an asymptotic expansion in inverse powers of $$L^2$$ L 2 . However, in both short- and long-baseline regimes, the main corrections lead to a decrease in number of neutrino events.
Astrophysics, Nuclear and particle physics. Atomic energy. Radioactivity
Abstract We investigate the subleading-power corrections to the exclusive B → Dℓν ℓ form factors at O $$ \mathcal{O} $$ ( α s 0 $$ {\alpha}_s^0 $$ ) in the light-cone sum rules (LCSR) framework by including the two- and three-particle higher-twist contributions from the B-meson light-cone distribution amplitudes up to the twist-six accuracy, by taking into account the subleading terms in expanding the hard-collinear charm-quark propagator, and by evaluating the hadronic matrix element of the subleading effective current . Employing further the available leading-power results for the semileptonic B → D form factors at the next-to- leading-logarithmic level and combining our improved LCSR predictions with the recent lattice determinations, we then carry out a comprehensive phenomenological analysis on the semi-leptonic B → Dℓν ℓ decay. We extract V cb = 40.2 − 0.5 + 0.6 th − 1.4 + 1.4 exp × 10 − 3 V cb = 40.9 − 0.5 + 0.6 th − 1.0 + 1.0 exp × 10 − 3 $$ \left|{V}_{cb}\right|=\left({40.2}_{-0.5}^{+0.6}{\left|{{}_{\mathrm{th}}}_{-1.4}^{+1.4}\right|}_{\mathrm{exp}}\right)\times {10}^{-3}\left(\left|{V}_{cb}\right|=\left({40.9}_{-0.5}^{+0.6}{\left|{{}_{\mathrm{th}}}_{-1.0}^{+1.0}\right|}_{\mathrm{exp}}\right)\times {10}^{-3}\right) $$ using the BaBar (Belle) experimental data, and particularly obtain for the gold-plated ratio R(D) = 0.302 ± 0.003.
Nuclear and particle physics. Atomic energy. Radioactivity
Abstract We propose that the electroweak and flavour quantum numbers of the Standard Model (SM) could be unified at high energies in an SU(4) × Sp(6) L × Sp(6) R anomaly-free gauge model. All the SM fermions are packaged into two fundamental fields, Ψ L ∼ (4 , 6 , 1) and Ψ R ∼ (4 , 1 , 6), thereby explaining the origin of three families of fermions. The SM Higgs, being electroweakly charged, necessarily becomes charged also under flavour when embedded in the UV model. It is therefore natural for its vacuum expectation value to couple only to the third family. The other components of the UV Higgs fields are presumed heavy. Extra scalars are needed to break this symmetry down to the SM, which can proceed via ‘flavour-deconstructed’ gauge groups; for instance, we propose a pattern Sp(6) L → ∏ i = 1 3 SU 2 L , i → SU 2 L $$ {\prod}_{i=1}^3\mathrm{SU}{(2)}_{L,i}\to \mathrm{SU}{(2)}_L $$ for the left-handed factor. When the heavy Higgs components are integrated out, realistic quark Yukawa couplings with in-built hierarchies are naturally generated without any further ingredients, if we assume the various symmetry breaking scalars condense at different scales. The CKM matrix that we compute is not a generic unitary matrix, but it can precisely fit the observed values.
Nuclear and particle physics. Atomic energy. Radioactivity
Igor A. Valuev, Gianluca Colò, Xavier Roca-Maza
et al.
A long-standing problem of fine-structure anomalies in muonic atoms is revisited by considering the $Δ2p$ splitting in muonic $^{90}\mathrm{Zr}$, $^{120}\mathrm{Sn}$ and $^{208}\mathrm{Pb}$ and the $Δ3p$ splitting in muonic $^{208}\mathrm{Pb}$. State-of-the-art techniques from both nuclear and atomic physics are brought together in order to perform the most comprehensive to date calculations of nuclear-polarization energy shifts. Barring the more subtle case of muonic $^{208}\mathrm{Pb}$, the results suggest that the dominant calculation uncertainty is much smaller than the persisting discrepancies between theory and experiment. We conclude that the resolution to the anomalies is likely to be rooted in refined QED corrections or even some other previously unaccounted-for contributions.
Abstract In this paper, we present a comprehensive study of ϒ inclusive production in Z boson decay, including the first complete next-to-leading-order calculations of the color-octet (CO) contributions. With the inclusion of the newly-calculated remarkable QCD corrections, the CO processes exhibit crucially phenomenological influence on the existing predictions built on the color-singlet mechanism. We also include the exhaustive evaluations of the feed-down contributions, which remained ignored in the literature, and find them to be considerable. Summing up all the contributions, the ℬ Z → ϒ(nS) + X still notably undershoot the data released by the L3 Collaboration.
Nuclear and particle physics. Atomic energy. Radioactivity
Jan Ambjorn, Zbigniew Drogosz, Jakub Gizbert-Studnicki
et al.
Lattice formulations of gravity can be used to study non-perturbative aspects of quantum gravity. Causal Dynamical Triangulations (CDT) is a lattice model of gravity that has been used in this way. It has a built-in time foliation but is coordinate-independent in the spatial directions. The higher-order phase transitions observed in the model may be used to define a continuum limit of the lattice theory. Some aspects of the transitions are better studied when the topology of space is toroidal rather than spherical. In addition, a toroidal spatial topology allows us to understand more easily the nature of typical quantum fluctuations of the geometry. In particular, this topology makes it possible to use massless scalar fields that are solutions to Laplace’s equation with special boundary conditions as coordinates that capture the fractal structure of the quantum geometry. When such scalar fields are included as dynamical fields in the path integral, they can have a dramatic effect on the geometry.