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Tag: Particle, Atomic & Nuclear Physics

  • Adjoint QCD2 can exhibit supersymmetry at special fermion masses

    What the study found

    The study finds that adjoint QCD2, a 1+1-dimensional SU(N) gauge theory with an adjoint Majorana fermion, has supersymmetry at a specific fermion mass. The authors also identify related generalizations where a supersymmetric massive sector can appear, and in some cases both the massive and gapless sectors are supersymmetric.

    Why the authors say this matters

    The authors conclude that constructing a gauge-invariant, Lorentz-covariant supercurrent gives a deeper understanding of how the supersymmetry works. They also suggest that the generalized models show how supersymmetry can appear in both massive and non-supersymmetric conformal field theory sectors, and in some cases in both sectors together.

    What the researchers tested

    The researchers constructed the gauge-invariant, Lorentz-covariant supercurrent j_μ^A for adjoint QCD2 and examined how its conservation depends on a quantum anomaly. They then extended the construction to a class of gauge theories with an adjoint Majorana fermion of an appropriate mass plus additional massless fermions, allowing the gauge group to be more general than SU(N).

    What worked and what didn't

    For adjoint QCD2, supersymmetry appears at fermion mass sqrt(g^2N/2π). In the generalized models, the authors report that there is generally a supersymmetric massive sector and a non-supersymmetric conformal field theory sector, but they also identify cases where both sectors are supersymmetric; one example is SU(N) gauge theory with three adjoint Majorana fermions, two massless and one with mass sqrt(3g^2N/2π).

    What to keep in mind

    The abstract does not describe experimental data, numerical tests, or the full derivation, so only the stated theoretical results can be summarized here. It also does not give limitations beyond the fact that the supersymmetry appears at specific mass values and in specific classes of models.

    • Adjoint QCD2 has supersymmetry at fermion mass sqrt(g^2N/2π).
    • The authors construct a gauge-invariant, Lorentz-covariant supercurrent.
    • The supercurrent conservation relies on a quantum anomaly.
    • Generalized models can have a supersymmetric massive sector and a non-supersymmetric conformal field theory sector.
    • A fully supersymmetric gapless example is SU(N) gauge theory with three adjoint Majorana fermions.

  • 2HDM-I explains reported 650 GeV and 95 GeV anomalies

    What the study found

    The authors report that the 2-Higgs doublet model type-I, a theory with two Higgs fields, can explain the reported 650 GeV and 95 GeV anomalies. They state that this is achieved while accounting for the constraints they considered.

    Why the authors say this matters

    The authors conclude that their study can account for multiple experimental anomalies at once. They present this as support for the 2-Higgs doublet model type-I as an interpretation of the reported signals.

    What the researchers tested

    The researchers studied a 2-Higgs doublet model type-I with a softly broken Z2 symmetry. They examined production of a CP-odd Higgs boson A around 650 GeV, followed by its decay into a Standard Model-like Higgs H and a Z boson, and they also included a light CP-even Higgs h around 95 GeV to address other reported anomalies.

    What worked and what didn't

    According to the abstract, the model can explain the 650 GeV excess in the specified final state and additional clusters near 125 GeV and 90-100 GeV. The authors say the same framework also explains anomalies seen in other final states from LEP and LHC searches. No separate failures are described in the abstract.

    What to keep in mind

    The summary does not provide the detailed data analysis, parameter choices, or statistical procedure behind the quoted significance level. It also does not describe limitations beyond noting that the authors accounted for experimental and theoretical constraints.

    • The study proposes the 2-Higgs doublet model type-I as an explanation for a reported 650 GeV excess.
    • The authors also include a light Higgs state around 95 GeV to address additional anomalies.
    • The underlying process involves a CP-odd Higgs boson A decaying into a Standard Model-like Higgs H and a Z boson.
    • The abstract says the model can explain the reported anomalies while satisfying the stated constraints.
    • No detailed limitations or alternative explanations are described in the abstract.
  • He2 rovibrational levels match spectroscopy after high-accuracy corrections

    He2 rovibrational levels match spectroscopy after high-accuracy corrections

    What the study found

    The study found that calculated rovibrational intervals and fine-structure splittings for the He2 a 3 Σ u + state agree remarkably well with available high-resolution spectroscopy data. The work also produced a potential energy curve accurate to a fraction of 1 part per million.

    Why the authors say this matters

    The findings indicate that including relativistic and quantum electrodynamics (QED) corrections, along with nonadiabatic effects, can support highly accurate molecular energy calculations. The authors conclude this is relevant because the computed energy levels closely match experimental spectroscopy.

    What the researchers tested

    The researchers computed a potential energy curve for the a 3 Σ u + state of helium dimer (He2) with relativistic and QED corrections. They then solved the nuclear Schrödinger equation on this curve, including diagonal Born-Oppenheimer and nonadiabatic mass corrections, to obtain rotational-vibrational levels.

    What worked and what didn't

    The calculated rovibrational intervals and fine-structure splittings, spanning several orders of magnitude in energy, were found to be in remarkable agreement with the available high-resolution spectroscopy data. The abstract does not describe any major mismatches or failed cases.

    What to keep in mind

    The summary only reports results for the He2 a 3 Σ u + state. It does not describe limitations, uncertainty estimates beyond the stated accuracy of the potential energy curve, or details of any discrepancies.

    • A potential energy curve for the He2 a 3 Σ u + state was computed to within a fraction of 1 part per million.
    • Relativistic and QED corrections were included in the calculations.
    • The nuclear Schrödinger equation was solved with diagonal Born-Oppenheimer and nonadiabatic mass corrections.
    • Computed rovibrational intervals and fine-structure splittings matched available high-resolution spectroscopy data closely.
    • The abstract does not report major limitations or failures.

  • Interference effects can be neglected in muonic hydrogen measurement

    What the study found

    The study found that, for the experimental conditions considered, interference effects in the multi-pass cell can be safely neglected when estimating the laser-induced transition probability in muonic hydrogen. Muonic hydrogen is a bound system of a negative muon and a proton.

    Why the authors say this matters

    The authors suggest that methods that neglect wave-interference effects, such as ray-tracing, can overestimate the transition probability because they underestimate saturation effects. The study suggests a way to estimate the possible impact of interference in other experiments involving coherent light in multi-pass systems.

    What the researchers tested

    The researchers studied how interference effects in a multi-pass cell affect the laser-induced transition probability between hyperfine levels in muonic hydrogen. They developed a simple model to estimate the maximal possible interference effects for given laser and multi-pass cell parameters, without requiring exact knowledge of the intra-cavity field.

    What worked and what didn't

    The model provided an upper bound for the decrease in transition probability that could result from interference effects being ignored. A numerical evaluation of this upper bound for muonic hydrogen showed that, under the experimental conditions described, the effect is small enough to be neglected.

    What to keep in mind

    The abstract does not provide detailed limitations beyond the statement that the calculation gives an upper bound rather than an exact interference effect. The conclusion is specific to the muonic hydrogen conditions studied here.

    • Neglecting wave-interference effects can overestimate laser-induced transition probability.
    • The study examined hyperfine transitions in muonic hydrogen, a negative muon-proton bound system.
    • A simple model was built to estimate the maximal possible interference effect in a multi-pass cell.
    • For the experimental conditions studied, interference effects were found to be safely negligible.
    • The authors say the method could be used in other coherent-light multi-pass experiments.

  • Muon-induced neutron spectra show possible high-multiplicity anomalies in lead

    What the study found

    The study found possible anomalies in neutron multiplicity spectra from lead (Pb) targets, especially at the highest multiplicities. The authors report that a single power-law model does not fully fit the data and that the excess resembles a second power-law component.

    Why the authors say this matters

    The authors suggest these anomalies may limit the accuracy of modelling muon-induced neutron multiplicity spectra with a single power-law function. They also conclude that the weak dependence on depth makes the excess unlikely to be directly linked to the muon flux.

    What the researchers tested

    The researchers examined neutron multiplicity spectra emitted from massive targets at depths of 3, 40, 210, 583, 1166, and 4000 m.w.e. (meters water equivalent, a measure of underground depth). They used three experimental setups with 14 or 60 helium-3 neutron detectors and lead targets weighing 306, 565, or 1134 kg, with data collected between 2001 and 2024 over more than six years of total acquisition time.

    What worked and what didn't

    Where available, the measured spectra were compared with Monte Carlo simulations. The single-power-law approach failed to account for a small but statistically significant excess of events at the highest multiplicities, even at shallow depths. The highest-quality data, from 583 m.w.e., suggested a possible pattern like emission of about 74, 106, 143, and 214 neutrons from the target.

    What to keep in mind

    The abstract describes the findings as potential anomalies, so the origin of the effect is not established. The authors propose new underground measurements with low-cost, large-area, position-sensitive neutron arrays around multi-ton lead targets to verify and investigate the suspected anomalies.

    • The study reports a small but statistically significant excess at the highest neutron multiplicities.
    • A single power-law model did not fully describe the muon-induced neutron spectra from lead targets.
    • The anomaly changed only slightly with depth, so it was unlikely to be directly tied to muon flux.
    • The strongest data, at 583 m.w.e., suggested possible structure near 74, 106, 143, and 214 neutrons.
    • The authors propose further underground measurements with position-sensitive neutron arrays and larger lead targets.

  • Modified scattering cross section reconciles two photon descriptions

    What the study found

    The study found that a modified version of a scattering cross section can reconcile two ways of describing Compton scattering for annihilation photons: the Pryce-Ward description for entangled photon pairs and the Klein-Nishina description for single photons. The authors frame this as a way to bring together the correlations of entangled photons and the statistics of individual photons.

    Why the authors say this matters

    The authors say this matters because the singlet state of orthogonal polarizations is rotationally invariant, so it does not provide physical information about the initial polarizations of the individual photons. In that setting, the study suggests a way to handle the otherwise mutually exclusive Pryce-Ward and Klein-Nishina descriptions in semi-classical simulations.

    What the researchers tested

    The researchers considered two photons from ground-state para-positronium annihilation, which are emitted in a maximally entangled singlet state of orthogonal polarizations. They discussed Compton scattering of both photons and compared the Pryce-Ward cross section, which depends on the difference of azimuthal scattering angles in a fixed coordinate frame, with the Klein-Nishina cross section, which depends on the azimuthal angle relative to each photon's initial polarization. They then used semi-classical simulations that treated the photons as separate entities while implementing the Pryce-Ward cross section and a modified scattering cross section presented in the paper.

    What worked and what didn't

    The paper states that semi-classical simulations of joint Compton scattering can reconcile the Pryce-Ward correlations with the Klein-Nishina statistics for single photons when the modified scattering cross section is used. It also states that the standard Pryce-Ward and Klein-Nishina descriptions are mutually exclusive in this rotationally invariant singlet-state setting.

    What to keep in mind

    The abstract does not describe detailed numerical results, experimental validation, or specific performance measures. It also does not provide broader limits beyond the stated scope of semi-classical simulations of annihilation-photon correlations.

    • The paper describes a modified scattering cross section for entangled annihilation photons.
    • It says this modification can reconcile Pryce-Ward correlations with Klein-Nishina statistics.
    • The discussion concerns two photons from ground-state para-positronium annihilation in a singlet state.
    • The abstract states that the singlet state's rotational invariance makes the usual angular origin for Klein-Nishina undefined.
    • The authors treat the Pryce-Ward and Klein-Nishina descriptions as mutually exclusive without the modification.