Universe

17 pages, 277 KiB

Open AccessArticle

On-Shell Calculation of Low-Energy Photon–Photon Scattering

by Barry R. Holstein

Universe 2025, 11(5), 134; https://doi.org/10.3390/universe11050134 - 24 Apr 2025

Although photon–photon scattering does not exist at the tree level, this is no longer the case at loop order and was first calculated by Euler and Heisenberg. The existence of this phenomenon has now been confirmed experimentally by the ATLAS collaboration and plays [...] Read more.

Although photon–photon scattering does not exist at the tree level, this is no longer the case at loop order and was first calculated by Euler and Heisenberg. The existence of this phenomenon has now been confirmed experimentally by the ATLAS collaboration and plays a small but important role in the calculation of

g_{μ}

-2. We show how the low-energy form of the

γ γ

scattering amplitude can be determined via causal (on-shell) methods using Compton scattering helicity amplitudes as input for the case of charged S = 0, S =

1 / 2

, and S = 1 intermediate state fields. Full article

(This article belongs to the Section Field Theory)

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18 pages, 431 KiB

Open AccessArticle

Reconciling the Waiting Time Peaks Variations of Repeating FRBs with an Eccentric Neutron Star–White Dwarf Binary

by Hao-Yan Chen

Universe 2025, 11(5), 133; https://doi.org/10.3390/universe11050133 - 22 Apr 2025

Abstract

Fast radio bursts (FRBs) are luminous radio transients with millisecond duration. For some active repeaters, such as FRBs 20121102A and 20201124A, more than a thousand bursts have been detected by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The waiting time (WT) distributions of [...] Read more.

Fast radio bursts (FRBs) are luminous radio transients with millisecond duration. For some active repeaters, such as FRBs 20121102A and 20201124A, more than a thousand bursts have been detected by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The waiting time (WT) distributions of both repeaters, defined as the time intervals between adjacent (detected) bursts, exhibit a bimodal structure well-fitted by two log-normal functions. Notably, the time scales of the long-duration WT peaks for both repeaters show a decreasing trend over time. These similar burst features suggest that there may be a common physical mechanism for FRBs 20121102A and 20201124A. In this paper, we revisit the neutron star (NS)–white dwarf (WD) binary model with an eccentric orbit to account for the observed changes in the long-duration WT peaks. According to our model, the shortening of the WT peaks corresponds to the orbital period decay of the NS-WD binary. We consider two mass transfer modes, namely, stable and unstable mass transfer, to examine how the orbital period evolves. Our findings reveal distinct evolutionary pathways for the two repeaters: for FRB 20121102A, the NS-WD binary likely undergoes a combination of common envelope (CE) ejection and Roche lobe overflow, whereas for FRB 20201124A the system may experience multiple CE ejections. These findings warrant further validation through follow-up observations. Full article

(This article belongs to the Special Issue New Insights into High-Energy Astrophysics, Galaxies, and Cosmology—Celebrating the 10th Anniversary of the Re-establishment of the Department of Astronomy at Xiamen University (2012–2022))

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22 pages, 4740 KiB

Open AccessArticle

Determining the Scale Length and Height of the Milky Way’s Thick Disc Using RR Lyrae

by Roman Tkachenko, Katherine Vieira, Artem Lutsenko, Vladimir Korchagin and Giovanni Carraro

Universe 2025, 11(4), 132; https://doi.org/10.3390/universe11040132 - 17 Apr 2025

Abstract

Using the RR Lyrae surveys Gaia DR3 Specific Objects Study, PanSTARRS1 and ASAS-SN-II, we determine the Milky Way’s thick disc scale length and scale height as well as the radial scale length of the galaxy’s inner halo. We use a Bayesian approach to [...] Read more.

Using the RR Lyrae surveys Gaia DR3 Specific Objects Study, PanSTARRS1 and ASAS-SN-II, we determine the Milky Way’s thick disc scale length and scale height as well as the radial scale length of the galaxy’s inner halo. We use a Bayesian approach to estimate these values using two independent techniques: Markov chain Monte Carlo sampling, and importance nested sampling. We consider two vertical density profiles for the thick disc. In the exponential model, the scale length of the thick disc is

h_{R} = {2.14}_{- 0.17}^{+ 0.19}

kpc, and its scale height is

h_{z} = {0.64}_{- 0.06}^{+ 0.06}

kpc. In the squared hyperbolic secant profile

s e c h^{2}

, those values are correspondingly

h_{R} = {2.10}_{- 0.17}^{+ 0.19}

kpc and

h_{z} = {1.02}_{- 0.08}^{+ 0.09}

kpc. The density distribution of the inner halo can be described as a power law function with the exponent

n = - {2.35}_{- 0.05}^{+ 0.05}

and flattening

q = {0.57}_{- 0.02}^{+ 0.02}

. We also estimate the halo to disc concentration ratio as

γ = {0.19}_{- 0.02}^{+ 0.02}

for the exponential disc and

γ = {0.32}_{- 0.03}^{+ 0.03}

for the

s e c h^{2}

disc. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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18 pages, 492 KiB

Open AccessArticle

Inflection Point Dynamics of Minimally Coupled Tachyonic Scalar Fields

by Jaskirat Kaur, S. D. Pathak, Maxim Khlopov and Manabendra Sharma

Universe 2025, 11(4), 131; https://doi.org/10.3390/universe11040131 - 14 Apr 2025

Abstract

In this paper, we explore the behavior of a minimally coupled tachyonic scalar field at an inflection point within an accelerating universe. We examine various cosmic expansion factors, including power-law, exponential, and a hybrid form combining power-law and exponential growth. For each of [...] Read more.

In this paper, we explore the behavior of a minimally coupled tachyonic scalar field at an inflection point within an accelerating universe. We examine various cosmic expansion factors, including power-law, exponential, and a hybrid form combining power-law and exponential growth. For each of these scenarios, we derive the corresponding potentials of the tachyonic scalar field. Subsequently, we calculate the inflection points of the spatially homogeneous tachyonic scalar field for these potentials. To further analyze the system, we employ dynamical system analysis techniques to identify equilibrium points and assess their stability. Full article

(This article belongs to the Special Issue The 10th Anniversary of Universe: Standard Cosmological Models, and Modified Gravity and Cosmological Tensions)

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17 pages, 3782 KiB

Open AccessArticle

Observability of Acausal and Uncorrelated Optical Quasar Pairs for Quantum-Mechanical Experiments

by Eric Steinbring

Universe 2025, 11(4), 130; https://doi.org/10.3390/universe11040130 - 13 Apr 2025

Abstract

Viewing high-redshift sources at near-opposite directions on the sky can ensure, using light-travel-time arguments, acausality between their emitted photons. One utility would be true random-number generation through sensing these via two independent telescopes that each flip a switch based on the latest-arrived colours; [...] Read more.

Viewing high-redshift sources at near-opposite directions on the sky can ensure, using light-travel-time arguments, acausality between their emitted photons. One utility would be true random-number generation through sensing these via two independent telescopes that each flip a switch based on the latest-arrived colours; for example, to autonomously control a quantum-mechanical (QM) experiment. Although demonstrated with distant quasars, those were not fully acausal pairs, which are restricted when simultaneously viewed from the ground at any single observatory. In optical light, such faint sources also require a large telescope aperture to avoid sampling assumptions when imaged at fast camera framerates: unsensed intrinsic correlations between them or equivalently correlated noise may ruin the expectation of pure randomness. One such case that could spoil a QM test is considered. Based on that, the allowed geometries and instrumental limits are modelled for any two ground-based sites, and their data are simulated. For comparison, an analysis of photometry from the Gemini twin 8 m telescopes is presented using the archival data of well-separated bright stars obtained with the instruments ‘Alopeke (on Gemini North in Hawai’i) and Zorro (on Gemini-South in Chile) simultaneously in two bands (centred at

562 nm

and

832 nm

) with 17 Hz framerate. No flux correlation is found; these results were used to calibrate an analytic model predicting where a search with a signal-to-noise over 50 at 50 Hz can be made using the same instrumentation. Finally, the software PDQ (Predict Different Quasars) is presented, which searches a large catalogue of known quasars, reporting those with a brightness and visibility suitable to verify acausal, uncorrelated photons at these limits. Full article

(This article belongs to the Section Foundations of Quantum Mechanics and Quantum Gravity)

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15 pages, 1746 KiB

Open AccessArticle

The Impact of Stellar Initial Mass Function on the Epoch of Reionization: Insights from Semi-Analytic Galaxy Modeling

by Qingbo Ma, Lei Liu and Peiai Liu

Universe 2025, 11(4), 129; https://doi.org/10.3390/universe11040129 - 12 Apr 2025

Abstract

The adequate choice of stellar initial mass function (IMF) is crucial when studying high-z galaxy formation and the epoch of reionization (EoR) models. We employ the semi-analytical galaxy model L-Galaxies2020 and the dark matter simulation Millennium-II, in combination with the BPASS [...] Read more.

The adequate choice of stellar initial mass function (IMF) is crucial when studying high-z galaxy formation and the epoch of reionization (EoR) models. We employ the semi-analytical galaxy model L-Galaxies2020 and the dark matter simulation Millennium-II, in combination with the BPASS spectral model, to investigate the effects of different stellar IMFs on the properties of high-z galaxies and their ionizing photon budget during EoR. We find that different stellar IMFs lead to different SED of high-z galaxies, and thus different ultraviolet luminosity functions (UVLF) and budgets of ionizing photons for EoR. Specifically, at

z < 10

, the UVLF with Salpeter and Chabrier IMF models are closer to the observed results, while at

z > 10

, the ones with a Top-Heavy model are more consistent with the JWST observations. The increase in the upper limit of star mass within stellar IMF from

100 M_{⊙}

to

300 M_{⊙}

results in the increase in the UVLF and the ionizing photon number density. Full article

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19 pages, 846 KiB

Open AccessArticle

Scaling Invariance of Perturbations in k-Inflation Models

by Neven Bilić, Dragoljub D. Dimitrijević, Goran S. Djordjević, Milan Milošević and Marko Stojanović

Universe 2025, 11(4), 128; https://doi.org/10.3390/universe11040128 - 9 Apr 2025

Abstract

We study the background and perturbations in k-essence inflation models and show that a general k-essence exhibits a simple scaling property. In particular, we study two classes of k-inflation models with the potential characterized by an inflection point. We demonstrate [...] Read more.

We study the background and perturbations in k-essence inflation models and show that a general k-essence exhibits a simple scaling property. In particular, we study two classes of k-inflation models with the potential characterized by an inflection point. We demonstrate that these models enjoy scaling properties that could be used to redefine input parameters so that the perturbations spectra satisfy the correct normalization at the CMB pivot scale. The background and perturbation equations are integrated numerically for two specific models. Full article

(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy, 2nd Edition)

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11 pages, 9181 KiB

Open AccessArticle

Extraplanar [C II] and Hα in the Edge-On Galaxy NGC 5775

by William T. Reach, Dario Fadda, Richard J. Rand and Gordon J. Stacey

Universe 2025, 11(4), 127; https://doi.org/10.3390/universe11040127 - 9 Apr 2025

Abstract

Spiral galaxies are thin and susceptible to being disrupted vertically. The largest star clusters, and nuclear starbursts, generate enough energy from winds and supernovae to send disk material to the halo. Observations of edge-on galaxies allow for the clearest view of vertical disruptions. [...] Read more.

Spiral galaxies are thin and susceptible to being disrupted vertically. The largest star clusters, and nuclear starbursts, generate enough energy from winds and supernovae to send disk material to the halo. Observations of edge-on galaxies allow for the clearest view of vertical disruptions. We present new observations of the nearby, edge-on galaxy NGC 5775 with SOFIA in [C II]

157.7 μ

m and archival images from Hubble in H

α

to search for extraplanar gas. The extraplanar [C II] extends 2 kpc from the midplane over much of the star-forming disk. The extraplanar [C II] at 2 kpc from the midplane approximately follows the rotation of the disk, with a lag of approximately 40 km

s^{- 1}

; this lag is similar to what has been previously reported in H

α

. Significant vertical extensions (to 3 kpc) are seen on the northeast side of the galaxy, potentially due to super star clusters in the NGC 5775 disk combined with gravitational interaction with the companion galaxy NGC 5774. The H

α

narrow-band image reveals a narrow plume that extends 7 kpc from the nucleus and is almost exactly perpendicular to the disk. The plume shape is similar to that seen from the comparable galaxy NGC 3628 and may arise from the nuclear starburst. Alternatively, the H

α

plume could be a relic of past activity. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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35 pages, 541 KiB

Open AccessArticle

Negation of the Smooth Poincare Conjecture in Dimension 4 and Negation of the Tsirelson’s Conjecture Shed Light on Quantum Gravity

by Jerzy Król and Torsten Asselmeyer-Maluga

Universe 2025, 11(4), 126; https://doi.org/10.3390/universe11040126 - 8 Apr 2025

Abstract

If spacetime is a physical object, it is conceivable that it loses its integrity or is destroyed in some way as a continuum in an abrupt process initiated in spacetime itself. An example is a gravitational collapse leading to a spacetime singularity, as [...] Read more.

If spacetime is a physical object, it is conceivable that it loses its integrity or is destroyed in some way as a continuum in an abrupt process initiated in spacetime itself. An example is a gravitational collapse leading to a spacetime singularity, as in the interior of a black hole. We find a conservative extension of quantum mechanics by quantum set theory over the singular domain and show that it is reconcilable with the special extension of spacetime 4-diffeomorphisms by automorphisms of Boolean models of set theory. The extension of quantum mechanics supports the random sequences of the quantum mechanical outcomes that can negate Tsirelson’s conjecture, whereas the extension of 4-diffeomorphisms indicates the role of exotic smooth 4-spheres as gravitational instantons. This leads to the negation of the smooth 4-dimensional Poincaré conjecture before its final resolution by mathematicians. We also discuss the case where the Poincaré conjecture would remain true. Full article

(This article belongs to the Section Foundations of Quantum Mechanics and Quantum Gravity)

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13 pages, 292 KiB

Open AccessArticle

Polyadic Supersymmetry

by Steven Duplij

Universe 2025, 11(4), 125; https://doi.org/10.3390/universe11040125 - 8 Apr 2025

Abstract

We introduce a polyadic analog of supersymmetry by considering the polyadization procedure (proposed by the author) applied to the toy model of one-dimensional supersymmetric quantum mechanics. The supercharges are generalized to polyadic ones using the n-ary sigma matrices defined in earlier work. [...] Read more.

We introduce a polyadic analog of supersymmetry by considering the polyadization procedure (proposed by the author) applied to the toy model of one-dimensional supersymmetric quantum mechanics. The supercharges are generalized to polyadic ones using the n-ary sigma matrices defined in earlier work. In this way, polyadic analogs of supercharges and Hamiltonians take the cyclic shift block matrix form, and they are different from the N-extended and multigraded SQM. While constructing the corresponding supersymmetry as an n-ary Lie superalgebra (n is the arity of the initial associative multiplication), we have found new brackets with a reduced arity of

2 \leq m < n

and a related series of m-ary superalgebras (which is impossible for binary superalgebras). In the case of even reduced arity m, we obtain a tower of higher-order (as differential operators) even Hamiltonians, while for m odd we obtain a tower of higher-order odd supercharges, and the corresponding algebra consists of the odd sector only. Full article

13 pages, 1735 KiB

Open AccessArticle

Performance of Reduced Polarimetric Optical Switching Demodulation Technique in Different Spatio-Temporal Polarization Modulation Schemes

by Zhi Xu and Yue Zhong

Universe 2025, 11(4), 124; https://doi.org/10.3390/universe11040124 - 7 Apr 2025

Abstract

The beam exchange is a classical supplementary technique for spatio-temporal modulation in a dual-beam setup. In order to save time, the reduced polarimetric-optical-switching (RPOS) technique was propsed as an alternative technique. In this work, we revisit the assumptions of several formulas specifically constructed [...] Read more.

The beam exchange is a classical supplementary technique for spatio-temporal modulation in a dual-beam setup. In order to save time, the reduced polarimetric-optical-switching (RPOS) technique was propsed as an alternative technique. In this work, we revisit the assumptions of several formulas specifically constructed for this technique and evaluate their validity in different modulation schemes (e.g., dependent modulation), especially when reference measurements are acquired using specific Stokes signals. Subsequently, we compare the RPOS technique based on the most appropriate formula with the demodulation method based on the demodulation matrix by using synthesized observation data. The artificial observation takes into account the influence several factors have on the modulated intensities, including dark current, gain variation, atmospheric seeing fluctuations, and photon noise. Our numerical tests demonstrate that the RPOS technique has an advantage in mitigating the effects of atmospheric seeing fluctuations and gain variations between two beams. However, the selection of a specific Stokes signal for reference measurements has a notable impact on performance in minimizing the effect of photon noise. Full article

(This article belongs to the Special Issue Measurements, Observations and Theoretical Studies on the Solar Magnetic Field—Celebrating the 40th Anniversary of the Huairou Solar Observing Station)

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15 pages, 828 KiB

Open AccessArticle

New Results of the Experiment to Search for Double Beta Decay of ¹⁰⁶Cd with Enriched ¹⁰⁶CdWO₄ Scintillator

by P. Belli, R. Bernabei, F. Cappella, V. Caracciolo, R. Cerulli, F. A. Danevich, A. Incicchitti, D. V. Kasperovych, V. R. Klavdiienko, V. V. Kobychev, A. Leoncini, V. Merlo, O. G. Polischuk and V. I. Tretyak

Universe 2025, 11(4), 123; https://doi.org/10.3390/universe11040123 - 7 Apr 2025

Abstract

In this article, we present current results of the experiment searching for double beta decay of ¹⁰⁶Cd with the help of an enriched ¹⁰⁶CdWO₄ crystal scintillator in coincidence with two CdWO₄ scintillation detectors. The experiment is carried out at [...] Read more.

In this article, we present current results of the experiment searching for double beta decay of ¹⁰⁶Cd with the help of an enriched ¹⁰⁶CdWO₄ crystal scintillator in coincidence with two CdWO₄ scintillation detectors. The experiment is carried out at the Gran Sasso underground laboratory of the National Institute for Nuclear Physics (LNGS INFN, Italy). After 1075 days of data-taking, no double-beta effects were observed. New half-life limits have been set for the different modes and channels of double beta processes in ¹⁰⁶Cd at the level of

lim T_{1 / 2} = 10^{20} - 10^{22}

years. Full article

(This article belongs to the Special Issue Exploring Double Beta Decay: Probing Fundamental Properties of Neutrinos and Beyond)

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32 pages, 3983 KiB

Open AccessArticle

Parameter Estimation Precision with Geocentric Gravitational Wave Interferometers: Monochromatic Signals

by Manoel Felipe Sousa, Tabata Aira Ferreira and Massimo Tinto

Universe 2025, 11(4), 122; https://doi.org/10.3390/universe11040122 - 7 Apr 2025

Abstract

We present a Fisher information matrix study of the parameter estimation precision achievable by a class of future space-based, “mid-band”, gravitational wave interferometers observing monochromatic signals. The mid-band is the frequency region between that accessible by the Laser Interferometer Space Antenna (LISA) and [...] Read more.

We present a Fisher information matrix study of the parameter estimation precision achievable by a class of future space-based, “mid-band”, gravitational wave interferometers observing monochromatic signals. The mid-band is the frequency region between that accessible by the Laser Interferometer Space Antenna (LISA) and ground-based interferometers. We analyze monochromatic signals observed by the TianQin mission, gLISA (a LISA-like interferometer in a geosynchronous orbit) and a descoped gLISA mission, gLISA_d, characterized by an acceleration noise level that is three orders of magnitude worse than that of gLISA. We find that all three missions achieve their best angular source reconstruction precision in the higher part of their accessible frequency band, with an error box better than

10^{- 10}

sr in the frequency band [

10^{- 1}, 10

] Hz when observing a monochromatic gravitational wave signal of amplitude

h_{0} = 10^{- 21}

that is incoming from a given direction. In terms of their reconstructed frequencies and amplitudes, TianQin achieves its best precision values in both quantities in the frequency band [

10^{- 2}, 4 \times 10^{- 1}

] Hz, with a frequency precision

σ_{f_{g w}} = 2 \times 10^{- 11}

Hz and an amplitude precision

σ_{h_{0}} = 2 \times 10^{- 24}

. gLISA matches these precisions in a frequency band slightly higher than that of TianQin, [

3 \times 10^{- 2}, 1

] Hz, as a consequence of its smaller arm length. gLISA_d, on the other hand, matches the performance of gLISA only over the narrower frequency region, [

7 \times 10^{- 1}, 1

] Hz, as a consequence of its higher acceleration noise at lower frequencies. The angular, frequency, and amplitude precisions as functions of the source sky location are then derived by assuming an average signal-to-noise ratio of 10 at a selected number of gravitational wave frequencies covering the operational bandwidth of TianQin and gLISA. Similar precision functions are then derived for gLISA_d by using the amplitudes resulting in the gLISA average SNR being equal to 10 at the selected frequencies. We find that, for any given source location, all three missions display a marked precision improvement in the three reconstructed parameters at higher gravitational wave frequencies. Full article

(This article belongs to the Special Issue Exploring Low-Frequency Gravitational Wave Sources: Waveforms, Detection and Sciences)

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15 pages, 565 KiB

Open AccessArticle

Scanning the Universe for Large-Scale Structures Using Gamma-Ray Bursts

by Istvan Horvath, Zsolt Bagoly, Lajos G. Balazs, Jon Hakkila, Bendeguz Koncz, Istvan I. Racz, Peter Veres and Sandor Pinter

Universe 2025, 11(4), 121; https://doi.org/10.3390/universe11040121 - 6 Apr 2025

Abstract

In the past few decades, large universal structures have been found that challenge the homogeneity and isotropy expected in standard cosmological models. The largest of these, identified as the Hercules–Corona Borealis Great Wall, was found in 2014 in the northern galactic hemisphere in [...] Read more.

In the past few decades, large universal structures have been found that challenge the homogeneity and isotropy expected in standard cosmological models. The largest of these, identified as the Hercules–Corona Borealis Great Wall, was found in 2014 in the northern galactic hemisphere in the redshift range of

1.6 \leq z \leq 2.1

. Subsequent studies used an increasing gamma-ray burst database to show that the cluster was unlikely to have been caused by statistical sampling uncertainties. This study re-examines burst clustering in the northern galactic hemisphere using a recently developed methodology. Evidence is provided that the Hercules–Corona Borealis Great Wall cluster is larger than previously thought, with members potentially spanning the redshift range of

0.33 \leq z \leq 2.43

. The extension of this cluster’s size does not appear to have been due to statistical variations or sampling biases. Full article

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13 pages, 885 KiB

Open AccessArticle

Machine Learning to Simulate Quantum Computing System Errors from Physical Observations

by Jie Feng, Xingchen Zhang, Guanhao Feng and Hong-Hao Zhang

Universe 2025, 11(4), 120; https://doi.org/10.3390/universe11040120 - 4 Apr 2025

Abstract

In the context of quantum computing, error correction remains a pivotal challenge, primarily due to imperfect gate operations and environmental interactions. This study introduces a machine learning-based method to simulate and analyze these errors. Utilizing a minimal scalable 2-Majorana-zero-mode (2-MZM) island model within [...] Read more.

In the context of quantum computing, error correction remains a pivotal challenge, primarily due to imperfect gate operations and environmental interactions. This study introduces a machine learning-based method to simulate and analyze these errors. Utilizing a minimal scalable 2-Majorana-zero-mode (2-MZM) island model within a one-dimensional p-wave topological superconductor, this research employs a detailed Hamiltonian approach combined with a bosonic thermal bath interaction. The analysis is conducted using the Pauli master equation and Monte Carlo simulations. This work’s novel contribution lies in applying Boosted Decision Tree with Gradient boosting (BDTG) and Multi-Layer Perceptron (MLP) machine learning techniques. These methods, trained on Monte Carlo simulation data, showed proficiency in predicting the evolution of error probabilities in the quantum system. The results indicate a significant potential for machine learning to offer a more efficient alternative for simulating quantum computing errors, thereby contributing to developing more robust quantum computing systems. Full article

(This article belongs to the Section Foundations of Quantum Mechanics and Quantum Gravity)

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11 pages, 432 KiB

Open AccessArticle

Inclusive Neutrino and Antineutrino Scattering on the ¹²C Nucleus Within the Coherent Density Fluctuation Model

by Martin V. Ivanov and Anton N. Antonov

Universe 2025, 11(4), 119; https://doi.org/10.3390/universe11040119 - 4 Apr 2025

Abstract

We investigate quasielastic (anti)neutrino scattering on the ¹²C nucleus utilizing a novel scaling variable,

ψ^{*}

. This variable is derived from the interacting relativistic Fermi gas model, which incorporates both scalar and vector interactions, leading to a relativistic effective mass for [...] Read more.

We investigate quasielastic (anti)neutrino scattering on the ¹²C nucleus utilizing a novel scaling variable,

ψ^{*}

. This variable is derived from the interacting relativistic Fermi gas model, which incorporates both scalar and vector interactions, leading to a relativistic effective mass for the interacting nucleons. For inclusive lepton scattering from nuclei, we develop a new scaling function, denoted as

f^{QE} (ψ^{*})

, based on the coherent density fluctuation model (CDFM). This model serves as a natural extension of the relativistic Fermi gas (RFG) model applicable to finite nuclei. In this study, we compute theoretical predictions and compare them with experimental data from Miner

ν

a and T2K for inclusive (anti)neutrino cross-sections. The scaling function is derived within the CDFM framework, employing a relativistic effective mass of

m_{N}^{*} = 0.8 m_{N}

. The findings demonstrate a high degree of consistency with experimental data across all (anti)neutrino energy ranges. Full article

(This article belongs to the Special Issue Neutrino Insights: Peering into the Subatomic Universe)

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33 pages, 1207 KiB

Open AccessArticle

Running Vacuum and H⁴ Inflation

by Joan Solà Peracaula, Cristian Moreno-Pulido and Alex González-Fuentes

Universe 2025, 11(4), 118; https://doi.org/10.3390/universe11040118 - 2 Apr 2025

Abstract

Recent studies of QFT in cosmological spacetime indicate that the speeding up of the present universe may not just be associated with a rigid cosmological term but with a running one that evolves with the expansion rate

Λ = Λ (H)

[...] Read more.

Recent studies of QFT in cosmological spacetime indicate that the speeding up of the present universe may not just be associated with a rigid cosmological term but with a running one that evolves with the expansion rate

Λ = Λ (H)

. This running is inherited from the cosmic evolution of the vacuum energy density (VED),

ρ_{vac}

, which is sensitive to quantum effects in curved spacetime that ultimately trigger that running. The VED is a function of the Hubble rate and its time derivatives

ρ_{vac} = ρ_{vac} (H, \dot{H}, \ddot{H}, \dots)

. Two nearby points of cosmic evolution during the FLRW epoch are smoothly related as

δ ρ_{vac} \sim O (H^{2})

. In the very early universe, in contrast, the higher powers of the Hubble rate take over and bring about a period of fast inflation. They originate from quantum effects on the effective action of a vacuum, which we compute. Herein, we focus on the lowest possible power for inflation to occur:

H^{4}

. During the inflationary phase, H remains approximately constant and very large. Subsequently, the universe enters the usual FLRW radiation epoch. This new mechanism (‘RVM inflation’) is not based on any supplementary ‘inflaton’ field; it is fueled by pure QFT effects on the dynamical background and is different from Starobinsky’s inflation, in which H is never constant. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—'Cosmology')

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17 pages, 2736 KiB

Open AccessArticle

Using Machine Learning for Lunar Mineralogy-I: Hyperspectral Imaging of Volcanic Samples

by Fatemeh Fazel Hesar, Mojtaba Raouf, Peyman Soltani, Bernard Foing, Michiel J. A. de Dood and Fons J. Verbeek

Universe 2025, 11(4), 117; https://doi.org/10.3390/universe11040117 - 2 Apr 2025

Abstract

This study examines the mineral composition of volcanic samples similar to lunar materials, focusing on olivine and pyroxene. Using hyperspectral imaging (HSI) from 400 to 1000 nm, we created data cubes to analyze the reflectance characteristics of samples from Vulcano, a volcanically active [...] Read more.

This study examines the mineral composition of volcanic samples similar to lunar materials, focusing on olivine and pyroxene. Using hyperspectral imaging (HSI) from 400 to 1000 nm, we created data cubes to analyze the reflectance characteristics of samples from Vulcano, a volcanically active island in the Aeolian archipelago, north of Sicily, Italy, categorizing them into nine regions of interest (ROIs) and analyzing spectral data for each. We applied various unsupervised clustering algorithms, including K-Means, hierarchical clustering, Gaussian mixture models (GMMs), and spectral clustering, to classify the spectral profiles. Principal component analysis (PCA) revealed distinct spectral signatures associated with specific minerals, facilitating precise identification. The clustering performance varied by region, with K-Means achieving the highest silhouette score of 0.47, whereas GMMs performed poorly with a score of only 0.25. Non-negative matrix factorization (NMF) aided in identifying similarities among clusters across different methods and reference spectra for olivine and pyroxene. Hierarchical clustering emerged as the most reliable technique, achieving a 94% similarity with the olivine spectrum in one sample, whereas GMMs exhibited notable variability. Overall, the analysis indicated that both the hierarchical and K-Means methods yielded lower errors in total measurements, with K-Means demonstrating superior performance in estimated dispersion and clustering. Additionally, GMMs showed a higher root mean square error (RMSE) compared to the other models. The RMSE analysis confirmed K-Means as the most consistent algorithm across all samples, suggesting a predominance of olivine in the Vulcano region relative to pyroxene. This predominance is likely linked to historical formation conditions similar to volcanic processes on the Moon, where olivine-rich compositions are common in ancient lava flows and impact-melt rocks. These findings provide a deeper context for mineral distribution and formation processes in volcanic landscapes. Full article

(This article belongs to the Special Issue Planetary Radar Astronomy)

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26 pages, 5021 KiB

Open AccessArticle

Protoplanet and Proto-Brown Dwarf Clumps in Gravitationally Unstable Protoplanetary Disks of Various Metallicity

by Eduard Vorobyov and Carina Schoenhacker

Universe 2025, 11(4), 116; https://doi.org/10.3390/universe11040116 - 2 Apr 2025

Abstract

Gravitational fragmentation of a protoplanetary disk is considered a possible mechanism for the formation of planets and brown dwarfs. In this process, transitory objects are formed that are known as clumps, which are compact gas–dust condensations with a size of several astronomical units. [...] Read more.

Gravitational fragmentation of a protoplanetary disk is considered a possible mechanism for the formation of planets and brown dwarfs. In this process, transitory objects are formed that are known as clumps, which are compact gas–dust condensations with a size of several astronomical units. The contraction of these clumps to planetary sizes via the dissociation of molecular hydrogen or tidal downsizing can ultimately lead to planet or brown dwarf formation. Here, we present a comprehensive numerical and statistical study of the clump properties in protoplanetary disks formed from cloud cores of similar mass (0.9–1.0

M_{⊙}

). We focus on possible differences in their characteristics depending on the metallicity of the parental disk. We show that notable differences can be expected in the clump characteristics in terms of their number, internal energetics, mass, and distance to the star. For all metallicities considered, the propensity to forming planets or brown dwarfs via disk fragmentation is challenged by large amounts of gravitationally unbound clumps. We conclude that giant planet formation via disk fragmentation is possible down to 1/100 solar metallicity but it should be a rare outcome. Brown dwarf formation via disk fragmentation is possible only down to 1/10 solar metallicity. Our results stand for similar masses of the central star on the order of the Sun. Full article

(This article belongs to the Section Planetary Sciences)

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