Research

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18 pages, 2936 KiB

Open AccessArticle

A Novel, Low-Cost, Position-Sensitive Neutron Detector to Support Thick-Target Inverse Kinematics Experiments for Nuclear Data Measurements

by R. Smith, J. P. Stowell, D. Barker and L. F. Thompson

Universe 2023, 9(6), 274; https://doi.org/10.3390/universe9060274 - 06 Jun 2023

Viewed by 935

Abstract

High quality nuclear data lie at the heart of accurately modelling stellar systems and terrestrial nuclear reactors. However, some key reaction cross sections have large uncertainties, which limit such models in predicting isotopic abundances and other aspects of stellar evolution, along with key [...] Read more.

High quality nuclear data lie at the heart of accurately modelling stellar systems and terrestrial nuclear reactors. However, some key reaction cross sections have large uncertainties, which limit such models in predicting isotopic abundances and other aspects of stellar evolution, along with key operational parameters for nuclear reactors. Reactions involving neutrons are particularly difficult to measure experimentally in laboratories, not least due to the unique challenges involved when detecting neutrons. We present a new approach to measuring nuclear reactions involving neutrons by exploiting the Thick-Target Inverse Kinematics (TTIK) approach. For such measurements, a new detector called ATTIKUS (A Thick-Target Inverse Kinematics detector by Universities in Sheffield) is under construction. Here we present designs and Geant4 Monte-Carlo simulations of the detector. The simulations indicate that a neutron position reconstruction resolution of 10 cm is obtainable and demonstrate how this device could be applied to the ¹³C(α,n) reaction, which is considered to be the main neutron source for the s-process in low-mass Asymptotic Giant Branch stars. In the TTIK method, the emission position of the neutron (the nuclear interaction position in a gaseous target) is directly linked to the centre-of-mass energy of the reaction. Therefore, a position resolution will translate into an energy resolution, depending on the beam-target combination. The inverse reaction, ¹⁶O(n,α), causes a large uncertainty in calculating the effective neutron multiplication factor, K_eff in nuclear reactors, so improvements are required here. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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7 pages, 308 KiB

Open AccessCommunication

On the Possibility of Observing Negative Shapiro-like Delay Using Michelson–Morley-Type Experiments

by Arunava Bhadra, Ramil N. Izmailov and Kamal K. Nandi

Universe 2023, 9(6), 263; https://doi.org/10.3390/universe9060263 - 31 May 2023

Cited by 1 | Viewed by 682

Abstract

The possibility of observing negative Shapiro-like gravitational time delay (or time advancement) due to the Earth’s gravity employing interferometric experiments on the Earth’s surface is discussed. It is suggested that such a measurement may be realized in the near future with the help [...] Read more.

The possibility of observing negative Shapiro-like gravitational time delay (or time advancement) due to the Earth’s gravity employing interferometric experiments on the Earth’s surface is discussed. It is suggested that such a measurement may be realized in the near future with the help of modern versions of Michelson–Morley-type experiments. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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19 pages, 515 KiB

Open AccessArticle

Leptogenesis and Dark Matter–Nucleon Scattering Cross Section in the SE₆SSM

by Roman Nevzorov

Universe 2023, 9(3), 137; https://doi.org/10.3390/universe9030137 - 06 Mar 2023

Cited by 2 | Viewed by 902

Abstract

The

E_{6}

-inspired extension of the minimal supersymmetric (SUSY) standard model (MSSM) with an extra

U {(1)}_{N}

gauge symmetry, under which right-handed neutrinos have zero charge, involves exotic matter beyond the MSSM to ensure anomaly cancellation. We consider the [...] Read more.

The

E_{6}

-inspired extension of the minimal supersymmetric (SUSY) standard model (MSSM) with an extra

U {(1)}_{N}

gauge symmetry, under which right-handed neutrinos have zero charge, involves exotic matter beyond the MSSM to ensure anomaly cancellation. We consider the variant of this extension (SE

_{6}

SSM) in which the cold dark matter is composed of the lightest neutral exotic fermion and gravitino. The observed baryon asymmetry can be induced in this case via the decays of the lightest right-handed neutrino/sneutrino into exotic states even for relatively low reheating temperatures

T_{R} ≲ 10^{6 - 7} G e V

. We argue that there are some regions of the SE

_{6}

SSM parameter space, which are safe from all current constraints, and discuss the implications of this model for collider phenomenology. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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14 pages, 309 KiB

Open AccessArticle

Confinement Potential in a Soft-Wall Holographic Model with a Hydrogen-like Spectrum

by Sergey Afonin and Timofey Solomko

Universe 2023, 9(3), 114; https://doi.org/10.3390/universe9030114 - 22 Feb 2023

Cited by 4 | Viewed by 635

Abstract

It is well known that the soft-wall holographic model for QCD successfully reproduces not only the linear Regge spectrum, but also, via the holographic Wilson confinement criterion, the “linear plus Coulomb” confinement potential, which is similar to the Cornell potential. This property could [...] Read more.

It is well known that the soft-wall holographic model for QCD successfully reproduces not only the linear Regge spectrum, but also, via the holographic Wilson confinement criterion, the “linear plus Coulomb” confinement potential, which is similar to the Cornell potential. This property could be interpreted as a holographic counterpart of the hadron string picture, where the linearly rising potential and Regge-like spectrum are directly related. However, such a relation does not exist in the bottom-up holographic approach. Namely, the Cornell-like potentials arise in a broad class of bottom-up holographic models. The standard soft-wall model is merely a particular representative of this class. This fact is relatively unknown, so we provide a comprehensive discussion of the point. As an example, we consider a soft-wall-like model with linear dilaton background in the metric. This model leads to a hydrogen-like spectrum. A “linear plus Coulomb” confinement potential within this model is calculated. The calculation of renormalized potential at short distances turns out to be complicated by a new subtlety that was skipped in general discussions of the issue existing in the literature. However, the confinement potential of the model is shown to be not very different from the potential obtained in the standard soft-wall model with a quadratic background. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

14 pages, 320 KiB

Open AccessArticle

On the Appearance of Time in the Classical Limit of Quantum Gravity

by Roger I. Ayala Oña, Darya P. Kislyakova and Tatyana P. Shestakova

Universe 2023, 9(2), 85; https://doi.org/10.3390/universe9020085 - 05 Feb 2023

Cited by 1 | Viewed by 1985

Abstract

A possible solution of the problem of time in the Wheeler–DeWitt quantum geometrodynamics is that time appears within a semiclassical limit. Following this line of thinking, one can come to the Schrodinger equation for matter fields in curved spacetime with quantum-gravitational corrections. In [...] Read more.

A possible solution of the problem of time in the Wheeler–DeWitt quantum geometrodynamics is that time appears within a semiclassical limit. Following this line of thinking, one can come to the Schrodinger equation for matter fields in curved spacetime with quantum-gravitational corrections. In the present paper, we study the semiclassical limit in the case of a closed isotropic model with a scalar field decomposed into modes. We analyse calculations made within frameworks of three approaches. The first approach was proposed by Kiefer and Singh. Since the Wheeler–DeWitt equation does not contain a time derivative, it is constructed by means of a special mathematical procedure, a time variable being a parameter along a classical trajectory of gravitational field. The second method was suggested in the paper of Maniccia and Montani, who introduced the Kuchař–Torre reference fluid as an origin of time. Furthermore, the third is the extended phase space approach to the quantisation of gravity. In this approach, the temporal Schrodinger equation is argued to be more fundamental than the Wheeler–DeWitt equation, and there is no problem of time. Time is introduced due to fixing a reference frame of a certain observer, who can register the macroscopic consequences of quantum gravitational phenomena in the Very Early Universe. To go to the semiclassical limit, the Born–Oppenheimer approximation for gravity is used. In each of the approaches, in the order of

O (1 / M)

, a temporal Schrödinger equation for matter fields in curved spacetime with quantum gravitational corrections is obtained. However, equations and corrections are different in various approaches, and the results depend on the additional assumptions made within the scopes of these approaches. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

21 pages, 690 KiB

Open AccessArticle

The Higgs Trilinear Coupling and the Scale of New Physics for the SM-Axion-Seesaw-Higgs Portal Inflation (SMASH) Model

by C.R. Das, Katri Huitu and Timo J. Kärkkäinen

Universe 2023, 9(1), 43; https://doi.org/10.3390/universe9010043 - 09 Jan 2023

Viewed by 1019

Abstract

In the extended scalar sector of the SMASH (Standard Model - Axion-Seesaw-Higgs portal inflation) framework, we conduct a phenomenological investigation of the observable effects. In a suitable region of the SMASH scalar parameter spaces, we solve the vacuum metastability problem and discuss the [...] Read more.

In the extended scalar sector of the SMASH (Standard Model - Axion-Seesaw-Higgs portal inflation) framework, we conduct a phenomenological investigation of the observable effects. In a suitable region of the SMASH scalar parameter spaces, we solve the vacuum metastability problem and discuss the one-loop correction to the triple Higgs coupling,

λ_{H H H}

. The

λ_{H H H}

and SM Higgs quartic coupling

λ_{H}

corrections are found to be proportional to the threshold correction. A large

λ_{H H H}

correction (≳5%) implies vacuum instability in the model and thus limits the general class of theories that use threshold correction. We performed a full two-loop renormalization group analysis of the SMASH model. The SMASH framework has also been used to estimate the evolution of lepton asymmetry in the universe. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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13 pages, 870 KiB

Open AccessArticle

How to Strengthen Constraints on Non-Newtonian Gravity from Measuring the Lateral Casimir Force

by Galina L. Klimchitskaya and Vladimir M. Mostepanenko

Universe 2023, 9(1), 34; https://doi.org/10.3390/universe9010034 - 03 Jan 2023

Cited by 1 | Viewed by 1029

Abstract

It has been known that in the nanometer interaction range the available experimental data do not exclude the Yukawa-type corrections to Newton’s gravitational law, which exceed the Newtonian gravitational force by many orders of magnitude. The strongest constraints on the parameters of Yukawa-type [...] Read more.

It has been known that in the nanometer interaction range the available experimental data do not exclude the Yukawa-type corrections to Newton’s gravitational law, which exceed the Newtonian gravitational force by many orders of magnitude. The strongest constraints on the parameters of Yukawa-type interaction in this interaction range follow from the experiments on neutron scattering and from measurements of the lateral and normal Casimir forces between corrugated surfaces. In this work, we demonstrate that by optimizing the experimental configuration at the expense of the higher corrugation amplitudes and smaller periods of corrugations it is possible to considerably strengthen the currently available constraints within the wide interaction range from 4.5 to 37 nm. We show that the maximum strengthening by more than a factor of 40 is reachable for the interaction range of 19 nm. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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15 pages, 308 KiB

Open AccessFeature PaperArticle

Quadratic Theory of Gravity with a Scalar Field and Type I Shapovalov Wave Spacetimes

by Konstantin Osetrin, Ilya Kirnos and Altair Filippov

Universe 2022, 8(12), 664; https://doi.org/10.3390/universe8120664 - 19 Dec 2022

Cited by 1 | Viewed by 1205

Abstract

For the quadratic theory of gravity with a scalar field, exact solutions are found for gravitational-wave models in Shapovalov I-type spacetimes, which do not arise in models of the general theory of relativity. The theory of gravity under consideration can effectively describe the [...] Read more.

For the quadratic theory of gravity with a scalar field, exact solutions are found for gravitational-wave models in Shapovalov I-type spacetimes, which do not arise in models of the general theory of relativity. The theory of gravity under consideration can effectively describe the early stages of the universe. Type I Shapovalov spaces are the most general forms of gravitational-wave Shapovalov spacetimes, whose metrics in privileged coordinate systems depend on three variables, including the wave variable. For Einstein vacuum spacetimes, these wave models degenerate into simpler types. The exact models of gravitational waves in the quadratic theory of gravity can be used to test the realism of such theories of gravity. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

5 pages, 232 KiB

Open AccessCommunication

Towards the Explanation of Flatness of Galaxies Rotation Curves

by Sergey A. Larin

Universe 2022, 8(12), 632; https://doi.org/10.3390/universe8120632 - 29 Nov 2022

Cited by 2 | Viewed by 1019

Abstract

We suggest a new explanation of the flatness of galaxies rotation curves without invoking dark matter. For this purpose, a new gravitational tensor field is introduced in addition to the metric tensor. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

11 pages, 459 KiB

Open AccessArticle

BTZ Black-Bounce to Traversable Wormhole

by Job Furtado and Geová Alencar

Universe 2022, 8(12), 625; https://doi.org/10.3390/universe8120625 - 26 Nov 2022

Cited by 6 | Viewed by 1659

Abstract

In this paper, we study the charged and uncharged BTZ counterpart of the black-bounce proposed by Simpson and Visser recently. For the uncharged case, we find that the temperature is not modified by the bounce parameter. We also find that the wormhole side [...] Read more.

In this paper, we study the charged and uncharged BTZ counterpart of the black-bounce proposed by Simpson and Visser recently. For the uncharged case, we find that the temperature is not modified by the bounce parameter. We also find that the wormhole side of the solution must always be supported by exotic matter over the throat. For the charged case, we find that the thermodynamics is changed and the bounce parameter controls a phase transition, affecting the sign of the heat capacity and therefore the stability of the system. For the uncharged case, we find that there are no stable orbits for both massive and massless incoming particles, while stable orbits are present for the charged case and the bounce parameter affects the points of stability. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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9 pages, 266 KiB

Open AccessArticle

On the Birth of the Universe and Time

by Natalia Gorobey, Alexander Lukyanenko and Alexander V. Goltsev

Universe 2022, 8(11), 568; https://doi.org/10.3390/universe8110568 - 30 Oct 2022

Cited by 2 | Viewed by 1078

Abstract

A theory of the initial state of the universe is proposed within the framework of the Euclidean quantum theory of gravity. The theory is based on a quantum representation in which the action functional is implemented as an operator on the space of [...] Read more.

A theory of the initial state of the universe is proposed within the framework of the Euclidean quantum theory of gravity. The theory is based on a quantum representation in which the action functional is implemented as an operator on the space of wave functionals depending on the 4D space metric and matter fields. The initial construction object is the eigenvalue of the action operator in the area of the origin of the universe with the given values of the 3D metric and matter fields on the boundary. The wave function of the initial state is plotted as an exponential of this eigenvalue, after a Wick rotation in the complex plane of the radial variable of the Euclidean 4D space. An estimate of the initial radius of the universe is proposed. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

27 pages, 6928 KiB

Open AccessArticle

MASTER Real-Time Multi-Message Observations of High Energy Phenomena

by Vladimir M. Lipunov, Viktor G. Kornilov, Kirill Zhirkov, Artem Kuznetsov, Evgenii Gorbovskoy, Nikolai M. Budnev, David A. H. Buckley, Rafael Rebolo Lopez, Miquel Serra-Ricart, Carlos Francile, Nataly Tyurina, Oleg Gress, Pavel Balanutsa, Gleb Antipov, Daniil Vlasenko, Vladislav Topolev, Aristarkh Chasovnikov, Sergei I. Svertilov, Ricardo Podesta, Federico Podesta, Ekaterina Minkina, Andrei G. Tlatov, Vladimir V. Yurkov, Alexandre Gabovich, Olga Ershova, Viktor Senik and Dmitrii Kuvshinov Show full author list Hide full author list

Universe 2022, 8(5), 271; https://doi.org/10.3390/universe8050271 - 05 May 2022

Cited by 8 | Viewed by 2105

Abstract

This review considers synchronous and follow-up MASTER Global Robotic Net optical observations of high energy astrophysical phenomena such as fast radio bursts (FRB), gamma-ray bursts (including prompt optical emission polarization discovery), gravitational-wave events, detected by LIGO/VIRGO (including GW170817 and independent Kilonova discovery), high [...] Read more.

This review considers synchronous and follow-up MASTER Global Robotic Net optical observations of high energy astrophysical phenomena such as fast radio bursts (FRB), gamma-ray bursts (including prompt optical emission polarization discovery), gravitational-wave events, detected by LIGO/VIRGO (including GW170817 and independent Kilonova discovery), high energy neutrino sources (including the detection of IC-170922A progenitor) and others. We report on the first large optical monitoring campaign of the closest at that moment radio burster FRB 180916.J0158+65 simultaneously with a radio burst. We obtained synchronous limits on the optical flux of the FRB 180916.J0158+65 and FRB 200428 (soft gamma repeater SGR 1935+2154) (The CHIME/FRB Collaboration, Nature 2020, 587) at 155093 MASTER images with the total exposure time equal to 2,705,058 s, i.e., 31.3 days. It follows from these synchronous limitations that the ratio of the energies released in the optical and radio ranges does not exceed 4 × 10⁵. Our optical monitoring covered a total of 6 weeks. On 28 April 2020, MASTER automatically following up on a Swift alert began to observe the galactic soft gamma repeater SGR 1935+2154 experienced another flare. On the same day, radio telescopes detected a short radio burst FRB 200428 and MASTER-Tavrida telescope determined the best prompt optical limit of FRB/SGR 1935+2154. Our optical limit shows that X-ray and radio emissions are not explained by a single power-law spectrum. In the course of our observations, using special methods, we found a faint extended afterglow in the FRB 180916.J0158+65 direction associated with the extended emission of the host galaxy. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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17 pages, 333 KiB

Open AccessArticle

Two Approaches to Hamiltonian Bigravity

by Vladimir Olegovich Soloviev

Universe 2022, 8(2), 119; https://doi.org/10.3390/universe8020119 - 12 Feb 2022

Cited by 1 | Viewed by 1461

Abstract

Bigravity is one of the most natural modifications of General Relativity (GR), as it is based on the equivalence principle. However, its canonical structure appears rather complicated because of the unusual form of the interaction between two metrics. As a consequence, there are [...] Read more.

Bigravity is one of the most natural modifications of General Relativity (GR), as it is based on the equivalence principle. However, its canonical structure appears rather complicated because of the unusual form of the interaction between two metrics. As a consequence, there are different approaches that are difficult to compare in detail. This work is a first attempt to obtain a synthetic picture of the Hamiltonian formalism for bigravity. Here, we are trying to combine two rather different approaches to gain a binocular view of the theory. The first publications on the subject were based on metric formalism. It was proved that both massive gravity and bigravity with de Rham–Gabadadze–Tolley (dRGT) potential were free of Boulware–Deser (BD) ghosts. This proof was based on the transformation of variables involving a

3 \times 3

-matrix which could be treated as the root of a quadratic equation involving two spatial metrics and a new 3-vector introduced instead of the standard shift variable. Therefore, this matrix occurred as an implicit function of the abovementioned variables. After a substantial amount of time, it became possible to calculate the algebra of constraints in full using this method. However, in another approach also based on metric variables and implicit functions, similar calculations were completed earlier. It is not a new matrix, but the potential itself has been taken as an implicit function of two spatial metrics and four functions constructed of two pairs of lapses and shifts. Finally, a straightforward route to canonical bigravity is to apply tetrad (or vierbein) variables. The matrix square root involved in the dRGT potential can be explicitly extracted if tetrads fulfill the symmetry condition. A full treatment has been developed in first-order formalism by treating tetrads and connections as independent variables. In that case, the theory contains many more variables and constraints than in metric formalism. An essential simplification occurs in second-order vierbein formalism. The potential is given explicitly as a polynomial of bilinear combinations of the two tetrads. The

3 \times 3

-matrix introduced in the pioneer papers can be expressed explicitly through canonical coordinates, and the celebrated transformation of variables arises in the Dirac constraint analysis. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

Review

Jump to: Research

10 pages, 245 KiB

Open AccessReview

Development of Two-Phase Emission Detectors in Russia

by Dmitry Akimov and Alexander Bolozdynya

Universe 2022, 8(3), 139; https://doi.org/10.3390/universe8030139 - 22 Feb 2022

Viewed by 1719

Abstract

This paper reviews the history of the development of two-phase emission detector technology that was invented 50 years ago at the Moscow Engineering Physics Institute and is currently being used to search for dark matter, novel neutrino physics and double beta-decay in several [...] Read more.

This paper reviews the history of the development of two-phase emission detector technology that was invented 50 years ago at the Moscow Engineering Physics Institute and is currently being used to search for dark matter, novel neutrino physics and double beta-decay in several internationally running experiments. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

24 pages, 815 KiB

Open AccessReview

Abnormal Bound Systems

by Vladimir A. Karmanov

Universe 2022, 8(2), 95; https://doi.org/10.3390/universe8020095 - 03 Feb 2022

Viewed by 977

Abstract

It is taken for granted that bound systems are made of massive constituents that interact through particle exchanges (charged particles interacting via photon exchanges, quarks in elementary particles interacting via gluon exchanges, and nucleons in nuclei interacting via meson exchanges). However, as was [...] Read more.

It is taken for granted that bound systems are made of massive constituents that interact through particle exchanges (charged particles interacting via photon exchanges, quarks in elementary particles interacting via gluon exchanges, and nucleons in nuclei interacting via meson exchanges). However, as was recently theoretically found, there exist systems dominated by exchange particles (at least for the zero exchange masses). In these systems, the contribution of massive constituents is negligible. These systems have a relativistic nature (since they are mainly made of massless particles moving at the speed of light), and therefore, they cannot be described by the Schrödinger equation. Though these results were found so far in the simple Wick–Cutkosky model (spinless constituents interacting via the ladder of spinless massless exchanges), the physical ground for their existence seems to be rather general. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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