Universe

2024

Jump to: 2022, 2021

17 pages, 921 KiB

Open AccessArticle

Characterisation of the Atmosphere in Very High Energy Gamma-Astronomy for Imaging Atmospheric Cherenkov Telescopes

by Dijana Dominis Prester, Jan Ebr, Markus Gaug, Alexander Hahn, Ana Babić, Jiří Eliášek, Petr Janeček, Sergey Karpov, Marta Kolarek, Marina Manganaro and Razmik Mirzoyan

Universe 2024, 10(9), 349; https://doi.org/10.3390/universe10090349 - 30 Aug 2024

Viewed by 935

Abstract

Ground-based observations of Very High Energy (VHE) gamma rays from extreme astrophysical sources are significantly influenced by atmospheric conditions. This is due to the atmosphere being an integral part of the detector when utilizing Imaging Atmospheric Cherenkov Telescopes (IACTs). Clouds and dust particles [...] Read more.

Ground-based observations of Very High Energy (VHE) gamma rays from extreme astrophysical sources are significantly influenced by atmospheric conditions. This is due to the atmosphere being an integral part of the detector when utilizing Imaging Atmospheric Cherenkov Telescopes (IACTs). Clouds and dust particles diminish atmospheric transmission of Cherenkov light, thereby impacting the reconstruction of the air showers and consequently the reconstructed gamma-ray spectra. Precise measurements of atmospheric transmission above Cherenkov observatories play a pivotal role in the accuracy of the analysed data, among which the corrections of the reconstructed energies and fluxes of incoming gamma rays, and in establishing observation strategies for different types of gamma-ray emitting sources. The Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes and the Cherenkov Telescope Array Observatory (CTAO), both located on the Observatorio del Roque de los Muchachos (ORM), La Palma, Canary Islands, use different sets of auxiliary instruments for real-time characterisation of the atmosphere. In this paper, historical data taken by MAGIC LIDAR (LIght Detection And Ranging) and CTAO FRAM (F/Photometric Robotic Telescope) are presented. From the atmospheric aerosol transmission profiles measured by the MAGIC LIDAR and CTAO FRAM aerosol optical depth maps, we obtain the characterisation of the clouds above the ORM at La Palma needed for data correction and optimal observation scheduling. Full article

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2022

Jump to: 2024, 2021

17 pages, 349 KiB

Open AccessEditor’s ChoiceArticle

Galaxy Phase-Space Density Data Preclude That Bose–Einstein Condensate Be the Total Dark Matter

by Héctor J. de Vega and Norma G. Sanchez

Universe 2022, 8(8), 419; https://doi.org/10.3390/universe8080419 - 11 Aug 2022

Cited by 13 | Viewed by 2211

Abstract

Ultralight scalars with a typical mass of the order

m \sim 10^{- 22}

eV and light scalars forming a Bose–Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were therefore proposed as dark matter (DM) candidates. Our treatment here [...] Read more.

Ultralight scalars with a typical mass of the order

m \sim 10^{- 22}

eV and light scalars forming a Bose–Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were therefore proposed as dark matter (DM) candidates. Our treatment here is generic, independent of the particle physics model and applies to all DM BEC, in both in or out of equilibrium situations. Two observed quantities crucially constrain DM in an inescapable way: the average DM density

ρ_{D M}

and the phase-space density Q. The observed values of

ρ_{D M}

and Q in galaxies today constrain both the possibility to form a BEC, and the DM mass m. These two constraints robustly exclude the axion DM that decouples after inflation. Moreover, the value

m \sim 10^{- 22}

eV can only be obtained with a number of ultrarelativistic degrees of freedom at decoupling in the trillions, which is impossible for decoupling in the radiation dominated era. In addition, we find for the axion vacuum misalignment scenario that axions are produced strongly out of thermal equilibrium and that the axion mass in such a scenario turns to be 17 orders of magnitude too large to reproduce the observed galactic structures. Moreover, we also consider inhomogenous gravitationally bounded BEC’s supported by the bosonic quantum pressure independently of any particular particle physics scenario. For a typical size

R \sim

kpc and compact object masses

M \sim 10^{7} M_{⊙}

they remarkably lead to the same particle mass

m \sim 10^{- 22}

eV as the BEC free-streaming length. However, the phase-space density for the gravitationally bounded BEC’s turns out to be more than sixty orders of magnitude smaller than the galaxy-observed values. We conclude that the BEC cannot be the total DM. The axion can be candidates to be only part of the DM of the universe. Besides, an axion in the mili-eV scale may be a relevant source of dark energy through the zero point cosmological quantum fluctuations. Full article

18 pages, 644 KiB

Open AccessArticle

Search for Dark Higgs Inflation with Curvature Corrections at LHC Experiments

by Lucia Aurelia Popa

Universe 2022, 8(4), 235; https://doi.org/10.3390/universe8040235 - 12 Apr 2022

Cited by 3 | Viewed by 2289

Abstract

We analyse the dark Higgs inflation model with curvature corrections and explore the possibility to test its predictions by the particle physics experiments at LHC. We show that the dark Higgs inflation model with curvature corrections is strongly favoured by the present cosmological [...] Read more.

We analyse the dark Higgs inflation model with curvature corrections and explore the possibility to test its predictions by the particle physics experiments at LHC. We show that the dark Higgs inflation model with curvature corrections is strongly favoured by the present cosmological observation. The cosmological predictions of this model, including the quantum corrections of dark Higgs coupling constants and the uncertainty in estimation of the reheating temperature, lead to the dark Higgs mass

m_{φ} = 0.919 \pm

0.211 GeV and the mixing angle (at 68% CL). We evaluate the FASER and MAPP-1 experiments reach for dark Higgs inflation mass and mixing angle in the 95% CL cosmological confidence region for an integrated luminosity of 3ab

^{- 1}

at 13 TeV LHC, assuming 100% detection efficiency. We conclude that the dark Higgs inflation model with curvature corrections is a compelling inflation scenario based on particle physics theory favoured by the present cosmological measurements that can leave imprints in the dark Higgs boson searchers at LHC. Full article

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21 pages, 382 KiB

Open AccessArticle

Hidden Conformal Symmetry in Higher Derivative Dynamics for the Kerr Black Hole

by Valentina Giangreco M. Puletti and Victoria L. Martin

Universe 2022, 8(3), 155; https://doi.org/10.3390/universe8030155 - 28 Feb 2022

Cited by 1 | Viewed by 1938

Abstract

The Kerr/CFT correspondence provides a holographic description of spinning black holes that exist in our universe and the notion of hidden conformal symmetry allows for a formulation of this correspondence that is away from extremality. In this study, we examined how hidden conformal [...] Read more.

The Kerr/CFT correspondence provides a holographic description of spinning black holes that exist in our universe and the notion of hidden conformal symmetry allows for a formulation of this correspondence that is away from extremality. In this study, we examined how hidden conformal symmetry is manifest when we consider dynamics beyond the Klein–Gordon equation through studying the analytic structure of the higher derivative equations of the motion of a massless probe scalar field on a Kerr background, using the monodromy method. Since such higher derivative dynamics appear in known examples of holographic AdS/logCFT correspondences, we investigated whether or not a Kerr/logCFT correspondence could be possible. Full article

13 pages, 919 KiB

Open AccessArticle

(Un)balanced Holographic Superconductors with Electric and Spin Motive Force Coupling

by Nathália P. Aprile, Betti Hartmann and Jutta Kunz

Universe 2022, 8(2), 107; https://doi.org/10.3390/universe8020107 - 8 Feb 2022

Viewed by 1495

Abstract

We study holographic phase transitions in (2+1) dimensions that possess interacting phases which result from a direct coupling between the two U(1) gauge fields. This can be interpreted as a non-minimal interaction between the electric and spin motive forces of the dual model. [...] Read more.

We study holographic phase transitions in (2+1) dimensions that possess interacting phases which result from a direct coupling between the two U(1) gauge fields. This can be interpreted as a non-minimal interaction between the electric and spin motive forces of the dual model. We first present a new analytical solution of the Einstein-Maxwell equations that describes a black hole with charge non-equivalent to the sum of the asymptotic charges of the two U(1) gauge fields and briefly discuss formation of uncharged scalar hair on this solution. We then study the formation of charged scalar hair on an uncharged black hole background and discuss the dual description of balanced as well as unbalanced superconductors. Full article

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18 pages, 448 KiB

Open AccessArticle

𝒩 = 1 Curves on Generalized Coulomb Branches of Supersymmetric Gauge Theories

by Thomas Bourton, Elli Pomoni and Xinyu Zhang

Universe 2022, 8(2), 101; https://doi.org/10.3390/universe8020101 - 4 Feb 2022

Cited by 3 | Viewed by 1666

Abstract

We study the low energy effective dynamics of four-dimensional

N = 1

superconformal theories on their generalized Coulomb branch. The low energy effective gauge couplings are naturally encoded in algebraic curves

X

, which we derive for general values of the couplings and [...] Read more.

We study the low energy effective dynamics of four-dimensional

N = 1

superconformal theories on their generalized Coulomb branch. The low energy effective gauge couplings are naturally encoded in algebraic curves

X

, which we derive for general values of the couplings and mass deformations. We then recast these IR curves

X

to the UV or M-theory form

C

: the punctured Riemann surfaces on which the M5 branes are compactified giving the four-dimensional theories. We find that the UV curves

C

and their corresponding meromorphic differentials take the same form as those for their mother four-dimensional

N = 2

theories of class

S

. They have the same poles, and their residues are functions of all the exactly marginal couplings and the bare mass parameters which we can compute exactly. Full article

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2021

Jump to: 2024, 2022

22 pages, 380 KiB

Open AccessReview

A Systematic Approach to Consistent Truncations of Supergravity Theories

by Michela Petrini

Universe 2021, 7(12), 485; https://doi.org/10.3390/universe7120485 - 9 Dec 2021

Viewed by 1939

Abstract

Exceptional generalised geometry is a reformulation of eleven/ten-dimensional supergravity that unifies ordinary diffeomorphisms and gauge transformations of the higher-rank potentials of the theory in an extended notion of diffeormorphisms. These features make exceptional generalised geometry a very powerful tool to study consistent truncations [...] Read more.

Exceptional generalised geometry is a reformulation of eleven/ten-dimensional supergravity that unifies ordinary diffeomorphisms and gauge transformations of the higher-rank potentials of the theory in an extended notion of diffeormorphisms. These features make exceptional generalised geometry a very powerful tool to study consistent truncations of eleven/ten-dimensional supergravities. In this article, we review how the notion of generalised G-structure allows us to derive consistent truncations to supergravity theories in various dimensions and with different amounts of supersymmetry. We discuss in detail the truncations of eleven-dimensional supergravity to

N = 4

and

N = 2

supergravity in five dimensions. Full article

42 pages, 599 KiB

Open AccessArticle

Near-AdS₂ Spectroscopy: Classifying the Spectrum of Operators and Interactions in

N = 2

4D Supergravity

by Alejandra Castro and Evita Verheijden

Universe 2021, 7(12), 475; https://doi.org/10.3390/universe7120475 - 4 Dec 2021

Cited by 15 | Viewed by 2566

Abstract

We describe holographic properties of near-AdS

_{2}

spacetimes that arise within spherically symmetric configurations of

N = 2

4D

U {(1)}^{4}

supergravity for both gauged and ungauged theories. These theories pose a rich space of AdS

_{2} \times S^{2}

[...] Read more.

We describe holographic properties of near-AdS

_{2}

spacetimes that arise within spherically symmetric configurations of

N = 2

4D

U {(1)}^{4}

supergravity for both gauged and ungauged theories. These theories pose a rich space of AdS

_{2} \times S^{2}

backgrounds, and their responses in the near-AdS

_{2}

region are not universal. In particular, we show that the spectrum of operators is dual to the matter fields, and their cubic interactions are sensitive to properties of the background and the theory it is embedded in. The properties that have the most striking effect are whether the background is supersymmetric or not and if the theory is gauged or ungauged. Interesting effects are due to the appearance of operators with

Δ < 2

, which depending on the background, can lead to, for instance, instabilities or extremal correlators. The resulting differences will have an imprint on the quantum nature of the microstates of near-extremal black holes, reflecting that not all extremal black holes respond equally when kicked away from extremality. Full article

34 pages, 508 KiB

Open AccessArticle

On the Geometric Approach to the Boundary Problem in Supergravity

by Laura Andrianopoli and Lucrezia Ravera

Universe 2021, 7(12), 463; https://doi.org/10.3390/universe7120463 - 28 Nov 2021

Cited by 8 | Viewed by 2053

Abstract

We review the geometric superspace approach to the boundary problem in supergravity, retracing the geometric construction of four-dimensional supergravity Lagrangians in the presence of a non-trivial boundary of spacetime. We first focus on pure

N = 1

and

N = 2

theories with [...] Read more.

We review the geometric superspace approach to the boundary problem in supergravity, retracing the geometric construction of four-dimensional supergravity Lagrangians in the presence of a non-trivial boundary of spacetime. We first focus on pure

N = 1

and

N = 2

theories with negative cosmological constant. Here, the supersymmetry invariance of the action requires the addition of topological (boundary) contributions which generalize at the supersymmetric level the Euler-Gauss-Bonnet term. Moreover, one finds that the boundary values of the super field-strengths are dynamically fixed to constant values, corresponding to the vanishing of the

OSp (N | 4)

-covariant supercurvatures at the boundary. We then consider the case of vanishing cosmological constant where, in the presence of a non-trivial boundary, the inclusion of boundary terms involving additional fields, which behave as auxiliary fields for the bulk theory, allows to restore supersymmetry. In all the cases listed above, the full, supersymmetric Lagrangian can be recast in a MacDowell-Mansouri(-like) form. We then report on the application of the results to specific problems regarding cases where the boundary is located asymptotically, relevant for a holographic analysis. Full article

26 pages, 6790 KiB

Open AccessReview

Particle-in-Cell Simulations of Astrophysical Relativistic Jets

by Athina Meli and Ken-ichi Nishikawa

Universe 2021, 7(11), 450; https://doi.org/10.3390/universe7110450 - 19 Nov 2021

Cited by 4 | Viewed by 2351

Abstract

Astrophysical relativistic jets in active galactic nuclei, gamma-ray bursts, and pulsars is the main key subject of study in the field of high-energy astrophysics, especially regarding the jet interaction with the interstellar or intergalactic environment. In this work, we review studies of particle-in-cell [...] Read more.

Astrophysical relativistic jets in active galactic nuclei, gamma-ray bursts, and pulsars is the main key subject of study in the field of high-energy astrophysics, especially regarding the jet interaction with the interstellar or intergalactic environment. In this work, we review studies of particle-in-cell simulations of relativistic electron–proton (

e^{-} - p^{+}

) and electron–positron (

e^{\pm}

) jets, and we compare simulations that we have conducted with the relativistic 3D TRISTAN-MPI code for unmagnetized and magnetized jets. We focus on how the magnetic fields affect the evolution of relativistic jets of different compositions, how the jets interact with the ambient media, how the kinetic instabilities such as the Weibel instability, the kinetic Kelvin–Helmholtz instability and the mushroom instability develop, and we discuss possible particle acceleration mechanisms at reconnection sites. Full article

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26 pages, 472 KiB

Open AccessReview

Superconformal Line Defects in 3D

by Silvia Penati

Universe 2021, 7(9), 348; https://doi.org/10.3390/universe7090348 - 15 Sep 2021

Cited by 9 | Viewed by 1685

Abstract

We review the recent progress in the study of line defects in three-dimensional Chern–Simons-matter superconformal field theories, notably the ABJM theory. The first part is focused on kinematical defects, supporting a topological sector of the theory. After reviewing the construction of this sector, [...] Read more.

We review the recent progress in the study of line defects in three-dimensional Chern–Simons-matter superconformal field theories, notably the ABJM theory. The first part is focused on kinematical defects, supporting a topological sector of the theory. After reviewing the construction of this sector, we concentrate on the evaluation of topological correlators from the partition function of the mass-deformed ABJM theory and provide evidence on the existence of topological quantum mechanics living on the line. In the second part, we consider the dynamical defects realized as latitude BPS Wilson loops for which an exact evaluation is available in terms of a latitude Matrix Model. We discuss the fundamental relation between these operators, the defect superconformal field theory and bulk physical quantities, such as the Bremsstrahlung function. This relation assigns a privileged role to BPS Wilson operators, which become the meeting point for three exact approaches: localization, integrability and conformal bootstrap. Full article

14 pages, 848 KiB

Open AccessArticle

Dark Matter Sterile Neutrino from Scalar Decays

by Lucia Aurelia Popa

Universe 2021, 7(8), 309; https://doi.org/10.3390/universe7080309 - 21 Aug 2021

Viewed by 2013

Abstract

We place constraints on DM sterile neutrino scalar decay production (SDP) assuming that sterile neutrinos representa fraction from the total Cold Dark Matter energy density. For the cosmological analysis we complement the CMB anisotropy measurements with CMB lensing gravitational potential measurements, that are [...] Read more.

We place constraints on DM sterile neutrino scalar decay production (SDP) assuming that sterile neutrinos representa fraction from the total Cold Dark Matter energy density. For the cosmological analysis we complement the CMB anisotropy measurements with CMB lensing gravitational potential measurements, that are sensitive to the DM distribution to high redshifts and with the cosmic shear data that constrain the gravitational potential at lower redshifts than CMB. We also use the most recent low-redshift BAO measurements that are insensitive to the non-linear effects, providing robust geometrical tests. We show that our datasets have enough sensitivity to constrain the sterile neutrino mass

m_{ν_{s}}

and the mass fraction

f_{S}

inside the co-moving free-streaming horizon. We find that the best fit value

m_{ν_{s}} = 7.88 \pm 0.73

keV (68% CL) is in the parameter space of interest for DM sterile neutrino decay interpretation of the 3.5 keV X-ray line and that

f_{S} = 0.86 \pm 0.07

(68% CL) is in agreement with the upper limit constraint on

f_{S}

from the X-ray non-detection and Ly-

α

forest measurements that rejects

f_{S} = 1

at 3

σ

. However, we expect that the future BAO and weak lensing surveys, such as EUCLID, will provide much more robust constraints. Full article

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30 pages, 1507 KiB

Open AccessReview

The Swampland Conjectures: A Bridge from Quantum Gravity to Particle Physics

by Mariana Graña and Alvaro Herráez

Universe 2021, 7(8), 273; https://doi.org/10.3390/universe7080273 - 28 Jul 2021

Cited by 130 | Viewed by 5128

Abstract

The swampland is the set of seemingly consistent low-energy effective field theories that cannot be consistently coupled to quantum gravity. In this review we cover some of the conjectural properties that effective theories should possess in order not to fall in the swampland, [...] Read more.

The swampland is the set of seemingly consistent low-energy effective field theories that cannot be consistently coupled to quantum gravity. In this review we cover some of the conjectural properties that effective theories should possess in order not to fall in the swampland, and we give an overview of their main applications to particle physics. The latter include predictions on neutrino masses, bounds on the cosmological constant, the electroweak and QCD scales, the photon mass, the Higgs potential and some insights about supersymmetry. Full article

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20 pages, 809 KiB

Open AccessReview

New Advancements in AdS/CFT in Lower Dimensions

by Yolanda Lozano and Anayeli Ramirez

Universe 2021, 7(7), 250; https://doi.org/10.3390/universe7070250 - 19 Jul 2021

Cited by 6 | Viewed by 2011

Abstract

We review recent developments in the study of the AdS/CFT correspondence in lower dimensions. We start by summarising the classification of AdS

_{3} \times S^{2}

solutions in massive type IIA supergravity with (0, 4) supersymmetries and the construction of their 2D dual [...] Read more.

We review recent developments in the study of the AdS/CFT correspondence in lower dimensions. We start by summarising the classification of AdS

_{3} \times S^{2}

solutions in massive type IIA supergravity with (0, 4) supersymmetries and the construction of their 2D dual quiver CFTs. These theories are the seed for further developments that we review next. First, we construct a new class of AdS

_{3}

solutions in M-theory that describe M-strings in M5-brane intersections. Second, we generate a new class of AdS

_{2} \times S^{3}

solutions in massive IIA with four supercharges that we interpret as describing backreacted baryon vertices within the 5D

N = 1

QFT living in D4-D8 branes. Third, we construct two classes of AdS

_{2}

solutions in Type IIB. The first are dual to discrete light-cone quantised quantum mechanics living in null cylinders. The second class is interpreted as dual to backreacted baryon vertices within 4D

N = 2

QFT living in D3-D7 branes. Explicit dual quiver field theories are given for all classes of solutions. These are used to compute the central charges of the CFTs that are shown to agree with the holographic expressions. Full article

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24 pages, 415 KiB

Open AccessReview

Two Applications of the Analytic Conformal Bootstrap: A Quick Tour Guide

by Agnese Bissi, Parijat Dey and Giulia Fardelli

Universe 2021, 7(7), 247; https://doi.org/10.3390/universe7070247 - 15 Jul 2021

Cited by 4 | Viewed by 2089

Abstract

We reviewed the recent developments in the study of conformal field theories in generic space time dimensions using the methods of the conformal bootstrap, in its analytic aspect. These techniques are solely based on symmetries, particularly on the analytic structure and in the [...] Read more.

We reviewed the recent developments in the study of conformal field theories in generic space time dimensions using the methods of the conformal bootstrap, in its analytic aspect. These techniques are solely based on symmetries, particularly on the analytic structure and in the associativity of the operator product expansion. We focused on two applications of the analytic conformal bootstrap: the study of the

ϵ

expansion of the Wilson–Fisher model via the introduction of a dispersion relation and the large N expansion of the maximally supersymmetric Super Yang–Mills theory in four dimensions. Full article

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