Applying the junction conditions to the slowly rotating Kerr spacetime with a thin shell, when higher order terms in the spin parameter $\textit{a}$ can be neglected, we find that while the angular momentum $\textit{L}$ and Carter constant $\textit{C}$ of the ray remain unchanged upon crossing the shell, its energy $\textit{E}$ does not. Consequently, the impact parameters $$\eta =L/E$$ and $$\xi =C/E^2$$ of the ray are discontinued at the shell. Utilizing this transformation, we study the shadow of this spacetime and the corresponding images from an equatorial thin accretion disk. The presence of the shell gives rise to distinctive features in the observed images. Notably, we observe distinct double photon rings in the images, which can gradually merge into a single ring. Moreover, the shadow boundaries and the photon rings do not exhibit a one-to-one correspondence. The abrupt changes in redshift factor and the truncated photon regions profoundly influence the image, producing distinctive features such as the step-like structures. These features in shell-equipped spacetimes can help evaluate, through future astronomical observations, the applicability of the Israel junction condition and the shell model in real astrophysical systems.

China

Long-Yue Li

Li-Ming Cao

Yungui Gong

Xia-Yuan Liu

Wenting Zhou

Signatures of the Israel junction II: double photon rings in slowly rotating Kerr spacetime with thin shell

The residual atmospheric muon flux was measured at a candidate site for a new underground, low-radiation physics laboratory beneath the $\textit{Kokhav HaYarden}$ national park in Israel. Located inside the tunnels of a hydroelectric pumped-storage facility, the proposed site benefits from a vertical rock overburden of 361 m, large potential floorspace, and easy access by road. A muon hodoscope of vertically stacked wide-area plastic scintillator plates was employed to measure the suppression in the integrated muon flux at the site as compared with above ground at sea level. The suppression factor is reported at $$4456 \pm 77$$ , expressed as $$3.75 \pm 0.2 \times 10^{-6}$$ $$\text {cm}^{-2}$$ s $$^{-1}$$ in absolute terms, corresponding to an effective overburden of roughly 873 m.w.e.. Furthermore, the asymmetric topography of the mountain above and its muon shadow are clearly visible in the angular data. Finally, auxiliary environmental measurements recorded low background radon activity at $$28.3 \pm 14.0$$ Bq $$\text {m}^{-3}$$ . The experimental campaign thus succeeded in demonstrating the viability of the site’s working conditions for future scientific research.

Israel

Nadav Hargittai

Igor Zolkin

Yiftah Silver

Yan Benhammou

Gilad Mizrachi

Hagar Landsman

Erez Etzion

Ran Budnik

Atmospheric muon flux suppression at potential new low-radiation Underground Physics Laboratory in Israel

The identification of jets originating from quarks and gluons, often referred to as quark/gluon tagging, plays an important role in various analyses performed at the Large Hadron Collider, as Standard Model measurements and searches for new particles decaying to quarks often rely on suppressing a large gluon-induced background. This paper describes the measurement of the efficiencies of quark/gluon taggers developed within the ATLAS Collaboration, using $\sqrt{s} = 13$ TeV proton–proton collision data with an integrated luminosity of 140 fb $^{-1}$ collected by the ATLAS experiment. Two taggers with high performances in rejecting jets from gluon over jets from quarks are studied: one tagger is based on requirements on the number of inner-detector tracks associated with the jet, and the other combines several jet substructure observables using a boosted decision tree. A method is established to determine the quark/gluon fraction in data, by using quark/gluon-enriched subsamples defined by the jet pseudorapidity. Differences in tagging efficiency between data and simulation are provided for jets with transverse momentum between 500 GeV and 2 TeV and for multiple tagger working points.

France

G. Aad

B. Abbott

Germany

K. Abeling

N.J. Abicht

S.H. Abidi

Morocco

A. Aboulhorma

H. Abramowicz

H. Abreu

Y. Abulaiti

Italy

United Kingdom

B.S. Acharya

C. Adam Bourdarios

Poland

L. Adamczyk

S.V. Addepalli

M.J. Addison

J. Adelman

A. Adiguzel

T. Adye

A.A. Affolder

Switzerland

Y. Afik

Spain

M.N. Agaras

J. Agarwala

A. Aggarwal

Romania

C. Agheorghiesei

A. Ahmad

Azerbaijan

F. Ahmadov

Canada

W.S. Ahmed

S. Ahuja

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

B. Aitbenchikh

I. Aizenberg

M. Akbiyik

Sweden

T.P.A. Åkesson

A.V. Akimov

Japan

D. Akiyama

N.N. Akolkar

K. Al Khoury

G.L. Alberghi

J. Albert

P. Albicocco

G.L. Albouy

S. Alderweireldt

M. Aleksa

I.N. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

H.M.J. Ali

S. Ali

S.W. Alibocus

M. Aliev

G. Alimonti

W. Alkakhi

C. Allaire

B.M.M. Allbrooke

J.F. Allen

Chile

C.A. Allendes Flores

P.P. Allport

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

M. Alvarez Estevez

A. Alvarez Fernandez

M. Alves Cardoso

M.G. Alviggi

M. Aly

Brazil

Y. Amaral Coutinho

A. Ambler

C. Amelung

M. Amerl

C.G. Ames

D. Amidei

Portugal

S.P. Amor Dos Santos

K.R. Amos

Norway

V. Ananiev

C. Anastopoulos

T. Andeen

J.K. Anders

S.Y. Andrean

A. Andreazza

S. Angelidakis

A. Angerami

A.V. Anisenkov

A. Annovi

C. Antel

M.T. Anthony

E. Antipov

M. Antonelli

F. Anulli

M. Aoki

T. Aoki

J.A. Aparisi Pozo

M.A. Aparo

L. Aperio Bella

C. Appelt

Performance and calibration of quark/gluon-jet taggers using 140 fb$^{−1}$ of $\textit{pp}$ collisions at ${{\sqrt{\boldsymbol s}\bf = 13}}$ TeV with the ATLAS detector * We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; ANID, Chile; CAS, MOST and NSFC, China; Minciencias, Colombia; MEYS CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRI, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MEiN, Poland; FCT, Portugal; MNE/IFA, Romania; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DSI/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taipei; TENMAK, Türkiye; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, CANARIE, CRC and DRAC, Canada; PRIMUS 21/SCI/017 and UNCE SCI/013, Czech Republic; COST, ERC, ERDF, Horizon 2020, ICSC-Next Generation EU and Marie Skłodowska-Curie Actions, European Union; Investissements d'Avenir Labex, Investissements d'Avenir Idex and ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and MINERVA, Israel; Norwegian Financial Mechanism 2014-2021, Norway; NCN and NAWA, Poland; La Caixa Banking Foundation, CERCA Programme Generalitat de Catalunya and PROMETEO and GenT Programmes Generalitat Valenciana, Spain; Göran Gustafssons Stiftelse, Sweden; The Royal Society and Leverhulme Trust, United Kingdom.

Linear stability of Israel-Stewart theory in the presence of net-charge diffusion was investigated in [C. V. Brito and G. S. Denicol, Linear stability of Israel-Stewart theory in the presence of net-charge diffusion, Phys. Rev. D 102, 116009 (2020)] for the case of a massless, classical gas of noninteracting particles. However, in that work only a vanishing net-charge background was considered. In this work, we extend that study to the case of a nonvanishing background charge. We find that this effectively results in a change of the numeric value of the charge-diffusion coefficient, in a way that when the background charge goes to infinity, this coefficient can become at most four times its value at zero background charge. We also extend the analysis of Brito and Denicol [Linear stability of Israel-Stewart theory in the presence of net-charge diffusion, Phys. Rev. D 102, 116009 (2020)] by performing a systematic parameter study in the plane of charge-diffusion coefficient vs the coupling term between shear-stress and net-charge diffusion. In this plane, we identify regions where the solutions remain stable and causal and where they become acausal and/or unstable.

Julia Sammet

Markus Mayer

Dirk H. Rischke

Linear stability analysis of Israel-Stewart theory in the case of a nonzero background charge

We show that the recently formulated causal and stable first-order hydrodynamics has the same dynamics as Israel-Stewart theory for boost-invariant, Bjorken expanding systems with an ideal gas equation of state and a regulating sector determined by a constant relaxation time. In this case, the general solution of the new first-order formulation can be determined analytically.

Arpan Das

Wojciech Florkowski

United States

Jorge Noronha

Radoslaw Ryblewski

Equivalence between first-order causal and stable hydrodynamics and Israel-Stewart theory for boost-invariant systems with a constant relaxation time

We investigate the implications of the general frame approach for conformal Bjorken flow beyond the earlier studies. We show that the power series solution at late times is not unique and is accompanied by an exact solution of the form <math><mn>1</mn><mo>/</mo><mi>τ</mi></math>, which becomes unphysical if taken on shell. In contrast to the Müller-Israel-Stewart formalism, a matching between <math><mi>N</mi><mo>=</mo><mn>4</mn><mi>SYM</mi></math> results and the hydro expansion is only possible up to the first order, which gives rise to <math><mi>η</mi><mo>/</mo><mi>s</mi><mo>=</mo><mn>1</mn><mo>/</mo><mn>4</mn><mi>π</mi></math>. Matching the results to the next order gives rise to causality/stability-violating values. Furthermore, we show that the pressure anisotropy in the general frame cannot capture the hydrodynamization, and we introduce an alternative measure to find the attractor. Using slow-roll expansion, we find an analytical approximation form for the attractor. We also show that the early-time behavior of attractors is related to stability and causality conditions. The attractor solutions outside the stable and causal regime give rise to reheating and negative longitudinal pressures in early times, in contrast to the stable and causal ones. We also comment on the violation of the second law of thermodynamics by the off-shell parameters. We show that for the stable and causal choice of parameters, the off-shell canonical entropy of the attractors, which is not a physical quantity, has a negative divergence in early times before tending to its on-shell limit. On the other hand, the unstable and acausal attractors have non-negative entropy divergence. We speculate that the violation of the second law by stable and causal off-shell parameters is required for stability of the first-order hydrodynamics. We investigate the analytical structure of the Borel-transformed series and find the proper relation between the poles and nonhydro modes.

Iran

M. Shokri

F. Taghinavaz

Conformal Bjorken flow in the general frame and its attractor: Similarities and discrepancies with the Müller-Israel-Stewart formalism

Applying the Casimir operator to four-point functions in CFTs allows us to find the conformal blocks for any external operators. In this work, we initiate the program to find the superconformal blocks, using the super Casimir operator, for 4D   <math> <mi>N</mi> <mo>=</mo> <mn>1</mn> </math>  $$ \mathcal{N}=1 $$  SCFTs. We begin by finding the most general four-point function with zero U(1) R -charge, including all the possible nilpotent structures allowed by the superconformal algebra. We then study particular cases where some of the operators satisfy shortening conditions. Finally, we obtain the super Casimir equations for four point-functions which contain a chiral and an anti-chiral field. We solve the super Casimir equations by writing the superconformal blocks as a sum of several conformal blocks.

Belgium

Israel Ramírez

Towards general super Casimir equations for 4D   <math> <mi>N</mi> <mo>=</mo> <mn>1</mn> </math>  $$ \mathcal{N}=1 $$  SCFTs

In this paper we present a phantom solution with a big rip singularity in a non-linear regime of the Israel–Stewart formalism. In this framework it is possible to extend this causal formalism in order to describe accelerated expansion, where assumption of near equilibrium is no longer valid. We assume a flat universe filled with a single viscous fluid ruled by a barotropic EoS, p=ωρ , which can represent a late time accelerated phase of the cosmic evolution. The solution allows to cross the phantom divide without evoking an exotic matter fluid and the effective EoS parameter is always lesser than −1 and constant in time.

Mexico

Miguel Cruz

Norman Cruz

Samuel Lepe

Phantom solution in a non-linear Israel–Stewart theory

A phantom solution in the framework of the causal Israel–Stewart (IS) formalism is discussed. We assume a late time behavior of the cosmic evolution by considering only one dominant matter fluid with viscosity. In the model it is assumed a bulk viscosity of the form ξ=ξ0ρ1/2 , where ρ is the energy density of the fluid. We evaluate and discuss the behavior of the thermodynamical parameters associated to this solution, like the temperature, rate of entropy, entropy, relaxation time, effective pressure and effective EoS. A discussion about the assumption of near equilibrium of the formalism and the accelerated expansion of the solution is presented. The solution allows to cross the phantom divide without evoking an exotic matter fluid and the effective EoS parameter is always lesser than −1 and time independent. A future singularity (big rip) occurs, but different from the Type I (big rip) solution classified in S. Nojiri, S.D. Odintsov and S. Tsujikawa (2005) [2] , if we consider other thermodynamics parameters like, for example, the effective pressure in the presence of viscosity or the relaxation time.

Crossing the phantom divide with dissipative normal matter in the Israel–Stewart formalism

This paper reports a study on the truncated Israel-Stewart formalism for bulk viscosity using the extended holographic Ricci dark energy (EHRDE). Under the consideration that the universe is dominated by EHRDE, the evolution equation for the bulk viscous pressure <math id="M1"><mrow><mi>Π</mi></mrow></math> in the framework of the truncated Israel-Stewart theory has been taken as <math id="M2"><mi>τ</mi><mover><mrow><mi>Π</mi></mrow><mo>˙</mo></mover><mo>+</mo><mi>Π</mi><mo>=</mo><mo>-</mo><mn>3</mn><mi>ξ</mi><mi>H</mi></math>, where <math id="M3"><mrow><mi>τ</mi></mrow></math> is the relaxation time and <math id="M4"><mrow><mi>ξ</mi></mrow></math> is the bulk viscosity coefficient. Considering effective pressure as a sum of thermodynamic pressure of EHRDE and bulk viscous pressure, it has been observed that under the influence of bulk viscosity the EoS parameter <math id="M5"><mrow><msub><mrow><mi>w</mi></mrow><mrow><mi>D</mi><mi>E</mi></mrow></msub></mrow></math> is behaving like phantom, that is, <math id="M6"><msub><mrow><mi>w</mi></mrow><mrow><mi>D</mi><mi>E</mi></mrow></msub><mo>≤</mo><mo>-</mo><mn>1</mn></math>. It has been observed that the magnitude of the effective pressure <math id="M7"><msub><mrow><mi>p</mi></mrow><mrow><mi>e</mi><mi>f</mi><mi>f</mi></mrow></msub><mo>=</mo><mi>p</mi><mo>+</mo><mi>Π</mi></math> is decaying with time. We also investigated the case for a specific choice of scale factor; namely, <math id="M8"><mi>a</mi><mo>(</mo><mi>t</mi><mo>)</mo><mo>=</mo><mo>(</mo><mi>t</mi><mo>-</mo><msub><mrow><mi>t</mi></mrow><mrow><mn>0</mn></mrow></msub><msup><mrow><mo>)</mo></mrow><mrow><mi>β</mi><mo>/</mo><mo>(</mo><mn>1</mn><mo>-</mo><mi>α</mi><mo>)</mo></mrow></msup></math>. For this choice we have observed that a transition from quintessence to phantom is possible for the equation of state parameter. However, the <math id="M9"><mrow><mi>Λ</mi></mrow></math>CDM phase is not attainable by the state-finder trajectories for this choice. Finally it has been observed that in both of the cases the generalized second law of thermodynamics is valid for the viscous EHRDE dominated universe enveloped by the apparent horizon.

India

Surajit Chattopadhyay

Israel-Stewart Approach to Viscous Dissipative Extended Holographic Ricci Dark Energy Dominated Universe