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Prof Subir Sarkar

Professor Emeritus

Research theme

  • Particle astrophysics & cosmology
  • Fundamental particles and interactions

Sub department

  • Rudolf Peierls Centre for Theoretical Physics

Research groups

  • Particle theory
  • FASER2
Subir.Sarkar@physics.ox.ac.uk
Telephone: 01865 (2)73962
Rudolf Peierls Centre for Theoretical Physics, room 60.12
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Brief CV
  • About
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  • IceCube@Oxford
  • Publications

IceCube

Physics World 2013 Breakthrough of the Year
IceCube at Oxford

I am a member since 2004 of the IceCube collaboration which discovered cosmic high energy neutrinos and identified some of their astrophysical sources.

IceCube @ Oxford

Laboratory realization of relativistic pair-plasma beams

Nature Communications Springer Nature 15:1 (2024) 5029

Authors:

CD Arrowsmith, P Simon, PJ Bilbao, Archie FA Bott, S Burger, H Chen, FD Cruz, T Davenne, I Efthymiopoulos, DH Froula, A Goillot, JT Gudmundsson, D Haberberger, Jonathan WD Halliday, Thomas Hodge, Brian T Huffman, Sam Iaquinta, Francesco Miniati, B Reville, Subir Sarkar, Alexander Schekochihin, LO Silva, R Simpson, Vasiliki Stergiou, RMGM Trines, N Charitonidis, R Bingham, Gianluca Gregori

Abstract:

Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black-hole and neutron-star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with electron-positron pairs. Their role in the dynamics of such environments is in many cases believed to be fundamental, but their behavior differs significantly from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies, which are rather limited. We present the first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN’s Super Proton Synchrotron (SPS) accelerator. Monte Carlo simulations agree well with the experimental data and show that the characteristic scales necessary for collective plasma behavior, such as the Debye length and the collisionless skin depth, are exceeded by the measured size of the produced pair beams. Our work opens up the possibility of directly probing the microphysics of pair plasmas beyond quasi-linear evolution into regimes that are challenging to simulate or measure via astronomical observations.
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Ruling out light axions: the writing is on the wall

SciPost Physics SciPost 15 (2023) 003

Authors:

Konstantin A Beyer, Subir Sarkar

Abstract:

We revisit the domain wall problem for QCD axion models with more than one quark charged under the Peccei-Quinn symmetry. Symmetry breaking during or after inflation results in the formation of a domain wall network which would cause cosmic catastrophe if it comes to dominate the Universe. The network may be made unstable by invoking a ‘tilt’ in the axion potential due to Planck scale suppressed non-renormalisable operators. Alternatively the random walk of the axion field during inflation can generate a ‘bias’ favouring one of the degenerate vacua, but we find that this mechanism is in practice irrelevant. Consideration of the axion abundance generated by the decay of the wall network then requires the Peccei-Quinn scale to be rather low — thus e.g. ruling out the DFSZ axion with mass below ∼ 11 meV, where most experimental searches are in fact focused.
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A challenge to the standard cosmological model

IOP Publishing 937:2 (2022) L31

Authors:

Nathan Secrest, Sebastian von Hausegger, Mohamed Rameez, Roya Mohayaee, Subir Sarkar

Abstract:

We present the first joint analysis of catalogs of radio galaxies and quasars to determine whether their sky distribution is consistent with the standard ΛCDM model of cosmology. This model is based on the cosmological principle, which asserts that the universe is statistically isotropic and homogeneous on large scales, so the observed dipole anisotropy in the cosmic microwave background (CMB) must be attributed to our local peculiar motion. We test the null hypothesis that there is a dipole anisotropy in the sky distribution of radio galaxies and quasars consistent with the motion inferred from the CMB, as is expected for cosmologically distant sources. Our two samples, constructed respectively from the NRAO VLA Sky Survey and the Wide-field Infrared Survey Explorer, are systematically independent and have no shared objects. Using a completely general statistic that accounts for correlation between the found dipole amplitude and its directional offset from the CMB dipole, the null hypothesis is independently rejected by the radio galaxy and quasar samples with p-values of 8.9 × 10−3 and 1.2 × 10−5, respectively, corresponding to 2.6σ and 4.4σ significance. The joint significance, using sample-size-weighted Z-scores, is 5.1σ. We show that the radio galaxy and quasar dipoles are consistent with each other and find no evidence for any frequency dependence of the amplitude. The consistency of the two dipoles improves if we boost to the CMB frame assuming its dipole to be fully kinematic, suggesting that cosmologically distant radio galaxies and quasars may have an intrinsic anisotropy in this frame.
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Blast from the past: Constraints on the dark sector from the BEBC WA66 beam dump experiment

SciPost Physics SciPost 10 (2021) 043

Authors:

Giacomo Marocco, Subir Sarkar

Abstract:

We derive limits on millicharged dark states, as well as particles with electric or magnetic dipole moments, from the number of observed forward electron scattering events at the Big European Bubble Chamber in the 1982 CERN-WA-066 beam dump experiment. The dark states are produced by the 400 GeV proton beam primarily through the decays of mesons produced in the beam dump, and the lack of excess events places bounds extending up to GeV masses. These improve on bounds from all other experiments, in particular CHARM II.
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The Forward Physics Facility at the High-Luminosity LHC

(2022)

Authors:

Jonathan L Feng, Felix Kling, Mary Hall Reno, Juan Rojo, Dennis Soldin, Luis A Anchordoqui, Jamie Boyd, Ahmed Ismail, Lucian Harland-Lang, Kevin J Kelly, Vishvas Pandey, Sebastian Trojanowski, Yu-Dai Tsai, Jean-Marco Alameddine, Takeshi Araki, Akitaka Ariga, Tomoko Ariga, Kento Asai, Alessandro Bacchetta, Kincso Balazs, Alan J Barr, Michele Battistin, Jianming Bian, Caterina Bertone, Weidong Bai, Pouya Bakhti, A Baha Balantekin, Basabendu Barman, Brian Batell, Martin Bauer, Brian Bauer, Mathias Becker, Asher Berlin, Enrico Bertuzzo, Atri Bhattacharya, Marco Bonvini, Stewart T Boogert, Alexey Boyarsky, Joseph Bramante, Vedran Brdar, Adrian Carmona, David W Casper, Francesco Giovanni Celiberto, Francesco Cerutti, Grigorios Chachamis, Garv Chauhan, Matthew Citron, Emanuele Copello, Jean-Pierre Corso, Luc Darmé, Raffaele Tito D'Agnolo, Neda Darvishi, Arindam Das, Giovanni De Lellis, Albert De Roeck, Jordy de Vries, Hans P Dembinski, Sergey Demidov, Patrick deNiverville, Peter B Denton, Frank F Deppisch, PS Bhupal Dev, Antonia Di Crescenzo, Keith R Dienes, Milind V Diwan, Herbi K Dreiner, Yong Du, Bhaskar Dutta, Pit Duwentäster, Lucie Elie, Sebastian AR Ellis, Rikard Enberg, Yasaman Farzan, Max Fieg, Ana Luisa Foguel, Patrick Foldenauer, Saeid Foroughi-Abari, Jean-François Fortin, Alexander Friedland, Elina Fuchs, Michael Fucilla, Kai Gallmeister, Alfonso Garcia, Carlos A García Canal, Maria Vittoria Garzelli, Rhorry Gauld, Sumit Ghosh, Anish Ghoshal, Stephen Gibson, Francesco Giuli, Victor P Gonçalves, Dmitry Gorbunov, Srubabati Goswami, Silvia Grau, Julian Y Günther, Marco Guzzi, Andrew Haas, Timo Hakulinen, Steven P Harris, Julia Harz, Juan Carlos Helo Herrera, Christopher S Hill, Martin Hirsch, Timothy J Hobbs, Stefan Höche, Andrzej Hryczuk, Fei Huang, Tomohiro Inada, Angelo Infantino, Ameen Ismail, Richard Jacobsson, Sudip Jana, Yu Seon Jeong, Tomas Ježo, Yongsoo Jho, Krzysztof Jodłowski, Dmitry Kalashnikov, Timo J Kärkkäinen, Cynthia Keppel, Jongkuk Kim, Michael Klasen, Spencer R Klein, Pyungwon Ko, Dominik Köhler, Masahiro Komatsu, Karol Kovařík, Suchita Kulkarni, Jason Kumar, Karan Kumar, Jui-Lin Kuo, Frank Krauss, Aleksander Kusina, Maxim Laletin, Chiara Le Roux, Seung J Lee, Hye-Sung Lee, Helena Lefebvre, Jinmian Li, Shuailong Li, Yichen Li, Wei Liu, Zhen Liu, Mickael Lonjon, Kun-Feng Lyu, Rafal Maciula, Roshan Mammen Abraham, Mohammad R Masouminia, Josh McFayden, Oleksii Mikulenko, Mohammed MA Mohammed, Kirtimaan A Mohan, Jorge G Morfín, Ulrich Mosel, Martin Mosny, Khoirul F Muzakka, Pavel Nadolsky, Toshiyuki Nakano, Saurabh Nangia, Angel Navascues Cornago, Laurence J Nevay, Pierre Ninin, Emanuele R Nocera, Takaaki Nomura, Rui Nunes, Nobuchika Okada, Fred Olness, John Osborne, Hidetoshi Otono, Maksym Ovchynnikov, Alessandro Papa, Junle Pei, Guillermo Peon, Gilad Perez, Luke Pickering, Simon Plätzer, Ryan Plestid, Tanmay Kumar Poddar, Mudit Rai, Meshkat Rajaee, Digesh Raut, Peter Reimitz, Filippo Resnati, Wolfgang Rhode, Peter Richardson, Adam Ritz, Hiroki Rokujo, Leszek Roszkowski, Tim Ruhe, Richard Ruiz, Marta Sabate-Gilarte, Alexander Sandrock, Ina Sarcevic, Subir Sarkar, Osamu Sato, Christiane Scherb, Ingo Schienbein, Holger Schulz, Pedro Schwaller, Sergio J Sciutto, Dipan Sengupta, Lesya Shchutska, Takashi Shimomura, Federico Silvetti, Kuver Sinha, Torbjörn Sjöstrand, Jan T Sobczyk, Huayang Song, Jorge F Soriano, Yotam Soreq, Anna Stasto, David Stuart, Shufang Su, Wei Su, Antoni Szczurek, Zahra Tabrizi, Yosuke Takubo, Marco Taoso, Brooks Thomas, Pierre Thonet, Douglas Tuckler, Agustin Sabio Vera, Heinz Vincke, KN Vishnudath, Zeren Simon Wang, Martin W Winkler, Wenjie Wu, Keping Xie, Xun-Jie Xu, Tevong You, Ji-Young Yu, Jiang-Hao Yu, Korinna Zapp, Yongchao Zhang, Yue Zhang, Guanghui Zhou, Renata Zukanovich Funchal
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