Prof Subir Sarkar: Publications

IceCube

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

Constraints on large scale inhomogeneities from WMAP-5 and SDSS: confrontation with recent observations

ArXiv 0807.4508 (2008)

Authors:

Paul Hunt, Subir Sarkar

Abstract:

Measurements of the SNe Ia Hubble diagram which suggest that the universe is accelerating due to the effect of dark energy may be biased because we are located in a 200-300 Mpc underdense "void" which is expanding 20-30% faster than the average rate. With the smaller global Hubble parameter, the WMAP-5 data on cosmic microwave background anisotropies can be fitted without requiring dark energy if there is some excess power in the spectrum of primordial perturbations on 100 Mpc scales. The SDSS data on galaxy clustering can also be fitted if there is a small component of hot dark matter in the form of 0.5 eV mass neutrinos. We show however that if the primordial fluctuations are gaussian, the expected variance of the Hubble parameter and the matter density are far too small to allow such a large local void. Nevertheless many such large voids have been identified in the SDSS LRG survey in a search for the late-ISW effect due to dark energy. The observed CMB temperature decrements imply that they are nearly empty, thus these real voids too are in gross conflict with the concordance LCDM model. The recently observed high peculiar velocity flow presents another challenge for the model. Therefore whether a large local void actually exists must be tested through observations and cannot be dismissed a priori.

Constraints on large scale inhomogeneities from WMAP-5 and SDSS: confrontation with recent observations

(2008)

Authors:

Paul Hunt, Subir Sarkar

Upper limit on the diffuse flux of ultrahigh energy tau neutrinos from the Pierre Auger Observatory.

Phys Rev Lett 100:21 (2008) 211101

Authors:

J Abraham, P Abreu, M Aglietta, C Aguirre, D Allard, I Allekotte, J Allen, P Allison, J Alvarez-Muñiz, M Ambrosio, L Anchordoqui, S Andringa, A Anzalone, C Aramo, S Argirò, K Arisaka, E Armengaud, F Arneodo, F Arqueros, T Asch, H Asorey, P Assis, BS Atulugama, J Aublin, M Ave, G Avila, T Bäcker, D Badagnani, AF Barbosa, D Barnhill, SLC Barroso, P Bauleo, JJ Beatty, T Beau, BR Becker, KH Becker, JA Bellido, S BenZvi, C Berat, T Bergmann, P Bernardini, X Bertou, PL Biermann, P Billoir, O Blanch-Bigas, F Blanco, P Blasi, C Bleve, H Blümer, M Bohácová, C Bonifazi, R Bonino, M Boratav, J Brack, P Brogueira, WC Brown, P Buchholz, A Bueno, RE Burton, NG Busca, KS Caballero-Mora, B Cai, DV Camin, L Caramete, R Caruso, W Carvalho, A Castellina, O Catalano, G Cataldi, L Cazon, R Cester, J Chauvin, A Chiavassa, JA Chinellato, A Chou, J Chye, PDJ Clark, RW Clay, E Colombo, R Conceição, B Connolly, F Contreras, J Coppens, A Cordier, U Cotti, S Coutu, CE Covault, A Creusot, A Criss, J Cronin, A Curutiu, S Dagoret-Campagne, K Daumiller, BR Dawson, RM de Almeida, C De Donato, SJ de Jong, G De La Vega, WJM de Mello Junior, JRT de Mello Neto, I DeMitri, V de Souza, L del Peral, O Deligny, A Della Selva, C Delle Fratte, H Dembinski, C Di Giulio, JC Diaz, C Dobrigkeit, JC D'Olivo, D Dornic, A Dorofeev, JC dos Anjos, MT Dova, D D'Urso, I Dutan, MA DuVernois, R Engel, L Epele, M Erdmann, CO Escobar, A Etchegoyen, P Facal San Luis, H Falcke, G Farrar, AC Fauth, N Fazzini, F Ferrer, S Ferry, B Fick, A Filevich, A Filipcic, I Fleck, R Fonte, CE Fracchiolla, W Fulgione, B García, D García Gámez, D Garcia-Pinto, X Garrido, H Geenen, G Gelmini, H Gemmeke, PL Ghia, M Giller, H Glass, MS Gold, G Golup, F Gomez Albarracin, M Gómez Berisso, R Gómez Herrero, P Gonçalves, M Gonçalves do Amaral, D Gonzalez, JG Gonzalez, M González, D Góra, A Gorgi, P Gouffon, V Grassi, AF Grillo, C Grunfeld, Y Guardincerri, F Guarino, GP Guedes, J Gutiérrez, JD Hague, JC Hamilton, P Hansen, D Harari, S Harmsma, JL Harton, A Haungs, T Hauschildt, MD Healy, T Hebbeker, G Hebrero, D Heck, C Hojvat, VC Holmes, P Homola, J Hörandel, A Horneffer, M Horvat, M Hrabovský, T Huege, M Hussain, M Iarlori, A Insolia, F Ionita, A Italiano, M Kaducak, KH Kampert, T Karova, B Kégl, B Keilhauer, E Kemp, RM Kieckhafer, HO Klages, M Kleifges, J Kleinfeller, R Knapik, J Knapp, D-H Koang, A Krieger, O Krömer, D Kuempel, N Kunka, A Kusenko, G La Rosa, C Lachaud, BL Lago, D Lebrun, P Lebrun, J Lee, MA Leigui de Oliveira, A Letessier-Selvon, M Leuthold, I Lhenry-Yvon, R López, A Lopez Agüera, J Lozano Bahilo, R Luna García, MC Maccarone, C Macolino, S Maldera, G Mancarella, ME Manceñido, D Mandat, P Mantsch, AG Mariazzi, IC Maris, HR Marquez Falcon, D Martello, J Martínez, O Martínez Bravo, HJ Mathes, J Matthews, JAJ Matthews, G Matthiae, D Maurizio, PO Mazur, T McCauley, M McEwen, RR McNeil, MC Medina, G Medina-Tanco, A Meli, D Melo, E Menichetti, A Menschikov, Chr Meurer, R Meyhandan, MI Micheletti, G Miele, W Miller, S Mollerach, M Monasor, D Monnier Ragaigne, F Montanet, B Morales, C Morello, JC Moreno, C Morris, M Mostafá, MA Muller, R Mussa, G Navarra, JL Navarro, S Navas, P Necesal, L Nellen, C Newman-Holmes, D Newton, T Nguyen Thi, N Nierstenhoefer, D Nitz, D Nosek, L Nozka, J Oehlschläger, T Ohnuki, A Olinto, VM Olmos-Gilbaja, M Ortiz, F Ortolani, S Ostapchenko, L Otero, N Pacheco, D Pakk Selmi-Dei, M Palatka, J Pallotta, G Parente, E Parizot, S Parlati, S Pastor, M Patel, T Paul, V Pavlidou, K Payet, M Pech, J Pekala, R Pelayo, IM Pepe, L Perrone, S Petrera, P Petrinca, Y Petrov, Diep Pham Ngoc, Dong Pham Ngoc, TN Pham Thi, A Pichel, R Piegaia, T Pierog, M Pimenta, T Pinto, V Pirronello, O Pisanti, M Platino, J Pochon, P Privitera, M Prouza, EJ Quel, J Rautenberg, A Redondo, S Reucroft, B Revenu, FAS Rezende, J Ridky, S Riggi, M Risse, C Rivière, V Rizi, M Roberts, C Robledo, G Rodriguez, D Rodríguez Frías, J Rodriguez Martino, J Rodriguez Rojo, I Rodriguez-Cabo, G Ros, J Rosado, M Roth, B Rouillé-d'Orfeuil, E Roulet, AC Rovero, F Salamida, H Salazar, G Salina, F Sánchez, M Santander, CE Santo, EM Santos, F Sarazin, S Sarkar, R Sato, V Scherini, H Schieler, A Schmidt, F Schmidt, T Schmidt, O Scholten, P Schovánek, F Schüssler, SJ Sciutto, M Scuderi, A Segreto, D Semikoz, M Settimo, RC Shellard, I Sidelnik, BB Siffert, G Sigl, N Smetniansky De Grande, A Smiałkowski, R Smída, AGK Smith, BE Smith, GR Snow, P Sokolsky, P Sommers, J Sorokin, H Spinka, R Squartini, E Strazzeri, A Stutz, F Suarez, T Suomijärvi, AD Supanitsky, MS Sutherland, J Swain, Z Szadkowski, J Takahashi, A Tamashiro, A Tamburro, O Taşcău, R Tcaciuc, D Thomas, R Ticona, J Tiffenberg, C Timmermans, W Tkaczyk, CJ Todero Peixoto, B Tomé, A Tonachini, I Torres, D Torresi, P Travnicek, A Tripathi, G Tristram, D Tscherniakhovski, M Tueros, V Tunnicliffe, R Ulrich, M Unger, M Urban, JF Valdés Galicia, I Valiño, L Valore, AM van den Berg, V van Elewyck, RA Vázquez, D Veberic, A Veiga, A Velarde, T Venters, V Verzi, M Videla, L Villaseñor, S Vorobiov, L Voyvodic, H Wahlberg, O Wainberg, P Walker, D Warner, AA Watson, S Westerhoff, G Wieczorek, L Wiencke, B Wilczyńska, H Wilczyński, C Wileman, MG Winnick, H Wu, B Wundheiler, T Yamamoto, P Younk, E Zas, D Zavrtanik, M Zavrtanik, A Zech, A Zepeda, M Ziolkowski, Pierre Auger Collaboration

Abstract:

The surface detector array of the Pierre Auger Observatory is sensitive to Earth-skimming tau neutrinos that interact in Earth's crust. Tau leptons from nu(tau) charged-current interactions can emerge and decay in the atmosphere to produce a nearly horizontal shower with a significant electromagnetic component. The data collected between 1 January 2004 and 31 August 2007 are used to place an upper limit on the diffuse flux of nu(tau) at EeV energies. Assuming an E(nu)(-2) differential energy spectrum the limit set at 90% C.L. is E(nu)(2)dN(nu)(tau)/dE(nu)<1.3 x 10(-7) GeV cm(-2) s(-1) sr(-1) in the energy range 2 x 10(17) eV< E(nu)< 2 x 10(19) eV.

Intergalactic propagation of ultrahigh energy cosmic ray nuclei: An analytic approach

Physical Review D Particles Fields Gravitation and Cosmology 77:10 (2008)

Authors:

D Hooper, S Sarkar, AM Taylor

Abstract:

It is likely that ultrahigh energy cosmic rays contain a significant component of heavy or intermediate mass nuclei. The propagation of ultrahigh energy nuclei through cosmic radiation backgrounds is more complicated than that of protons and its study has required the use of Monte Carlo techniques. We present an analytic method for calculating the spectrum and the composition at Earth of ultrahigh energy cosmic rays which start out as heavy nuclei from their extragalactic sources. The results obtained are in good agreement with those obtained using numerical methods. © 2008 The American Physical Society.

Fine tuning and the ratio of tensor to scalar density fluctuations from cosmological inflation

(2008)

Authors:

Shaun Hotchkiss, Gabriel German, Graham G Ross, Subir Sarkar

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