Related papers: Cosmic Microwave Weak lensing data as a test for t…

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results

We present new full-sky temperature and polarization maps in five frequency bands from 23 to 94 GHz, based on data from the first five years of the WMAP sky survey. The five-year maps incorporate several improvements in data processing made…

Astrophysics · Physics 2009-02-18 G. Hinshaw , J. L. Weiland , R. S. Hill , N. Odegard , D. Larson , C. L. Bennett , J. Dunkley , B. Gold , M. R. Greason , N. Jarosik , E. Komatsu , M. R. Nolta , L. Page , D. N. Spergel , E. Wollack , M. Halpern , A. Kogut , M. Limon , S. S. Meyer , G. S. Tucker , E. L. Wright

Weighing the Giants IV: Cosmology and Neutrino Mass

We employ robust weak gravitational lensing measurements to improve cosmological constraints from measurements of the galaxy cluster mass function and its evolution, using X-ray selected clusters detected in the ROSAT All-Sky Survey. Our…

Cosmology and Nongalactic Astrophysics · Physics 2015-06-22 Adam B. Mantz , Anja von der Linden , Steven W. Allen , Douglas E. Applegate , Patrick L. Kelly , R. Glenn Morris , David A. Rapetti , Robert W. Schmidt , Saroj Adhikari , Mark T. Allen , Patricia R. Burchat , David L. Burke , Matteo Cataneo , David Donovon , Harald Ebeling , Sarah Shandera , Adam Wright

Significant effects of weak gravitational lensing on determinations of the cosmology from Type Ia Supernov\ae

Significant adjustments to the values of the cosmological parameters estimated from high-redshift Type Ia Supernov\ae data are reported, almost an order of magnitude greater than previously found. They arise from the effects of weak…

Astrophysics · Physics 2009-10-31 Andrew J. Barber

Dark Energy Survey Year 1 Results: Cross-correlation between DES Y1 galaxy weak lensing and SPT+Planck CMB weak lensing

We cross-correlate galaxy weak lensing measurements from the Dark Energy Survey (DES) year-one (Y1) data with a cosmic microwave background (CMB) weak lensing map derived from South Pole Telescope (SPT) and Planck data, with an effective…

Cosmology and Nongalactic Astrophysics · Physics 2019-08-21 Y. Omori , E. Baxter , C. Chang , D. Kirk , A. Alarcon , G. M. Bernstein , L. E. Bleem , R. Cawthon , A. Choi , R. Chown , T. M. Crawford , C. Davis , J. De Vicente , J. DeRose , S. Dodelson , T. F. Eifler , P. Fosalba , O. Friedrich , M. Gatti , E. Gaztanaga , T. Giannantonio , D. Gruen , W. G. Hartley , G. P. Holder , B. Hoyle , D. Huterer , B. Jain , M. Jarvis , E. Krause , N. MacCrann , R. Miquel , J. Prat , M. M. Rau , C. L. Reichardt , E. Rozo , S. Samuroff , C. Sánchez , L. F. Secco , E. Sheldon , G. Simard , M. A. Troxel , P. Vielzeuf , R. H. Wechsler , J. Zuntz , T. M. C. Abbott , F. B. Abdalla , S. Allam , J. Annis , S. Avila , K. Aylor , B. A. Benson , E. Bertin , S. L. Bridle , D. Brooks , D. L. Burke , J. E. Carlstrom , A. Carnero Rosell , M. Carrasco Kind , J. Carretero , F. J. Castander , C. L. Chang , H-M. Cho , A. T. Crites , M. Crocce , C. E. Cunha , L. N. da Costa , T. de Haan , S. Desai , H. T. Diehl , J. P. Dietrich , M. A. Dobbs , W. B. Everett , E. Fernandez , B. Flaugher , J. Frieman , J. García-Bellido , E. M. George , R. A. Gruendl , G. Gutierrez , N. W. Halverson , N. L. Harrington , D. L. Hollowood , K. Honscheid , W. L. Holzapfel , Z. Hou , J. D. Hrubes , D. J. James , T. Jeltema , K. Kuehn , N. Kuropatkin , M. Lima , H. Lin , A. T. Lee , E. M. Leitch , D. Luong-Van , M. A. G. Maia , A. Manzotti , D. P. Marrone , J. L. Marshall , P. Martini , J. J. McMahon , P. Melchior , F. Menanteau , S. S. Meyer , L. M. Mocanu , J. J. Mohr , T. Natoli , R. L. C. Ogando , S. Padin , A. A. Plazas , C. Pryke , A. K. Romer , A. Roodman , J. E. Ruhl , E. S. Rykoff , E. Sanchez , V. Scarpine , K. K. Schaffer , R. Schindler , I. Sevilla-Noarbe , E. Shirokoff , M. Smith , R. C. Smith , M. Soares-Santos , F. Sobreira , Z. Staniszewski , A. A. Stark , K. T. Story , E. Suchyta , M. E. C. Swanson , G. Tarle , D. Thomas , K. Vanderlinde , J. D. Vieira , V. Vikram , A. R. Walker , J. Weller , R. Williamson , W. L. K. Wu , O. Zahn

Dark Synergy: Gravitational Lensing and the CMB

Power spectra and cross-correlation measurements from the weak gravitational lensing of the cosmic microwave background (CMB) and the cosmic shearing of faint galaxies images will help shed light on quantities hidden from the CMB…

Astrophysics · Physics 2009-07-09 Wayne Hu

The Atacama Cosmology Telescope: DR6 Power Spectra, Likelihoods and $\Lambda$CDM Parameters

We present power spectra of the cosmic microwave background (CMB) anisotropy in temperature and polarization, measured from the Data Release 6 maps made from Atacama Cosmology Telescope (ACT) data. These cover 19,000 deg$^2$ of sky in bands…

Cosmology and Nongalactic Astrophysics · Physics 2025-06-25 Thibaut Louis , Adrien La Posta , Zachary Atkins , Hidde T. Jense , Irene Abril-Cabezas , Graeme E. Addison , Peter A. R. Ade , Simone Aiola , Tommy Alford , David Alonso , Mandana Amiri , Rui An , Jason E. Austermann , Eleonora Barbavara , Nicholas Battaglia , Elia Stefano Battistelli , James A. Beall , Rachel Bean , Ali Beheshti , Benjamin Beringue , Tanay Bhandarkar , Emily Biermann , Boris Bolliet , J Richard Bond , Erminia Calabrese , Valentina Capalbo , Felipe Carrero , Shi-Fan Chen , Grace Chesmore , Hsiao-mei Cho , Steve K. Choi , Susan E. Clark , Nicholas F. Cothard , Kevin Coughlin , William Coulton , Devin Crichton , Kevin T. Crowley , Omar Darwish , Mark J. Devlin , Simon Dicker , Cody J. Duell , Shannon M. Duff , Adriaan J. Duivenvoorden , Jo Dunkley , Rolando Dunner , Carmen Embil Villagra , Max Fankhanel , Gerrit S. Farren , Simone Ferraro , Allen Foster , Rodrigo Freundt , Brittany Fuzia , Patricio A. Gallardo , Xavier Garrido , Martina Gerbino , Serena Giardiello , Ajay Gill , Jahmour Givans , Vera Gluscevic , Samuel Goldstein , Joseph E. Golec , Yulin Gong , Yilun Guan , Mark Halpern , Ian Harrison , Matthew Hasselfield , Erin Healy , Shawn Henderson , Brandon Hensley , Carlos Hervías-Caimapo , J. Colin Hill , Gene C. Hilton , Matt Hilton , Adam D. Hincks , Renée Hložek , Shuay-Pwu Patty Ho , John Hood , Erika Hornecker , Zachary B. Huber , Johannes Hubmayr , Kevin M. Huffenberger , John P. Hughes , Margaret Ikape , Kent Irwin , Giovanni Isopi , Neha Joshi , Ben Keller , Joshua Kim , Kenda Knowles , Brian J. Koopman , Arthur Kosowsky , Darby Kramer , Aleksandra Kusiak , Alex Lague , Victoria Lakey , Eunseong Lee , Yaqiong Li , Zack Li , Michele Limon , Martine Lokken , Marius Lungu , Niall MacCrann , Amanda MacInnis , Mathew S. Madhavacheril , Diego Maldonado , Felipe Maldonado , Maya Mallaby-Kay , Gabriela A. Marques , Joshiwa van Marrewijk , Fiona McCarthy , Jeff McMahon , Yogesh Mehta , Felipe Menanteau , Kavilan Moodley , Thomas W. Morris , Tony Mroczkowski , Sigurd Naess , Toshiya Namikawa , Federico Nati , Simran K. Nerval , Laura Newburgh , Andrina Nicola , Michael D. Niemack , Michael R. Nolta , John Orlowski-Scherer , Luca Pagano , Lyman A. Page , Shivam Pandey , Bruce Partridge , Karen Perez Sarmiento , Heather Prince , Roberto Puddu , Frank J. Qu , Damien C. Ragavan , Bernardita Ried Guachalla , Keir K. Rogers , Felipe Rojas , Tai Sakuma , Emmanuel Schaan , Benjamin L. Schmitt , Neelima Sehgal , Shabbir Shaikh , Blake D. Sherwin , Carlos Sierra , Jon Sievers , Cristóbal Sifón , Sara Simon , Rita Sonka , David N. Spergel , Suzanne T. Staggs , Emilie Storer , Kristen Surrao , Eric R. Switzer , Niklas Tampier , Robert Thornton , Hy Trac , Carole Tucker , Joel Ullom , Leila R. Vale , Alexander Van Engelen , Jeff Van Lanen , Cristian Vargas , Eve M. Vavagiakis , Kasey Wagoner , Yuhan Wang , Lukas Wenzl , Edward J. Wollack , Kaiwen Zheng

Dark Energy Survey Year 3 Results: Cosmology from Cosmic Shear and Robustness to Modeling Uncertainty

This work and its companion paper, Amon et al. (2021), present cosmic shear measurements and cosmological constraints from over 100 million source galaxies in the Dark Energy Survey (DES) Year 3 data. We constrain the lensing amplitude…

Cosmology and Nongalactic Astrophysics · Physics 2022-01-17 L. F. Secco , S. Samuroff , E. Krause , B. Jain , J. Blazek , M. Raveri , A. Campos , A. Amon , A. Chen , C. Doux , A. Choi , D. Gruen , G. M. Bernstein , C. Chang , J. DeRose , J. Myles , A. Ferté , P. Lemos , D. Huterer , J. Prat , M. A. Troxel , N. MacCrann , A. R. Liddle , T. Kacprzak , X. Fang , C. Sánchez , S. Pandey , S. Dodelson , P. Chintalapati , K. Hoffmann , A. Alarcon , O. Alves , F. Andrade-Oliveira , E. J. Baxter , K. Bechtol , M. R. Becker , A. Brandao-Souza , H. Camacho , A. Carnero Rosell , M. Carrasco Kind , R. Cawthon , J. P. Cordero , M. Crocce , C. Davis , E. Di Valentino , A. Drlica-Wagner , K. Eckert , T. F. Eifler , M. Elidaiana , F. Elsner , J. Elvin-Poole , S. Everett , P. Fosalba , O. Friedrich , M. Gatti , G. Giannini , R. A. Gruendl , I. Harrison , W. G. Hartley , K. Herner , H. Huang , E. M. Huff , M. Jarvis , N. Jeffrey , N. Kuropatkin , P. -F. Leget , J. Muir , J. Mccullough , A. Navarro Alsina , Y. Omori , Y. Park , A. Porredon , R. Rollins , A. Roodman , R. Rosenfeld , A. J. Ross , E. S. Rykoff , J. Sanchez , I. Sevilla-Noarbe , E. S. Sheldon , T. Shin , I. Tutusaus , T. N. Varga , N. Weaverdyck , R. H. Wechsler , B. Yanny , B. Yin , Y. Zhang , J. Zuntz , T. M. C. Abbott , M. Aguena , S. Allam , J. Annis , D. Bacon , E. Bertin , S. Bhargava , S. L. Bridle , D. Brooks , E. Buckley-Geer , D. L. Burke , J. Carretero , M. Costanzi , L. N. da Costa , J. De Vicente , H. T. Diehl , J. P. Dietrich , P. Doel , I. Ferrero , B. Flaugher , J. Frieman , J. García-Bellido , E. Gaztanaga , D. W. Gerdes , T. Giannantonio , J. Gschwend , G. Gutierrez , S. R. Hinton , D. L. Hollowood , K. Honscheid , B. Hoyle , D. J. James , T. Jeltema , K. Kuehn , O. Lahav , M. Lima , H. Lin , M. A. G. Maia , J. L. Marshall , P. Martini , P. Melchior , F. Menanteau , R. Miquel , J. J. Mohr , R. Morgan , R. L. C. Ogando , A. Palmese , F. Paz-Chinchón , D. Petravick , A. Pieres , A. A. Plazas Malagón , M. Rodriguez-Monroy , A. K. Romer , E. Sanchez , V. Scarpine , M. Schubnell , D. Scolnic , S. Serrano , M. Smith , M. Soares-Santos , E. Suchyta , M. E. C. Swanson , G. Tarle , D. Thomas , C. To

Cosmic Microwave Background Anisotropy Observing Strategy Assessment

I develop a method for assessing the ability of an instrument, coupled with an observing strategy, to measure the angular power spectrum of the cosmic microwave background (CMB). It allows for efficient calculation of expected parameter…

Astrophysics · Physics 2009-10-28 Lloyd Knox

Ellipticity in Cosmic Microwave Background as a Tracer of Large-Scale Universe

Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data confirm the ellipticity of anisotropies of Cosmic Microwave Background (CMB) maps, found previously for Boomerang and WMAP 1-year high sensitivity maps. The low noise level of the WMAP…

Astrophysics · Physics 2008-11-26 V. G. Gurzadyan , C. L. Bianco , A. L. Kashin , H. Kuloghlian , G. Yegorian

The last stand before MAP: cosmological parameters from lensing, CMB and galaxy clustering

Cosmic shear measurements have now improved to the point where they deserve to be treated on par with CMB and galaxy clustering data for cosmological parameter analysis, using the full measured aperture mass variance curve rather than a…

Astrophysics · Physics 2009-10-07 Xiaomin Wang , Max Tegmark , Bhuvnesh Jain , Matias Zaldarriaga

Cosmological implications of the MAXIMA-I high resolution Cosmic Microwave Background anisotropy measurement

We discuss the cosmological implications of the new constraints on the power spectrum of the Cosmic Microwave Background Anisotropy derived from a new high resolution analysis of the MAXIMA-1 measurement (Lee et al. 2001). The power…

Astrophysics · Physics 2009-11-06 R. Stompor , M. Abroe , P. Ade , A. Balbi , D. Barbosa , J. Bock , J. Borrill , A. Boscaleri , P. De Bernardis , P. G. Ferreira , S. Hanany , V. Hristov , A. H. Jaffe , A. T. Lee , E. Pascale , B. Rabii , P. L. Richards , G. F. Smoot , C. D. Winant , J. H. P. Wu

Planck 2018 results. VI. Cosmological parameters

We present cosmological parameter results from the final full-mission Planck measurements of the CMB anisotropies. We find good consistency with the standard spatially-flat 6-parameter $\Lambda$CDM cosmology having a power-law spectrum of…

Cosmology and Nongalactic Astrophysics · Physics 2021-08-10 Planck Collaboration , N. Aghanim , Y. Akrami , M. Ashdown , J. Aumont , C. Baccigalupi , M. Ballardini , A. J. Banday , R. B. Barreiro , N. Bartolo , S. Basak , R. Battye , K. Benabed , J. -P. Bernard , M. Bersanelli , P. Bielewicz , J. J. Bock , J. R. Bond , J. Borrill , F. R. Bouchet , F. Boulanger , M. Bucher , C. Burigana , R. C. Butler , E. Calabrese , J. -F. Cardoso , J. Carron , A. Challinor , H. C. Chiang , J. Chluba , L. P. L. Colombo , C. Combet , D. Contreras , B. P. Crill , F. Cuttaia , P. de Bernardis , G. de Zotti , J. Delabrouille , J. -M. Delouis , E. Di Valentino , J. M. Diego , O. Doré , M. Douspis , A. Ducout , X. Dupac , S. Dusini , G. Efstathiou , F. Elsner , T. A. Enßlin , H. K. Eriksen , Y. Fantaye , M. Farhang , J. Fergusson , R. Fernandez-Cobos , F. Finelli , F. Forastieri , M. Frailis , A. A. Fraisse , E. Franceschi , A. Frolov , S. Galeotta , S. Galli , K. Ganga , R. T. Génova-Santos , M. Gerbino , T. Ghosh , J. González-Nuevo , K. M. Górski , S. Gratton , A. Gruppuso , J. E. Gudmundsson , J. Hamann , W. Handley , F. K. Hansen , D. Herranz , S. R. Hildebrandt , E. Hivon , Z. Huang , A. H. Jaffe , W. C. Jones , A. Karakci , E. Keihänen , R. Keskitalo , K. Kiiveri , J. Kim , T. S. Kisner , L. Knox , N. Krachmalnicoff , M. Kunz , H. Kurki-Suonio , G. Lagache , J. -M. Lamarre , A. Lasenby , M. Lattanzi , C. R. Lawrence , M. Le Jeune , P. Lemos , J. Lesgourgues , F. Levrier , A. Lewis , M. Liguori , P. B. Lilje , M. Lilley , V. Lindholm , M. López-Caniego , P. M. Lubin , Y. -Z. Ma , J. F. Macías-Pérez , G. Maggio , D. Maino , N. Mandolesi , A. Mangilli , A. Marcos-Caballero , M. Maris , P. G. Martin , M. Martinelli , E. Martínez-González , S. Matarrese , N. Mauri , J. D. McEwen , P. R. Meinhold , A. Melchiorri , A. Mennella , M. Migliaccio , M. Millea , S. Mitra , M. -A. Miville-Deschênes , D. Molinari , L. Montier , G. Morgante , A. Moss , P. Natoli , H. U. Nørgaard-Nielsen , L. Pagano , D. Paoletti , B. Partridge , G. Patanchon , H. V. Peiris , F. Perrotta , V. Pettorino , F. Piacentini , L. Polastri , G. Polenta , J. -L. Puget , J. P. Rachen , M. Reinecke , M. Remazeilles , A. Renzi , G. Rocha , C. Rosset , G. Roudier , J. A. Rubiño-Martín , B. Ruiz-Granados , L. Salvati , M. Sandri , M. Savelainen , D. Scott , E. P. S. Shellard , C. Sirignano , G. Sirri , L. D. Spencer , R. Sunyaev , A. -S. Suur-Uski , J. A. Tauber , D. Tavagnacco , M. Tenti , L. Toffolatti , M. Tomasi , T. Trombetti , L. Valenziano , J. Valiviita , B. Van Tent , L. Vibert , P. Vielva , F. Villa , N. Vittorio , B. D. Wandelt , I. K. Wehus , M. White , S. D. M. White , A. Zacchei , A. Zonca

Parameter constraints from weak lensing tomography of galaxy shapes and cosmic microwave background fluctuations

Recently, it has been shown that cross-correlating CMB lensing and 3D cosmic shear allows to considerably tighten cosmological parameter constraints. We investigate whether similar improvement can be achieved in a conventional tomographic…

Cosmology and Nongalactic Astrophysics · Physics 2017-07-27 Philipp M. Merkel , Bjoern Malte Schaefer

CMB lensing and primordial non-Gaussianity

We study the effects of gravitational lensing on the estimation of non-Gaussianity from the bispectrum of the cosmic microwave background (CMB) temperature anisotropies. We find that the effect of lensing on the bispectrum may qualitatively…

Cosmology and Nongalactic Astrophysics · Physics 2010-06-21 Duncan Hanson , Kendrick M. Smith , Anthony Challinor , Michele Liguori

4-Year COBE DMR Cosmic Microwave Background Observations: Maps and Basic Results

The cosmic microwave background radiation provides unique constraints on cosmological models. In this Letter we present a summary of the spatial properties of the cosmic microwave background radiation based on the full 4 years of COBE DMR…

Astrophysics · Physics 2009-10-28 C. L. Bennett , A. Banday , K. M. Gorski , G. Hinshaw , P. Jackson , P. Keegstra , A. Kogut , G. F. Smoot , D. T. Wilkinson , E. L. Wright

The Atacama Cosmology Telescope: Temperature and Gravitational Lensing Power Spectrum Measurements from Three Seasons of Data

We present the temperature power spectra of the cosmic microwave background (CMB) derived from the three seasons of data from the Atacama Cosmology Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the…

Cosmology and Nongalactic Astrophysics · Physics 2015-06-12 Sudeep Das , Thibaut Louis , Michael R. Nolta , Graeme E. Addison , Elia S. Battistelli , J Richard Bond , Erminia Calabrese , Devin Crichton Mark J. Devlin , Simon Dicker , Joanna Dunkley , Rolando Dünner , Joseph W. Fowler , Megan Gralla , Amir Hajian , Mark Halpern , Matthew Hasselfield , Matt Hilton , Adam D. Hincks , Renée Hlozek , Kevin M. Huffenberger , John P. Hughes , Kent D. Irwin , Arthur Kosowsky , Robert H. Lupton , Tobias A. Marriage , Danica Marsden , Felipe Menanteau , Kavilan Moodley , Michael D. Niemack , Lyman A. Page , Bruce Partridge , Erik D. Reese , Benjamin L. Schmitt , Neelima Sehgal , Blake D. Sherwin , Jonathan L. Sievers , David N. Spergel , Suzanne T. Staggs , Daniel S. Swetz , Eric R. Switzer , Robert Thornton , Hy Trac , Ed Wollack

Evidence for Gravitational Lensing of the Cosmic Microwave Background Polarization from Cross-correlation with the Cosmic Infrared Background

We reconstruct the gravitational lensing convergence signal from Cosmic Microwave Background (CMB) polarization data taken by the POLARBEAR experiment and cross-correlate it with Cosmic Infrared Background (CIB) maps from the Herschel…

Cosmology and Nongalactic Astrophysics · Physics 2014-04-23 POLARBEAR Collaboration , P. A. R. Ade , Y. Akiba , A. E. Anthony , K. Arnold , M. Atlas , D. Barron , D. Boettger , J. Borrill , C. Borys , S. Chapman , Y. Chinone , M. Dobbs , T. Elleflot , J. Errard , G. Fabbian , C. Feng , D. Flanigan , A. Gilbert , W. Grainger , N. W. Halverson , M. Hasegawa , K. Hattori , M. Hazumi , W. L. Holzapfel , Y. Hori , J. Howard , P. Hyland , Y. Inoue , G. C. Jaehnig , A. Jaffe , B. Keating , Z. Kermish , R. Keskitalo , T. Kisner , M. Le Jeune , A. T. Lee , E. M. Leitch , E. Linder , M. Lungu , F. Matsuda , T. Matsumura , X. Meng , N. J. Miller , H. Morii , S. Moyerman , M. J. Myers , M. Navaroli , H. Nishino , H. Paar , J. Peloton , E. Quealy , G. Rebeiz , C. L. Reichardt , P. L. Richards , C. Ross , K. Rotermund , I. Schanning , D. E. Schenck , B. D. Sherwin , A. Shimizu , C. Shimmin , M. Shimon , P. Siritanasak , G. Smecher , H. Spieler , N. Stebor , B. Steinbach , R. Stompor , A. Suzuki , S. Takakura , A. Tikhomirov , T. Tomaru , B. Wilson , A. Yadav , O. Zahn

The shape of the CMB power spectrum

The recent WMAP data represents a milestone in cosmology and helps constrain cosmological parameters with unprecedented accuracy. In this work we combine the WMAP data with previous CMB anisotropy measurements at smaller angular scales to…

Astrophysics · Physics 2015-06-24 C. J. Odman

CMB Lensing Bispectrum from Nonlinear Growth of the Large Scale Structure

We discuss detectability of the nonlinear growth of the large-scale structure in the cosmic microwave background (CMB) lensing. Lensing signals involved in CMB anisotropies have been measured from multiple CMB experiments, such as Atacama…

Cosmology and Nongalactic Astrophysics · Physics 2016-06-22 Toshiya Namikawa

Cosmological constraints from a joint analysis of cosmic microwave background and spectroscopic tracers of the large-scale structure

The standard model of cosmology, {\Lambda}CDM, is the simplest model that matches the current observations, but it relies on two hypothetical components, to wit, dark matter and dark energy. Future galaxy surveys and cosmic microwave…

Cosmology and Nongalactic Astrophysics · Physics 2018-08-13 Cyrille Doux , Mariana Penna-Lima , Sandro D. P. Vitenti , Julien Tréguer , Eric Aubourg , Ken Ganga