Resumen: We report on a new search for solar chameleons with the CERN Axion Solar Telescope (CAST). A GridPix detector was used to search for soft X-ray photons in the energy range from 200 eV to 10 keV from converted solar chameleons. No significant excess over the expected background has been observed in the data taken in 2014 and 2015. We set an improved limit on the chameleon photon coupling, beta(gamma) less than or similar to 5.7 x 10(10) for 1 < beta(m) < 10(6) at 95% C.L. improving our previous results by a factor two and for the first time reaching sensitivity below the solar luminosity bound for tachocline magnetic fields up to 12.5 T. Idioma: Inglés DOI: 10.1088/1475-7516/2019/01/032 Año: 2019 Publicado en: Journal of Cosmology and Astroparticle Physics 2019, 1 (2019), 032 [18 pp.] ISSN: 1475-7516 Factor impacto JCR: 5.21 (2019) Categ. JCR: PHYSICS, PARTICLES & FIELDS rank: 5 / 29 = 0.172 (2019) - Q1 - T1 Categ. JCR: ASTRONOMY & ASTROPHYSICS rank: 13 / 68 = 0.191 (2019) - Q1 - T1 Factor impacto SCIMAGO: 0.813 - Astronomy and Astrophysics (Q2)