arXiv subjects

Carlos Contreras

Publications and source records attributed to Carlos Contreras.

102 records · Page 6Linked to original sources

arXiv2010

Simple analytic QCD model with perturbative QCD behavior at high momenta

Analytic QCD models are those where the QCD running coupling has the physically correct analytic behavior, i.e., no Landau singularities in the Euclidean regime. We present a simple analytic QCD model in which the discontinuity function of the running coupling at high momentum scales is the same as in perturbative QCD (just like in the analytic QCD model of Shirkov and Solovtsov), but at low scales it is replaced by a delta function which parametrizes the unknown behavior there. We require that the running coupling agree to a high degree with the perturbative coupling at high energies, which reduces the number of free parameters of the model from four to one. The remaining parameter is fixed by requiring the reproduction of the correct value of the semihadronic tau decay ratio.

hep-ph↗

arXiv2009

The Carnegie Supernova Project: Analysis of the First Sample of Low-Redshift Type-Ia Supernovae

We present the analysis of the first set of low-redshift Type Ia supernovae (SNe Ia) by the Carnegie Supernova Project. Well-sampled, high-precision optical (ugriBV) and near-infrared (NIR; YJHKs) light curves obtained in a well-understood photometric system are used to provide light-curve parameters, and ugriBVYJH template light curves. The intrinsic colors at maximum light are calibrated to compute optical--NIR color excesses for the full sample, thus allowing the properties of the reddening law in the host galaxies to be studied. A low value of Rv~1.7, is derived when using the entire sample of SNe. However, when the two highly reddened SNe in the sample are excluded, a value Galactic standard of Rv~3.2 is obtained. The colors of these two events are well matched by a reddening model due to circumstellar dust. The peak luminosities are calibrated using a two-parameter linear fit to the decline rates and the colors, or alternatively, the color excesses. In both cases, dispersions in absolute magnitude of 0.12--0.16 mag are obtained, depending on the filter-color combination. In contrast to the results obtained from color excesses, these fits give Rv~1--2, even when the two highly reddened SNe are excluded. This discrepancy suggests that, beyond the "normal" interstellar reddening produced in the host galaxies, there is an intrinsic dispersion in the colors of SNe Ia which is correlated with luminosity but independent of the decline rate. Finally, a Hubble diagram is produced by combining the results of the fits for each filter. The resulting scatter of 0.12 mag appears to be limited by peculiar velocities as evidenced by the strong correlation between the distance-modulus residuals among the different filters. The implication is that the actual precision of SN Ia distances is 3--4%.

astro-ph.CO↗

arXiv2009

The Carnegie Supernova Project: First Photometry Data Release of Low-Redshift Type Ia Supernovae

The Carnegie Supernova Project (CSP) is a five-year survey being carried out at the Las Campanas Observatory to obtain high-quality light curves of ~100 low-redshift Type Ia supernovae in a well-defined photometric system. Here we present the first release of photometric data that contains the optical light curves of 35 Type Ia supernovae, and near-infrared light curves for a subset of 25 events. The data comprise 5559 optical (ugriBV) and 1043 near-infrared (YJHKs) data points in the natural system of the Swope telescope. Twenty-eight supernovae have pre-maximum data, and for 15 of these, the observations begin at least 5 days before B maximum. This is one of the most accurate datasets of low-redshift Type Ia supernovae published to date. When completed, the CSP dataset will constitute a fundamental reference for precise determinations of cosmological parameters, and serve as a rich resource for comparison with models of Type Ia supernovae.

astro-ph.CO↗

arXiv2009

SN 2003bg: The First Type IIb Hypernova

Optical and near-infrared photometry and optical spectroscopy are reported for SN 2003bg, starting a few days after explosion and extending for a period of more than 300 days. Our early-time spectra reveal the presence of broad, high-velocity Balmer lines. The nebular-phase spectra, on the other hand, show a remarkable resemblance to those of Type Ib/c supernovae, without clear evidence for hydrogen. Near maximum brightness SN 2003bg displayed a bolometric luminosity comparable to that of other Type I hypernovae unrelated to gamma-ray bursts, implying a rather normal amount of 56Ni production (0.1-0.2 Msun) compared with other such objects. The bolometric light curve of SN 2003bg, on the other hand, is remarkably broad, thus suggesting a relatively large progenitor mass at the moment of explosion. These observations, together with the large value of the kinetic energy of expansion established in the accompanying paper (Mazzali et al. 2009), suggest that SN 2003bg can be regarded as a Type IIb hypernova.

astro-ph.CO↗

arXiv2009

The Carnegie Supernova Project: First Near-Infrared Hubble Diagram to z~0.7

The Carnegie Supernova Project (CSP) is designed to measure the luminosity distance for Type Ia supernovae (SNe Ia) as a function of redshift, and to set observational constraints on the dark energy contribution to the total energy content of the Universe. The CSP differs from other projects to date in its goal of providing an I-band {rest-frame} Hubble diagram. Here we present the first results from near-infrared (NIR) observations obtained using the Magellan Baade telescope for SNe Ia with 0.1 < z < 0.7. We combine these results with those from the low-redshift CSP at z <0.1 (Folatelli et al. 2009). We present light curves and an I-band Hubble diagram for this first sample of 35 SNe Ia and we compare these data to 21 new SNe Ia at low redshift. These data support the conclusion that the expansion of the Universe is accelerating. When combined with independent results from baryon acoustic oscillations (Eisenstein et al. 2005), these data yield Omega_m = 0.27 +/- 0.0 (statistical), and Omega_DE = 0.76 +/- 0.13 (statistical) +/- 0.09 (systematic), for the matter and dark energy densities, respectively. If we parameterize the data in terms of an equation of state, w, assume a flat geometry, and combine with baryon acoustic oscillations, we find that w = -1.05 +/- 0.13 (statistical) +/- 0.09 (systematic). The largest source of systematic uncertainty on w arises from uncertainties in the photometric calibration, signaling the importance of securing more accurate photometric calibrations for future supernova cosmology programs. Finally, we conclude that either the dust affecting the luminosities of SNe Ia has a different extinction law (R_V = 1.8) than that in the Milky Way (where R_V = 3.1), or that there is an additional intrinsic color term with luminosity for SNe Ia independent of the decline rate.

astro-ph.CO↗

arXiv2009

The He-rich core-collapse supernova 2007Y: Observations from X-ray to Radio Wavelengths

A detailed study spanning approximately a year has been conducted on the Type Ib supernova 2007Y. Imaging was obtained from X-ray to radio wavelengths, and a comprehensive set of multi-band (w2m2w1u'g'r'i'UBVYJHKs) light curves and optical spectroscopy is presented. A virtually complete bolometric light curve is derived, from which we infer a (56)Ni-mass of 0.06 M_sun. The early spectrum strongly resembles SN 2005bf and exhibits high-velocity features of CaII and H_alpha; during late epochs the spectrum shows evidence of a ejecta-wind interaction. Nebular emission lines have similar widths and exhibit profiles that indicate a lack of major asymmetry in the ejecta. Late phase spectra are modeled with a non-LTE code, from which we find (56)Ni, O and total-ejecta masses (excluding He) to be 0.06, 0.2 and 0.42 M_sun, respectively, below 4,500 km/s. The (56)Ni mass confirms results obtained from the bolometric light curve. The oxygen abundance suggests the progenitor was most likely a ~3.3 M_sun He core star that evolved from a zero-age-main-sequence mass of 10-13 M_sun. The explosion energy is determined to be ~10^50 erg, and the mass-loss rate of the progenitor is constrained from X-ray and radio observations to be <~10^-6 M_sun/yr. SN 2007Y is among the least energetic normal Type Ib supernovae ever studied.

astro-ph.HE↗

arXiv2008

A New Distance to The Antennae Galaxies (NGC 4038/39) Based on the Type Ia Supernova 2007sr

Traditionally, the distance to NGC 4038/39 has been derived from the systemic recession velocity, yielding about 20 Mpc for H_0 = 72 km/s/Mpc. Recently, this widely adopted distance has been challenged based on photometry of the presumed tip of the red giant branch (TRGB), which seems to yield a shorter distance of 13.3+-1.0 Mpc and, with it, nearly 1 mag lower luminosities and smaller radii for objects in this prototypical merger. Here we present a new distance estimate based on observations of the Type Ia supernova (SN) 2007sr in the southern tail, made at Las Campanas Observatory as part of the Carnegie Supernova Project. The resulting distance of D(SN Ia) = 22.3+-2.8 Mpc [(m-M)_0 = 31.74+-0.27 mag] is in good agreement with a refined distance estimate based on the recession velocity and the large-scale flow model developed by Tonry and collaborators, D(flow) = 22.5+-2.8 Mpc. We point out three serious problems that a short distance of 13.3 Mpc would entail, and trace the claimed short distance to a likely misidentification of the TRGB. Reanalyzing Hubble Space Telescope (HST) data in the Archive with an improved method, we find a TRGB fainter by 0.9 mag and derive from it a preliminary new TRGB distance of D(TRGB) = 20.0+-1.6 Mpc. Finally, assessing our three distance estimates we recommend using a conservative, rounded value of D = 22+-3 Mpc as the best currently available distance to The Antennae.

astro-ph↗

arXiv2005

SN 2005bf: A Possible Transition Event Between Type Ib/c Supernovae and Gamma Ray Bursts

We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first ~100 days following discovery. The u'g'BV light curves displayed a double-peaked morphology, which is among Type Ib/Ic supernovae. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u'g'BV was accompanied by the presence in the spectrum of high velocity absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations which attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 x 10^{51} erg), asymmetric explosion of a massive (8.3 M_sun) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of 1) a polar explosion containing a small fraction of the total mass and moving at high velocity, and 2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically-thin, revealing the slower-moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and gamma ray bursts.

astro-ph↗

arXiv2005

The Carnegie Supernova Project: The Low-Redshift Survey

Supernovae are essential to understanding the chemical evolution of the Universe. Type Ia supernovae also provide the most powerful observational tool currently available for studying the expansion history of the Universe and the nature of dark energy. Our basic knowledge of supernovae comes from the study of their photometric and spectroscopic properties. However, the presently available data sets of optical and near-infrared light curves of supernovae are rather small and/or heterogeneous, and employ photometric systems that are poorly characterized. Similarly, there are relatively few supernovae whose spectral evolution has been well sampled, both in wavelength and phase, with precise spectrophotometric observations. The low-redshift portion of the Carnegie Supernova Project (CSP) seeks to remedy this situation by providing photometry and spectrophotometry of a large sample of supernovae taken on telescope/filter/detector systems that are well understood and well characterized. During a five-year program which began in September 2004, we expect to obtain high-precision u'g'r'i'BVYJHKs light curves and optical spectrophotometry for about 250 supernovae of all types. In this paper we provide a detailed description of the CSP survey observing and data reduction methodology. In addition, we present preliminary photometry and spectra obtained for a few representative supernovae during the first observing campaign.

astro-ph↗

arXiv2002

Determination of $α_s$ from Gross-Llewellyn Smith sum rule by accounting for infrared renormalon

We recapitulate the method which resums the truncated perturbation series of a physical observable in a way which takes into account the structure of the leading infrared renormalon. We apply the method to the Gross-Llewellyn Smith (GLS) sum rule. By confronting the obtained result with the experimentally extracted GLS value, we determine the value of the QCD coupling parameter which turns out to agree with the present world average.

hep-ph↗

arXiv2002

Extraction of alpha_s from the Gross--Llewellyn Smith sum rule using Borel resummation

Using the CCFR data for the Gross--Llewellyn Smith (GLS) sum rule, we extract the strong coupling constant via Borel resummation of the perturbative QCD calculation. The method incorporates the correct nature of the first infrared renormalon singularity, and employs a conformal mapping to improve the convergence of the QCD perturbation expansion. The important twist-four contribution is calculated from resummation of the perturbation theory, which is based on the ansatz that the higher--twist contribution has a cut singularity only along the positive real axis on the complex coupling plane. Thus obtained, the strong coupling constant corresponding to the central GLS experimental value is in good agreement with the world average.

hep-ph↗

arXiv1996

The Nielsen Identities for the generalized $R_ξ$-gauge

We show that it is possible, in opposition to a previous conjecture, to derive a Nielsen identity for the effective action in the case of the generalized $R_ξ$-gauge, where the gauge function explicitly depends on the gauge parameter $ξ$. Also the Nielsen identity for the effective potential is verified to one-loop in the Abelian Higgs model and the corresponding identity for the physical Higgs mass is derived.

hep-th↗