Chandra/ACIS-I study of the X-ray properties of the NGC 6611 and M16 stellar population

Mechanisms regulating the origin of X-rays in YSOs and the correlation with their evolutionary stage are under debate. Studies of the X-ray properties in young clusters allow to understand these mechanisms. One ideal target for this analysis is the Eagle Nebula (M16), with its central cluster NGC6611. At 1750 pc from the Sun, it harbors 93 OB stars, together with a population of low-mass stars from embedded protostars to disk-less Class III objects, with age <= 3Myrs. We study an archival 78 ksec Chandra/ACIS-I observation of NGC6611, and two new 80ksec observations of the outer region of M16, one centered on the Column V, and one on a region of the molecular cloud with ongoing star-formation. We detect 1755 point sources, with 1183 candidate cluster members (219 disk-bearing and 964 disk-less). We study the global X-ray properties of M16 and compare them with those of the Orion Nebula Cluster. We also compare the level of X-ray emission of Class II and Class III stars, and analyze the X-ray spectral properties of OB stars. Our study supports the lower level of X-ray activity for the disk-bearing stars with respect to the disk-less members. The X-ray Luminosity Function (XLF) of M16 is similar to that of Orion, supporting the universality of the XLF in young clusters. 85% of the O stars of NGC6611 have been detected in X-rays. With only one possible exception, they show soft spectra with no hard component, indicating that mechanisms for the production of hard X-ray emission in O stars are not operating in NGC 6611.Comment: Accepted in Ap

Faint emission lines in the Galactic H II regions M16, M20 and NGC 3603

We present deep echelle spectrophotometry of the Galactic {\hii} regions M16, M20 and NGC 3603. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100 to 10400 \AA range. We have detected more than 200 emission lines in each region. Physical conditions have been derived using different continuum and line intensity ratios. We have derived He$^{+}$, C$^{++}$ and O$^{++}$ abundances from pure recombination lines as well as abundances from collisionally excited lines for a large number of ions of different elements. We have obtained consistent estimations of the temperature fluctuation parameter, {\ts}, using different methods. We also report the detection of deuterium Balmer lines up to D$\delta$ (M16) and to D$\gamma$ (M20) in the blue wings of the hydrogen lines, which excitation mechanism seems to be continuum fluorescence. The temperature fluctuations paradigm agree with the results obtained from optical CELs and the more uncertain ones from far IR fine structure CELs in NGC 3603, although, more observations covering the same volume of the nebula are necessary to obtain solid conclusions.Comment: 22 pages, 13 Tables, 7 Figures. Accepted for publication by MNRA

Chronology of star formation and disk evolution in the Eagle Nebula

Massive SFR are characterized by intense ionizing fluxes, strong stellar winds and supernovae explosions, all of which have important effects on the surrounding media, on the star-formation (SF) process and on the evolution of YSOs and their disks. We present a multiband study of the massive young cluster NGC6611 and M16, to study how OB stars affect the early stellar evolution and the SF. We search for evidence of triggered SF by OB stars in NGC6611 on a large spatial scale (~10 pc) and how the efficiency of disks photoevaporation depends on the central stars mass. We assemble a multiband catalog with photometric data, from B band to 8.0micron, and X-ray data obtained with 2 new and 1 archival ACIS-I observation. We select the stars with disks from IR photometry and disk-less from X-ray emission, both in NGC6611 and the outer region of M16. We study induced photoevaporation searching for the spatial variation of disk frequency for distinct stellar mass ranges. The triggering of SF by OB stars has been investigated by deriving the history of SF across the nebula. We find evidence of sequential SF in the Eagle Nebula going from the SE (2.6 Myrs) to the NW (0.3 Myrs), with the median age of ~1 Myear. We observe a drop of the disk frequency close to OB stars (up to an average distance of 1 pc), without effects at larger distances. Furthermore, disks are more frequent around low-mass stars (<1 M(solar)) than in high-mass stars, regardless of the distance from OB stars. The SF chronology in M16 does not support the hypothesis of a large-scale SF triggered by OB stars in NGC6611. Instead, we speculate that it was triggered by the encounter (~3 Myrs ago) with a giant molecular shell created ~6 Myrs ago.Comment: Accepted for publication at Astronomy and Astrophysic

Aspects of Supersymmetric Models with a Radiatively Driven Inverted Mass Hierarchy

A promising way to reconcile naturalness with a decoupling solution to the SUSY flavor and CP problems is suggested by models with a radiatively driven inverted mass hierarchy (RIMH). The RIMH models arise naturally within the context of SUSY SO(10) grand unified theories. In their original form, RIMH models suffer from two problems: 1.) obtaining the radiative breakdown of electroweak symmetry, and 2.) generating the correct masses for third generation fermions. The first problem can be solved by the introduction of SO(10) D-term contributions to scalar masses. We show that correct fermion masses can indeed be obtained, but at the cost of limiting the magnitude of the hierarchy that can be generated. We go on to compute predictions for the neutralino relic density as well as for the rate for the decay $b\to s\gamma$, and show that these yield significant constraints on model parameter space. We show that only a tiny corner of model parameter space is accessible to Fermilab Tevatron searches, assuming an integrated luminosity of 25~$fb^{-1}$. We also quantify the reach of the CERN LHC collider for this class of models, and find values of $m_{\tg}\sim 1600$ GeV to be accessible assuming just 10 fb$^{-1}$ of integrated luminosity. In an Appendix, we list the two loop renormalization group equations for the MSSM plus right handed neutrino model that we have used in our analysis.Comment: 45 page REVTEX file with 18 PS figures; added acknowledgement and UW preprint numbe

Yukawa Coupling Unification in Supersymmetric Models

We present an updated assessment of the viability of t-b-tau Yukawa coupling unification in supersymmetric models. For the superpotential Higgs mass parameter mu>0, we find unification to less than 1% is possible, but only for GUT scale scalar mass parameter m_{16}~8-20 TeV, and small values of gaugino mass m_{1/2}<400 GeV. Such models require that a GUT scale mass splitting exists amongst Higgs scalars with m_{H_u}^2<m_{H_d}^2. Viable solutions lead to a radiatively generated inverted scalar mass hierarchy, with third generation and Higgs scalars being lighter than other sfermions. These models have very heavy sfermions, so that unwanted flavor changing and CP violating SUSY processes are suppressed, but may suffer from some fine-tuning requirements. While the generated spectra satisfy b->s gamma and (g-2)_mu constraints, there exists tension with the dark matter relic density unless m_{16}<3 TeV. These models offer prospects for a SUSY discovery at the Fermilab Tevatron collider via the search for chargino_1 neutralino_2 -> 3 leptons events, or via gluino pair production. If mu<0, Yukawa coupling unification to less than 5% can occur for m_{16} and m_{1/2}>1-2 TeV. Consistency of negative mu Yukawa unified models with b->s gamma, (g-2)_mu, and relic density all imply very large values of m_{1/2} typically greater than about 2.5 TeV, in which case direct detection of sparticles may be a challenge even at the LHC.Comment: 38 pages, 15 figures. Fig.15 changed, some references were added. A copy of the paper with better resolution figures can be found at http://www.hep.fsu.edu/~balazs/Physics/Papers/2003

Dark matter allowed scenarios for Yukawa-unified SO(10) SUSY GUTs

Simple supersymmetric grand unified models based on the gauge group SO(10) require --in addition to gauge and matter unification-- the unification of t-b-\tau Yukawa couplings. Yukawa unification, however, only occurs for very special values of the soft SUSY breaking parameters. We perform a search using a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also require the relic density of neutralino dark matter to saturate the WMAP-measured abundance. We find the spectrum is characterizd by three mass scales: first/second generation scalars in the multi-TeV range, third generation scalars in the TeV range, and gauginos in the \sim 100 GeV range. Most solutions give far too high a relic abundance of neutralino dark matter. The dark matter discrepancy can be rectified by 1. allowing for neutralino decay to axino plus photon, 2. imposing gaugino mass non-universality or 3. imposing generational non-universality. In addition, the MCMC approach finds 4. a compromise solution where scalar masses are not too heavy, and where neutralino annihilation occurs via the light Higgs h resonance. By imposing weak scale Higgs soft term boundary conditions, we are also able to generate 5. low \mu, m_A solutions with neutralino annihilation via a light A resonance, though these solutions seem to be excluded by CDF/D0 measurements of the B_s\to \mu^+\mu^- branching fraction. Based on the dual requirements of Yukawa coupling unification and dark matter relic density, we predict new physics signals at the LHC from pair production of 350--450 GeV gluinos. The events are characterized by very high b-jet multiplicity and a dilepton mass edge around mz2-mz1 \sim 50-75 GeV.Comment: 35 pages with 21 eps figure

Yukawa Unified Supersymmetric SO(10) Model: Cosmology, Rare Decays and Collider Searches

It has recently been pointed out that viable sparticle mass spectra can be generated in Yukawa unified SO(10) supersymmetric grand unified models consistent with radiative breaking of electroweak symmetry. Model solutions are obtained only if $\tan\beta \sim 50$, $\mu <0$ and positive $D$-term contributions to scalar masses from SO(10) gauge symmetry breaking are used. In this paper, we attempt to systematize the parameter space regions where solutions are obtained. We go on to calculate the relic density of neutralinos as a function of parameter space. No regions of the parameter space explored were actually cosmologically excluded, and very reasonable relic densities were found in much of parameter space. Direct neutralino detection rates could exceed 1 event/kg/day for a $^{73}$Ge detector, for low values of GUT scale gaugino mass $m_{1/2}$. We also calculate the branching fraction for $b\to s \gamma$ decays, and find that it is beyond the 95% CL experimental limits in much, but not all, of the parameter space regions explored. However, recent claims have been made that NLO effects can reverse the signs of certain amplitudes in the $b\to s\gamma$ calculation, leading to agreement between theory and experiment in Yukawa unified SUSY models. For the Fermilab Tevatron collider, significant regions of parameter space can be explored via $b\bar{b}A$ and $b\bar{b}H$ searches. There also exist some limited regions of parameter space where a trilepton signal can be seen at TeV33. Finally, there exist significant regions of parameter space where direct detection of bottom squark pair production can be made, especially for large negative values of the GUT parameter $A_0$.Comment: Added comparison to Blazek/Raby results and added Comments on de Boer et al. b->s gamma result

Spin(9)-structures and connections with totally skew-symmetric torsion

We study Spin(9)-structures on 16-dimensional Riemannian manifolds and characterize the geometric types admitting a connection with totally skew-symmetric torsion.Comment: Latex2e, 8 page