116938894
A Subaru Archival Search for Faint TNOs
We present the results of a survey for trans-neptunian objects (TNOs) based on Subaru archival images, originally collected by Sheppard et al. (2005) as part of a search for irregular satellites of Uranus. The survey region covers 2.8 deg^2, centered on Uranus and observed near opposition on two adjacent nights. Our survey reaches half its maximum detection efficiency at R=25.69$\pm$0.01. The objects detected correspond to 82 TNOs, five Centaurs, and five irregular satellites. We model the cumulative number of TNOs brighter than a given apparent magnitude with both a single and double power law. The best fit single power law, with one object per square degree at magnitude $R_0 =22.6_{-0.4}^{+0.3}$ and a slope of $\alpha = 0.51_{-0.6}^{+0.5}$, is inconsistent with the results of similar searches with shallower limiting magnitudes. The best fit double power law, with a bright-end slope $\alpha_1 = 0.7_{-0.1}^{+0.2}$, a faint-end slope $\alpha_2=0.3_{-0.2}^{+0.2}$, a differential number density at R=23, $\sigma_{23} = 2.0_{-0.5}^{+0.5}$ and a magnitude break in the slope at $R_{eq} = 24.3_{-0.1}^{+0.8}$, is more likely than the single power law by a Bayes factor of ~26. This is the first survey with sufficient depth and areal coverage to identify the magnitude at which the break occurs without relying on the results of other surveys. ...
14122353
Ground-Based Multisite Observations of Two Transits of HD 80606b
We present ground-based optical observations of the 2009 September and 2010 January transits of HD 80606b. Based on three partial light curves of the 2009 September event, we derive a midtransit time of T_c [HJD] = 2455099.196 ± 0.026, which is about 1σ away from the previously predicted time. We observed the 2010 January event from nine different locations, with most phases of the transit being observed by at least three different teams. We determine a midtransit time of Tc [HJD] = 2455210.6502 ± 0.0064, which is within 1.3σ of the time derived from a Spitzer observation of the same event.
55660788
Trans-Neptunian Objects with Hubble Space Telescope ACS/WFC
We introduce a novel search technique that can identify trans-Neptunian objects in three to five exposures of a pointing within a single Hubble Space Telescope (HST) orbit. The process is fast enough to allow the discovery of candidates soon after the data are available. This allows sufficient time to schedule follow-up observations with HST within a month. We report the discovery of 14 slow-moving objects found within 5° of the ecliptic in archival data taken with the Wide Field Channel of the Advanced Camera for Surveys. The luminosity function of these objects is consistent with previous ground-based and space-based results. We show evidence that the size distribution of both high and low inclination populations is similar for objects smaller than 100 km, as expected from collisional evolution models, while their size distribution differs for brighter objects. We suggest that the two populations formed in different parts of the protoplanetary disk and after being dynamically mixed have collisionally evolved together. Among the objects discovered there is an equal-mass binary with an angular separation ~053.
55713175
On the Rotation Period of (90377) Sedna
We present precise, ~1%, r-band relative photometry of the unusual solar system object (90377) Sedna. Our data consist of 143 data points taken over eight nights in 2004 October and 2005 January 2005. The rms variability over the longest contiguous stretch of five nights of data spanning 9 days is only ~1.3%. This subset of data alone constrains the amplitude of any long-period variations with period P to be A 1%(P/20 days)2. Over the course of any given ~5 hr segment, the data exhibit significant linear trends not seen in a comparison star of similar magnitude, and in a few cases these segments show clear evidence of curvature at the level of a few millimagnitudes per hour squared. These properties imply that the rotation period of Sedna is O(10 hr); it cannot be 5 hr nor can it be 10 days, unless the intrinsic light curve has significant and comparable power on multiple timescales, which is unlikely. A sinusoidal fit yields a period of P = 10.273 ± 0.002 hr and a semiamplitude of A = 1.1% ± 0.1%. There are additional acceptable fits with flanking periods separated by ~3 minutes as well as another class of fits with P ~ 18 hr, although these later fits appear less viable based on visual inspection. Our results indicate that the period of Sedna is likely consistent with typical rotation periods of solar system objects, thus obviating the need for a massive companion to slow its rotation.
15085947
The origin of chaos in the outer solar system
Classical analytic theories of the solar system indicate that it is stable, but numerical integrations suggest that it is chaotic. This disagreement is resolved by a new analytic theory. The theory shows that the chaos among the jovian planets results from the overlap of the components of a mean motion resonance among Jupiter, Saturn, and Uranus, and provides rough estimates of the Lyapunov time (10(7) years) and the dynamical lifetime of Uranus (10(18) years). The jovian planets must have entered the resonance after all the gas and most of the planetesimals in the protoplanetary disk were removed.
9838894
PUSHING THE LIMITS OF GROUND-BASED PHOTOMETRIC PRECISION: SUBMILLIMAGNITUDE TIME-SERIES PHOTOMETRY OF THE OPEN CLUSTER NGC 6791
We present the results from a three-night, time-series study of the open cluster NGC 6791 using the Megacam wide-field mosaic CCD camera on the 6.5 m MMT telescope. The aim of this study was to demonstrate the ability to obtain very high precision photometry for a large number of stars. We achieved better than 1% precision for more than 8000 stars with 14.3 < R < 20.1 and submillimagnitude (as low as 0.36 mmag) precision for over 300 stars with 14.6 < R < 16.3 in the field of this cluster. We also discovered 10 new variable stars, including a possible δ Scuti variable with an amplitude of 2%, eight likely W UMa contact binaries, and a possible RS CVn star, and we identified seven suspected low-amplitude variables, including one star with an amplitude of 4 mmag. We comment on the implications of this study for a ground-based survey for transiting planets as small as Neptune.
118491144
Physical Degrees of Freedom in Higgs Models
Despite the clear-cut prediction and subsequent experimental detection of the weak interaction bosons, the Higgs sector of the standard model of elementary particle physics has long remained one of its most obscure features. Here, it is demonstrated through a very basic argument that standard accounts of the Higgs mechanism suffer from a serious conceptual consistency problem, in that they incorrectly identify physical degrees of freedom. The point at issue, is that the reasoning which leads to a removal of the unphysical excitation modes is valid in both phases of the theory - i.e. both after and before the phase transition occurs. Consistently removing unphysical degrees of freedom implies a discrepancy in the number of physical degrees of freedom. In particular, the longitudinally polarized, massive gauge boson degrees of freedom do not have physical counterparts before the phase transition and are thus effectively “created ex nihilio” at the transition, within the context of ordinary Higgs models. Possible scenarios for removing the discrepancy are briefly considered. The results obtained here strongly indicate that although standard, perturbative formulations of the Higgs mechanism provide a convenient parametrization of electroweak physics over a certain range of scales, they cannot provide a sensible explanation of all relevant physical degrees of freedom involved.
8995520
On Arguments for Linear Quantum Dynamics
Two recent arguments for linear dynamics in quantum theory are critically re-examined. Neither argument is found to be satisfactory as it stands, although an improved version of one of the arguments can in fact be given. This improved version turns out to be still not completely unproblematic, but it is argued that it contains only a single actual loophole, which is identical to a loophole that remains in experimental proofs of nonlocality of Bell-type. It is concluded that - within the context of the standard quantum kinematical framework and in agreement with what has been concluded by earlier authors - a nonlinear dynamics of density operators is inconsistent with relativistic causality. However, it is also stressed that this conclusion in itself has little implication for the nature of dynamics at the Hilbert space level - in particular, it does not force dynamics to be linear at this level - nor does it continue to be valid in contexts that go beyond the standard quantum kinematical framework. Despite their seeming triviality, these last two points have not always been appreciated in the literature. Finally, it is also pointed out that the argument for complete positivity, as given in conjunction with one of the two recent arguments for linear dynamics, in fact only establishes a condition that is weaker than complete positivity.
119105755
Foundations of Quantum Gravity : The Role of Principles Grounded in Empirical Reality
Abstract When attempting to assess the strengths and weaknesses of various principles in their potential role of guiding the formulation of a theory of quantum gravity, it is crucial to distinguish between principles which are strongly supported by empirical data – either directly or indirectly – and principles which instead (merely) rely heavily on theoretical arguments for their justification. Principles in the latter category are not necessarily invalid, but their a priori foundational significance should be regarded with due caution. These remarks are illustrated in terms of the current standard models of cosmology and particle physics, as well as their respective underlying theories, i.e., essentially general relativity and quantum (field) theory. For instance, it is clear that both standard models are severely constrained by symmetry principles: an effective homogeneity and isotropy of the known universe on the largest scales in the case of cosmology and an underlying exact gauge symmetry of nuclear and electromagnetic interactions in the case of particle physics. However, in sharp contrast to the cosmological situation, where the relevant symmetry structure is more or less established directly on observational grounds, all known, nontrivial arguments for the “gauge principle” are purely theoretical (and far less conclusive than usually advocated). Similar remarks apply to the larger theoretical structures represented by general relativity and quantum (field) theory, where – actual or potential – empirical principles, such as the (Einstein) equivalence principle or EPR-type nonlocality, should be clearly differentiated from theoretical ones, such as general covariance or renormalizability. It is argued that if history is to be of any guidance, the best chance to obtain the key structural features of a putative quantum gravity theory is by deducing them, in some form, from the appropriate empirical principles (analogous to the manner in which, say, the idea that gravitation is a curved spacetime phenomenon is arguably implied by the equivalence principle). Theoretical principles may still be useful however in formulating a concrete theory (analogous to the manner in which, say, a suitable form of general covariance can still act as a sieve for separating theories of gravity from one another). It is subsequently argued that the appropriate empirical principles for deducing the key structural features of quantum gravity should at least include (i) quantum nonlocality, (ii) irreducible indeterminacy (or, essentially equivalently, given (i), relativistic causality), (iii) the thermodynamic arrow of time, (iv) homogeneity and isotropy of the observable universe on the largest scales. In each case, it is explained – when appropriate – how the principle in question could be implemented mathematically in a theory of quantum gravity, why it is considered to be of fundamental significance and also why contemporary accounts of it are insufficient. For instance, the high degree of uniformity observed in the Cosmic Microwave Background is usually regarded as theoretically problematic because of the existence of particle horizons, whereas the currently popular attempts to resolve this situation in terms of inflationary models are, for a number of reasons, less than satisfactory. However, rather than trying to account for the required empirical features dynamically , an arguably much more fruitful approach consists in attempting to account for these features directly, in the form of a lawlike initial condition within a theory of quantum gravity.
118505140
Generalized Noether Theorems for Field Theories Formulated in Minkowski Spacetime
New symmetry theorems are obtained for field theories formulated in Minkowski spacetime, based on the recognition that such theories should be diffeomorphism invariant. These theorems, which are in fact generalized Noether theorems, have several nontrivial ramifications. One immediate consequence is the necessity to re-evaluate some of the default characterizations of the original Noether theorems as general statements - for instance, the statement that every global invariance of the action gives rise to a conserved current. As it turns out, this latter statement remains valid, but apparently only as a consequence of both the generalized first and second Noether theorem (at any rate, it is very far from clear how to avoid such a conclusion). A ramification of a more constructive nature consists in a novel expression for the so-called Belinfante stress-energy tensor, for which it is evident that it generalizes to the correct stress-energy tensor within the context of general relativity. The crucial symmetry property here is diffeomorphism invariance, rather than Poincar\'e invariance. Using this new form for the stress-energy tensor, an alternative route to general relativity also becomes available, which, in contrast to many standard treatments, is intrinsically based on a variational formulation - i.e. without the need to have prior knowledge of the form of Einstein's equation. The connection of these results to related results previously established in the literature (although in a completely different context) will be pointed out where applicable.