Effect of signal jitter on the spectrum of rotor impulsive noise

The effect of randomness or jitter of the acoustic waveform on the spectrum of rotor impulsive noise is studied because of its importance for data interpretation. An acoustic waveform train is modelled representing rotor impulsive noise. The amplitude, shape, and period between occurrences of individual pulses are allowed to be randomized assuming normal probability distributions. Results, in terms of the standard deviations of the variable quantities, are given for the autospectrum as well as special processed spectra designed to separate harmonic and broadband rotor noise components. Consideration is given to the effect of accuracy in triggering or keying to a rotor one per revolution signal. An example is given showing the resultant spectral smearing at the high frequencies due to the pulse signal period variability

HD 49798: Its History of Binary Interaction and Future Evolution

The bright subdwarf-O star (sdO), HD 49798, is in a 1.55 day orbit with a compact companion that is spinning at 13.2 seconds. Using the measurements of the effective temperature ($T_{\rm eff}$), surface gravity ($\log g$), and surface abundances of the sdO, we construct models to study the evolution of this binary system using Modules for Experiments in Stellar Astrophysics ($\texttt{MESA}$). Previous studies of the compact companion have disagreed on whether it is a white dwarf (WD) or a neutron star (NS). From the published measurements of the companion's spin and spin-up rate, we agree with Mereghetti and collaborators that a NS companion is more likely. However, since there remains the possibility of a WD companion, we use our constructed $\texttt{MESA}$ models to run simulations with both WD and NS companions that help us constrain the past and future evolution of this system. If it presently contains a NS, the immediate mass transfer evolution upon Roche lobe (RL) filling will lead to mass transfer rates comparable to that implied in ultraluminous X-ray sources (ULXs). Depending on the rate of angular momentum extraction via a wind, the fate of this system is either a wide ($P_{\rm orb}{\approx} 3$ day) intermediate mass binary pulsar (IMPB) with a relatively rapidly spinning NS (${\approx} 0.3$ s) and a high mass WD (${\approx} 0.9 M_\odot$), or a solitary millisecond pulsar (MSP).Comment: 6 pages, 4 figure

Distinguishing Dynamical Dark Matter at the LHC

Dynamical dark matter (DDM) is a new framework for dark-matter physics in which the dark sector comprises an ensemble of individual component fields which collectively conspire to act in ways that transcend those normally associated with dark matter. Because of its non-trivial structure, this DDM ensemble --- unlike most traditional dark-matter candidates --- cannot be characterized in terms of a single mass, decay width, or set of scattering cross-sections, but must instead be described by parameters which describe the collective behavior of its constituents. Likewise, the components of such an ensemble need not be stable so long as lifetimes are balanced against cosmological abundances across the ensemble as a whole. In this paper, we investigate the prospects for identifying a DDM ensemble at the LHC and for distinguishing such a dark-matter candidate from the candidates characteristic of traditional dark-matter models. In particular, we focus on DDM scenarios in which the component fields of the ensemble are produced at colliders alongside some number of Standard-Model particles via the decays of additional heavy fields. The invariant-mass distributions of these Standard-Model particles turn out to possess several unique features that cannot be replicated in most traditional dark-matter models. We demonstrate that in many situations it is possible to differentiate between a DDM ensemble and a traditional dark-matter candidate on the basis of such distributions. Moreover, many of our results also apply more generally to a variety of other extensions of the Standard Model which involve multiple stable or metastable neutral particles.Comment: 17 pages, LaTeX, 10 figure

Kaluza-Klein Towers in the Early Universe: Phase Transitions, Relic Abundances, and Applications to Axion Cosmology

We study the early-universe cosmology of a Kaluza-Klein (KK) tower of scalar fields in the presence of a mass-generating phase transition, focusing on the time-development of the total tower energy density (or relic abundance) as well as its distribution across the different KK modes. We find that both of these features are extremely sensitive to the details of the phase transition and can behave in a variety of ways significant for late-time cosmology. In particular, we find that the interplay between the temporal properties of the phase transition and the mixing it generates are responsible for both enhancements and suppressions in the late-time abundances, sometimes by many orders of magnitude. We map out the complete model parameter space and determine where traditional analytical approximations are valid and where they fail. In the latter cases we also provide new analytical approximations which successfully model our results. Finally, we apply this machinery to the example of an axion-like field in the bulk, mapping these phenomena over an enlarged axion parameter space that extends beyond those accessible to standard treatments. An important by-product of our analysis is the development of an alternate "UV-based" effective truncation of KK theories which has a number of interesting theoretical properties that distinguish it from the more traditional "IR-based" truncation typically used in the extra-dimension literature.Comment: 30 pages, LaTeX, 18 figures. Replaced to match published versio

Isospectral But Physically Distinct: Modular Symmetries and their Implications for Carbon Nanotori

Recently there has been considerable interest in the properties of carbon nanotori. Such nanotori can be parametrized according to their radii, their chiralities, and the twists that occur upon joining opposite ends of the nanotubes from which they are derived. In this paper, however, we demonstrate that many physically distinct nanotori with wildly different parameters nevertheless share identical band structures, energy spectra, and electrical conductivities. This occurs as a result of certain geometric symmetries known as modular symmetries which are direct consequences of the properties of the compactified graphene sheet. Using these symmetries, we show that there is a dramatic reduction in the number of spectrally distinct carbon nanotori compared with the number of physically distinct carbon nanotori. The existence of these modular symmetries also allows us to demonstrate that many statements in the literature concerning the electronic properties of nanotori are incomplete because they fail to respect the spectral equivalences that follow from these symmetries. We also find that as a result of these modular symmetries, the fraction of spectrally distinct nanotori which are metallic is approximately three times greater than would naively be expected on the basis of standard results in the literature. Finally, we demonstrate that these modular symmetries also extend to cases in which our carbon nanotori enclose non-zero magnetic fluxes.Comment: 12 pages, ReVTeX, 6 figures, 1 table. Replaced to match published versio