865 research outputs found

    A Kaluza-Klein Model with Spontaneous Symmetry Breaking: Light-Particle Effective Action and its Compactification Scale Dependence

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    We investigate decoupling of heavy Kaluza-Klein modes in an Abelian Higgs model with space-time topologies R3,1√óS1\mathbb{R}^{3,1} \times S^{1} and R3,1√óS1/Z2\mathbb{R}^{3,1} \times S^{1}/\mathbb{Z}_{2}. After integrating out heavy KK modes we find the effective action for the zero mode fields. We find that in the R3,1√óS1\mathbb{R}^{3,1} \times S^{1} topology the heavy modes do not decouple in the effective action, due to the zero mode of the 5-th component of the 5-d gauge field A5A_{5}. Because A5A_{5} is a scalar under 4-d Lorentz transformations, there is no gauge symmetry protecting it from getting mass and A54A_{5}^{4} interaction terms after loop corrections. In addition, after symmetry breaking, we find new divergences in the A5A_{5} mass that did not appear in the symmetric phase. The new divergences are traced back to the gauge-goldstone mixing that occurs after symmetry breaking. The relevance of these new divergences to Symanzik's theorem is discussed. In order to get a more sensible theory we investigate the S1/Z2S^{1}/\mathbb{Z}_{2} compactification. With this kind of compact topology, the A5A_{5} zero mode disappears. With no A5A_{5}, there are no new divergences and the heavy modes decouple. We also discuss the dependence of the couplings and masses on the compactification scale. We derive a set of RG-like equations for the running of the effective couplings with respect to the compactification scale. It is found that magnitudes of both couplings decrease as the scale MM increases. The effective masses are also shown to decrease with increasing compactification scale. All of this opens up the possibility of placing constraints on the size of extra dimensions.Comment: 35 pages, 6 figure

    Non-Canonical Scalar Fields and Their Applications in Cosmology and Astrophysics.

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    In this thesis we will discuss several issues concerning cosmological applications of non-canonical scalar fields, which are generically referred to as k-essence. First, we consider two examples of k-essence. These are the rolling tachyon and static spherically symmetric solutions of non-canonical scalar fields in flat space. Next, we consider static spherically symmetric solutions of non-canonical scalar fields coupled to gravity as a way to explain dark matter halos as a coherent state of the scalar field. The non-trivial solutions have negative energy density near the origin, though the total energy is positive. After this we show that, for general scalar fields, stationary configurations are possible for shift symmetric theories only. The next discussion outlines a general program for reconstructing the action of non-canonical single field inflation models from CMBR power spectrum data. Finally, we study a novel means of coupling neutrinos to a Lorentz violating k-essence background. We first look into the effect k-essence has on the neutrino dispersion relation, and derive the neutrino velocity in a k-essence background. Next, we look at the effect on neutrino oscillations.Ph.D.PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/77882/1/csg_1.pd

    Decoupling of Heavy Kaluza-Klein Modes In Models With Five-Dimensional Scalar Fields

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    We investigate the decoupling of heavy Kaluza-Klein modes in Ōē4\phi^{4} theory and scalar QED with space-time topology R3,1√óS1\mathbb{R}^{3,1} \times S^{1}. We calculate the effective action due to integrating out heavy KK modes. We construct generalized RGE's for the couplings with respect to the compactification scale MM. With the solutions to the RGE's we find the MM-scale dependence of the effective theory due to higher dimensional quantum effects. We find that the heavy modes decouple in Ōē4\phi^{4} theory, but do not decouple in scalar QED. This is due to the zero mode of the 5-th component A5A_{5} of the 5-d gauge field. Because A5A_{5} is a scalar under 4-d Lorentz transformations, there is no gauge symmetry protecting it from getting mass and A54A_{5}^{4} interaction terms after loop corrections. In light of these unpleasant features, we explore S1/Z2S^{1}/\mathbb{Z}_{2} compactifications, which eliminate A5A_{5}, allowing for the heavy modes to decouple at low energies. We also explore the possibility of decoupling by including higher dimensional operators. It is found that this is possible, but a high degree of fine tuning is required.Comment: 9 pages, no figures; sign error on equations 20, 36, 37; Added additional reference

    Reconstructing the primordial power spectrum from the CMB

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    We propose a straightforward and model independent methodology for characterizing the sensitivity of CMB and other experiments to wiggles, irregularities, and features in the primordial power spectrum. Assuming that the primordial cosmological perturbations are adiabatic, we present a function space generalization of the usual Fisher matrix formalism, applied to a CMB experiment resembling Planck with and without ancillary data. This work is closely related to other work on recovering the inflationary potential and exploring specific models of non-minimal, or perhaps baroque, primordial power spectra. The approach adopted here, however, most directly expresses what the data is really telling us. We explore in detail the structure of the available information and quantify exactly what features can be reconstructed and at what statistical significance.Comment: 43 pages Revtex, 23 figure

    Stationary Configurations Imply Shift Symmetry: No Bondi Accretion for Quintessence / k-Essence

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    In this paper we show that, for general scalar fields, stationary configurations are possible for shift symmetric theories only. This symmetry with respect to constant translations in field space should either be manifest in the original field variables or reveal itself after an appropriate field redefinition. In particular this result implies that neither k-Essence nor Quintessence can have exact steady state / Bondi accretion onto Black Holes. We also discuss the role of field redefinitions in k-Essence theories. Here we study the transformation properties of observables and other variables in k-Essence and emphasize which of them are covariant under field redefinitions. Finally we find that stationary field configurations are necessarily linear in Killing time, provided that shift symmetry is realized in terms of these field variables.Comment: 8 page

    Distribution and relative abundance of caribou in the Hudson Plains Ecozone of Ontario

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    To determine past distribution and relative abundance of caribou (Rangifer tarandus caribou) in the Hudson Plains Ecozone (HPE) of Ontario, we reviewed past HPE-wide winter systematic aerial surveys, partial winter systematic surveys, summer photographic surveys, incidental observations of caribou, and other sources of information from the period 1950—2003. We conducted new HPE-wide aerial surveys in February 2003 and 2004 to evaluate current distribution patterns. From this information, we defined 9 core wintering areas in the HPE and differentiated between 3 catego¬ries of relative abundance. Wintering areas for the January—March period have changed relatively little over the past 45 years. Summer distribution of caribou along the Hudson Bay coast apparently shifted or expanded from the area west of the Severn River to the central and eastern portions of the coast since the 1980s, and caribou observations have become much more common in the area east of the Winisk River since 1998. Because major resource development activities in the HPE are proposed and some are imminent, we recommend additional caribou surveys to document current caribou population identity, size, and distribution, and research projects to better define caribou wintering areas, calving areas, and movement patterns in the HPE

    Reconstructing Single Field Inflationary Actions From CMBR Data

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    This paper describes a general program for deriving the action of single field inflation models with nonstandard kinetic energy terms using CMBR power spectrum data. This method assumes that an action depends on a set of undetermined functions, each of which is a function of either the inflaton wave function or its time derivative. The scalar, tensor and non-gaussianity of the curvature perturbation spectrum are used to derive a set of reconstruction equations whose solution set can specify up to three of the undetermined functions. The method is then used to find the undetermined functions in various types of actions assuming power law type scalar and tensor spectra. In actions that contain only two unknown functions, the third reconstruction equation implies a consistency relation between the non-gaussianty, sound speed and slow roll parameters. In particular we focus on reconstructing a generalized DBI action with an unknown potential and warp factor. We find that for realistic scalar and tensor spectra, the reconstructed warp factor and potential are very similar to the theoretically derived result. Furthermore, physical consistency of the reconstructed warp factor and potential imposes strict constraints on the scalar and tensor spectral indices.Comment: 33 pages, 3 figures: v3 - References adde
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