8,704 research outputs found
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
The Early Promise of TBRI Implementation in Schools
The program known as Trust Based Relational InterventionĀ® (TBRIĀ®) began as an exploration into the detrimental behaviors of foster and adopted children placed in homes with unsuspecting caregivers who assumed their living environment would result in positive results rather than fear based emotions and behaviors. The researchers at the Karyn Purvis Institute of Child Development (KPICD) at Texas Christian University held summer camps for adopted children and through that work developed an intervention to meet the needs of children who had experienced trauma. KPICD identifies these young people as āchildren from hard placesā (Purvis & Cross, 2005). Copeland et al (2007) reported that an estimated 68% of children in the United States have experienced some sort of trauma. This astounding statistic holds great meaning for teachers and administrators, because these children from hard places routinely manifest aggressive and undesired behaviors due to an altering of their physiology. The literature on TBRIĀ® at this point mostly has chronicled success with families, group homes and summer camps (McKenzie, Purvis, & Cross, 2014; Howard, Parris, Neilson, Lusk, Bush, Purvis & Cross, 2014; Purvis & Cross, 2006). TBRIĀ® has only recently been implemented in school settings. This report provides an overview of the impacts of trauma, trauma related work in schools, and the four articles published to this point related to the use of TBRIĀ® in schools
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