328 research outputs found
Precision Electroweak Observables in the Minimal Moose Little Higgs Model
Little Higgs theories, in which the Higgs particle is realized as the
pseudo-Goldstone boson of an approximate global chiral symmetry have generated
much interest as possible alternatives to weak scale supersymmetry. In this
paper we analyze precision electroweak observables in the Minimal Moose model
and find that in order to be consistent with current experimental bounds, the
gauge structure of this theory needs to be modified. We then look for viable
regions of parameter space in the modified theory by calculating the various
contributions to the S and T parameters.Comment: v2: 17 pages, 9 figures. Typeset in JHEP style. Added a references
and two figures showing parameter space for each of two reference points.
Corrected typo
On the Initial Conditions for Brane Inflation
String theory gives rise to various mechanisms to generate primordial
inflation, of which ``brane inflation'' is one of the most widely considered.
In this scenario, inflation takes place while two branes are approaching each
other, and the modulus field representing the separation between the branes
plays the role of the inflaton field. We study the phase space of initial
conditions which can lead to a sufficiently long period of cosmological
inflation, and find that taking into account the possibility of nonvanishing
initial momentum can significantly change the degree of fine tuning of the
required initial conditions.Comment: 11 pages, 2 figure
Sub-wavelength lithography over extended areas
We demonstrate a systematic approach to sub-wavelength resolution
lithographic image formation on films covering areas larger than a wavelength
squared. For example, it is possible to make a lithographic pattern with a
feature size resolution of by using a particular -photon, multi-mode entangled state, where , and banks of birefringent
plates. By preparing a statistically mixed such a state one can form any pixel
pattern on a pixel grid occupying a square
with a side of wavelengths. Hence, there is a trade-off between
the exposed area, the minimum lithographic feature size resolution, and the
number of photons used for the exposure. We also show that the proposed method
will work even under non-ideal conditions, albeit with somewhat poorer
performance.Comment: 8 pages, 8 figures, 1 table. Written in RevTe
Primeval Corrections to the CMB Anisotropies
We show that deviations of the quantum state of the inflaton from the thermal
vacuum of inflation may leave an imprint in the CMB anisotropies. The quantum
dynamics of the inflaton in such a state produces corrections to the
inflationary fluctuations, which may be observable. Because these effects
originate from IR physics below the Planck scale, they will dominate over any
trans-Planckian imprints in any theory which obeys decoupling. Inflation sweeps
away these initial deviations and forces its quantum state closer to the
thermal vacuum. We view this as the quantum version of the cosmic no-hair
theorem. Such imprints in the CMB may be a useful, independent test of the
duration of inflation, or of significant features in the inflaton potential
about 60 e-folds before inflation ended, instead of an unlikely discovery of
the signatures of quantum gravity. The absence of any such substructure would
suggest that inflation lasted uninterrupted much longer than
e-folds.Comment: 17 pages, latex, no figures; v3: added references and comments, final
version to appear in Phys. Rev.
A Two-Field Quintessence Model
We study the dynamics of a quintessence model based on two interacting scalar
fields. The model can account for the (recent) accelerated expansion of the
Universe suggested by astronomical observations. Acceleration can be permanent
or temporary and, for both scenarios, it is possible to obtain suitable values
for the cosmological parameters while satisfying the nucleosynthesis constraint
on the quintessence energy density. We argue that the model dynamics can be
made consistent with a stable zero-energy relaxing supersymmetric vacuum.Comment: 4 pages, 3 eps figures, to be published in Phys. Rev.
A Brane World Perspective on the Cosmological Constant and the Hierarchy Problems
We elaborate on the recently proposed static brane world scenario, where the
effective 4-D cosmological constant is exponentially small when parallel
3-branes are far apart. We extend this result to a compactified model with two
positive tension branes. Besides an exponentially small effective 4-D
cosmological constant, this model incorporates a Randall-Sundrum-like solution
to the hierarchy problem. Furthermore, the exponential factors for the
hierarchy problem and the cosmological constant problem obey an inequality that
is satisfied in nature. This inequality implies that the cosmological constant
problem can be explained if the hierarchy problem is understood. The basic idea
generalizes to the multibrane world scenario. We discuss models with piecewise
adjustable bulk cosmological constants (to be determined by the 5-dimensional
Einstein equation), a key element of the scenario. We also discuss the global
structure of this scenario and clarify the physical properties of the particle
(Rindler) horizons that are present. Finally, we derive a 4-D effective theory
in which all observers on all branes not separated by particle horizons measure
the same Newton's constant and 4-D cosmological constant.Comment: revtex, 63 pages, 8 figures, one table, revised version, more
discussions on the global structure, references adde
Popularity markers on YouTube’s attention economy: the case of Bubzbeauty
This article focuses on issues of attention and popularity development in YouTube’s beauty community. I conceptualise the role of views and subscriptions as popularity markers, based on a broader ethnographic examination of 22 months of immersed fieldwork on the platform. I consider the case of Bubz, a British-Chinese beauty guru, through a purposeful sample of 80 videos. A content typology is introduced, presenting four distinctive video categories: content-oriented, market-oriented, motivational, and relational. Drawing from the concepts of ‘attention economy’ and ‘metrics of popularity’, I explore content characteristics and affordances for the creation and maintenance of viewers’ attention. I argue that the guru’s uploads lead to two types of audiences–casual viewers and loyal subscribers. Vlogs renew attention and help maintain the interest first generated by tutorials, leading to treasured subscribers–an essential commodity within YouTube’s highly competitive environment
Constraining Strong Baryon-Dark Matter Interactions with Primordial Nucleosynthesis and Cosmic Rays
Self-interacting dark matter (SIDM) was introduced by Spergel & Steinhardt to
address possible discrepancies between collisionless dark matter simulations
and observations on scales of less than 1 Mpc. We examine the case in which
dark matter particles not only have strong self-interactions but also have
strong interactions with baryons. The presence of such interactions will have
direct implications for nuclear and particle astrophysics. Among these are a
change in the predicted abundances from big bang nucleosynthesis (BBN) and the
flux of gamma-rays produced by the decay of neutral pions which originate in
collisions between dark matter and Galactic cosmic rays (CR). From these
effects we constrain the strength of the baryon--dark matter interactions
through the ratio of baryon - dark matter interaction cross section to dark
matter mass, . We find that BBN places a weak upper limit to this ratio . CR-SIDM interactions, however, limit the possible DM-baryon cross
section to ; this rules out an energy-independent
interaction, but not one which falls with center-of-mass velocity as or steeper.Comment: 17 pages, 2 figures; plain LaTeX. To appear in PR
Why start a higher degree by research? An exploratory factor analysis of motivations to undertake doctoral studies
Despite the increasing numbers of candidates embarking on higher degrees by research (HDRs, e.g., PhD, professional doctorate, practice-based doctorate), we still have limited knowledge about why they are choosing this path. What are the factors that motivate students to embark on research degrees? Given that many of those who succeed in completing their doctorates will not go into academic positions, the motivations for choosing to undertake a research degree may not match the experience or outcomes (and hence, perhaps, contribute to incompletion rates). This article investigates the motivations of students in all faculties embarking on HDRs at an Australian university. A survey of 405 students was subjected to a factor analysis. Five factors emerged: family and friends, intrinsic motivation, lecturer influence, research experience, and career progression.Cally Guerin, Asangi Jayatilaka, Damith Ranasing
Knockdown of zebrafish Nav1.6 sodium channel impairs embryonic locomotor activities
[[abstract]]Although multiple subtypes of sodium channels are expressed in most neurons, the specific contributions of the individual sodium channels remain to be studied. The role of zebrafish Nav1.6 sodium channels in the embryonic locomotor movements has been investigated by the antisense morpholino (MO) knockdown. MO1 and MO2 are targeted at the regions surrounding the translation start site of zebrafish Nav1.6 mRNA. MO3 is targeted at the RNA splicing donor site of exon 2. The correctly spliced Nav1.6 mRNA of MO3 morphants is 6% relative to that of the wild-type embryos. Nav1.6-targeted MO1, MO2 and MO3 attenuate the spontaneous contraction, tactile sensitivity, and swimming in comparison with a scrambled morpholino and mutated MO3 morpholino. No significant defect is observed in the development of slow muscles, the axonal projection of primary motoneurons, and neuromuscular junctions. The movement impairments caused by MO1, MO2, and MO3 suggest that the function of Nav1.6 sodium channels is essential on the normal early embryonic locomotor activities.[[notice]]補正完畢[[journaltype]]國
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