74 research outputs found
Supersymmetric Galileons
Galileon theories are of considerable interest since they allow for stable
violations of the null energy condition. Since such violations could have
occurred during a high-energy regime in the history of our universe, we are
motivated to study supersymmetric extensions of these theories. This is carried
out in this paper, where we construct generic classes of N=1 supersymmetric
Galileon Lagrangians. They are shown to admit non-equivalent stress-energy
tensors and, hence, vacua manifesting differing conditions for violating the
null energy condition. The temporal and spatial fluctuations of all component
fields of the supermultiplet are analyzed and shown to be stable on a large
number of such backgrounds. In the process, we uncover a surprising connection
between conformal Galileon and ghost condensate theories, allowing for a deeper
understanding of both types of theories.Comment: 41 pages, v2: added a referenc
Textual Research on Phenomenon of Lawsuit-Weariness in Ancient China——Take the Contradiction of Lawsuit-Extinguishing and Lawsuit-Elation as an Entry Point
任何一个文明社会,都会有争财之事,都会有纠纷和诉讼,我们对此并不觉得奇怪,使我们感兴趣的是人们对于这类现象所持的态度。大多数论及传统中国法律意识的经典著作,都倾向于认为传统中国民众持有一种厌讼观,并用这个理论来解释传统中国乡民很少或几乎不去衙门打官司这个现象。但是,两宋已降史籍中关于当时民众好讼、健讼的风气的记载颇多。这说明官方的息讼立场与当时民众的健讼的实践是存在矛盾的。鉴于此,本文把目光紧紧锁定在“息讼与健讼”这一角度,来对传统中国厌讼现象进行考辨。本文除引言和结语外,正文部分共分四章。 第一章将介绍关于传统中国厌讼的理论及本文的进路。传统中国厌讼论是目前关于传统中国民众诉讼观念研究的通...We don't always feel surprised to recognize the fact that most civilizations would unavoidable to have disputes. The only thing which interested us is people’s special attitude towards this phenomenon. Most classic works about Chinese traditional law consciousness point out that traditional Chinese people held a view of lawsuit-weariness and this is the very reason why they seldom resorted to laws...学位:法学硕士院系专业:法学院法律系_法学理论学号:1362008115063
A smooth bouncing cosmology with scale invariant spectrum
We present a bouncing cosmology which evolves from the contracting to the
expanding phase in a smooth way, without developing instabilities or
pathologies and remaining in the regime of validity of 4d effective field
theory. A nearly scale invariant spectrum of perturbations is generated during
the contracting phase by an isocurvature scalar with a negative exponential
potential and then converted to adiabatic. The model predicts a slightly blue
spectrum, n_S >~ 1, no observable gravitational waves and a high (but model
dependent) level of non-Gaussianities with local shape. The model represents an
explicit and predictive alternative to inflation, although, at present, it is
clearly less compelling.Comment: 20 pages, 1 fig. v2: references added, JCAP published versio
Ekpyrotic collapse with multiple fields
A scale invariant spectrum of isocurvature perturbations is generated during
collapse in the scaling solution in models where two or more fields have steep
negative exponential potentials. The scale invariance of the spectrum is
realised by a tachyonic instability in the isocurvature field. We show that
this instability is due to the fact that the scaling solution is a saddle point
in the phase space. The late time attractor is identified with a single field
dominated ekpyrotic collapse in which a steep blue spectrum for isocurvature
perturbations is found. Although quantum fluctuations do not necessarily to
disrupt the classical solution, an additional preceding stage is required to
establish classical homogeneity.Comment: 13 pages, 1 figur
Ectoplasm with an Edge
The construction of supersymmetric invariant actions on a spacetime manifold
with a boundary is carried out using the "ectoplasm" formalism for the
construction of closed forms in superspace. Non-trivial actions are obtained
from the pull-backs to the bosonic bodies of closed but non-exact forms in
superspace; finding supersymmetric invariants thus becomes a cohomology
problem. For a spacetime with a boundary, the appropriate mathematical language
changes to relative cohomology, which we use to give a general formulation of
off-shell supersymmetric invariants in the presence of boundaries. We also
relate this construction to the superembedding formalism for the construction
of brane actions, and we give examples with bulk spacetimes of dimension 3, 4
and 5. The closed superform in the 5D example needs to be constructed as a
Chern-Simons type of invariant, obtained from a closed 6-form displaying Weil
triviality.Comment: 25 page
Curvature perturbations from ekpyrotic collapse with multiple fields
A scale-invariant spectrum of isocurvature perturbations is generated during
collapse in the ekpyrotic scaling solution in models where multiple fields have
steep negative exponential potentials. The scale invariance of the spectrum is
realized by a tachyonic instability in the isocurvature field. This instability
drives the scaling solution to the late time attractor that is the old
ekpyrotic collapse dominated by a single field. We show that the transition
from the scaling solution to the single field dominated ekpyrotic collapse
automatically converts the initial isocurvature perturbations about the scaling
solution to comoving curvature perturbations about the late-time attractor. The
final amplitude of the comoving curvature perturbation is determined by the
Hubble scale at the transition.Comment: 15 pages, 3 figures, a reference added, to be published in CQG, a
remark on the comoving density perturbation correcte
Cosmic Bounces and Cyclic Universes
Cosmological models involving a bounce from a contracting to an expanding
universe can address the standard cosmological puzzles and generate
"primordial" density perturbations without the need for inflation. Some such
models, in particular the ekpyrotic and cyclic models that we focus on, fit
rather naturally into string theory. We discuss a number of topics related to
these models: the reasoning that leads to the ekpyrotic phase, the predictions
for upcoming observations, the differences between singular and non-singular
models of the bounce as well as the predictive and explanatory power offered by
these models.Comment: 28 pages. Contribution to the CQG focus issue on String Cosmolog
Scale-invariance in expanding and contracting universes from two-field models
We study cosmological perturbations produced by the most general
two-derivative actions involving two scalar fields, coupled to Einstein
gravity, with an arbitrary field space metric, that admit scaling solutions.
For contracting universes, we show that scale-invariant adiabatic perturbations
can be produced continuously as modes leave the horizon for any equation of
state parameter . The corresponding background solutions are unstable,
which we argue is a universal feature of contracting models that yield
scale-invariant spectra. For expanding universes, we find that nearly
scale-invariant adiabatic perturbation spectra can only be produced for , and that the corresponding scaling solutions are attractors. The
presence of a nontrivial metric on field space is a crucial ingredient in our
results.Comment: 23 pages, oversight in perturbations calculation corrected,
conclusions for expanding models modifie
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