12,727 research outputs found
From the Big Bang Theory to the Theory of a Stationary Universe
We consider chaotic inflation in the theories with the effective potentials
phi^n and e^{\alpha\phi}. In such theories inflationary domains containing
sufficiently large and homogeneous scalar field \phi permanently produce new
inflationary domains of a similar type. We show that under certain conditions
this process of the self-reproduction of the Universe can be described by a
stationary distribution of probability, which means that the fraction of the
physical volume of the Universe in a state with given properties (with given
values of fields, with a given density of matter, etc.) does not depend on
time, both at the stage of inflation and after it. This represents a strong
deviation of inflationary cosmology from the standard Big Bang paradigm. We
compare our approach with other approaches to quantum cosmology, and illustrate
some of the general conclusions mentioned above with the results of a computer
simulation of stochastic processes in the inflationary Universe.Comment: No changes to the file, but original figures are included. They
substantially help to understand this paper, as well as eternal inflation in
general, and what is now called the "multiverse" and the "string theory
landscape." High quality figures can be found at
http://www.stanford.edu/~alinde/LLMbigfigs
Metastable supersymmetry breaking in N=2 non-linear sigma-models
We perform a general study of the issue of metastability for
supersymmetry-breaking vacua in theories with N=1 and N=2 global supersymmetry.
This problem turns out to capture all the important qualitative features of the
corresponding question in theories with local supersymmetry, where
gravitational effects induce only quantitative modifications. Moreover, it
allows to directly compare the conditions arising in the N=1 and N=2 cases,
since the latter becomes particular case of the former in the rigid limit. Our
strategy consists in a systematic investigation of the danger of instability
coming from the sGoldstini scalars, whose masses are entirely due to
supersymmetry breaking mass-splitting effects. We start by reviewing the
metastability conditions arising in general N=1 non-linear sigma-models with
chiral and vector multiplets. We then turn to the case of general N=2
non-linear sigma-models with hyper and vector multiplets. We first reproduce
and clarify the known no-go theorems applying to theories with only Abelian
vector multiplets and only hyper multiplets, and then derive new results
applying to more general cases. To make the comparison with N=1 models as clear
as possible, we rely on a formulation of N=2 models where one of the
supersymmetries is manifestly realized in terms of ordinary superfields,
whereas the other is realized through non-trivial transformations. We give a
self-contained account of such a construction of N=2 theories in N=1
superspace, generalizing previous work on various aspects to reach a general
and coordinate-covariant construction. We also present a direct computation of
the supertrace of the mass matrix.Comment: 50 pages, no figures; v2 minor corrections and addition of comments
and reference
N=2 supersymmetry breaking at two different scales
We study N=2 spontaneous supersymmetry breaking at two different scales with
matter fields in hypermultiplets charged under the gauge group that should
involve at least two U(1) factors. Off-shell analysis is possible in the dual
single-tensor formulation of the hypermultiplets. Massless fermions can
naturally arise from pseudo-real representations of the gauge group that allow
a reformulation of the problem of chirality in N=2 theories. The above
properties are necessary ingredients towards constructing viable extensions of
the Standard Model based on N=2 supersymmetry.Comment: 26 page
Chromomagnetic Catalysis of Color Superconductivity in a (2+1)-dimensional NJL Model
The influence of a constant uniform external chromomagnetic field on the
formation of color superconductivity has been investigated. The consideration
was performed in the framework of a (2+1)-dimensional Nambu--Jona-Lasinio model
with two different four-fermionic structures responsible for condensates. In particular, it was shown that there exists a
critical value of the external chromomagnetic field such that at
a nonvanishing diquark condensate is dynamically created (the so-called
chromomagnetic catalysis effect of color superconductivity). Moreover, external
chromomagnetic fields may in some cases enhance the diquark condensate of color
superconductivity.Comment: 32 pages, 2 figures, revte
Unit roots in macroeconomic time series: a post Keynesian interpretation
The theme of unit roots in macroeconomic time series has received a great amount of theoretical and applied research in the last two decades. This paper focuses on the implications of the existence of unit roots for macroeconomic theorizing. It is argued that the presence of unit roots in GNP time series provide support to the general perspective adopted by Keynes and post Keynesians on output and employment fluctuations, on the non-neutrality of money in the long run, and on some economic policy issues.time series, unit roots, post Keynesian economics
Effects of heavy modes on vacuum stability in supersymmetric theories
We study the effects induced by heavy fields on the masses of light fields in
supersymmetric theories, under the assumption that the heavy mass scale is much
higher than the supersymmetry breaking scale. We show that the square-masses of
light scalar fields can get two different types of significant corrections when
a heavy multiplet is integrated out. The first is an indirect level-repulsion
effect, which may arise from heavy chiral multiplets and is always negative.
The second is a direct coupling contribution, which may arise from heavy vector
multiplets and can have any sign. We then apply these results to the sGoldstino
mass and study the implications for the vacuum metastability condition. We find
that the correction from heavy chiral multiplets is always negative and tends
to compromise vacuum metastability, whereas the contribution from heavy vector
multiplets is always positive and tends on the contrary to reinforce it. These
two effects are controlled respectively by Yukawa couplings and gauge charges,
which mix one heavy and two light fields respectively in the superpotential and
the Kahler potential. Finally we also comment on similar effects induced in
soft scalar masses when the heavy multiplets couple both to the visible and the
hidden sector.Comment: LaTex, 24 pages, no figures; v2 some comments and references adde
Untenable nonstationarity: An assessment of the fitness for purpose of trend tests in hydrology
The detection and attribution of long-term patterns in hydrological time series have been important research topics for decades. A significant portion of the literature regards such patterns as âdeterministic componentsâ or âtrendsâ even though the complexity of hydrological systems does not allow easy deterministic explanations and attributions. Consequently, trend estimation techniques have been developed to make and justify statements about tendencies in the historical data, which are often used to predict future events. Testing trend hypothesis on observed time series is widespread in the hydro-meteorological literature mainly due to the interest in detecting consequences of human activities on the hydrological cycle. This analysis usually relies on the application of some null hypothesis significance tests (NHSTs) for slowly-varying and/or abrupt changes, such as Mann-Kendall, Pettitt, or similar, to summary statistics of hydrological time series (e.g., annual averages, maxima, minima, etc.). However, the reliability of this application has seldom been explored in detail. This paper discusses misuse, misinterpretation, and logical flaws of NHST for trends in the analysis of hydrological data from three different points of view: historic-logical, semantic-epistemological, and practical. Based on a review of NHST rationale, and basic statistical definitions of stationarity, nonstationarity, and ergodicity, we show that even if the empirical estimation of trends in hydrological time series is always feasible from a numerical point of view, it is uninformative and does not allow the inference of nonstationarity without assuming a priori additional information on the underlying stochastic process, according to deductive reasoning. This prevents the use of trend NHST outcomes to support nonstationary frequency analysis and modeling. We also show that the correlation structures characterizing hydrological time series might easily be underestimated, further compromising the attempt to draw conclusions about trends spanning the period of records. Moreover, even though adjusting procedures accounting for correlation have been developed, some of them are insufficient or are applied only to some tests, while some others are theoretically flawed but still widely applied. In particular, using 250 unimpacted stream flow time series across the conterminous United States (CONUS), we show that the test results can dramatically change if the sequences of annual values are reproduced starting from daily stream flow records, whose larger sizes enable a more reliable assessment of the correlation structures
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