1,931 research outputs found
Unstable fields in Kerr spacetimes
We show that both the interior region of a Kerr black
hole and the Kerr naked singularity admit unstable solutions of the
Teukolsky equation for any value of the spin weight. For every harmonic number
there is at least one axially symmetric mode that grows exponentially in time
and decays properly in the radial directions. These can be used as Debye
potentials to generate solutions for the scalar, Weyl spinor, Maxwell and
linearized gravity field equations on these backgrounds, satisfying appropriate
spatial boundary conditions and growing exponentially in time, as shown in
detail for the Maxwell case. It is suggested that the existence of the unstable
modes is related to the so called "time machine" region, where the axial
Killing vector field is time-like, and the Teukolsky equation, restricted to
axially symmetric fields, changes its character from hyperbolic to elliptic
The initial value problem for linearized gravitational perturbations of the Schwarzschild naked singularity
The coupled equations for the scalar modes of the linearized Einstein
equations around Schwarzschild's spacetime were reduced by Zerilli to a 1+1
wave equation with a potential , on a field . For smooth metric
perturbations is singular at , the
mode harmonic number, and has a second order pole at . This is
irrelevant to the black hole exterior stability problem, where , and
, but it introduces a non trivial problem in the naked singular case
where , and the singularity appears in the relevant range of
. We solve this problem by developing a new approach to the evolution of the
even mode, based on a {\em new gauge invariant function}, -related
to by an intertwiner operator- that is a regular function of the
metric perturbation {\em for any value of }. This allows to address the
issue of evolution of gravitational perturbations in this non globally
hyperbolic background, and to complete the proof of the linear instability of
the Schwarzschild naked singularity, by showing that a previously found
unstable mode is excitable by generic initial data. This is further illustrated
by numerically solving the linearized equations for suitably chosen initial
data.Comment: typos corrected, references adde
The economic crisis and changes in work-family arrangements in six European countries
Over the past decades, there has been a substantial increase in female labour force participation, and the
number of dual-earner and female-earner households has risen throughout western countries. However,
the recent economic crisis has caused large losses in employment for both women and men, potentially
yielding unexpected consequences for the evolution of work\u2013family arrangements. This article carries
out a comparative analysis of the relationship between the 2008/2009 economic crisis and work\u2013family
arrangements in Europe. Using data for six countries from the European Union Statistics on Income and
Living Conditions, this article fills a gap in the literature by addressing three issues: (1) whether work\u2013family
arrangements have changed from before to after the beginning of the economic downturn in countries with
different gender and welfare regimes (Germany, Greece, Spain, France, Sweden and the United Kingdom),
(2) whether changes in work\u2013family arrangements have occurred at different levels of the social strata and
(3) whether couples have moved from dual-earner to male- or female-breadwinner. The results indicate
changes in work\u2013family arrangements in those countries worst hit by the economic crisis, Greece and
Spain, where dual-earner and male-breadwinner households have decreased and no-earner and femalemain-
earner households have increased. Moreover, the results show that in these two countries, all social
strata \u2013 proxied through women\u2019s level of education \u2013 have been affected by the crisis. In contrast, only
moderate changes in work\u2013family arrangements among all women can be observed in countries less hit
by the economic downturn. The findings for the two southern European countries are troubling, as the
increases in no-earner and female-breadwinner households point to worsening economic conditions
throughout the population and to a halt in the process that for several decades had been leading to more
equality in the distribution of employment between gender
The Best Is Yet to Come? Attitudes towards gender roles among adolescents in 36 countries
In the present article, we look at attitudes toward
gender roles among young women and men in 36 countries
with different levels of societal gender inequality. By applying
multilevel models to data from the International Civic and
Citizenship Education Study 2009, the study contributes to
our understanding of gender inequality by showing that (a)
both young women and young men (in 8th grade;
Mage = 14.39 years) display more gender-egalitarian attitudes
in countries with higher levels of societal gender equality; (b)
young women in all countries have more egalitarian attitudes
toward gender roles than young men do, but (c) the gender gap
in attitudes is more evident in more egalitarian contexts; and
(d) a higher level of maternal education is associated with
more gender-egalitarian attitudes among young women. In
contrast, no statistically significant association emerges between
maternal employment and young men\u2019s attitudes.
Overall, the findings suggest that adolescents in different contexts
are influenced by the dominant societal discourse on
gender inequality, which they interiorize and display through
their own attitudes toward gender roles. However, the findings
also indicate that young women are more responsive to external
cues than young men are. This result, coupled with the fact
that young men in egalitarian contexts have not adopted
gender-egalitarian attitudes to the same extent as young women,
is concerning because it suggests a slowdown in the
achievement of societal gender equality that is still far from
being reache
Vacuum solutions with nontrivial boundaries for the Einstein-Gauss-Bonnet theory
The classification of certain class of static solutions for the
Einstein-Gauss-Bonnet theory in vacuum is presented. The spacelike section of
the class of metrics under consideration is a warped product of the real line
with a nontrivial base manifold. For arbitrary values of the Gauss-Bonnet
coupling, the base manifold must be Einstein with an additional scalar
restriction. The geometry of the boundary can be relaxed only when the
Gauss-Bonnet coupling is related with the cosmological and Newton constants, so
that the theory admits a unique maximally symmetric solution. This additional
freedom in the boundary metric allows the existence of three main branches of
geometries in the bulk, containing new black holes and wormholes in vacuum.Comment: Prepared for the proceedings of the 7th Alexander Friedmann
International Seminar on Gravitation and Cosmology, July 2008, Joao Pessoa,
Brasil. 4 pages, References adde
The Relationship Between the Civic Engagement of Parents and Children : a Cross-National Analysis of 18 European Countries
Although previous research has suggested the existence of a positive association
between the political activities of parents and children, little is known about
other forms of civic engagement. In particular, the literature lacks an international
comparative study on the intergenerational transmission of civic involvement. Using
Bayesian multilevel models on data from the European Union Statistics on Income
and Living Conditions (EU-SILC) 2006 special module on social participation, this
article tests hypotheses on the patterns of civic engagement of parents and children
in 18 European countries with different political legacies. Our results show a positive
association between the participation in associational activities of parents and
children in all the considered countries, above and beyond individual and contextual
characteristics. In particular, we do not find an evident East\u2013West gap in the
socialization process, suggesting that the Communist past of Eastern and Central
European countries has little influence on what can be considered a basic mechanism
of civic learning
- …