2,317 research outputs found
Solvable model of a self-gravitating system
We introduce and discuss an effective model of a self-gravitating system
whose equilibrium thermodynamics can be solved in both the microcanonical and
the canonical ensemble, up to a maximization with respect to a single variable.
Such a model can be derived from a model of self-gravitating particles confined
on a ring, referred to as the self-gravitating ring (SGR) model, allowing a
quantitative comparison between the thermodynamics of the two models. Despite
the rather crude approximations involved in its derivation, the effective model
compares quite well with the SGR model. Moreover, we discuss the relation
between the effective model presented here and another model introduced by
Thirring forty years ago. The two models are very similar and can be considered
as examples of a class of minimal models of self-gravitating systems.Comment: 21 pages, 6 figures; submitted to JSTAT for the special issue on
long-range interaction
First order thermal phase transition with 126 GeV Higgs mass
We study the strength of the electroweak phase transition in models with two
light Higgs doublets and a light SU(3)_c triplet by means of lattice
simulations in a dimensionally reduced effective theory. In the parameter
region considered the transition on the lattice is significantly stronger than
indicated by a 2-loop perturbative analysis. Within some ultraviolet
uncertainties, the finding applies to MSSM with a Higgs mass m_h approximately
126 GeV and shows that the parameter region useful for electroweak baryogenesis
is enlarged. In particular (even though only dedicated analyses can quantify
the issue), the tension between LHC constraints after the 7 TeV and 8 TeV runs
and frameworks where the electroweak phase transition is driven by light stops,
seems to be relaxed.Comment: Presented at 31st International Symposium on Lattice Field Theory -
LATTICE 201
Innovation, specialization and growth in a model of structural change
The aim of this paper is to investigate the nexus between demand patterns and innovation as it stems from research efforts and the extent of specialization. In the proposed model an innovation race conducted by entrants investing in research and development against established incumbents raises productivity at the industry level and leads to a shift in the aggregate demand pattern and consequently to a redistribution of the profit fund among industries and a restructuring of the production process in each industry. The paper argues that the degree of development as reflected in a demand share distribution is characterized by a corresponding distribution of specialized sectors that becomes more even across industries as the development process proceeds and investigates the consequences in terms of economic growth.
An Examination of the Spectral Variability in NGC 1365 with Suzaku
We present jointly analyzed data from three deep Suzaku observations of NGC
1365. These high signal-to-noise spectra enable us to examine the nature of
this variable, obscured AGN in unprecedented detail on timescales ranging from
hours to years. We find that, in addition to the power-law continuum and
absorption from ionized gas seen in most AGN, inner disk reflection and
variable absorption from neutral gas within the Broad Emission Line Region are
both necessary components in all three observations. We confirm the clumpy
nature of the cold absorbing gas, though we note that occultations of the inner
disk and corona are much more pronounced in the high-flux state (2008) than in
the low-flux state (2010) of the source. The onset and duration of the "dips"
in the X-ray light curve in 2010 are both significantly longer than in 2008,
however, indicating that either the distance to the gas from the black hole is
larger, or that the nature of the gas has changed between epochs. We also note
significant variations in the power-law flux over timescales similar to the
cold absorber, both within and between the three observations. The warm
absorber does not vary significantly within observations, but does show
variations in column density of a factor of more than 10 on timescales less
than 2 weeks that seem unrelated to the changes in the continuum, reflection or
cold absorber. By assuming a uniform iron abundance for the reflection and
absorption, we have also established that an iron abundance of roughly 3.5
times the solar value is sufficient to model the broad-band spectrum without
invoking an additional partial-covering absorber. Such a measurement is
consistent with previous published constraints from the 2008 Suzaku observation
alone, and with results from other Seyfert AGN in the literature.Comment: 19 pages, 11 figures, accepted for publication in MNRA
- ā¦