15,361 research outputs found
Clues to the nature of dark matter from first galaxies
We use thirty-eight high-resolution simulations of galaxy formation between
redshift 10 and 5 to study the impact of a 3 keV warm dark matter (WDM)
candidate on the high-redshift Universe. We focus our attention on the stellar
mass function and the global star formation rate and consider the consequences
for reionization, namely the neutral hydrogen fraction evolution and the
electron scattering optical depth. We find that three different effects
contribute to differentiate warm and cold dark matter (CDM) predictions: WDM
suppresses the number of haloes with mass less than few M; at
a fixed halo mass, WDM produces fewer stars than CDM; and finally at halo
masses below M, WDM has a larger fraction of dark haloes than
CDM post-reionization. These three effects combine to produce a lower stellar
mass function in WDM for galaxies with stellar masses at and below
M. For , the global star formation density is lower by a
factor of two in the WDM scenario, and for a fixed escape fraction, the
fraction of neutral hydrogen is higher by 0.3 at . This latter
quantity can be partially reconciled with CDM and observations only by
increasing the escape fraction from 23 per cent to 34 per cent. Overall, our
study shows that galaxy formation simulations at high redshift are a key tool
to differentiate between dark matter candidates given a model for baryonic
physics.Comment: 11 pages, 8 figures, submitted to MNRA
Radiation-induced nucleic acid synthesis in L cells under energy deprivation
Radiation induced nucleic acid synthesis in energy deprived L cell
Swimming in curved space or The Baron and the cat
We study the swimming of non-relativistic deformable bodies in (empty) static
curved spaces. We focus on the case where the ambient geometry allows for rigid
body motions. In this case the swimming equations turn out to be geometric. For
a small swimmer, the swimming distance in one stroke is determined by the
Riemann curvature times certain moments of the swimmer.Comment: 19 pages 6 figure
Asymmetric Non-Abelian Orbifolds and Model Building
The rules for the free fermionic string model construction are extended to
include general non-abelian orbifold constructions that go beyond the real
fermionic approach. This generalization is also applied to the asymmetric
orbifold rules recently introduced. These non-abelian orbifold rules are quite
easy to use. Examples are given to illustrate their applications.Comment: 30 pages, Revtex 3.
Localized Tachyons and the g_cl conjecture
We consider C/Z_N and C^2/Z_N orbifolds of heterotic string theories and Z_N
orbifolds of AdS_3. We study theories with N=2 worldsheet superconformal
invariance and construct RG flows. Following Harvey, Kutasov, Martinec and
Moore, we compute g_cl and show that it decreases monotonically along RG flows-
as conjectured by them. For the heterotic string theories, the gauge degrees of
freedom do not contribute to the computation of g_cl.Comment: Corrections and clarifications made, 19 page
Twistfield Perturbations of Vertex Operators in the Z_2-Orbifold Model
We apply Kadanoff's theory of marginal deformations of conformal field
theories to twistfield deformations of Z_2 orbifold models in K3 moduli space.
These deformations lead away from the Z_2 orbifold sub-moduli-space and hence
help to explore conformal field theories which have not yet been understood. In
particular, we calculate the deformation of the conformal dimensions of vertex
operators for p^2<1 in second order perturbation theory.Comment: Latex2e, 19 pages, 1 figur
A path unenvisaged to a destination unintended: A collaborative autoethnographic account of becoming a community of practice in an HEI
In this paper we explore how a disparate group of predominately foundation phase teacher educators unintentionally, over a period of time, came together to form a strong community of practice (CoP). Voluntary involvement in a research project positioned this group of lecturers in unaccustomed roles and necessitated that they engage with each other in a variety of ways to meet project outcomes. New relationships developed as people took on different roles and new responsibilities emerged as the group faced challenges. As this was a subjective interrogation of our experiences, a research method such as autoethnography where we could focus on the experience and processes of becoming a CoP, rather than the outcomes of the research itself, seemed appropriate. We outline our understandings of a CoP and show how, through a critical self-reflective process, we were able to strengthen both our teaching and research practices in a Higher Education Institution (HEI). The strengthening occurred, in part, due to the formation and development of this CoP
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