36,378 research outputs found
The Inert Doublet Model : a new archetype of WIMP dark matter?
The Inert Doublet Model (IDM) is a two doublet extension of the
Higgs-Brout-Englert sector of the Standard Model with a Z_2 symmetry in order
to prevent FCNC. If the Z_2 symmetry is not spontaneously broken, the lightest
neutral extra scalar is a dark matter candidate. We briefly review the
phenomenology of the model, emphasizing its relevance for the issue of
Electroweak Symmetry Breaking (EWSB) and the prospects for detection of dark
matter.Comment: Contribution the 10th International Conference on Topics in
Astroparticle and Underground Physics (TAUP 2007), Sendai, Japan, 11-15 Sep
200
Relating leptogenesis and dark matter
A scenario that relates the abundance of dark matter to the baryon asymmetry
of the Universe is presented. In this scenario, based on a left-right extension
of the Standard Model, dark matter is made of light, ~ 1 GeV, right-handed
Majorana neutrinos.Comment: 4 pages, 1 figure, to appear in the proceedings of 40th Rencontres de
Moriond, Electroweak Interactions and Unified Theories, March 11 - 18, 200
Reproductive Management of Dairy Cows with Particular Reference to Organic Systems
Reproductive efficiency is a major factor affecting production and economic efficiency indairy herds. In seasonally calving herds the requirement of good reproductive performance is of greater importance than in other production systems in order to maximally exploit the use of grazed grass in the diet of the cow. Reproductive
performance of lactating dairy cows worldwide has declined over the past 30 years in association with selection for milk yield. There is increasing and consistent evidence to
suggest that at least some part of the decline in cow reproductive performance is related to underlying changes in reproductive physiology caused by high milk production and or negative energy balance (NEB) in early lactation. Organic systems of milk production demand high tight seasonal calving patterns, maximal production from grazed grass, low involuntary culling rates and the continuous genetic improvement of the herd for commercially important traits. Organic milk production systems should also allow for replacement rates of 25% - 30% to ensure a young herd age structure and low somatic cell counts (SCC). The objective of this paper is to review the role of management factors in herd reproductive performance with particular reference to organic herds
Effective field theory approach to N=4 supersymmetric Yang-Mills at finite temperature
We study the perturbation expansion of the free energy of N=4 supersymmetric
SU(N) Yang-Mills at finite temperature in powers of 't Hooft's coupling g^2 N
in the large N limit. Infrared divergences are controlled by constructing a
hierarchy of two 3 dimensional effective field theories. This procedure is
applied to the calculation of the free energy to order (g^2 N)^(3/2), but it
can be extended to higher order corrections.Comment: LaTeX, 10 pages, 1 figure, uses eps
Constraints on Light WIMP candidates from the Isotropic Diffuse Gamma-Ray Emission
Motivated by the measurements reported by direct detection experiments, most
notably DAMA, CDMS-II, CoGeNT and Xenon10/100, we study further the constraints
that might be set on some light dark matter candidates, M_DM ~ few GeV, using
the Fermi-LAT data on the isotropic gamma-ray diffuse emission. In particular,
we consider a Dirac fermion singlet interacting through a new Z' gauge boson,
and a scalar singlet S interacting through the Higgs portal. Both candidates
are WIMP (Weakly Interacting Massive Particles), i.e. they have an annihilation
cross-section in the pbarn range. Also they may both have a spin-independent
elastic cross section on nucleons in the range required by direct detection
experiments. Although being generic WIMP candidates, because they have
different interactions with Standard Model particles, their phenomenology
regarding the isotropic diffuse gamma-ray emission is quite distinct. In the
case of the scalar singlet, the one-to-one correspondence between its
annihilation cross-section and its spin-independent elastic scattering
cross-section permits to express the constraints from the Fermi-LAT data in the
direct detection exclusion plot, sigma_n^0--M_DM. Depending on the
astrophysics, we argue that it is possible to exclude the singlet scalar dark
matter candidate at 95 % CL. The constraints on the Dirac singlet interacting
through a Z' are comparatively weaker.Comment: 18 pages, 13 figures, replaced to match with the published versio
Masses of the Goldstone modes in the CFL phase of QCD at finite density
We construct the U_L(3) x U_R(3) effective lagrangian which encodes the
dynamics of the low energy pseudoscalar excitations in the Color-Flavor-Locking
superconducting phase of QCD at finite quark density. We include the effects of
instanton-induced interactions and study the mass pattern of the pseudoscalar
mesons. A tentative comparison with the analytical estimate for the gap
suggests that some of these low energy momentum modes are not stable for
moderate values of the quark chemical potential.Comment: 15 pages, 5 figures; Discussion of quark mass effects at very large
densities amended, references adde
Confined hidden vector dark matter
We argue that the lightest vector bound states of a confining hidden sector
communicating with the Standard Model through the Higgs portal are stable and
are viable candidates of dark matter. The model is based on an SU(2) gauge
group with a scalar field in its fundamental representation and the stability
of the lightest vector bound state results from the existence of a custodial
symmetry. As the relic density depends essentially on the scale of confinement
in the hidden sector, Lambda_HS, agreement with WMAP abundance requires
Lambda_HS in the 20-120 TeV range.Comment: 6 page
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