52 research outputs found
Thermal production of axino Dark Matter
We reconsider thermal production of axinos in the early universe, adding: a)
missed terms in the axino interaction; b) production via gluon decays
kinematically allowed by thermal masses; c) a precise modeling of reheating. We
find an axino abunance a few times larger than previous computations.Comment: 6 pages, 2 figures. Final version, to appear on JHE
Goldstone Fermion Dark Matter
We propose that the fermionic superpartner of a weak-scale Goldstone boson
can be a natural WIMP candidate. The p-wave annihilation of this `Goldstone
fermion' into pairs of Goldstone bosons automatically generates the correct
relic abundance, whereas the XENON100 direct detection bounds are evaded due to
suppressed couplings to the Standard Model. Further, it is able to avoid
indirect detection constraints because the relevant s-wave annihilations are
small. The interactions of the Goldstone supermultiplet can induce non-standard
Higgs decays and novel collider phenomenology.Comment: 25 pages, 6 figures. References added, minor typos corrected.
Submitted to JHE
B-L Cosmic Strings in Heterotic Standard Models
E_{8} X E_{8} heterotic string and M-theory, when compactified on smooth
Calabi-Yau manifolds with SU(4) vector bundles, can give rise to softly broken
N=1 supersymmetric theories with the exact matter spectrum of the MSSM,
including three right-handed neutrinos and one Higgs-Higgs conjugate pair of
supermultiplets. These vacua have the SU(3)_{C} X SU(2)_{L} X U(1)_{Y} gauge
group of the standard model augmented by an additional gauged U(1)_{B-L}. Their
minimal content requires that the B-L symmetry be spontaneously broken by a
vacuum expectation value of at least one right-handed sneutrino. The soft
supersymmetry breaking operators can induce radiative breaking of the B-L gauge
symmetry with an acceptable B-L/electroweak hierarchy. In this paper, it is
shown that U(1)_{B-L} cosmic strings occur in this context, potentially with
both bosonic and fermionic superconductivity. We present a numerical analysis
that demonstrates that boson condensates can, in principle, form for theories
of this type. However, the weak Yukawa and gauge couplings of the right-handed
sneutrino suggests that bosonic superconductivity will not occur in the
simplest vacua in this context. The electroweak phase transition also disallows
fermion superconductivity, although substantial bound state fermion currents
can exist.Comment: 41 pages, 5 figure
Radiative contribution to neutrino masses and mixing in SSM
In an extension of the minimal supersymmetric standard model (popularly known
as the SSM), three right handed neutrino superfields are introduced to
solve the -problem and to accommodate the non-vanishing neutrino masses
and mixing. Neutrino masses at the tree level are generated through parity
violation and seesaw mechanism. We have analyzed the full effect of one-loop
contributions to the neutrino mass matrix. We show that the current three
flavour global neutrino data can be accommodated in the SSM, for both
the tree level and one-loop corrected analyses. We find that it is relatively
easier to accommodate the normal hierarchical mass pattern compared to the
inverted hierarchical or quasi-degenerate case, when one-loop corrections are
included.Comment: 51 pages, 14 figures (58 .eps files), expanded introduction, other
minor changes, references adde
Axino Cold Dark Matter Revisited
Axino arises in supersymmetric versions of axion models and is a natural
candidate for cold or warm dark matter. Here we revisit axino dark matter
produced thermally and non-thermally in light of recent developments. First we
discuss the definition of axino relative to low energy axion one for several
KSVZ and DFSZ models of the axion. Then we review and refine the computation of
the dominant QCD production in order to avoid unphysical cross-sections and,
depending on the model, to include production via SU(2) and U(1) interactions
and Yukawa couplings.Comment: 30 pages, 10 figures, version accepted by JHE
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
Recommended from our members
Phylogeographical analysis of the dominant multidrug-resistant H58 clade of Salmonella Typhi identifies inter-and intracontinental transmission events
Minimal Flavour Violation and Neutrino Masses without R-parity
We study the extension of the Minimal Flavour Violation (MFV) hypothesis to
the MSSM without R-parity. The novelty of our approach lies in the observation
that supersymmetry enhances the global symmetry of the kinetic term and in the
fact that we consider as irreducible sources of the flavour symmetry breaking
all the couplings of the superpotential including the R-parity violating ones.
If R-parity violation is responsible for neutrino masses, our setup can be seen
as an extension of MFV to the lepton sector. We analyze two patterns based on
the non-abelian flavour symmetries SU(3)^4 \otimes SU(4) and SU(3)^5. In the
former case the total lepton number and the lepton flavour number are broken
together, while in the latter the lepton number can be broken independently by
an abelian spurion, so that visible effects and peculiar correlations can be
envisaged in flavour changing charged lepton decays like \ell_i \rightarrow
\ell_j \gamma.Comment: 23 pages, 3 figures. References added. Minor changes, to appear in
JHE
Dilaton dominance relaxes LHC and cosmological constraints in supersymmetric models
It has been pointed out recently that the presence of dilaton field in the
early Universe can dilute the neutralino dark matter (DM) abundance, if
Universe is not radiation dominated at DM decoupling, due to its
dissipative-like coupling to DM. In this scenario two basic mechanisms compete,
the modified Hubble expansion rate tending to increase the relic density and a
dissipative force that tends to decrease it. The net effect can lead to an
overall dramatic decrease of the predicted relic abundance, sometimes by
amounts of the order of O(10^2) or so. This feature is rather generic,
independent of any particular assumption on the underlying string dynamics,
provided dilaton dominates at early eras after the end of inflation but before
Big Bang Nucleosynthesis (BBN). The latter ensures that BBN is not upset by the
presence of the dilaton. In this paper, within the context of such a scenario,
we study the phenomenology of the constrained minimal supersymmetric model
(CMSSM) by taking into account all recent experimental constraints, including
those from the LHC searches. We find that the allowed parameter space is
greatly enlarged and includes regions that are beyond the reach of LHC. The
allowed regions are compatible with Direct Dark Matter searches since the small
neutralino annihilation rates, that are now in accord with the cosmological
data on the relic density, imply small neutralino-nucleon cross sections below
the sensitivities of the Direct Dark Matter experiments. It is also important
that the new cosmologically accepted regions are compatible with Higgs boson
masses larger than 120 GeV, as it is indicated from the LHC experimental data.
The smaller annihilation cross sections needed to explain WMAP data require
that the detector performances of current and planned indirect DM search
experiments through gamma rays should be greatly improved in order to probe the
CMSSM regions.Comment: 20 pages, 10 eps figures. Revised and extended version to appear in
JHEP; a section on gamma rays adde
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