9,513 research outputs found
Supersymmetric Dark Matter Candidates
After reviewing the theoretical, phenomenological and experimental
motivations for supersymmetric extensions of the Standard Model, we recall that
supersymmetric relics from the Big Bang are expected in models that conserve R
parity. We then discuss possible supersymmetric dark matter candidates,
focusing on the lightest neutralino and the gravitino. In the latter case, the
next-to-lightest supersymmetric particle is expected to be long-lived, and
possible candidates include spartners of the tau lepton, top quark and
neutrino. We then discuss the roles of the renormalization-group equations and
electroweak symmetry breaking in delimiting the supersymmetric parameter space.
We discuss in particular the constrained minimal extension of the Standard
Model (CMSSM), in which the supersymmetry-breaking parameters are assumed to be
universal at the grand unification scale, presenting predictions from a
frequentist analysis of its parameter space. We also discuss astrophysical and
cosmological constraints on gravitino dark matter models, as well as the
parameter space of minimal supergravity (mSUGRA) models in which there are
extra relations between the trilinear and bilinear supersymmetry-breaking
parameters, and between the gravitino and scalar masses. Finally, we discuss
models with non-universal supersymmetry-breaking contributions to Higgs masses,
and models in which the supersymmetry-breaking parameters are universal at some
scale below that of grand unification.
http://cambridge.org/us/catalogue/catalogue.asp?isbn=9780521763684Comment: 38 pages, 10 figure
Varying the Universality of Supersymmetry-Breaking Contributions to MSSM Higgs Boson Masses
We consider the minimal supersymmetric extension of the Standard Model (MSSM)
with varying amounts of non-universality in the soft supersymmetry-breaking
contributions to the Higgs scalar masses. In addition to the constrained MSSM
(CMSSM) in which these are universal with the soft supersymmetry-breaking
contributions to the squark and slepton masses at the input GUT scale, we
consider scenarios in which both the Higgs scalar masses are non-universal by
the same amount (NUHM1), and scenarios in which they are independently
non-universal (NUHM2). We show how the NUHM1 scenarios generalize the (m_{1/2},
m_0) planes of the CMSSM by allowing either mu or m_A to take different (fixed)
values and we also show how the NUHM1 scenarios are embedded as special cases
of the more general NUHM2 scenarios. Generalizing from the CMSSM, we find
regions of the NUHM1 parameter space that are excluded because the LSP is a
selectron. We also find new regions where the neutralino relic density falls
within the range preferred by astrophysical and cosmological measurements,
thanks to rapid annihilation through direct-channel Higgs poles, or
coannihilation with selectrons, or because the LSP composition crosses over
from being mainly bino to mainly Higgsino. Generalizing further to the NUHM2,
we find regions of its parameter space where a sneutrino is the LSP, and others
where neutralino coannihilation with sneutrinos is important for the relic
density. In both the NUHM1 and the NUHM2, there are slivers of parameter space
where the LHC has fewer prospects for discovering sparticles than in the CMSSM,
because either m_{1/2} and/or m_0 may be considerably larger than in the CMSSM.Comment: 39 pages, 16 figure
The MSSM Parameter Space with Non-Universal Higgs Masses
Without assuming that Higgs masses have the same values as other scalar
masses at the input GUT scale, we combine constraints on the minimal
supersymmetric extension of the Standard Model (MSSM) coming from the cold dark
matter density with the limits from direct searches at accelerators such as
LEP, indirect measurements such as b to s gamma decay and the anomalous
magnetic moment of the muon. The requirement that Higgs masses-squared be
positive at the GUT scale imposes important restrictions on the MSSM parameter
space, as does the requirement that the LSP be neutral. We analyze the
interplay of these constraints in the (mu, m_A), (mu, m_{1/2}), (m_{1/2}, m_0)
and (m_A, tan beta) planes. These exhibit new features not seen in the
corresponding planes in the constrained MSSM in which universality is extended
to Higgs masses.Comment: 18 pages, latex, 10 eps figure
Gluino Coannihilation Revisited
Some variants of the MSSM feature a strip in parameter space where the
lightest neutralino is identified as the lightest supersymmetric particle
(LSP), the gluino is the next-to-lightest supersymmetric particle (NLSP) and is
nearly degenerate with the LSP, and the relic cold dark matter density is
brought into the range allowed by astrophysics and cosmology by coannihilation
with the gluino NLSP. We calculate the relic density along this gluino
coannihilation strip in the MSSM, including the effects of gluino-gluino bound
states and initial-state Sommerfeld enhancement, and taking into account the
decoupling of the gluino and LSP densities that occurs for large values of the
squark mass. We find that bound-state effects can increase the maximum LSP mass
for which the relic cold dark matter density lies within the range favoured by
astrophysics and cosmology by as much as ~ 50% if the squark to gluino mass
ratio is 1.1, and that the LSP may weigh up to ~ 8 TeV for a wide range of the
squark to gluino mass ratio \lesssim 100.Comment: 36 pages, 9 figures, matches version to appear in JHE
Uncertainties in WIMP Dark Matter Scattering Revisited
We revisit the uncertainties in the calculation of spin-independent
scattering matrix elements for the scattering of WIMP dark matter particles on
nuclear matter. In addition to discussing the uncertainties due to limitations
in our knowledge of the nucleonic matrix elements of the light quark scalar
densities , we also discuss the
importances of heavy quark scalar densities < N |{\bar c} c, {\bar b} b, {\bar
t} t| N >, and comment on uncertainties in quark mass ratios. We analyze
estimates of the light-quark densities made over the past decade using lattice
calculations and/or phenomenological inputs. We find an uncertainty in the
combination that is larger than has been
assumed in some phenomenological analyses, and a range of
that is smaller but compatible with earlier estimates. We also analyze the
importance of the {\cal O}(\alpha_s^3) calculations of the heavy-quark matrix
elements that are now available, which provide an important refinement of the
calculation of the spin-independent scattering cross section. We use for
illustration a benchmark CMSSM point in the focus-point region that is
compatible with the limits from LHC and other searches.Comment: 25 pages, 17 figure
Agriculture's Role in Greenhouse Gas Mitigation
Examines technical, economic, and policy trends. Explores efforts to encourage farmers to adopt new agricultural practices that reduce agricultural greenhouse gas emissions. Reviews biofuel options, and related policy implications
Educational Mismatch Among Ph.D.s: Determinants and Consequences
Using the Survey of Doctoral Recipients, the magnitude and consequences of job mismatch are estimated for Ph.D.s in science. Approximately one-sixth of academics and nearly one-half of nonacademics report some degree of mismatch. The influence of job mismatch is estimated for three job outcomes: earnings, job satisfaction and turnover. Surprisingly large and robust influences emerge. Mismatch is associated with substantially lower earnings, lower job satisfaction and a higher rate of turnover. These results persist across a variety of specifications and hold for both academics and nonacademics. Estimates of the determinants of mismatch indicate that older workers and those in rapidly changing disciplines are more likely to be mismatched and there is a suggestion that women are more likely to be mismatched.
A No-Scale Framework for Sub-Planckian Physics
We propose a minimal model framework for physics below the Planck scale with
the following features: (i) it is based on no-scale supergravity, as favoured
in many string compactifications, (ii) it incorporates Starobinsky-like
inflation, and hence is compatible with constraints from the Planck satellite,
(iii) the inflaton may be identified with a singlet field in a see-saw model
for neutrino masses, providing an efficient scenario for reheating and
leptogenesis, (iv) supersymmetry breaking occurs with an arbitrary scale and a
cosmological constant that vanishes before radiative corrections, (v) regions
of the model parameter space are compatible with all LHC, Higgs and dark matter
constraints.Comment: 6 pages, 2 figures, some minor corrections and additions. Final
versio
From Gravity to No-Scale Supergravity
We show that gravity coupled conformally to scalar fields is equivalent
to the real bosonic sector of SU(N,1)/SU(N)U(1) no-scale supergravity,
where the conformal factor can be identified with the K\"ahler potential, and
we review the construction of Starobinsky-like models of inflation within this
framework.Comment: 15 pages, version accepted for publicatio
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