2,827 research outputs found
Russian Roulette- Expenditure Inequality and Instability in Russia, 1994-1998
This paper uses the second phase of the Russian Longitudinal Monitoring Survey to investigate the changes in expenditure inequality and instability in Russia between the autumn of 1994 and the autumn of 1998. The expenditure distribution is stable in spite of the economic and political turmoil Russia is going through. However, that does not imply much economic stability. Households' expenditure fluctuated considerably, with over 60 percent of the population's expenditure either more than doubling or falling to less than half their previous levels. Only about 10 percent of all households experienced an expenditure shock of less than 10 percent. The measured level of expenditure mobility is very high. This raises the question whether the observed mobility is in fact the expenditure instability. Distinguishing between the two is crucial for policy makers. While the mobility is often viewed as favorable, the high instability may affect the incentives of Russians to support the economic reforms, acquire human capital, and undertake entrepreneurial activities.http://deepblue.lib.umich.edu/bitstream/2027.42/39742/3/wp358.pd
Softness and Amplitudes' Positivity for Spinning Particles
We derive positivity bounds for scattering amplitudes of particles with
arbitrary spin using unitarity, analyticity and crossing symmetry. The bounds
imply the positivity of certain low-energy coefficients of the effective action
that controls the dynamics of the light degrees of freedom. We show that
low-energy amplitudes strictly softer than do not admit unitary
ultraviolet completions unless the theory is free. This enforces a bound on the
energy growth of scattering amplitudes in the region of validity of the
effective theory. We discuss explicit examples including the Goldstino from
spontaneous supersymmetry breaking, and the theory of a spin-1/2 fermion with a
shift symmetry.Comment: 28 pages + refs and 3 appendices, 2 figures; v2: extra refs, improved
discussions, typos fixed, accepted on JHE
Photophilic Higgs from sgoldstino mixing
The spontaneous breaking of linearly realized N=1 supersymmetry implies the
existence of a pseudo-Goldstone fermion, the goldstino, and of its complex
scalar superpartner, the sgoldstino. The latter has generically sizable
tree-level couplings to Standard Model gauge bosons while its couplings to SM
fermions are suppressed. We consider a light sgoldstino, with a mass around 1
TeV, that mixes with a SM-like Higgs scalar at around 125 GeV. We show that
such a mixing can enhance the Higgs to di-photon signal rate while evading all
the relevant experimental bounds and without significantly affecting the other
decay channels.Comment: 8 pages, 6 figures and 1 tabl
Composite Higgses
We present an overview of composite Higgs models in light of the discovery of
the Higgs boson. The small value of the physical Higgs mass suggests that the
Higgs quartic is likely loop generated, thus models with tree-level quartics
will generically be more tuned. We classify the various models (including bona
fide composite Higgs, little Higgs, holographic composite Higgs, twin Higgs and
dilatonic Higgs) based on their predictions for the Higgs potential, review the
basic ingredients of each of them, and quantify the amount of tuning needed,
which is not negligible in any model. We explain the main ideas for generating
flavor structure and the main mechanisms for protecting against large flavor
violating effects, and present a summary of the various coset models that can
result in realistic pseudo-Goldstone Higgses. We review the current
experimental status of such models by discussing the electroweak precision,
flavor and direct search bounds, and comment on UV completions and on ways to
incorporate dark matter.Comment: 58 Pages, 5 Figures, 5 Tables. Invited review article accepted for
publication in The European Physical Journal
Symmetries, Sum Rules and Constraints on Effective Field Theories
Using unitarity, analyticity and crossing symmetry, we derive universal sum
rules for scattering amplitudes in theories invariant under an arbitrary
symmetry group. The sum rules relate the coefficients of the energy expansion
of the scattering amplitudes in the IR to total cross sections integrated all
the way up to the UV. Exploiting the group structure of the symmetry, we
systematically determine all the independent sum rules and positivity
conditions on the expansion coefficients. For effective field theories the
amplitudes in the IR are calculable and hence the sum rules set constraints on
the parameters of the effective Lagrangian. We clarify the impact of gauging on
the sum rules for Goldstone bosons in spontaneously broken gauge theories. We
discuss explicit examples that are relevant for WW-scattering, composite Higgs
models, and chiral perturbation theory. Certain sum rules based on custodial
symmetry and its extensions provide constraints on the Higgs boson coupling to
the electroweak gauge bosons.Comment: 50 pages, 5 figures, 5 appendices; several typos fixed, discussions
improved, references added; results unchange
Off-critical Luttinger Junctions
We investigate Luttinger junctions of quantum wires away from criticality.
The one-body scattering matrix, corresponding to the off-critical boundary
conditions at the junction, admits in general antibound and/or bound states.
Their contribution to the theory is fixed by causality. The presence/absence of
bound states determines the existence of two different regimes with
inequivalent physical properties. A scattering matrix without bound states
defines an isolated equilibrium system. Bound states instead drive the system
away from equilibrium, giving raise to non-trivial incoming or outgoing energy
flows in the junction. We derive in both regimes and in explicit form the
electromagnetic conductance tensor, pointing out the different impact of bound
and antibound states.Comment: LaTex, 9 pages, 1 figur
Quantum Gravity Constraints from Unitarity and Analyticity
We derive rigorous bounds on corrections to Einstein gravity using unitarity
and analyticity of graviton scattering amplitudes. In spacetime
dimensions, these consistency conditions mandate positive coefficients for
certain quartic curvature operators. We systematically enumerate all such
positivity bounds in and before extending to . Afterwards,
we derive positivity bounds for supersymmetric operators and verify that all of
our constraints are satisfied by weakly-coupled string theories. Among
quadratic curvature operators, we find that the Gauss-Bonnet term in
is inconsistent unless new degrees of freedom enter at the natural cutoff scale
defined by the effective theory. Our bounds apply to perturbative ultraviolet
completions of gravity.Comment: 26 page
Charming Higgs
We present a simple supersymmetric model where the dominant decay mode of the
lightest Higgs boson is h->2eta->4c where eta is a light pseudoscalar and c is
the charm quark. For such decays the Higgs mass can be smaller than 100 GeV
without conflict with experiment. Together with the fact that both the Higgs
and the pseudoscalar eta are pseudo-Goldstone bosons, this resolves the little
hierarchy problem.Comment: 6 pages, 2 figure
- …