1,186 research outputs found
Dividing the Indivisible: Procedures for Allocating Cabinet Ministries to Political Parties in a Parliamentary System
Political parties in Northern Ireland recently used a divisor method of apportionment to choose, in sequence, ten cabinet ministries. If the parties have complete information about each others' preferences, we show that it may not be rational for them to act sincerely by choosing their most-preferred ministry that is available. One consequence of acting sophisticatedly is that the resulting allocation may not be Pareto-optimal, making all the parties worse off. Another is nonmonotonicty-choosing earlier may hurt rather than help a party. We introduce a mechanism that combines sequential choices with a structured form of trading that results in sincere choices for two parties. Although there are difficulties in extending this mechanism to more than two parties, other approaches are explored, such as permitting parties to making consecutive choices not prescribed by an apportionment method. But certain problems, such as eliminating envy, remain.APPORTIONMENT METHODS; CABINETS; SEQUENTIAL ALLOCATION; MECHANISM DESIGN; FAIRNESS
Fermions on an Interval: Quark and Lepton Masses without a Higgs
We consider fermions on an extra dimensional interval. We find the boundary
conditions at the ends of the interval that are consistent with the variational
principle, and explain which ones arise in various physical circumstances. We
apply these results to higgsless models of electroweak symmetry breaking, where
electroweak symmetry is not broken by a scalar vacuum expectation value, but
rather by the boundary conditions of the gauge fields. We show that it is
possible to find a set of boundary conditions for bulk fermions that would give
a realistic fermion mass spectrum without the presence of a Higgs scalar, and
present some sample fermion mass spectra for the standard model quarks and
leptons as well as their resonances.Comment: LaTeX, 36 pages, 5 figure
RS1, Custodial Isospin and Precision Tests
We study precision electroweak constraints within a RS1 model with gauge
fields and fermions in the bulk. The electroweak gauge symmetry is enhanced to
SU(2)_L \times SU(2)_R \times U(1)_{B-L}, thereby providing a custodial isospin
symmetry sufficient to suppress excessive contributions to the T parameter. We
then construct complete models, complying with all electroweak constraints, for
solving the hierarchy problem, without supersymmetry or large hierarchies in
the fundamental couplings. Using the AdS/CFT correspondence our models can be
interpreted as dual to a strongly coupled conformal Higgs sector with global
custodial symmetry, gauge and fermionic matter being fundamental fields
external to the CFT. This scenario has interesting collider signals, distinct
from other RS models in the literature.Comment: 32 pages, 6 figures, latex2e, minor changes, references adde
Cosmological Consequences of Nearly Conformal Dynamics at the TeV scale
Nearly conformal dynamics at the TeV scale as motivated by the hierarchy
problem can be characterized by a stage of significant supercooling at the
electroweak epoch. This has important cosmological consequences. In particular,
a common assumption about the history of the universe is that the reheating
temperature is high, at least high enough to assume that TeV-mass particles
were once in thermal equilibrium. However, as we discuss in this paper, this
assumption is not well justified in some models of strong dynamics at the TeV
scale. We then need to reexamine how to achieve baryogenesis in these theories
as well as reconsider how the dark matter abundance is inherited. We argue that
baryonic and dark matter abundances can be explained naturally in these setups
where reheating takes place by bubble collisions at the end of the strongly
first-order phase transition characterizing conformal symmetry breaking, even
if the reheating temperature is below the electroweak scale GeV. We
also discuss inflation as well as gravity wave smoking gun signatures of this
class of models.Comment: 22 pages, 7 figure
K* nucleon hyperon form factors and nucleon strangeness
A crucial input for recent meson hyperon cloud model estimates of the nucleon
matrix element of the strangeness current are the nucleon-hyperon-K* (NYK*)
form factors which regularize some of the arising loops. Prompted by new and
forthcoming information on these form factors from hyperon-nucleon potential
models, we analyze the dependence of the loop model results for the
strange-quark observables on the NYK* form factors and couplings. We find, in
particular, that the now generally favored soft N-Lambda-K* form factors can
reduce the magnitude of the K* contributions in such models by more than an
order of magnitude, compared to previous results with hard form factors. We
also discuss some general implications of our results for hadronic loop models.Comment: 9 pages, 8 figures, new co-author, discussion extended to the
momentum dependence of the strange vector form factor
The phase transition in QCD with broken SU(2) flavour symmetry
We report the first investigation of the QCD transition temperature, T_c, for
two flavours of staggered quarks with unequal masses at lattice spacings of
1/4T. On changing the u/d quark mass ratio in such a way that
m(pi_0)^2/m(pi_+)^2 changes from 1 to 0.78, thus bracketing the physical value
of this ratio, we find that T_c remains unchanged in units of both m_rho and
Lambda_MSbar.Comment: 12 pages, 5 figure
Effective Field Theory for Dilute Fermions with Pairing
Effective field theory (EFT) methods for a uniform system of fermions with
short-range, natural interactions are extended to include pairing correlations,
as part of a program to develop a systematic Kohn-Sham density functional
theory (DFT) for medium and heavy nuclei. An effective action formalism for
local composite operators leads to a free-energy functional that includes
pairing by applying an inversion method order by order in the EFT expansion. A
consistent renormalization scheme is demonstrated for the uniform system
through next-to-leading order, which includes induced-interaction corrections
to pairing.Comment: 31 pages, 10 figures, affiliation updated, paper unchange
Energy Loss versus Shadowing in the Drell-Yan Reaction on Nuclei
We present a new analysis of the E772 and E866 experiments on the nuclear
dependence of Drell-Yan (DY) lepton pair production resulting from the
bombardment of , Be, C, Ca, Fe, and W targets by 800 GeV/c protons at
Fermilab. We employ a light-cone formulation of the DY reaction in the rest
frame of the nucleus, where the dimuons detected at small values of Bjorken x_2
<< 1 may be considered to originate from the decay of a heavy photon radiated
from an incident quark in a bremsstrahlung process. We infer the energy loss of
the quark by examining the suppression of the nuclear-dependent DY ratios seen
as a function of projectile momentum fraction x_1 and dimuon mass M. Shadowing,
which also leads to nuclear suppression of dimuons, is calculated within the
same approach employing the results of phenomenological fits to deep inelastic
scattering data from HERA. The analysis yields -dE/dz =2.73 +/- 0.37 +/- 0.5
GeV/fm for the rate of quark energy loss per unit path length, a value
consistent with theoretical expectations including the effects of the inelastic
interaction of the incident proton at the surface of the nucleus. This is the
first observation of a nonzero energy loss effect in such experiments.Comment: 43 pages including 17 figure
Improved results for N=(2,2) super Yang-Mills theory using supersymmetric discrete light-cone quantization
We consider the (1+1)-dimensional super Yang--Mills theory
which is obtained by dimensionally reducing super Yang--Mills
theory in four dimension to two dimensions. We do our calculations in the
large- approximation using Supersymmetric Discrete Light Cone
Quantization. The objective is to calculate quantities that might be
investigated by researchers using other numerical methods. We present a
precision study of the low-mass spectrum and the stress-energy correlator
. We find that the mass gap of this theory closes as the
numerical resolution goes to infinity and that the correlator in the
intermediate region behaves like .Comment: 18 pages, 8 figure
A classification of smooth embeddings of 3-manifolds in 6-space
We work in the smooth category. If there are knotted embeddings S^n\to R^m,
which often happens for 2m<3n+4, then no concrete complete description of
embeddings of n-manifolds into R^m up to isotopy was known, except for disjoint
unions of spheres. Let N be a closed connected orientable 3-manifold. Our main
result is the following description of the set Emb^6(N) of embeddings N\to R^6
up to isotopy.
The Whitney invariant W : Emb^6(N) \to H_1(N;Z) is surjective. For each u \in
H_1(N;Z) the Kreck invariant \eta_u : W^{-1}u \to Z_{d(u)} is bijective, where
d(u) is the divisibility of the projection of u to the free part of H_1(N;Z).
The group Emb^6(S^3) is isomorphic to Z (Haefliger). This group acts on
Emb^6(N) by embedded connected sum. It was proved that the orbit space of this
action maps under W bijectively to H_1(N;Z) (by Vrabec and Haefliger's
smoothing theory). The new part of our classification result is determination
of the orbits of the action. E. g. for N=RP^3 the action is free, while for
N=S^1\times S^2 we construct explicitly an embedding f : N \to R^6 such that
for each knot l:S^3\to R^6 the embedding f#l is isotopic to f.
Our proof uses new approaches involving the Kreck modified surgery theory or
the Boechat-Haefliger formula for smoothing obstruction.Comment: 32 pages, a link to http://www.springerlink.com added, to appear in
Math. Zei
- âŠ