1,057 research outputs found

### Orthogonal U(1)'s, Proton Stability and Extra Dimensions

In models with a low quantum gravity scale, one might expect that all
operators consistent with gauge symmetries are present in the low-energy
effective theory. If this is the case, some mechanism must be present to
adequately suppress operators that violate baryon number. Here we explore the
possibility that the desired suppression is a consequence of an additional,
spontaneously-broken, non-anomalous U(1) symmetry that is orthogonal to
hypercharge. We show that successful models can be constructed in which the
additional particle content necessary to cancel anomalies is minimal, and
compatible with the constraints from precision electroweak measurements and
gauge unification. If unification is sacrificed, and only the new U(1) and its
associated Higgs fields live in the bulk, it is possible that the gauge field
zero mode and first few Kaluza-Klein excitations lie within the kinematic reach
of the Tevatron. For gauge couplings not much smaller than that of hypercharge,
we show that these highly leptophobic states could evade detection at Run I,
but be discovered at Run II. Our scenario presents an alternative to the
`cartographic' solution to baryon number violation in which leptons and quarks
are separated in an extra dimension.Comment: 16 pages LaTeX, 4 figure

### Unusual High-Energy Phenomenology of Lorentz-Invariant Noncommutative Field Theories

It has been suggested that one may construct a Lorentz-invariant
noncommutative field theory by extending the coordinate algebra to additional,
fictitious coordinates that transform nontrivially under the Lorentz group.
Integration over these coordinates in the action produces a four-dimensional
effective theory with Lorentz invariance intact. Previous applications of this
approach, in particular to a specific construction of noncommutative QED, have
been studied only in a low-momentum approximation. Here we discuss
Lorentz-invariant field theories in which the relevant physics can be studied
without requiring an expansion in the inverse scale of noncommutativity.
Qualitatively, we find that tree-level scattering cross sections are
dramatically suppressed as the center-of-mass energy exceeds the scale of
noncommutativity, that cross sections that are isotropic in the commutative
limit can develop a pronounced angular dependence, and that nonrelativistic
potentials (for example, the Coloumb potential) become nonsingular at the
origin. We consider a number of processes in noncommutative QED that may be
studied at a future linear collider. We also give an example of scattering via
a four-fermion operator in which the noncommutative modifications of the
interaction can unitarize the tree-level amplitude, without requiring any other
new physics in the ultraviolet.Comment: 24 pages LaTeX, 4 eps figures (v2: reference added, v3: minor
clarifications

### Competition between standard and exotic double beta decays

We discuss the contributions of higher order terms in weak Hamiltonian to the
standard two-neutrino double beta decay. The formalism for the unique first
forbidden transitions has been developed, and it is shown that they can alter
the two-electron energy spectrum. Yet, their effect is too small to screen the
detection of exotic neutrinoless double beta decays, which are candidates for
testing the physics beyond the standard model.Comment: 9 pages, latex, 1ps figures, minor changes, to appear in Phys. Lett.

### Long-term labour productivity and GDP projections for the EU25 Member States : a production function framework

This paper presents the results of long run labour productivity and GDP growth rate projections (until 2050) for each of the 25 EU Member States and provides a detailed overview of the forecast methodology used. These projections were undertaken in order to provide an internationally comparable macroeconomic framework against which to assess the potential economic and fiscal effects of ageing populations. This assessment was carried out as part of the work undertaken by the EU's Economic Policy Committee, in its Ageing Working Group, to project the public expenditure implications of ageing on pensions, health care, long-term care, unemployment insurance and education.labour productivity, GDP projections, ageing populations, public expenditure, pensions, health care, long-term care, unemployment, education, Carone, Denis, Mc Morrow, Mourre, Rïżœger

### 1/Nc Countings in Baryons

The $1/N_c$ power countings for baryon decays and configuration mixings are
determined by means of a non-relativistic quark picture. Such countings are
expected to be robust under changes in the quark masses, and therefore valid as
these become light. It is shown that excited baryons have natural widths of
${\cal{O}}(N_c^0)$. These dominant widths are due to the decays that proceed
directly to the ground state baryons, with cascade decays being suppressed to
${\cal{O}}(1/N_c)$. Configuration mixings, defined as mixings between states
belonging to different $O(3)\times SU(2 N_f)$ multiplets, are shown to be
sub-leading in an expansion in $1/\sqrt{N_c}$ when they involve the ground
state baryons, while the mixings between excited states can be
${\cal{O}}(N_c^0)$.Comment: 19 pages, 1 figure An omission that changes the conclusions on
configuration mixings has been correcte

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