3,234 research outputs found
Equivalence Principle tests, Equivalence theorems and New long-range forces
We discuss the possible existence of new long-range forces mediated by spin-1
or spin-0 particles. By adding their effects to those of gravity, they could
lead to apparent violations of the Equivalence Principle. While the vector part
in the couplings of a new spin-1 U boson involves, in general, a combination of
the B and L currents, there may also be, in addition, an axial part as well. If
the new force has a finite range \lambda, its intensity is proportional to
1/(\lambda^2 F^2), F being the extra U(1) symmetry-breaking scale.
Quite surprisingly, particle physics experiments can provide constraints on
such a new force, even if it is extremely weak, the corresponding gauge
coupling being extremely small (<< 10^-19 !). An ``equivalence theorem'' shows
that a very light spin-1 U boson does not in general decouple even when its
gauge coupling vanishes, but behaves as a quasimassless spin-0 particle, having
pseudoscalar couplings proportional to 1/F. Similarly, in supersymmetric
theories, a very light spin-3/2 gravitino might be detectable as a quasi
massless spin-1/2 goldstino, despite the extreme smallness of Newton's
gravitational constant G_N, provided the supersymmetry-breaking scale is not
too large.
Searches for such U bosons in \psi and \Upsilon decays restrict F to be
larger than the electroweak scale (the U actually becoming, as an axion, quasi
``invisible'' in particle physics for sufficiently large F). This provides
strong constraints on the corresponding new force and its associated EP
violations. We also discuss briefly new spin-dependent forces.Comment: 19 page
Constraints on the parity-violating couplings of a new gauge boson
High-energy particle physics experiments allow for the possible existence of
a new light, very weakly coupled, neutral gauge boson (the U boson). This one
permits for light (spin-1/2 or spin-0) particles to be acceptable Dark Matter
candidates, by inducing sufficient (stronger than weak) annihilation cross
sections into e+e-. They could be responsible for the bright 511 keV gamma ray
line observed by INTEGRAL from the galactic bulge.
Such a new interaction may have important consequences, especially at lower
energies. Parity-violation atomic-physics experiments provide strong
constraints on such a U boson, if its couplings to quarks and electrons violate
parity. With the constraints coming from an unobserved axionlike behaviour of
this particle, they privilegiate a pure vector coupling of the U boson to
quarks and leptons, unless the corresponding symmetry is broken sufficiently
above the electroweak scale.Comment: 6 page
Light spin-1/2 or spin-0 Dark Matter particles
We recall and precise how light spin-0 particles could be acceptable Dark
Matter candidates, and extend this analysis to spin-1/2 particles. We evaluate
the (rather large) annihilation cross sections required, and show how they may
be induced by a new light neutral spin-1 boson U. If this one is vectorially
coupled to matter particles, the (spin-1/2 or spin-0) Dark Matter annihilation
cross section into e+e- automatically includes a v_dm^2 suppression factor at
threshold, as desirable to avoid an excessive production of gamma rays from
residual Dark Matter annihilations. We also relate Dark Matter annihilations
with production cross sections in e+e- scatterings. Annihilation cross sections
of spin-1/2 and spin-0 Dark Matter particles are given by exactly the same
expressions. Just as for spin-0, light spin-1/2 Dark Matter particles
annihilating into e+e- could be responsible for the bright 511 keV gamma ray
line observed by INTEGRAL from the galactic bulge.Comment: 10 page
Some Comments on an MeV Cold Dark Matter Scenario
We discuss several aspects of astroparticle physics pertaining to a new model
with MeV cold dark matter particles, which annihilate to electron-positron
pairs in a manner yielding the correct CDM density required today, and
explaining the enhanced electron-positron annihilation line from the center of
the Galaxy. We note that the mass of the vector meson mediating the
annihilations, should exceed the mass of CDM particle, and comment on possible
enhancement due to CDM clustering, on the detectability of the new CDM, and on
particle physics models incorporating this scenario.Comment: 13 pages, 2 figures. v2 - Added some remarks regarding a more
stringent mass bound. References added, some typos corrected. v3 - Added a
comment regarding the invalidity of perturbative calculation in the case of a
very small coupling g'. Removed the comment regarding the smallness of the
angular width of the 511 keV lin
About R-parity and the Supersymmetric Standard Model
We recall the obstacles which seemed, long ago, to prevent one from viewing
supersymmetry as a possible fundamental symmetry of Nature. Is spontaneous
supersymmetry breaking possible ? Where is the spin-1/2 Goldstone fermion of
supersymmetry, if not a neutrino ? Which bosons and fermions could be related ?
Can one define conserved baryon and lepton numbers in such theories, although
they systematically involve self-conjugate Majorana fermions ? If we have to
postulate the existence of new bosons carrying B and L (the new spin-0 squarks
and sleptons), can we prevent them from mediating new unwanted interactions ?
We then recall how we obtained the three basic ingredients of the
Supersymmetric Standard Model: 1) the SU(3) x SU(2) x U(1) gauge superfields;
2) the chiral quark and lepton superfields; 3) the two doublet Higgs
superfields responsible for the electroweak breaking, and the generation of
quark and lepton masses. The original continuous ``R-invariance'' of this model
was soon abandoned in favor of its discrete version, R-parity, so that the
gravitino, and gluinos, can acquire masses - gluinos getting their masses from
supergravity, or radiative corrections.
R-parity forbids unwanted squark and slepton exchanges, and guarantees the
stability of the ``lightest supersymmetric particle''. It is present only since
we restricted the initial superpotential to be an even function of quark and
lepton superfields (so as to allow for B and L conservation laws), as made
apparent by the formula re-expressing R-parity as (-1)^2S (-1)^(3B+L). Whether
it turns out to be absolutely conserved, or not, R-parity plays an essential
role in the phenomenology of supersymmetric theories, and the experimental
searches for the new sparticles.Comment: 23 pages, Latex, no figures. To be published as a contribution to the
Yuri Gol'fand Memorial Volume, M.Shifman ed., World Scientifi
Invisible Upsilon decays into Light Dark Matter
Invisible psi and Upsilon decays into light neutralinos, within the MSSM or
N(n)MSSM, are smaller than for nu nubar production, even if light spin-0
particles are coupled to quarks and neutralinos. In a more general way, light
dark matter particles are normally forbidden, unless they can annihilate
sufficiently through a new interaction stronger than weak interactions (at
lower energies), as induced by a light spin-1 U boson, or heavy-fermion
exchanges in the case of scalar dark matter. We discuss the possible
contributions of U-boson, heavy-fermion, or spin-0 exchanges to invisible psi
and Upsilon decays.
U-exchanges could lead, but not necessarily, to significant branching
fractions for invisible decays into light dark matter. We show how one can get
the correct relic density together with sufficiently small invisible branching
fractions, and the resulting constraints on the U couplings to ordinary
particles and dark matter, in particular |c_chi.f_bV| < 5 10^-3 from Upsilon
decays, for 2 m_chi smaller than a few GeV. We also explain why there is no
model-independent way to predict psi and Upsilon branching fractions into light
dark matter, from dark matter annihilation cross sections at freeze-out time.Comment: 10 pages, 9 figures, to appear in Phys. Rev.
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