1,079 research outputs found
Electric Dipole Moments as Probes of CPT Invariance
Electric dipole moments (EDMs) of elementary particles and atoms probe
violations of T and P symmetries and consequently of CP if CPT is an exact
symmetry. We point out that EDMs can also serve as sensitive probes of CPT-odd,
CP-even interactions, that are not constrained by any other existing
experiments. Analyzing models with spontaneously broken Lorentz invariance, we
calculate EDMs in terms of the leading CPT-odd operators to show that
experimental sensitivity probes the scale of CPT breaking as high as
10^{12}GeV.Comment: 4 pages, typos correcte
Environmental Dependence of Masses and Coupling Constants
We construct a class of scalar field models coupled to matter that lead to
the dependence of masses and coupling constants on the ambient matter density.
Such models predict a deviation of couplings measured on the Earth from values
determined in low-density astrophysical environments, but do not necessarily
require the evolution of coupling constants with the redshift in the recent
cosmological past. Additional laboratory and astrophysical tests of \Delta
\alpha and \Delta(m_p/m_e) as functions of the ambient matter density are
warranted.Comment: 20 pages, no figures, references added, minor editorial change
Dark matter scattering on electrons: Accurate calculations of atomic excitations and implications for the DAMA signal
We revisit the WIMP-type dark matter scattering on electrons that results in
atomic ionization, and can manifest itself in a variety of existing
direct-detection experiments. Unlike the WIMP-nucleon scattering, where current
experiments probe typical interaction strengths much smaller than the Fermi
constant, the scattering on electrons requires a much stronger interaction to
be detectable, which in turn requires new light force carriers. We account for
such new forces explicitly, by introducing a mediator particle with scalar or
vector couplings to dark matter and to electrons. We then perform state of the
art numerical calculations of atomic ionization relevant to the existing
experiments. Our goals are to consistently take into account the atomic physics
aspect of the problem (e.g., the relativistic effects, which can be quite
significant), and to scan the parameter space: the dark matter mass, the
mediator mass, and the effective coupling strength, to see if there is any part
of the parameter space that could potentially explain the DAMA modulation
signal. While we find that the modulation fraction of all events with energy
deposition above 2 keV in NaI can be quite significant, reaching ~50%, the
relevant parts of the parameter space are excluded by the XENON10 and XENON100
experiments
Multi-lepton Signatures of a Hidden Sector in Rare B Decays
We explore the sensitivity of flavour changing b -> s transitions to a
(sub-)GeV hidden sector with generic couplings to the Standard Model through
the Higgs, vector and axion portals. The underlying two-body decays of B
mesons, B -> X_s S and B0 -> SS, where S denotes a generic new GeV-scale
particle, may significantly enhance the yield of monochromatic lepton pairs in
the final state via prompt decays of S to a dilepton pair. Existing
measurements of the charged lepton spectrum in neutral-current semileptonic B
decays provide bounds on the parameters of the light sector that are
significantly more stringent than the requirements of naturalness. New search
modes, such as B -> X_s + n(l+l-) and B0 -> n(l+l-) with n > 1 can provide
additional sensitivity to scenarios in which both the Higgs and vector portals
are active, and are accessible to (super-)B factories and hadron colliders.Comment: 12 pages, 2 figures; v2: reference added, minor correction
Ghosts and Tachyons in the Fifth Dimension
We present several solutions for the five dimensional gravity models in the
presence of bulk ghosts and tachyons to argue that these "troublesome" fields
can be a useful model-building tool. The ghost-like signature of the kinetic
term for a bulk scalar creates a minimum in the scale factor, removing the
necessity for a negative tension brane in models with the compactified fifth
dimension. It is shown that the model with the positive tension branes and a
ghost field in the bulk leads to the radion stabilization. The bulk scalar with
the variable sign kinetic term can be used to model both positive and negative
tension branes of a finite width in the compact dimension. Finally, we present
several ghost and tachyon field configurations in the bulk that lead to the
localization of gravity in four dimensions, including one solution with the
Gaussian profile for the metric, g_{\mu\nu}(y)=\eta_{\mu\nu}\exp{-\alpha y^2},
which leads to a stronger localization of gravity than the Randall-Sundrum
model.Comment: New references adde
Probing CP Violation with the Deuteron Electric Dipole Moment
We present an analysis of the electric dipole moment (EDM) of the deuteron as
induced by CP-violating operators of dimension 4, 5 and 6 including theta QCD,
the EDMs and color EDMs of quarks, four-quark interactions and the Weinberg
operator. We demonstrate that the precision goal of the EDM Collaboration's
proposal to search for the deuteron EDM, (1-3)\times 10^{-27} e cm, will
provide an improvement in sensitivity to these sources of one-two orders of
magnitude relative to the existing bounds. We consider in detail the level to
which CP-odd phases can be probed within the MSSM.Comment: 5 pages, 4 figures; precision estimates clarified, to appear in Phys.
Rev.
Neutrino Physics with Dark Matter Experiments and the Signature of New Baryonic Neutral Currents
New neutrino states \nu_b, sterile under the Standard Model interactions, can
be coupled to baryons via the isoscalar vector currents that are much stronger
than the Standard Model weak interactions. If some fraction of solar neutrinos
oscillate into \nu_b on their way to Earth, the coherently enhanced elastic
\nu_b-nucleus scattering can generate a strong signal in the dark matter
detectors. For the interaction strength a few hundred times stronger than the
weak force, the elastic \nu_b-nucleus scattering via new baryonic currents may
account for the existing anomalies in the direct detection dark matter
experiments at low recoil. We point out that for solar neutrino energies the
baryon-current-induced inelastic scattering is suppressed, so that the possible
enhancement of new force is not in conflict with signals at dedicated neutrino
detectors. We check this explicitly by calculating the \nu_b-induced deuteron
breakup, and the excitation of 4.4 MeV \gamma-line in ^{12}C.
Stronger-than-weak force coupled to baryonic current implies the existence of
new abelian gauge group U(1)_B with a relatively light gauge boson.Comment: 20 pages, 5 figures. References added, inconsistent treatment of
neutrino oscillations corrected, conclusions unchange
Metastable GeV-scale particles as a solution to the cosmological lithium problem
The persistent discrepancy between observations of 7Li with putative
primordial origin and its abundance prediction in Big Bang Nucleosynthesis
(BBN) has become a challenge for the standard cosmological and astrophysical
picture. We point out that the decay of GeV-scale metastable particles X may
significantly reduce the BBN value down to a level at which it is reconciled
with observations. The most efficient reduction occurs when the decay happens
to charged pions and kaons, followed by their charge exchange reactions with
protons. Similarly, if X decays to muons, secondary electron antineutrinos
produce a similar effect. We consider the viability of these mechanisms in
different classes of new GeV-scale sectors, and find that several minimal
extensions of the Standard Model with metastable vector and/or scalar particles
are capable of solving the cosmological lithium problem. Such light states can
be a key to the explanation of recent cosmic ray anomalies and can be searched
for in a variety of high-intensity medium-energy experiments.Comment: 50 pages, 13 figures; references added, typo correcte
Atomic electric dipole moments of He and Yb induced by nuclear Schiff moments
We have calculated the atomic electric dipole moments (EDMs) d of ^3He and
^{171}Yb induced by their respective nuclear Schiff moments S. Our results are
d(He)= 8.3x10^{-5} and d(Yb)= -1.9 in units 10^{-17}S/(e{fm}^3)e cm. By
considering the nuclear Schiff moments induced by the parity and time-reversal
violating nucleon-nucleon interaction we find d(^{171}Yb)~0.6d(^{199}Hg). For
^3He the nuclear EDM coupled with the hyperfine interaction gives a larger
atomic EDM than the Schiff moment. The result for ^3He is required for a
neutron EDM experiment that is under development, where ^3He is used as a
comagnetometer. We find that the EDM for He is orders of magnitude smaller than
the neutron EDM. The result for Yb is needed for the planning and
interpretation of experiments that have been proposed to measure the EDM of
this atom.Comment: 4 page
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