1,732 research outputs found
The Heavy Quark Spin Symmetry Partners of the X(3872)
We explore the consequences of heavy quark spin symmetry for the charmed
meson-antimeson system in a contact-range (or pionless) effective field theory.
As a trivial consequence, we theorize the existence of a heavy quark spin
symmetry partner of the X(3872), with , which we call X(4012) in
reference to its predicted mass. If we additionally assume that the X(3915) is
a heavy spin symmetry partner of the X(3872), we end up predicting a
total of six molecular states. We also discuss the error
induced by higher order effects such as finite heavy quark mass corrections,
pion exchanges and coupled channels, allowing us to estimate the expected
theoretical uncertainties in the position of these new states.Comment: 18 pages; final version accepted for publicatio
Momentum-dependent contributions to the gravitational coupling of neutrinos in a medium
When neutrinos travel through a normal matter medium, the electron neutrinos
couple differently to gravity compared to the other neutrinos, due to the
presence of electrons in the medium and the absence of the other charged
leptons. We calculate the momentum-dependent part of the matter-induced
gravitational couplings of the neutrinos under such conditions, which arise at
order , and determine their contribution to the neutrino dispersion
relation in the presence of a gravitational potential .
These new contributions vanish for the muon and tau neutrinos. For electron
neutrinos with momentum , they are of the order of the usual Wolfenstein
term times the factor , for high energy
neutrinos. In environments where the gravitational potential is substantial,
such as those in the vicinity of Active Galactic Nuclei, they could be the
dominant term in the neutrino dispersion relation. They must also be taken into
account in the analysis of possible violations of the Equivalence Principle in
the neutrino sector, in experimental settings involving high energy neutrinos
traveling through a matter background.Comment: Minor corrections in the references; one reference adde
Gate induced enhancement of spin-orbit coupling in dilute fluorinated graphene
We analyze the origin of spin-orbit coupling (SOC) in fluorinated graphene
using Density Functional Theory (DFT) and a tight-binding model for the
relevant orbitals. As it turns out, the dominant source of SOC is the atomic
spin-orbit of fluorine adatoms and not the impurity induced SOC based on the
distortion of the graphene plane as in hydrogenated graphene. More
interestingly, our DFT calculations show that SOC is strongly affected by both
the type and concentrations of the graphene's carriers, being enhanced by
electron doping and reduced by hole doping. This effect is due to the charge
transfer to the fluorine adatom and the consequent change in the
fluorine-carbon bonding. Our simple tight-binding model, that includes the SOC
of the orbitals of F and effective parameters based on maximally localized
Wannier functions, is able to account for the effect. The strong enhancement of
the SOC induced by graphene doping opens the possibility to tune the spin
relaxation in this material.Comment: 9 pages, 8 figure
Diffusion of fluorine adatoms on doped graphene
We calculate the diffusion barrier of fluorine adatoms on doped graphene in
the diluted limit using Density Functional Theory. We found that the barrier
strongly depends on the magnitude and character of the graphene's
doping (): it increases for hole doping () and decreases
for electron doping (). Near the neutrality point the functional
dependence can be approximately by where
meVcm. This effect leads to significant
changes of the diffusion constant with doping even at room temperature and
could also affect the low temperature diffusion dynamics due to the presence of
substrate induced charge puddles. In addition, this might open up the
possibility to engineer the F dynamics on graphene by using local gates.Comment: 4 pages, 4 figure
Reply to Comment on ``Can gravity distinguish between Dirac and Majorana neutrinos?''
This is a reply to a comment (gr-qc/0610098) written by Nieves and Pal about
our paper (gr-qc/0605153) published in Phys. Rev. Lett. 97, 041101 (2006).Comment: 1 page, no figures, REVTe
Theoretical Response to the Discovery of Deeply Bound Pionic States in 208Pb(d,3He) reactions
Recently, deeply bound pionic states were found experimentally in (d, He)
reactions on Pb. They found an isolated peak structure in the bound
region below the pion production threshold. We study theoretically these
excitation functions in (d, He) reactions on Pb at T=600 MeV.
We found very good agreement with the (d, He) excitation functions and
could identify the underlying structures of the pionic states. We study the
energy dependence of the (d, He) reactions and the change of the excitation
functions with the incident energy.Comment: 5 pages, Latex, Figures available on request, Z.Phys.A.accepte
The X(3872) and other X,Y,Z Resonances as Hidden Charm Meson-Meson Molecules
We report on some ideas concerning the nature of the X(3872) resonance and
the need for approximately equal charged and neutral components of . Then we discuss how some hidden charm states are obtained from the
interaction between vector mesons with charm and can be associated to some of
the charmonium-like X,Y,Z states. Finally we discuss how the nature of these
states could be investigated through different types of radiative decay.Comment: Presented at the Charm2010 Workshop, Beijing, Oct. 201
Deriving the existence of bound states from the X(3872) and Heavy Quark Symmetry
We discuss the possibility and the description of bound states between
and mesons. We argue that the existence of such a bound state can
be deduced from (i) the weakly bound X(3872) state, (ii) certain assumptions
about the short range dynamics of the system and (iii) heavy quark
symmetry. From these assumptions the binding energy of the possible
bound states is determined, first in a theory containing only
contact interactions which serves as a straightforward illustration of the
method, and then the effects of including the one pion exchange potential are
discussed. In this latter case three isoscalar states are predicted: a positive
and negative C-parity state with a binding energy of and below threshold respectively, and a positive C-parity
shallow state located almost at the threshold. However,
large uncertainties are generated as a consequence of the corrections
from heavy quark symmetry. Finally, the newly discovered isovector
state can be easily accommodated within the present framework by a minor
modification of the short range dynamics.Comment: 21 pages, 3 figures; a sign error in the potential has been corrected
and new predictions have been compute
- …