28 research outputs found
Heavy-light quark pseudoscalar and vector mesons at finite temperature
The temperature dependence of the mass, leptonic decay constant, and width of
heavy-light quark peseudoscalar and vector mesons is obtained in the framework
of thermal Hilbert moment QCD sum rules. The leptonic decay constants of both
pseudoscalar and vector mesons decrease with increasing , and vanish at a
critical temperature , while the mesons develop a width which increases
dramatically and diverges at , where is the temperature for
chiral-symmetry restoration. These results indicate the disappearance of
hadrons from the spectral function, which then becomes a smooth function of the
energy. This is interpreted as a signal for deconfinement at . In
contrast, the masses show little dependence on the temperature, except very
close to , where the pseudoscalar meson mass increases slightly by 10-20
%, and the vector meson mass decreases by some 20-30
Hydrodynamic obstruction to bubble expansion
We discuss a hydrodynamic obstruction to bubble wall acceleration during a
cosmological first-order phase transition. The obstruction results from the
heating of the plasma in the compression wave in front of the phase transition
boundary. We provide a simple criterion for the occurrence of the obstruction
at subsonic bubble wall velocity in terms of the critical temperature, the
phase transition temperature, and the latent heat of the model under
consideration. The criterion serves as a sufficient condition of subsonic
bubble wall velocities as required by electroweak baryogenesis.Comment: 18 pages, 4 figures; comments and reference added, published versio
Strange quark mass from Finite Energy QCD sum rules to five loops
The strange quark mass is determined from a new QCD Finite Energy Sum Rule
(FESR) optimized to reduce considerably the systematic uncertainties arising
from the hadronic resonance sector. As a result, the main uncertainty in this
determination is due to the value of . The correlator of
axial-vector divergences is used in perturbative QCD to five-loop order,
including quark and gluon condensate contributions, in the framework of both
Fixed Order (FOPT), and Contour Improved Perturbation Theory (CIPT). The latter
exhibits very good convergence, leading to a remarkably stable result in the
very wide range , where is the radius of the
integration contour in the complex energy (squared) plane. The value of the
strange quark mass in this framework at a scale of 2 GeV is for , respectively.Comment: Additional comments added at the end of the Conclusions, and one
extra reference is given. A note added in proof uses the most recent
determination of Lambda_QCD from ALEPH to narrow down the predictio
Higher order dilaton gravity: brane equations of motion in the covariant formulation
Dilaton gravity with general brane localized interactions is investigated.
Models with corrections up to arbitrary order in field derivatives are
considered. Effective gravitational equations of motion at the brane are
derived in the covariant approach. Dependence of such brane equations on the
bulk quantities is discussed. It is shown that the number of the bulk
independent brane equations of motion depends strongly on the symmetries
assumed for the model and for the background. Examples with two and four
derivatives of the fields are presented in more detail.Comment: 32 pages, references added, discussion extended, typos corrected,
version to be publishe
Energy Budget of Cosmological First-order Phase Transitions
The study of the hydrodynamics of bubble growth in first-order phase
transitions is very relevant for electroweak baryogenesis, as the baryon
asymmetry depends sensitively on the bubble wall velocity, and also for
predicting the size of the gravity wave signal resulting from bubble
collisions, which depends on both the bubble wall velocity and the plasma fluid
velocity. We perform such study in different bubble expansion regimes, namely
deflagrations, detonations, hybrids (steady states) and runaway solutions
(accelerating wall), without relying on a specific particle physics model. We
compute the efficiency of the transfer of vacuum energy to the bubble wall and
the plasma in all regimes. We clarify the condition determining the runaway
regime and stress that in most models of strong first-order phase transitions
this will modify expectations for the gravity wave signal. Indeed, in this
case, most of the kinetic energy is concentrated in the wall and almost no
turbulent fluid motions are expected since the surrounding fluid is kept mostly
at rest.Comment: 36 pages, 14 figure
Strange quark condensate from QCD sum rules to five loops
It is argued that it is valid to use QCD sum rules to determine the scalar
and pseudoscalar two-point functions at zero momentum, which in turn determine
the ratio of the strange to non-strange quark condensates with (). This is done in the framework
of a new set of QCD Finite Energy Sum Rules (FESR) that involve as integration
kernel a second degree polynomial, tuned to reduce considerably the systematic
uncertainties in the hadronic spectral functions. As a result, the parameters
limiting the precision of this determination are , and to a
major extent the strange quark mass. From the positivity of there
follows an upper bound on the latter: , for Comment: Minor changes to Sections 2 and
Thermal production of ultrarelativistic right-handed neutrinos: Complete leading-order results
The thermal production of relativistic right-handed Majorana neutrinos is of
importance for models of thermal leptogenesis in the early Universe.
Right-handed neutrinos can be produced both by 1 2 decay or inverse decay
and by 2 -> 2 scattering processes. In a previous publication, we have studied
the production via 1 2 (inverse) decay processes. There we have shown that
multiple scattering mediated by soft gauge boson exchange also contributes to
the production rate at leading order, and gives a strong enhancement. Here we
complete the leading order calculation by adding 2 -> 2 scattering processes
involving either electroweak gauge bosons or third-generation quarks. We find
that processes with gauge interactions give the most important contributions.
We also obtain a new sum rule for the Hard Thermal Loop resummed fermion
propagator.Comment: 27 pages, 7 figures. Error in the matrix element for the
(subdominant) subprocess with s-channel fermion exchange corrected. This
changes the corresponding phase space integral and the constant c_V.
Numerically it increases the total 2 -> 2 rate by about 2 percent and the
complete rate by about 1 percent. The main results and conclusions are
unaffecte
Rationale for UV-filtered clover fermions
We study the contributions Sigma_0 and Sigma_1, proportional to a^0 and a^1,
to the fermion self-energy in Wilson's formulation of lattice QCD with
UV-filtering in the fermion action. We derive results for m_{crit} and the
renormalization factors Z_S, Z_P, Z_V, Z_A to 1-loop order in perturbation
theory for several filtering recipes (APE, HYP, EXP, HEX), both with and
without a clover term. The perturbative series is much better behaved with
filtering, in particular tadpole resummation proves irrelevant. Our
non-perturbative data for m_{crit} and Z_A/(Z_m*Z_P) show that the combination
of filtering and clover improvement efficiently reduces the amount of chiral
symmetry breaking -- we find residual masses am_{res}=O(10^{-2}).Comment: 25 pages, 4 figures; v2: typo in eqn. (37) fixed [agrees with
published version
Direct, Indirect and Collider Detection of Neutralino Dark Matter In SUSY Models with Non-universal Higgs Masses
In supersymmetric models with gravity-mediated SUSY breaking, universality of
soft SUSY breaking sfermion masses m_0 is motivated by the need to suppress
unwanted flavor changing processes. The same motivation, however, does not
apply to soft breaking Higgs masses, which may in general have independent
masses from matter scalars at the GUT scale. We explore phenomenological
implications of both the one-parameter and two-parameter non-universal Higgs
mass models (NUHM1 and NUHM2), and examine the parameter ranges compatible with
Omega_CDM h^2, BF(b --> s,gamma) and (g-2)_mu constraints. In contrast to the
mSUGRA model, in both NUHM1 and NUHM2 models, the dark matter A-annihilation
funnel can be reached at low values of tan(beta), while the higgsino dark
matter annihilation regions can be reached for low values of m_0. We show that
there may be observable rates for indirect and direct detection of neutralino
cold dark matter in phenomenologically aceptable ranges of parameter space. We
also examine implications of the NUHM models for the Fermilab Tevatron, the
CERN LHC and a Sqrt(s)=0.5-1 TeV e+e- linear collider. Novel possibilities
include: very light s-top_R, s-charm_R squark and slepton_L masses as well as
light charginos and neutralinos and H, A and H^+/- Higgs bosons.Comment: LaTeX, 48pages, 26 Figures. The version with high resolution Figures
is available at http://hep.pa.msu.edu/belyaev/public/projects/nuhm/nuhm.p