1,173 research outputs found
Electromagnetic Cascade in the Early Universe and its Application to the Big-Bang Nucleosynthesis
We investigate the electromagnetic cascade initiated by injection of very
high energy photons in the early Universe and calculate the cascade spectrum by
solving a set of Boltzmann equations numerically. In the calculation we take
account of Compton scattering off the background electrons and pair creation
off the background nucleons as well as photon-photon processes and inverse
Compton scattering. We also apply our cascade spectrum to the big bang
nucleosynthesis with photo-dissociation processes due to heavy unstable
particles and obtain the constraint on their lifetime and abundance.Comment: 21pages (compressed and uuencoded postscript file including 6
figures
Gravitino Production in the Inflationary Universe and the Effects on Big-Bang Nucleosynthesis
Gravitino production and decay in the inflationary universe are reexamined.
Assuming that the gravitino mainly decays into a photon and a photino, we
calculate the upperbound on the reheating temperature. Compared to previous
works, we have essentially improved the following two points: (i) the helicity
gravitino production cross sections are calculated by using
the full relevant terms in the supergravity lagrangian, and (ii) the high
energy photon spectrum is obtained by solving the Boltzmann equations
numerically. Photo-dissociation of the light elements (D, T, He, He)
leads to the most stringent upperbound on the reheating temperature, which is
given by (--)GeV for the gravitino mass 100GeV--1TeV. On the
other hand, requiring that the present mass density of photino should be
smaller than the critical density, we find that the reheating temperature have
to be smaller than (--)GeV for the photino mass (10--100)GeV,
irrespectively of the gravitino mass. The effect of other decay channels is
also considered
Footprints of Supersymmetry on Higgs Decay
Motivated by future collider proposals that aim to measure the Higgs
properties precisely, we study the partial decay widths of the lightest Higgs
boson in the minimal supersymmetric standard model with an emphasis on the
parameter region where all superparticles and heavy Higgs bosons are not
accessible at the LHC. Taking account of phenomenological constraints such as
the Higgs mass, flavor constraints, vacuum stability, and perturbativity of
coupling constants up to the grand unification scale, we discuss how large the
deviations of the partial decay widths from the standard model predictions can
be. These constraints exclude large fraction of the parameter region where the
Higgs widths show significant deviation from the standard model predictions.
Nevertheless, even if superparticles and the heavy Higgses are out of the reach
of 14TeV LHC, the deviation may be large enough to be observed at future
collider experiments.Comment: 24 pages, 8 figures, version accepted in JHE
Supersymmetric Heavy Higgses at e^+e^- Linear Collider and Dark-Matter Physics
We consider the capability of the e^+e^- linear collider (which is recently
called as the International Linear Collider, or ILC) for studying the
properties of the heavy Higgs bosons in the supersymmetric standard model. We
pay special attention to the large \tan\beta region which is motivated, in
particular, by explaining the dark-matter density of the universe (i.e.,
so-called ``rapid-annihilation funnels''). We perform a systematic analysis to
estimate expected uncertainties in the masses and widths of the heavy Higgs
bosons assuming an energy and integrated luminosity of \sqrt{s}=1 TeV and L=1
ab^{-1}. We also discuss its implication to the reconstruction of the
dark-matter density of the universe.Comment: 28 pages, 13 figures, version to appear in PR
Gravitino Dark Matter with Weak-Scale Right-Handed Sneutrino
We consider cosmological implications of supersymmetric models with
right-handed (s)neutrinos where the neutrino masses are purely Dirac-type. We
pay particular attention to the case where gravitino is the lightest
superparticle while one of the right-handed sneutrinos is next-to-the-lightest
superparticle. We study constraints from big-bang nuleosynthesis and show that
the constraints could be relaxed compared to the case without right-handed
sneutrinos. As a result, the gravitino-dark-matter scenario becomes viable with
relatively large value of the gravitino mass. We also discuss constraints from
the structure formation; in our model, the free-streaming length of the
gravitino dark matter may be as long as O(1 Mpc), which is comparable to the
present observational upper bound on the scale of free-streaming.Comment: 18 pages, 6 figure
Exact Event Rates of Lepton Flavor Violating Processes in Supersymmetric SU(5) Model
Event rates of various lepton flavor violating processes in the minimal
supersymmetric SU(5) model are calculated, using exact formulas which include
Yukawa vertices of lepton-slepton-Higgsino. We find subtlety in evaluating
event rates due to partial cancellation between diagrams. This cancellation
typically reduces the event rates significantly, and the size of the reduction
strongly depends on superparticle mass spectrum.Comment: 11pages, 8 figures. Fig.5 where the mu-e conversion rates in nuclei
was shown was incorrect due to an error in our numerical computation.It is
replaced in this corrected version. All conclusions remain unchange
MSSM curvaton in the gauge-mediated SUSY breaking
We study the curvaton scenario using the MSSM flat directions in the
gauge-mediated SUSY breaking model. We find that the fluctuations in the both
radial and phase directions can be responsible for the density perturbations in
the universe through the curvaton mechanism. Although it has been considered
difficult to have a successful curvaton scenario with the use of those flat
directions, it is overcome by taking account of the finite temperature effects,
which induce a negative thermal logarithmic term in the effective potential of
the flat direction.Comment: 12 page
Renormalization-Scale Uncertainty in the Decay Rate of False Vacuum
We study radiative corrections to the decay rate of false vacua, paying
particular attention to the renormalization-scale dependence of the decay rate.
The decay rate exponentially depends on the bounce action. The bounce action
itself is renormalization scale dependent. To make the decay rate
scale-independent, radiative corrections, which are due to the field
fluctuations around the bounce, have to be included. We show quantitatively
that the inclusion of the fluctuations suppresses the scale dependence, and
hence is important for the precise calculation of the decay rate. We also apply
our analysis to a supersymmetric model and show that the radiative corrections
are important for the Higgs-stau system with charge breaking minima.Comment: 15 pages, 2 figures; added reference
On the Gauge Invariance of the Decay Rate of False Vacuum
We study the gauge invariance of the decay rate of the false vacuum for the
model in which the scalar field responsible for the false vacuum decay has
gauge quantum number. In order to calculate the decay rate, one should
integrate out the field fluctuations around the classical path connecting the
false and true vacua (i.e., so-called bounce). Concentrating on the case where
the gauge symmetry is broken in the false vacuum, we show a systematic way to
perform such an integration and present a manifestly gauge-invariant formula of
the decay rate of the false vacuum.Comment: 17 pages, published versio
Dilaton Destabilization at High Temperature
Many compactifications of higher-dimensional supersymmetric theories have
approximate vacuum degeneracy. The associated moduli fields are stabilized by
non-perturbative effects which break supersymmetry. We show that at finite
temperature the effective potential of the dilaton acquires a negative linear
term. This destabilizes all moduli fields at sufficiently high temperature. We
compute the corresponding critical temperature which is determined by the scale
of supersymmetry breaking, the beta-function associated with gaugino
condensation and the curvature of the K"ahler potential, T_crit ~ (m_3/2
M_P)^(1/2) (3/\beta)^(3/4) (K'')^(-1/4). For realistic models we find T_crit ~
10^11-10^12 GeV, which provides an upper bound on the temperature of the early
universe. In contrast to other cosmological constraints, this upper bound
cannot be circumvented by late-time entropy production.Comment: 19 pages, 9 figure
- …