382 research outputs found
Prospects for sgoldstino search at the LHC
In this paper we estimate the LHC sgoldstino discovery potential for the
signatures with gamma gamma and ZZ in a final state.Comment: 12 pages, 12 figures; journal version: minor change
Distinguishing between R^2-inflation and Higgs-inflation
We present three features which can be used to distinguish the R^2-inflation
Higgs-inflation from with ongoing, upcoming and planned experiments, assuming
no new physics (apart form sterile neutrinos) up to inflationary scale. (i)
Slightly different tilt of the scalar perturbation spectrum n_s and ratio r of
scalar-to-tensor perturbation amplitudes. (ii) Gravity waves produced within
R^2-model by collapsing, merging and evaporating scalaron clumps formed in the
post-inflationary Universe. (iii) Different ranges of the possible Standard
Model Higgs boson masses, where the electroweak vacuum remains stable while the
Universe evolves after inflation. Specifically, in the R^2-model Higgs boson
can be as light as 116 GeV. These effects mainly rely on the lower reheating
temperature in the R^2-inflation.Comment: 10 pages, updated to match the journal version (various
clarifications added compared to v1
Free scalar dark matter candidates in R^2-inflation: the light, the heavy and the superheavy
Gravity takes care of both inflation and subsequent reheating in
Starobinsky's R^2-model. The latter is due to inflaton gravitation decays
dominated by scalar particle production. It is tempting to suggest that dark
matter particles are also produced in this process. Since free scalars being
too hot cannot serve as viable dark matter (Phys.Lett.B700:157-162,2011), we
further study the issue considering two options: scalars with non-minimal
coupling to gravity and superheavy scalars generated at inflationary stage. We
found that the first option allows for viable warm or cold dark matter if
scalar mass exceeds 0.8 MeV. The second option implies supercold dark matter
with particle mass 10^16 GeV, which production is saturated at the end of
inflation when inflaton-dependent scalar mass rapidly changes and violates
adiabaticity. Similar result holds for superheavy fermion dark matter.Comment: 15 pages, 3 figures; journal versio
Non-renormalization of induced charges and constraints on strongly coupled theories
It is shown that global fermionic charges induced in vacuum by slowly
varying, topologically non-trivial background scalar fields are not
renormalized provided that expansion in momenta of background fields is valid.
This suggests that strongly coupled theories obey induced charge matching
conditions which are analogous, but generally not equivalent, to 't Hooft
anomaly matching conditions. We give a few examples of induced charge matching.
In particular, the corresponding constraints in softly broken supersymmetric
QCD suggest non-trivial low energy mass pattern, in full accord with the
results of direct analyses.Comment: 19 pages, LaTeX, two PS figures; Submitted to special issue of Phys.
Reports dedicated to 70th birthday of L.B.Oku
Scalaron the mighty: producing dark matter and baryon asymmetry at reheating
In R^2-inflation scalaron slow roll is responsible for the inflationary
stage, while its oscillations reheat the Universe. We find that the same
scalaron decays induced by gravity can also provide the dark matter production
and leptogenesis. With R^2-term and three Majorana fermions added to the
Standard Model, we arrive at the phenomenologically complete theory capable of
simultaneously explaining neutrino oscillations, inflation, reheating, dark
matter and baryon asymmetry of the Universe. Besides the seesaw mechanism in
neutrino sector, we use only gravity, which solves all the problems by
exploiting scalaron.Comment: 13 pages; v2: minor corrections; v3: 14 pages, journal versio
TESLA: Potentials of and Options in Stoponium Searches
In some supersymmetric extensions of the Standard Model fairly light
superpartner of t-quark is predicted, which may form bound states - stoponiums.
We estimate potentials of TESLA linear collider in search for stoponium,
considering the basic e+e- option and the gamma-gamma option (Photon Linear
Collider - PLC).
It is found that PLC could be the best machine for discovery of these new
narrow strong resonances. It can produce thousands stoponiums per 100 fb
integrated luminosity in the high energy peak. In the case of scenarios when
stoponium decays mainly into gluons the signal/background ratio is about 1/4.
The channel S->hh into two lightest Higgs bosons could be also seen with high
significance. Thus, several weeks run is sufficient for the stoponium
discovery, if its mass is approximately known (e.g. from observation of direct
stops production at LHC). Then, in MSSM scenarios with dominant S->hh decay PLC
shows excellent possibilities to discover bound state of stops, practically
immediately after beginning of operating.
The e+e- option also has some prospects to observe stoponium but only in the
case of scenarios with dominant decay into two lightest Higgs bosons, with tens
of events per 100 . Interesting possibility appears in the case when
the resonance is seated on 0.1% width luminosity peak - one could resolve the
stoponium exited states.Comment: Standard LaTeX, 15 pages, 2 figures, uses elsart.cls. Talk at the
International Workshop on High Energy Photon Colliders (GG2000, DESY,
Hamburg, June 14-17, 2000), to be published in Nucl. Instr. and Meth. A.
Numbers for e+e- production are change
A comparative study of correlations between arrival directions of ultra-high-energy cosmic rays and positions of their potential astrophysical sources
We consider various classes of persistent extragalactic astrophysical sources
which have been suggested in literature as possible emitters of
ultra-high-energy cosmic rays (UHECR). We compare the strength of the claimed
correlations by a uniform procedure for all classes of sources by making use of
the AGASA, Yakutsk and HiRes stereo data. BL Lac type objects correlate with
the cosmic rays detected by all three independent experiments and are more
probably, compared to other astrophysical sources, related to the UHECR origin.
With the account of the Galactic magnetic field (not possible for the HiRes
data at the moment), apart of BL Lac type objects, unidentified gamma-ray
sources may be correlated with AGASA and Yakutsk cosmic rays.Comment: 22 pages, 3 PS figure
Graviton emission from the brane in the bulk in a model with extra dimension
In a model of 3-brane embedded in 5D space-time we calculate the graviton
emission from the brane to the bulk. Matter is confined to the brane, gravitons
produced in reactions of matter on the brane escape to the bulk. The Einstein
equations which are modified by the terms due to graviton production are solved
perturbatively, the leading order being that without the graviton production.
In the period of late cosmology, in which in the generalized Friedmann equation
the term linear in the energy density of matter in dominant, we calculate the
spectrum of gravitons (of the tower of Kaluza-Klein states) and the collision
integral in the Boltzmann equation. We find the energy-momentum tensor of the
emitted gravitons in the bulk, and using it show that corrections due to
graviton production to the leading-order terms in the Einstein equations are
small, and the perturbative approach is justified. We calculate the difference
of abundances of produced in primordial nucleosynthesis in the models
with and without the graviton production, and find that the difference is a
very small number, much smaller than that estimated previously.Comment: 26 pages, LaTeX Published version with small modification
Technically natural dark energy from Lorentz breaking
We construct a model of dark energy with a technically natural small
contribution to cosmic acceleration, i.e. this contribution does not receive
corrections from other scales in the theory. The proposed acceleration
mechanism appears generically in the low-energy limit of gravity theories with
violation of Lorentz invariance that contain a derivatively coupled scalar
field Theta. The latter may be the Goldstone field of a broken global symmetry.
The model, that we call Theta-CDM, is a valid effective field theory up to a
high cutoff just a few orders of magnitude below the Planck scale. Furthermore,
it can be ultraviolet-completed in the context of Horava gravity. We discuss
the observational predictions of the model. Even in the absence of a
cosmological constant term, the expansion history of the Universe is
essentially indistinguishable from that of Lambda-CDM. The difference between
the two theories appears at the level of cosmological perturbations. We find
that in Theta-CDM the matter power spectrum is enhanced at subhorizon scales
compared to Lambda-CDM. This property can be used to discriminate the model
from Lambda-CDM with current cosmological data.Comment: A few equations in the Appendix correcte
Superluminal Travel Made Possible (in two dimensions)
We argue that superluminal signal propagation is possible in consistent
Poincare invariant quantum field theories in two space-time dimensions,
provided spatial parity is broken. This happens due to existence of the
``instantaneous'' causal structure, with one of the light cone variables being
a global time. In two dimensions this causal structure is invariant under the
Poincare group if one gives up the spatial parity. As a non-trivial example of
a consistent interacting quantum field theory with this causal structure we
discuss a non-linear SO(1,1) sigma-model, where SO(1,1) is the Lorentz
symmetry. We show that this theory is asymptotically free and argue that this
model is also well defined non-perturbatively, at least for some values of
parameters. It provides an example of a microscopic Poincare invariant quantum
field theory with local action, but non-local physical properties. Being
coupled to gravity this ``instantaneous'' theory mixes with the Liouville
field. If proves to be consistent, the resulting model can be used to construct
(non-critical) string theories with very unconventional properties by
introducing the instantaneous causal structure on the world-sheet.Comment: 33 pages, 13 figure
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