15,135 research outputs found
How heavy can the Fermions in Split Susy be? A study on Gravitino and Extradimensional LSP
In recently introduced Split Susy theories, in which the scale of Susy
breaking is very high, the requirement that the relic abundance of the Lightest
SuperPartner (LSP) provides the Dark Matter of the Universe leads to the
prediction of fermionic superpartners around the weak scale. This is no longer
obviously the case if the LSP is a hidden sector field, such as a Gravitino or
an other hidden sector fermion, so, it is interesting to study this scenario.
We consider the case in which the Next-Lightest SuperPartner (NLSP) freezes out
with its thermal relic abundance, and then it decays to the LSP. We use the
constraints from BBN and CMB, together with the requirement of attaining Gauge
Coupling Unification and that the LSP abundance provides the Dark Matter of the
Universe, to infer the allowed superpartner spectrum. As very good news for a
possible detaction of Split Susy at LHC, we find that if the Gravitino is the
LSP, than the only allowed NLSP has to be very purely photino like. In this
case, a photino from 700 GeV to 5 TeV is allowed, which is difficult to test at
LHC. We also study the case where the LSP is given by a light fermion in the
hidden sector which is naturally present in Susy breaking in Extra Dimensions.
We find that, in this case, a generic NLSP is allowed to be in the range 1-20
TeV, while a Bino NLSP can be as light as tens of GeV.Comment: 29 pages, 12 figures. v2: modified conclusions for bino NLSP. v3:
corrected small mistake in Gauge Coupling Unification, conclusions unchange
Conservation Laws and the Multiplicity Evolution of Spectra at the Relativistic Heavy Ion Collider
Transverse momentum distributions in ultra-relativistic heavy ion collisions
carry considerable information about the dynamics of the hot system produced.
Direct comparison with the same spectra from collisions has proven
invaluable to identify novel features associated with the larger system, in
particular, the "jet quenching" at high momentum and apparently much stronger
collective flow dominating the spectral shape at low momentum. We point out
possible hazards of ignoring conservation laws in the comparison of high- and
low-multiplicity final states. We argue that the effects of energy and momentum
conservation actually dominate many of the observed systematics, and that
collisions may be much more similar to heavy ion collisions than generally
thought.Comment: 15 pages, 14 figures, submitted to PRC; Figures 2,4,5,6,12 updated,
Tables 1 and 3 added, typo in Tab.V fixed, appendix B partially rephrased,
minor typo in Eq.B1 fixed, minor wording; references adde
Particle-Antiparticle Asymmetry Due to Non-Renormalizable Effective Interactions
We consider a model for generating a particle-antiparticle asymmetry through
out-of-equilibrium decays of a massive particle due to non-renormalizable,
effective interactions.Comment: preliminary version, 38 pages; LaTeX source, epsf.sty and EPS files
included in tar archiv
Comparison of Models of Critical Opacity in the Quark-Gluon Plasma
In this work we discuss two methods of calculation of quark propagation in
the quark-gluon plasma. Both methods make use of the Nambu-Jona-Lasinio model.
The essential difference of these calculations is the treatment of
deconfinement. A model of confinement is not included in the work of Gastineau,
Blanquier and Aichelin [hep-ph/0404207], however, the meson states they
consider are still bound for temperatures greater than the deconfinement
temperature T_c. On the other hand, our model deals with unconfined quarks and
includes a description of the q(bar)q resonances found in lattice QCD studies
that make use of the maximum entropy method (MEM). We compare the q{bar)q cross
sections calculated in these models.Comment: 7 pages and 4 figures RevTe
Axion constraints in non-standard thermal histories
It is usually assumed that dark matter is produced during the radiation
dominated era. There is, however, no direct evidence for radiation domination
prior to big-bang nucleosynthesis. Two non-standard thermal histories are
considered. In one, the low-temperature-reheating scenario, radiation
domination begins as late as 1 MeV, and is preceded by significant entropy
generation. Thermal axion relic abundances are then suppressed, and
cosmological limits to axions are loosened. For reheating temperatures less
than 35 MeV, the large-scale structure limit to the axion mass is lifted. The
remaining constraint from the total density of matter is significantly relaxed.
Constraints are also relaxed for higher reheating temperatures. In a kination
scenario, a more modest change to cosmological axion constraints is obtained.
Future possible constraints to axions and low-temperature reheating from the
helium abundance and next-generation large-scale-structure surveys are
discussed.Comment: 10 pages, 7 figures, revised to match version published in Phys. Rev.
D. Fig. 7 and Eq. (20) modifie
Gamma rays from ultracompact primordial dark matter minihalos
Ultracompact minihalos have recently been proposed as a new class of dark
matter structure. These minihalos would be produced by phase transitions in the
early Universe or features in the inflaton potential, and constitute
non-baryonic massive compact halo objects (MACHOs) today. We examine the
prospect of detecting ultracompact minihalos in gamma-rays if dark matter
consists of self-annihilating particles. We compute present-day fluxes from
minihalos produced in the electron-positron annihilation epoch, and the QCD and
electroweak phase transitions in the early Universe. Even at a distance of 100
pc, minihalos produced during the electron-positron annihilation epoch should
be eminently detectable today, either by the Fermi satellite, current Air
Cherenkov telescopes, or even in archival EGRET data. Within ~1 pc, minihalos
formed in the QCD phase transition would have similar predicted fluxes to the
dwarf spheroidal galaxies targeted by current indirect dark matter searches, so
might also be detectable by present or upcoming experiments.Comment: 5 pages, 3 figures. Minor update to match published version of
erratu
Pragmatic approach to the little hierarchy problem: the case for Dark Matter and neutrino physics
We show that the addition of real scalars (gauge singlets) to the Standard
Model can both ameliorate the little hierarchy problem and provide realistic
Dark Matter candidates. To this end, the coupling of the new scalars to the
standard Higgs boson must be relatively strong and their mass should be in the
1-3 TeV range, while the lowest cutoff of the (unspecified) UV completion must
be >~ 5 TeV, depending on the Higgs boson mass and the number of singlets
present. The existence of the singlets also leads to realistic and surprisingly
reach neutrino physics. The resulting light neutrino mass spectrum and mixing
angles are consistent with the constraints from the neutrino oscillations.Comment: discussion of multi singlet case adde
Heavy quarks and the collective properties of hot QCD
After reviewing the evidence that QCD matter at ultrarelativistic energies
behaves as a very good fluid, we describe the connection of QCD fluidity to
heavy quark observables. We review the way in which heavy quark spectra can
place tighter limits on the viscosity of QCD matter. Finally, we show that
correlations between flow observables and the event-by-event charm quark
abundance ("flavoring") can shed light on the system's equation of state.Comment: Talk given at BEACH2010 conference, Perugia, Italy Published in
Nuclear Physics B (proceedings supplement), NUPHBP1364
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