77 research outputs found
First direct limits on lightly ionizing particles with electric charge less than e/6
Artículo escrito por muchos autores, sólo se referencian el primero, los autores que firman como Universidad Autónoma de Madrid y el grupo de colaboración en el caso de que aparezca en el artículoWhile the standard model of particle physics does not include free particles with fractional charge, experimental searches have not ruled out their existence. We report results from the Cryogenic Dark Matter Search (CDMS II) experiment that give the first direct-detection limits for cosmogenically produced relativistic particles with electric charge lower than e/6. A search for tracks in the six stacked detectors of each of two of the CDMS II towers finds no candidates, thereby excluding new parameter space for particles with electric charges between e/6 and e/200This work is supported in part by the National Science Foundation, by the U.S. Department of Energy, by NSERC Canada, and by MultiDark (Spanish MINECO). Fermilab is operated by the Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359. SLAC is operated under Contract No. DE-AC02-76SF00515 with the U.S. Department of Energ
Hiding the Higgs at the LHC
We study a simple extension of the standard model where scalar singlets that
mix with the Higgs doublet are added. This modification to the standard model
could have a significant impact on Higgs searches at the LHC. The Higgs doublet
is not a mass eigenstate and therefore the expected nice peak of the standard
model Higgs disappears. We analyze this scenario finding the required
properties of the singlets in order to make the Higgs "invisible" at the LHC.
In some part of the parameter space even one singlet could make the discovery
of the SM Higgs problematic. In other parts, the Higgs can be discovered even
in the presence of many singlets.Comment: 9 pages, 1 figure. V2- References added. V3- Several examples and one
fig. adde
Reheating Temperature and Gauge Mediation Models of Supersymmetry Breaking
For supersymmetric theories with gravitino dark matter, the maximal reheating
temperature consistent with big bang nucleosynthesis bounds arises when the
physical gaugino masses are degenerate. We consider the cases of a stau or
sneutrino next-to-lightest superpartner, which have relatively less constraint
from big bang nucleosynthesis. The resulting parameter space is consistent with
leptogenesis requirements, and can be reached in generalized gauge mediation
models. Such models illustrate a class of theories that overcome the well-known
tension between big bang nucleosynthesis and leptogenesis.Comment: 30 pages, 4 figures; v2: refs adde
Theoretical predictions for the direct detection of neutralino dark matter in the NMSSM
We analyse the direct detection of neutralino dark matter in the framework of
the Next-to-Minimal Supersymmetric Standard Model. After performing a detailed
analysis of the parameter space, taking into account all the available
constraints from LEPII, we compute the neutralino-nucleon cross section, and
compare the results with the sensitivity of detectors. We find that sizable
values for the detection cross section, within the reach of dark matter
detectors, are attainable in this framework. For example, neutralino-proton
cross sections compatible with the sensitivity of present experiments can be
obtained due to the exchange of very light Higgses with m_{h_1^0}\lsim 70
GeV. Such Higgses have a significant singlet composition, thus escaping
detection and being in agreement with accelerator data. The lightest neutralino
in these cases exhibits a large singlino-Higgsino composition, and a mass in
the range 50\lsim m_{\tilde\chi_1^0}\lsim 100 GeV.Comment: Final version to appear in JHEP. References added. LaTeX, 53 pages,
23 figure
Effects of Residue Background Events in Direct Dark Matter Detection Experiments on the Determination of the WIMP Mass
In the earlier work on the development of a model-independent data analysis
method for determining the mass of Weakly Interacting Massive Particles (WIMPs)
by using measured recoil energies from direct Dark Matter detection experiments
directly, it was assumed that the analyzed data sets are background-free, i.e.,
all events are WIMP signals. In this article, as a more realistic study, we
take into account a fraction of possible residue background events, which pass
all discrimination criteria and then mix with other real WIMP-induced events in
our data sets. Our simulations show that, for the determination of the WIMP
mass, the maximal acceptable fraction of residue background events in the
analyzed data sets of O(50) total events is ~20%, for background windows of the
entire experimental possible energy ranges, or in low energy ranges; while, for
background windows in relatively higher energy ranges, this maximal acceptable
fraction of residue background events can not be larger than ~10%. For a WIMP
mass of 100 GeV with 20% background events in the windows of the entire
experimental possible energy ranges, the reconstructed WIMP mass and the
1-sigma statistical uncertainty are ~97 GeV^{+61%}_{-35%} (~94
GeV^{+55%}_{-33%} for background-free data sets).Comment: 27 pages, 22 eps figures; v2: revised version for publication,
references added and update
Lepton flavour violation in future linear colliders in the long-lived stau NLSP scenario
We analyze the prospects of observing lepton flavour violation in future e-e-
and e+e- linear colliders in scenarios where the gravitino is the lightest
supersymmetric particle, and the stau is the next-to-lightest supersymmetric
particle. The signals consist of multilepton final states with two heavily
ionizing charged tracks produced by the long-lived staus. The Standard Model
backgrounds are very small and the supersymmetric backgrounds can be kept well
under control by the use of suitable kinematical cuts. We discuss in particular
the potential of the projected International Linear Collider to discover lepton
flavour violation in this class of scenarios, and we compare the estimated
sensitivity with the constraints stemming from the non-observation of rare
decays.Comment: 30 pages, 12 figures. Discussion extended to include the efficiency
of identifying long-lived staus, references added. To appear in JHE
Determining Reheating Temperature at Colliders with Axino or Gravitino Dark Matter
After a period of inflationary expansion, the
Universe reheated and reached full thermal equilibrium at the reheating
temperature T_R. In this work we point out that, in the context of effective
low-energy supersymmetric models, LHC measurements may allow one to determine
T_R as a function of the mass of the dark matter particle assumed to be either
an axino or a gravitino. An upper bound on their mass may also be derived.Comment: 19 pages, some improvements, JHEP versio
An origin for small neutrino masses in the NMSSM
We consider the Next to Minimal Supersymmetric Standard Model (NMSSM) which
provides a natural solution to the so-called mu problem by introducing a new
gauge-singlet superfield S. We realize that a new mechanism of neutrino mass
suppression, based on the R-parity violating bilinear terms mu_i L_i H_u mixing
neutrinos and higgsinos, arises within the NMSSM, offering thus an original
solution to the neutrino mass problem (connected to the solution for the mu
problem). We generate realistic (Majorana) neutrino mass values without
requiring any strong hierarchy amongst the fundamental parameters, in contrast
with the alternative models. In particular, the ratio |mu_i/mu| can reach about
10^-1, unlike in the MSSM where it has to be much smaller than unity. We check
that the obtained parameters also satisfy the collider constraints and internal
consistencies of the NMSSM. The price to pay for this new cancellation-type
mechanism of neutrino mass reduction is a certain fine tuning, which get
significantly improved in some regions of parameter space. Besides, we discuss
the feasibility of our scenario when the R-parity violating bilinear terms have
a common origin with the mu term, namely when those are generated via a VEV of
the S scalar component from the couplings lambda_i S L_i H_u. Finally, we make
comments on some specific phenomenology of the NMSSM in the presence of
R-parity violating bilinear terms.Comment: 21 pages, 5 figures, Latex fil
On B_s -> mu+ mu- and Cold Dark Matter Scattering in the MSSM with Non-Universal Higgs Masses
We show that present experimental constraints on B_s -> mu+ mu- decay and the
CDMS upper limit on the cold dark matter elastic scattering cross section
already have significant impact on the parameter space of the minimal
supersymmetric extension of the Standard Model (MSSM) with non-universal
supersymmetry-breaking scalar masses for the Higgs multiplets (NUHM). The
relaxation of scalar universality in the MSSM allows the possibility of a
relatively light mass M_A for the pseudoscalar Higgs boson. The present upper
limit on B_s -> mu+ mu- already excludes much of the scope for this possibility
in the NUHM, in contrast to the constrained MSSM with universal scalar masses
(CMSSM), where B_s -> mu+ mu- decay does not exclude any ranges of parameters
not already excluded by b -> s \gamma decay. Cold dark matter scattering is
also enhanced for small M_A, but the impact of present upper limit on B_s ->
mu+ mu- on the NUHM parameter space is in many cases greater than that of the
CDMS scattering limit, particularly at large tanb.Comment: 17 pages, 14 eps figure
Non-universal gaugino masses: a signal-based analysis for the Large Hadron Collider
We discuss the signals at the Large Hadron Collider (LHC) for scenarios with
non-universal gaugino masses in supersymmetric (SUSY) theories. We perform a
multichannel analysis, and consider the ratios of event rates in different
channels such as , - and -
, as well as and final states
together with . Low-energy SUSY spectra corresponding to
high-scale gaugino non-universality arising from different breaking schemes of
SU(5) as well as SO(10) Grand Unified (GUT) SUSY models are considered, with
both degenerate low-energy sfermion masses and those arising from a
supergravity scenario. We present the numerical predictions over a wide range
of the parameter space using the event generator {\tt Pythia}, specifying the
event selection criteria and pointing out regions where signals are likely to
be beset with backgrounds. Certain broad features emerge from the study, which
may be useful in identifying the signatures of different GUT breaking schemes
and distinguishing them from a situation with a universal gaugino mass at high
scale. The absolute values of the predicted event rates for different scenarios
are presented together with the various event ratios, so that these can also be
used whenever necessary.Comment: 54 pages, 18 figure
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