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

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 $jets + {E}_T/$, $same$ - and $opposite$-$sign dileptons$ $+jets+ {E}_T/$, as well as $single-lepton$ and $trilepton$ final states together with $jets + {E}_T/$ . 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

μ−e\mu-e conversion in nuclei within the CMSSM seesaw: universality versus non-universality

In this paper we study $\mu-e$ conversion in nuclei within the context of the Constrained Minimal Supersymmetric Standard Model, enlarged by three right handed neutrinos and their supersymmetric partners, and where the neutrino masses are generated via a seesaw mechanism. Two different scenarios with either universal or non-universal soft supersymmetry breaking Higgs masses at the gauge coupling unification scale are considered. In the first part we present a complete one-loop computation of the conversion rate for this process that includes the photon-, $Z$-boson, and Higgs-boson penguins, as well as box diagrams, and compare their size in the two considered scenarios. Then, in these two scenarios we analyse the relevance of the various parameters on the conversion rates, particularly emphasising the role played by the heavy neutrino masses, $\tan \beta$, and especially $\theta_{13}$. In the case of hierachical heavy neutrinos, an extremely high sensitivity of the rates to $\theta_{13}$ is indeed found. The last part of this work is devoted to the study of the interesting loss of correlation between the $\mu-e$ conversion and $\mu \to e \gamma$ rates that occurs in the non-universal scenario. In the case of large $\tan \beta$ and light $H^0$ Higgs boson an enhanced ratio of the $\mu-e$ to $\mu \to e \gamma$ rates, with respect to the universal case is found, and this could be tested with the future experimental sensitivities.Comment: 48 pages, 15 figures. Minor typos corrected and some references adde