346 research outputs found
A Simple Way of Calculating Cosmological Relic Density
A simple procedure is presented which leads to a dramatic simplification in
the calculation of the relic density of stable particles in the Universe.Comment: 7 pages in LaTex, no figures; University of Michigan preprint
UM-TH-94-02 (February 1994). Changes: a coefficient in (Eq. 16)
corrected; added Acknowledgements and revised Note Added; plain LaTex only
(no need to use RevTex
Light Heavy MSSM Higgs Bosons at Large tan_beta
The region of MSSM Higgs parameter space currently excluded by the CDF
Collaboration, based on an analysis of ~1 fb^-1 of integrated luminosity, is
less than the expected sensitivity. We analyze the potential implications of
the persistence of this discrepancy within the MSSM, assuming that the soft
supersymmetry-breaking contributions to scalar masses are universal, apart from
those to the Higgs masses (the NUHM model). We find that a light heavy MSSM
Higgs signal in the unexcluded part of the sensitive region could indeed be
accommodated in this simple model, even after taking into account other
constraints from cold dark matter, electroweak precision observables and B
physics observables. In this case the NUHM suggests that supersymmetric
signatures should also be detectable in the near future in some other
measurements such as BR(B_s -> mu+ mu-), BR(b -> s gamma) and (g-2)_mu, and M_h
would have to be very close to the LEP exclusion limit. In addition, the dark
matter candidate associated with this model should be on the verge of detection
in direct detection experiments.Comment: 14 pages, 2 figure
Recommended from our members
TECHNICAL DESIGN REPORT OF THE FORWARD SILICON VERTEX (FVTX)
The main goal of the RHIC heavy ion program is the discovery of the novel ultra-hot high-density state of matter predicted by the fundamental theory of strong interactions and created in collisions of heavy nuclei, the Quark-Gluon Plasma (QGP). From measurements of the large elliptic flow of light mesons and baryons and their large suppression at high transverse momentum pT that have been made at RHIC, there is evidence that new degrees of freedom, characteristic of a deconfined QCD medium, drive the dynamics of nucleus-nucleus collisions. It has been recognized, however, that the potential of light quarks and gluons to characterize the properties of the QGP medium is limited and the next phase of the RHIC program calls for the precise determination of its density, temperature, opacity and viscosity using qualitatively new probes, such as heavy quarks. We propose the construction of two Forward Silicon Vertex Trackers (FVTX) for the PHENIX experiment that will directly identify and distinguish charm and beauty decays within the acceptance of the muon spectrometers. The FVTX will provide this essential coverage over a range of forward and backward rapidities (1.2 < |y| < 2.4)--a rapidity range coverage which not only brings significantly larger acceptance to PHENIX but which is critical for separating cold nuclear matter effects from QGP effects and is critical for measuring the proton spin contributions over a significant fraction of the kinematic range of interest. In addition, the FVTX will provide greatly reduced background and improved mass resolution for dimuon events, culminating in the first measurements of the {upsilon}{prime} and Drell-Yan at RHIC. These same heavy flavor and dimuon measurements in p+p collisions will allow us to place significant constraints on the gluon and sea quark contributions to the proton's spin and to make fundamentally new tests of the Sivers function universality
Looking for magnetic monopoles at LHC with diphoton events
Magnetic monopoles have been a subject of interest since Dirac established
the relation between the existence of monopoles and charge quantization. The
intense experimental search carried thus far has not met with success. The
Large Hadron Collider is reaching energies never achieved before allowing the
search for exotic particles in the TeV mass range. In a continuing effort to
discover these rare particles we propose here other ways to detect them. We
study the observability of monopoles and monopolium, a monopole-antimonopole
bound state, at the Large Hadron Collider in the channel for
monopole masses in the range 500-1000 GeV. We conclude that LHC is an ideal
machine to discover monopoles with masses below 1 TeV at present running
energies and with 5 fb of integrated luminosity.Comment: This manuscript contains information appeared in Looking for magnetic
monopoles at LHC, arXiv:1104.0218 [hep-ph] and Monopolium detection at the
LHC.,arXiv:1107.3684 [hep-ph] by the same authors, rewritten for joint
publication in The European Physica Journal Plus. 26 pages, 22 figure
The Higgs intense--coupling regime in constrained SUSY models and its astrophysical implications
We analyze the Higgs intense--coupling regime, in which all Higgs particles
of the Minimal Supersymmetric Standard Model are light with masses of the same
order and the value of \tb the ratio of vacuum expectation values of the two
Higgs fields is large, in the framework of Supergravity scenarios with
non--universal soft Supersymmetry breaking scalar masses in the Higgs sector.
In particular, we calculate the relic density abundance of the lightest
neutralino candidate for cold dark matter and the rates in direct and indirect
detection at present and future experiments. We first show that while in the
mSUGRA model this regime is disfavored by present data, there are regions in
the parameter space of models with non--universal Higgs masses where it can
occur. We then show that because of the large value of and the
relatively low values of the neutral Higgs boson masses, the cross section for
neutralino--nucleon scattering is strongly enhanced in this regime and would
allow for the observation of a signal in direct detection experiments such as
CDMS--Soudan. The expected sensitivity of gamma--ray detectors like GLAST might
be also sufficient to observe the annihilation of neutralinos in such a regime.Comment: 19 pages, 5 figure
Charged Higgs bosons in the Next-to MSSM (NMSSM)
The charged Higgs boson decays and
are studied in the framework of the next-to Minimal Supersymmetric Standard
Model (NMSSM). It is found that the decay rate for can
exceed the rates for the and channels both below and above
the top-bottom threshold. The dominance of is most readily
achieved when has a large doublet component and small mass. We also study
the production process at the LHC followed by the decay
which leads to the signature . We suggest
that is a promising discovery channel for a light charged
Higgs boson in the NMSSM with small or moderate and dominant decay
mode . This signature can also arise from
the Higgsstrahlung process followed by the decay . It is shown that there exist regions of parameter space where these
processes can have comparable cross sections and we suggest that their
respective signals can be distinguished at the LHC by using appropriate
reconstruction methods.Comment: 20 pages, 22 eps figures, more reference adde
Mixed Higgsino Dark Matter from a Large SU(2) Gaugino Mass
We observe that in SUSY models with non-universal GUT scale gaugino mass
parameters, raising the GUT scale SU(2) gaugino mass |M_2| from its unified
value results in a smaller value of -m_{H_u}^2 at the weak scale. By the
electroweak symmetry breaking conditions, this implies a reduced value of \mu^2
{\it vis \`a vis} models with gaugino mass unification. The lightest neutralino
can then be mixed Higgsino dark matter with a relic density in agreement with
the measured abundance of cold dark matter (DM). We explore the phenomenology
of this high |M_2| DM model. The spectrum is characterized by a very large wino
mass and a concomitantly large splitting between left- and right- sfermion
masses. In addition, the lighter chargino and three light neutralinos are
relatively light with substantial higgsino components. The higgsino content of
the LSP implies large rates for direct detection of neutralino dark matter, and
enhanced rates for its indirect detection relative to mSUGRA. We find that
experiments at the LHC should be able to discover SUSY over the portion of
parameter space where m_{\tg} \alt 2350-2750 ~GeV, depending on the squark
mass, while a 1 TeV electron-positron collider has a reach comparable to that
of the LHC. The dilepton mass spectrum in multi-jet + \ell^+\ell^- + \eslt
events at the LHC will likely show more than one mass edge, while its shape
should provide indirect evidence for the large higgsino content of the decaying
neutralinos.Comment: 36 pages with 26 eps figure
Neutralino, axion and axino cold dark matter in minimal, hypercharged and gaugino AMSB
Supersymmetric models based on anomaly-mediated SUSY breaking (AMSB)
generally give rise to a neutral wino as a WIMP cold dark matter (CDM)
candidate, whose thermal abundance is well below measured values. Here, we
investigate four scenarios to reconcile AMSB dark matter with the measured
abundance: 1. non-thermal wino production due to decays of scalar fields ({\it
e.g} moduli), 2. non-thermal wino production due to decays of gravitinos, 3.
non-thermal wino production due to heavy axino decays, and 4. the case of an
axino LSP, where the bulk of CDM is made up of axions and thermally produced
axinos. In cases 1 and 2, we expect wino CDM to constitute the entire measured
DM abundance, and we investigate wino-like WIMP direct and indirect detection
rates. Wino direct detection rates can be large, and more importantly, are
bounded from below, so that ton-scale noble liquid detectors should access all
of parameter space for m_{\tz_1}\alt 500 GeV. Indirect wino detection rates via
neutrino telescopes and space-based cosmic ray detectors can also be large. In
case 3, the DM would consist of an axion plus wino admixture, whose exact
proportions are very model dependent. In this case, it is possible that both an
axion and a wino-like WIMP could be detected experimentally. In case 4., we
calculate the re-heat temperature of the universe after inflation. In this
case, no direct or indirect WIMP signals should be seen, although direct
detection of relic axions may be possible. For each DM scenario, we show
results for the minimal AMSB model, as well as for the hypercharged and gaugino
AMSB models.Comment: 29 pages including 13 figure
Photon-Photon and Pomeron-Pomeron Processes in Peripheral Heavy Ion Collisions
We estimate the cross sections for the production of resonances, pion pairs
and a central cluster of hadrons in peripheral heavy-ion collisions through
two-photon and double-pomeron exchange, at energies that will be available at
RHIC and LHC. The effect of the impact parameter in the diffractive reactions
is introduced, and imposing the condition for realistic peripheral collisions
we verify that in the case of very heavy ions the pomeron-pomeron contribution
is indeed smaller than the electromagnetic one. However, they give a
non-negligible background in the collision of light ions. This diffractive
background will be more important at RHIC than at LHC.Comment: 22 pages, 1 Postscript figures, 4 tables, to appear in Phys. Rev.
The Minimal Supersymmetric Fat Higgs Model
We present a calculable supersymmetric theory of a composite ``fat'' Higgs
boson. Electroweak symmetry is broken dynamically through a new gauge
interaction that becomes strong at an intermediate scale. The Higgs mass can
easily be 200-450 GeV along with the superpartner masses, solving the
supersymmetric little hierarchy problem. We explicitly verify that the model is
consistent with precision electroweak data without fine-tuning. Gauge coupling
unification can be maintained despite the inherently strong dynamics involved
in electroweak symmetry breaking. Supersymmetrizing the Standard Model
therefore does not imply a light Higgs mass, contrary to the lore in the
literature. The Higgs sector of the minimal Fat Higgs model has a mass spectrum
that is distinctly different from the Minimal Supersymmetric Standard Model.Comment: 13 pages, 5 figures, REVTe
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