25 research outputs found
Mixed Axion/Axino Dark Matter in mSUGRA and Yukawa-unified SUSY
Axion/axino dark matter (DM) is explored in the minimal supergravity (mSUGRA)
and Yukawa-unified supersymmetric grand-unified theory (SUSY GUT) models with
surprising results. For this type of scenario, relic DM abundance has three
components: {\it i}.) cold axions, {\it ii.}) warm axinos from neutralino
decay, and {\it iii.}) cold or warm thermally produced axinos. Reheat
temperatures exceeding GeV are required in order to solve the
gravitino/Big Bang Nucleosynthesis (BBN) problem while also allowing for
baryogensis via non-thermal leptogenesis. In order to attain high enough reheat
temperatures, we also need high values of the Peccei-Quinn (PQ) breaking scale
on the order - GeV.Comment: Typographical corrections. 4 pages, 3 figures, parallel talk
presented at the 17th International Conference on Supersymmetry and the
Unification of Fundamental Interactions (SUSY09), Northeastern University,
Boston, MA, USA, 5-10 June 200
Prospects for Yukawa Unified SO(10) SUSY GUTs at the CERN LHC
The requirement of t-b-\tau Yukawa coupling unification is common in simple
grand unified models based on the gauge group SO(10), and it also places a
severe constraint on the expected spectrum of superpartners. For Yukawa-unified
models with \mu >0, the spectrum is characterized by three mass scales: {\it
i}). first and second generation scalars in the multi-TeV range, {\it ii}).
third generation scalars, \mu and m_A in the few-TeV range and {\it iii}).
gluinos in the \sim 350-500 GeV range with chargino masses around 100-160 GeV.
In such a scenario, gluino pair production should occur at large rates at the
CERN LHC, followed by gluino three-body decays into neutralinos or charginos.
Discovery of Yukawa-unified SUSY at the LHC should hence be possible with only
1 fb^{-1} of integrated luminosity, by tagging multi-jet events with 2--3
isolated leptons, without relying on missing E_T. A characteristic dilepton
mass edge should easily be apparent above Standard Model background. Combining
dileptons with b-jets, along with the gluino pair production cross section
information, should allow for gluino and neutralino mass reconstruction. A
secondary corroborative signal should be visible at higher integrated
luminosity in the W1Z2-> 3\ell channel, and should exhibit the same dilepton
mass edge as in the gluino cascade decay signal.Comment: 25 pages including 18 EPS figure
Precision gluino mass at the LHC in SUSY models with decoupled scalars
One way to ameliorate the SUSY flavor and CP problems is to postulate that
scalar masses lie in the TeV or beyond regime. For example, the focus point
(FP) region of the minimal supergravity (mSUGRA) model is especially compelling
in that heavy scalar masses can co-exist with low fine-tuning while yielding
the required relic abundance of cold dark matter (via a mixed higgsino-bino
neutralino). We examine many of the characteristics of collider events expected
to arise at the CERN LHC in models with multi-TeV scalars, taking the mSUGRA FP
region as a case study. The collider events are characterized by a hard
component arising from gluino pair production, plus a soft component arising
from direct chargino and neutralino production. Gluino decays in the FP region
are characterized by lengthy cascades yielding very large jet and lepton
multiplicities, and a large b-jet multiplicity. Thus, as one steps to higher
jet, b-jet or lepton multiplicity, signal-over-background rates should steadily
improve. The lengthy cascade decays make mass reconstruction via kinematic
edges difficult; however, since the hard component is nearly pure gluino pair
production, the gluino mass can be extracted to +- 8% via total rate for \eslt
+\ge 7-jet +\ge 2 b-jet events, assuming 100 fb^{-1} of integrated luminosity.
The distribution of invariant mass of opposite-sign/same-flavor dileptons in
the hard component exhibits two dilepton mass edges: m_{\tz_2}-m_{\tz_1} and
m_{\tz_3}-m_{\tz_1}. As a consistency check, the same mass edges should be seen
in isolated opposite-sign dileptons occurring in the soft component trilepton
signal which originates mainly from chargino-neutralino production.Comment: 24 pages with 20 EPS figure
Dark matter allowed scenarios for Yukawa-unified SO(10) SUSY GUTs
Simple supersymmetric grand unified models based on the gauge group SO(10)
require --in addition to gauge and matter unification-- the unification of
t-b-\tau Yukawa couplings. Yukawa unification, however, only occurs for very
special values of the soft SUSY breaking parameters. We perform a search using
a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and
sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also
require the relic density of neutralino dark matter to saturate the
WMAP-measured abundance. We find the spectrum is characterizd by three mass
scales: first/second generation scalars in the multi-TeV range, third
generation scalars in the TeV range, and gauginos in the \sim 100 GeV range.
Most solutions give far too high a relic abundance of neutralino dark matter.
The dark matter discrepancy can be rectified by 1. allowing for neutralino
decay to axino plus photon, 2. imposing gaugino mass non-universality or 3.
imposing generational non-universality. In addition, the MCMC approach finds 4.
a compromise solution where scalar masses are not too heavy, and where
neutralino annihilation occurs via the light Higgs h resonance. By imposing
weak scale Higgs soft term boundary conditions, we are also able to generate 5.
low \mu, m_A solutions with neutralino annihilation via a light A resonance,
though these solutions seem to be excluded by CDF/D0 measurements of the B_s\to
\mu^+\mu^- branching fraction. Based on the dual requirements of Yukawa
coupling unification and dark matter relic density, we predict new physics
signals at the LHC from pair production of 350--450 GeV gluinos. The events are
characterized by very high b-jet multiplicity and a dilepton mass edge around
mz2-mz1 \sim 50-75 GeV.Comment: 35 pages with 21 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
Beyond the Higgs boson at the Tevatron: detecting gluinos from Yukawa-unified SUSY
Simple SUSY GUT models based on the gauge group SO(10) require t-b-\tau
Yukawa coupling unification, in addition to gauge coupling and matter
unification. The Yukawa coupling unification places strong constraints on the
expected superparticle mass spectrum, with scalar masses \sim 10 TeV while
gluino masses are much lighter: in the 300--500 GeV range. The very heavy
squarks suppress negative interference in the q\bar{q}\to\tg\tg cross section,
leading to a large enhancement in production rates. The gluinos decay almost
always via three-body modes into a pair of b-quarks, so we expect at least four
b-jets per signal event. We investigate the capability of Fermilab Tevatron
collider experiments to detect gluino pair production in Yukawa-unified SUSY.
By requiring events with large missing E_T and \ge 2 or 3 tagged b-jets, we
find a 5\sigma reach in excess of m_{\tg}\sim 400 GeV for 5 fb^{-1} of data.
This range in m_{\tg} is much further than the conventional Tevatron SUSY
reach, and should cut a significant swath through the most favored region of
parameter space for Yukawa-unified SUSY models.Comment: 16 pages including 7 .eps figure
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
Gaugino Anomaly Mediated SUSY Breaking: phenomenology and prospects for the LHC
We examine the supersymmetry phenomenology of a novel scenario of
supersymmetry (SUSY) breaking which we call Gaugino Anomaly Mediation, or
inoAMSB. This is suggested by recent work on the phenomenology of flux
compactified type IIB string theory. The essential features of this scenario
are that the gaugino masses are of the anomaly-mediated SUSY breaking (AMSB)
form, while scalar and trilinear soft SUSY breaking terms are highly
suppressed. Renormalization group effects yield an allowable sparticle mass
spectrum, while at the same time avoiding charged LSPs; the latter are common
in models with negligible soft scalar masses, such as no-scale or gaugino
mediation models. Since scalar and trilinear soft terms are highly suppressed,
the SUSY induced flavor and CP-violating processes are also suppressed. The
lightest SUSY particle is the neutral wino, while the heaviest is the gluino.
In this model, there should be a strong multi-jet +etmiss signal from squark
pair production at the LHC. We find a 100 fb^{-1} reach of LHC out to
m_{3/2}\sim 118 TeV, corresponding to a gluino mass of \sim 2.6 TeV. A double
mass edge from the opposite-sign/same flavor dilepton invariant mass
distribution should be visible at LHC; this, along with the presence of short--
but visible-- highly ionizing tracks from quasi-stable charginos, should
provide a smoking gun signature for inoAMSB.Comment: 30 pages including 14 .eps figure
Neutralino versus axion/axino cold dark matter in the 19 parameter SUGRA model
We calculate the relic abundance of thermally produced neutralino cold dark
matter in the general 19 parameter supergravity (SUGRA-19) model. A scan over
GUT scale parameters reveals that models with a bino-like neutralino typically
give rise to a dark matter density \Omega_{\tz_1}h^2\sim 1-1000, i.e. between 1
and 4 orders of magnitude higher than the measured value. Models with higgsino
or wino cold dark matter can yield the correct relic density, but mainly for
neutralino masses around 700-1300 GeV. Models with mixed bino-wino or
bino-higgsino CDM, or models with dominant co-annihilation or A-resonance
annihilation can yield the correct abundance, but such cases are extremely hard
to generate using a general scan over GUT scale parameters; this is indicative
of high fine-tuning of the relic abundance in these cases. Requiring that
m_{\tz_1}\alt 500 GeV (as a rough naturalness requirement) gives rise to a
minimal probably dip in parameter space at the measured CDM abundance. For
comparison, we also scan over mSUGRA space with four free parameters. Finally,
we investigate the Peccei-Quinn augmented MSSM with mixed axion/axino cold dark
matter. In this case, the relic abundance agrees more naturally with the
measured value. In light of our cumulative results, we conclude that future
axion searches should probe much more broadly in axion mass, and deeper into
the axion coupling.Comment: 23 pages including 17 .eps figure