127 research outputs found

### Towards An Accurate Calculation of the Neutralino Relic Density

We compute the neutralino relic density in the minimal supersymmetric
standard model by using exact expressions for the neutralino annihilation cross
section into all tree-level final states, including all contributions and
interference terms. We find that several final states may give comparable
contributions to the relic density, which illustrates the importance of
performing a complete calculation. We compare the exact results with those of
the usual expansion method and demonstrate a sizeable discrepancy (of more than
10%) over a significant range of the neutralino mass of up to several tens of
GeV which is caused by the presence of resonances and new final-state
thresholds. We perform several related checks and comparisons. In particular,
we find that the often employed approximate iterative procedure of computing
the neutralino freeze-out temperature gives generally very accurate results,
except when the expansion method is used near resonances and thresholds.Comment: 23 pages, 4 eps figure

### New Cosmological and Experimental Constraints on the CMSSM

We analyze the implications of several recent cosmological and experimental
measurements for the mass spectra of the Constrained MSSM (CMSSM). We compute
the relic abundance of the neutralino and compare the new cosmologically
expected and excluded mass ranges with those ruled out by the final LEP bounds
on the lightest chargino and Higgs masses, with those excluded by current
experimental values of \br(B\to X_s \gamma), and with those favored by the
recent measurement of the anomalous magnetic moment of the muon. We find that
for tan\beta\lsim 45 there remains relatively little room for the mass
spectra to be consistent with the interplay of the several constraints. On the
other hand, at larger values of $tan\beta\$ the decreasing mass of the
pseudoscalar Higgs gives rise to a wide resonance in the neutralino WIMP
pair-annihilation, whose position depends on the ratio of top and bottom quark
masses. As a consequence, the cosmologically expected regions consistent with
other constraints often grow significantly and generally shift towards
superpartner masses in the$\tev$ range.Comment: LaTex, 21 pages, 4 PS figures. Version published in JHEP, for updates
see hep-ph/020617

### MSSM Forecast for the LHC

We perform a forecast of the MSSM with universal soft terms (CMSSM) for the
LHC, based on an improved Bayesian analysis. We do not incorporate ad hoc
measures of the fine-tuning to penalize unnatural possibilities: such
penalization arises from the Bayesian analysis itself when the experimental
value of $M_Z$ is considered. This allows to scan the whole parameter space,
allowing arbitrarily large soft terms. Still the low-energy region is
statistically favoured (even before including dark matter or g-2 constraints).
Contrary to other studies, the results are almost unaffected by changing the
upper limits taken for the soft terms. The results are also remarkable stable
when using flat or logarithmic priors, a fact that arises from the larger
statistical weight of the low-energy region in both cases. Then we incorporate
all the important experimental constrains to the analysis, obtaining a map of
the probability density of the MSSM parameter space, i.e. the forecast of the
MSSM. Since not all the experimental information is equally robust, we perform
separate analyses depending on the group of observables used. When only the
most robust ones are used, the favoured region of the parameter space contains
a significant portion outside the LHC reach. This effect gets reinforced if the
Higgs mass is not close to its present experimental limit and persits when dark
matter constraints are included. Only when the g-2 constraint (based on
$e^+e^-$ data) is considered, the preferred region (for $\mu>0$) is well inside
the LHC scope. We also perform a Bayesian comparison of the positive- and
negative-$\mu$ possibilities.Comment: 42 pages: added figures and reference

### The health of SUSY after the Higgs discovery and the XENON100 data

We analyze the implications for the status and prospects of supersymmetry of
the Higgs discovery and the last XENON data. We focus mainly, but not only, on
the CMSSM and NUHM models. Using a Bayesian approach we determine the
distribution of probability in the parameter space of these scenarios. This
shows that, most probably, they are now beyond the LHC reach . This negative
chances increase further (at more than 95% c.l.) if one includes dark matter
constraints in the analysis, in particular the last XENON100 data. However, the
models would be probed completely by XENON1T. The mass of the LSP neutralino
gets essentially fixed around 1 TeV. We do not incorporate ad hoc measures of
the fine-tuning to penalize unnatural possibilities: such penalization arises
automatically from the careful Bayesian analysis itself, and allows to scan the
whole parameter space. In this way, we can explain and resolve the apparent
discrepancies between the previous results in the literature. Although SUSY has
become hard to detect at LHC, this does not necessarily mean that is very
fine-tuned. We use Bayesian techniques to show the experimental Higgs mass is
at $\sim 2\ \sigma$ off the CMSSM or NUHM expectation. This is substantial but
not dramatic. Although the CMSSM or the NUHM are unlikely to show up at the
LHC, they are still interesting and plausible models after the Higgs
observation; and, if they are true, the chances of discovering them in future
dark matter experiments are quite high

### Curvaton Dynamics

In contrast to the inflaton's case, the curvature perturbations due to the
curvaton field depend strongly on the evolution of the curvaton before its
decay. We study in detail the dynamics of the curvaton evolution during and
after inflation. We consider that the flatness of the curvaton potential may be
affected by supergravity corrections, which introduce an effective mass
proportional to the Hubble parameter. We also consider that the curvaton
potential may be dominated by a quartic or by a non-renormalizable term. We
find analytic solutions for the curvaton's evolution for all these
possibilities. In particular, we show that, in all the above cases, the
curvaton's density ratio with respect to the background density of the Universe
decreases. Therefore, it is necessary that the curvaton decays only after its
potential becomes dominated by the quadratic term, which results in (Hubble
damped) sinusoidal oscillations. In the case when a non-renormalizable term
dominates the potential, we find a possible non-oscillatory attractor solution
that threatens to erase the curvature perturbation spectrum. Finally, we study
the effects of thermal corrections to the curvaton's potential and show that,
if they ever dominate the effective mass, they lead to premature thermalization
of the curvaton condensate. To avoid this danger, a stringent bound has to be
imposed on the coupling of the curvaton to the thermal bath.Comment: 24 pages, 3 Postscript figures, RevTe

### The case for 100 GeV bino dark matter: A dedicated LHC tri-lepton search

Global fit studies performed in the pMSSM and the photon excess signal
originating from the Galactic Center seem to suggest compressed electroweak
supersymmetric spectra with a $\sim$100 GeV bino-like dark matter particle. We
find that these scenarios are not probed by traditional electroweak
supersymmetry searches at the LHC. We propose to extend the ATLAS and CMS
electroweak supersymmetry searches with an improved strategy for bino-like dark
matter, focusing on chargino plus next-to-lightest neutralino production, with
a subsequent decay into a tri-lepton final state. We explore the sensitivity
for pMSSM scenarios with $\Delta m = m_{\rm NLSP} - m_{\rm LSP} \sim (5 - 50)$
GeV in the $\sqrt{s} = 14$ TeV run of the LHC. Counterintuitively, we find that
the requirement of low missing transverse energy increases the sensitivity
compared to the current ATLAS and CMS searches. With 300 fb$^{-1}$ of data we
expect the LHC experiments to be able to discover these supersymmetric spectra
with mass gaps down to $\Delta m \sim 9$ GeV for DM masses between 40 and 140
GeV. We stress the importance of a dedicated search strategy that targets
precisely these favored pMSSM spectra.Comment: Published in JHE

### LHC and dark matter phenomenology of the NUGHM

We present a Bayesian analysis of the NUGHM, a supersymmetric scenario with
non-universal gaugino masses and Higgs masses, including all the relevant
experimental observables and dark matter constraints. The main merit of the
NUGHM is that it essentially includes all the possibilities for dark matter
(DM) candidates within the MSSM, since the neutralino and chargino spectrum
-and composition- are as free as they can be in the general MSSM. We identify
the most probable regions in the NUHGM parameter space, and study the
associated phenomenology at the LHC and the prospects for DM direct detection.
Requiring that the neutralino makes all of the DM in the Universe, we identify
two preferred regions around $m_{\chi_1^0}= 1\ {\rm TeV},\; 3\ {\rm TeV}$,
which correspond to the (almost) pure Higgsino and wino case. There exist other
marginal regions (e.g. Higgs-funnel), but with much less statistical weight.
The prospects for detection at the LHC in this case are quite pessimistic, but
future direct detection experiments like LUX and XENON1T, will be able to probe
this scenario. In contrast, when allowing other DM components, the prospects
for detection at the LHC become more encouraging -- the most promising signals
being, beside the production of gluinos and squarks, the production of the
heavier chargino and neutralino states, which lead to WZ and same-sign WW final
states -- and direct detection remains a complementary, and even more powerful,
way to probe the scenario.Comment: The Sommerfeld enhancement has been included in the computation of
the relic density and in the discussion of indirect-detection limits. Some
references have been adde

### The degenerate gravitino scenario

In this work, we explore the "degenerate gravitino" scenario where the mass
difference between the gravitino and the lightest MSSM particle is much smaller
than the gravitino mass itself. In this case, the energy released in the decay
of the next to lightest sypersymmetric particle (NLSP) is reduced. Consequently
the cosmological and astrophysical constraints on the gravitino abundance, and
hence on the reheating temperature, become softer than in the usual case. On
the other hand, such small mass splittings generically imply a much longer
lifetime for the NLSP. We find that, in the constrained MSSM (CMSSM), for
neutralino LSP or NLSP, reheating temperatures compatible with thermal
leptogenesis are reached for small splittings of order 10^{-2} GeV. While for
stau NLSP, temperatures of 4x10^9 GeV can be obtained even for splittings of
order of tens of GeVs. This "degenerate gravitino" scenario offers a possible
way out to the gravitino problem for thermal leptogenesis in supersymmetric
theories.Comment: 27 pages, 10 figures and 1 table. Minor typos and references fixed.
Matches published version in JCAP

### Quantifying the tension between the Higgs mass and (g-2)_mu in the CMSSM

Supersymmetry has been often invoqued as the new physics that might reconcile
the experimental muon magnetic anomaly, a_mu, with the theoretical prediction
(basing the computation of the hadronic contribution on e^+ e^- data). However,
in the context of the CMSSM, the required supersymmetric contributions (which
grow with decreasing supersymmetric masses) are in potential tension with a
possibly large Higgs mass (which requires large stop masses). In the limit of
very large m_h supersymmetry gets decoupled, and the CMSSM must show the same
discrepancy as the SM with a_mu . But it is much less clear for which size of
m_h does the tension start to be unbearable. In this paper, we quantify this
tension with the help of Bayesian techniques. We find that for m_h > 125 GeV
the maximum level of discrepancy given current data (~ 3.3 sigma) is already
achieved. Requiring less than 3 sigma discrepancy, implies m_h < 120 GeV. For a
larger Higgs mass we should give up either the CMSSM model or the computation
of a_mu based on e^+ e^-; or accept living with such inconsistency

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