3,527 research outputs found
Vacuum Stability and the MSSM Higgs Mass
In the Minimal Supersymmetric Standard Model (MSSM), a Higgs boson mass of
125 GeV can be obtained with moderately heavy scalar top superpartners provided
they are highly mixed. The source of this mixing, a soft trilinear
stop-stop-Higgs coupling, can result in the appearance of charge- and
color-breaking minima in the scalar potential of the theory. If such a vacuum
exists and is energetically favorable, the Standard Model-like vacuum can decay
to it via quantum tunnelling. In this work we investigate the conditions under
which such exotic vacua arise, and we compute the tunnelling rates to them. Our
results provide new constraints on the scalar top quarks of the MSSM.Comment: 22 pages, 11 figures. References added. Matches published versio
The tension between gauge coupling unification, the Higgs boson mass, and a gauge-breaking origin of the supersymmetric mu-term
We investigate the possibility of generating the -term in the MSSM by
the condensation of a field that is a singlet under the SM gauge group but
charged under an additional family-independent gauge symmetry. We
attempt to do so while preserving the gauge coupling unification of the MSSM.
For this, we find that SM non-singlet exotics must be present in the spectrum.
We also prove that the pure anomalies can always be solved with
rationally charged fields, but that a large number of SM singlets are often
required. For charges that are consistent with an embedding of the
MSSM in SU(5) or SO(10), we show that the charges of the MSSM states
can always be expressed as a linear combination of abelian subgroups of .
However, the SM exotics do not appear to have a straightforward embedding into
GUT multiplets. We conclude from this study that if this approach to the
-term is correct, as experiment can probe, it will necessarily complicate
the standard picture of supersymmetric grand unification.Comment: 10 pages, no figure
New Limits on Light Hidden Sectors from Fixed-Target Experiments
New physics can be light if it is hidden, coupling very weakly to the
Standard Model. In this work we investigate the discovery prospects of Abelian
hidden sectors in lower-energy fixed-target and high-precision experiments. We
focus on a minimal supersymmetric realization consisting of an Abelian vector
multiplet, coupled to hypercharge by kinetic mixing, and a pair of chiral Higgs
multiplets. This simple theory can give rise to a broad range of experimental
signals, including both commonly-studied patterns of hidden vector decay as
well as new and distinctive hidden sector cascades. We find limits from the
production of hidden states other than the vector itself. In particular, we
show that if the hidden Abelian symmetry is higgsed, and the corresponding
hidden Higgs boson has visible decays, it severely restricts the ability of the
hidden sector to explain the anomalous muon magnetic moment.Comment: 44 pages + appendices/references, 28 figures. Figures in secs 5 and 7
updated to correct error in hadronic exclusions; limits slightly weaker, but
qualitative conclusions unchange
Non-Thermal Dark Matter from Cosmic Strings
Cosmic strings can be created in the early universe during symmetry-breaking
phase transitions, such as might arise if the gauge structure of the standard
model is extended by additional U(1) factors at high energies. Cosmic strings
present in the early universe form a network of long horizon-length segments,
as well as a population of closed string loops. The closed loops are unstable
against decay, and can be a source of non-thermal particle production. In this
work we compute the density of WIMP dark matter formed by the decay of gauge
theory cosmic string loops derived from a network of long strings in the
scaling regime or under the influence of frictional forces. We find that for
symmetry breaking scales larger than 10^10 GeV, this mechanism has the
potential to account for the observed relic density of dark matter. For
symmetry breaking scales lower than this, the density of dark matter created by
loop decays from a scaling string network lies below the observed value. In
particular, the cosmic strings originating from a U(1) gauge symmetry broken
near the electroweak scale, that could lead to a massive Z' gauge boson
observable at the LHC, produce a negligibly small dark matter relic density by
this mechanism.Comment: 22 pages, 4 figures, added discussion about boosted decay products
from loop cusp
Changes in Dark Matter Properties After Freeze-Out
The properties of the dark matter that determine its thermal relic abundance
can be very different from the dark matter properties today. We investigate
this possibility by coupling a dark matter sector to a scalar that undergoes a
phase transition after the dark matter freezes out. If the value of Omega_DM
h^2 calculated from parameters measured at colliders and by direct and indirect
detection experiments does not match the astrophysically observed value, a
novel cosmology of this type could provide the explanation. This mechanism also
has the potential to account for the "boost factor" required to explain the
PAMELA data.Comment: 5 pages; v2: Fixed minor typo, added short discussion of application
to PAMELA and appropriate references, results unchange
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