395 research outputs found

### Towards LHC Physics with Non-local Standard Model

We take a few steps towards constructing a string-inspired nonlocal extension
of the Standard Model. We start by illustrating how quantum loop calculations
can be performed in nonlocal scalar field theory. In particular, we show the
potential to address the hierarchy problem in the nonlocal framework. Next, we
construct a nonlocal abelian gauge model and derive modifications of the gauge
interaction vertex and field propagators. We apply the modifications to a toy
version of the nonlocal Standard Model and investigate collider phenomenology.
We find the lower bound on the scale of non-locality from the 8 TeV LHC data to
be $2.5-3$ TeV.Comment: Changes made to be consistent with the journal versio

### SU(5)$\times$U(1)$_X$ grand unification with minimal seesaw and $Z^\prime$-portal dark matter

We propose a grand unified SU(5)$\times$U(1)$_X$ model, where the standard
SU(5) grand unified theory is supplemented by minimal seesaw and a right-handed
neutrino dark matter with an introduction of a global $Z_2$-parity. In the
presence of three right-handed neutrinos (RHNs), the model is free from all
gauge and mixed-gravitational anomalies. The SU(5) symmetry is broken into the
Standard Model (SM) gauge group at $M_{\rm GUT} \simeq 4 \times 10^{16}$ GeV in
the standard manner, while the U(1)$_X$ symmetry breaking occurs at the TeV
scale, which generates the TeV-scale mass of the U(1)$_X$ gauge boson
($Z^\prime$ boson) and the three Majorana RHNs. A unique $Z_2$-odd RHN is
stable and serves as the dark matter (DM) in the present Universe, while the
remaining two RHNs work to generate the SM neutrino masses through the minimal
seesaw. We investigate the $Z^\prime$-portal RHN DM scenario in this model
context, and find that the constraints from the DM relic abundance and the
search results for a $Z^\prime$ boson resonance at the Large Hadron Collider
(LHC) are complementary to narrow down the allowed parameter region, which will
be fully covered by the future LHC experiments (for the $Z^\prime$ boson mass
$<$ 5 TeV). We also briefly discuss the successful implementation of
Baryogenesis and cosmological inflation scenarios in the present model.Comment: 6 pages, 2 figures, revised plots, accepted for publication in pl

### Natural mu-term generation in supergravity scenario

We discuss a natural way to generate the mu-term in supergravity scenario.
Once the supergravity effects are taken into account, the vacuum expectation
values (VEVs) of the heavy fields are in general shifted from the values in the
supersymmetric limit. We note that this fact is independent of any Kahler
ansatz and the values of the VEV shifts are of the order of the gravitino mass.
As an example, an explicit model is presented, in which both of the mu-term and
the B-term of the electroweak scale are generated by the VEV shifts through the
supergravity effects. This model is a kind of the next to minimal
supersymmetric standard model, but there is no light standard model singlet
field. Also, we emphasize that our discussion can be naturally applied to the
supersymmetric grand unified theory.Comment: 9 page

### Gravity Waves and Gravitino Dark Matter in $\mu$-Hybrid Inflation

We propose a novel reformulation of supersymmetric (more precisely $\mu$-)
hybrid inflation based on a local U(1) or any suitable extension of the minimal
supersymmetric standard model (MSSM) which also resolves the $\mu$ problem. We
employ a suitable Kahler potential which effectively yields quartic inflation
with non-minimal coupling to gravity. Imposing the gravitino Big Bang
Nucleosynthesis (BBN) constraint on the reheat temperature ($T_r \lesssim 10^6$
GeV) and requiring a neutralino LSP, the tensor to scalar ratio ($r$) has a
lower bound $r \gtrsim 0.004$. The U(1) symmetry breaking scale lies between
$10^8$ and $10^{12}$ GeV. We also discuss a scenario with gravitino dark matter
whose mass is a few GeV.Comment: 5 pages, 4 figures, revised version to appear in Physics Letters

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