Physics Letters B 765 (2017) 256–259
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Physics Letters B
www.elsevier.com/locate/physletb
Non-minimal quartic inflation in supersymmetric SO(10)
George K. Leontaris
a,b,∗
, Nobuchika Okada
c
, Qaisar Shafi
d
a
Theory Department, CERN, CH-1211, Geneva 23, Switzerland
b
Physics Department, Theory Division, Ioannina University, GR-45110 Ioannina, Greece
c
Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL 35487, USA
d
Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, DE 19716, Newark, USA
a r t i c l e i n f o a b s t r a c t
Article history:
Received
4 December 2016
Accepted
12 December 2016
Available
online 16 December 2016
Editor:
M. Cveti
ˇ
c
We describe how quartic (λφ
4
) inflation with non-minimal coupling to gravity is realized in realistic
supersymmetric SO(10) models. In a well-motivated example the 16 −16 Higgs multiplets, which break
SO(10) to SU(5) and yield masses for the right-handed neutrinos, provide the inflaton field φ. Thus,
leptogenesis is a natural outcome in this class of SO(10) models. Moreover, the adjoint (45-plet) Higgs
also acquires a GUT scale value during inflation so that the monopole problem is evaded. The scalar
spectral index n
s
is in good agreement with the observations and r, the tensor to scalar ratio, is predicted
for realistic values of GUT parameters to be of order 10
−3
–10
−2
.
© 2016 Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
By incorporating a single right-handed neutrino per genera-
tion
to cancel new anomalies from gauging the accidental global
U(1)
B−L
symmetry of the Standard Model (SM), both SU(4) ×
SU(2)
L
× SU(2)
R
[1] and SO(10) [2] provide particularly com-
pelling
examples of unifying the strong and electroweak forces.
A non-supersymmetric model of SO(10) inflation [3], based on an
earlier SU(5) model [4], was proposed a longtime ago. In this class
of SO(10) inflation models, driven by a gauge singlet field with
minimal coupling to gravity and utilizing the Coleman–Weinberg
potential [5], the scalar to tensor ratio r, a canonical measure of
gravity waves generated during inflation, is estimated to be 0.02,
for n
s
= 0.96–0.97 [6]. Depending on the SO(10) symmetry break-
ing
pattern, an observable number density of intermediate mass
magnetic monopoles may be present in our galaxy [7].
In
this letter we propose to implement primordial inflation in
realistic supersymmetric SO(10) models [8]. We do this with a
supergravity generalization of non-minimal λφ
4
inflation [9]. Re-
call
that λφ
4
inflation with a minimal coupling to gravity pre-
dicts
an r value close to 0.25–0.3, depending on the number of
e-foldings (N
0
= 60–50). This prediction for r lies well outside the
2-σ range allowed by Planck [10] and WMAP 9 [11]. In contrast,
λφ
4
inflation with a suitable non-minimal coupling to gravity is
in good agreement with the data regarding the key parameters
n
s
and r. The quantity r, in particular, can be as low as 0.003 or
*
Corresponding author.
E-mail
addresses: leonta@uoi.gr (G.K. Leontaris), okadan@ua.edu (N. Okada),
shafi@bartol.udel.edu (Q. Shafi).
so, for n
s
= 0.96–0.97. The discussion closely follows a previous
model [12] based on supersymmetric SU(5).
In order to retain perturbative unification of the MSSM gauge
couplings in supersymmetric SO(10) we prefer to work with lower
dimensional SO(10) representations. We employ 16 − 16 Higgs
to break SO(10) to SU(5) while keeping supersymmetry unbro-
ken.
The 16 vacuum expectation value (VEV) also provides large
masses ( 10
14
GeV), via higher dimensional operators, to the
right-handed neutrinos. In addition, the adjoint 45-plet, in con-
junction
either with a 54-plet or using higher dimensional op-
erators,
is employed to complete the breaking of SO(10) to the
MSSM gauge symmetry. Finally, following [13], we can employ two
Higgs 10-plets to implement electroweak symmetry breaking and
accommodate the charged fermion masses and mixings as well as
neutrino oscillation data. This summarizes the basic structure of a
realistic supersymmetric SO(10) model.
Recall that a non-minimal λφ
4
inflation scenario is defined by
the following action in the Jordan frame:
S
J
=
d
4
x
√
−g
−
1
2
(1 +ξ ϕ
2
) R +
1
2
g
μν
∂
μ
ϕ∂
ν
ϕ −
λ
16
ϕ
4
,
(1)
where we have set to unity the reduced Planck mass, M
P
= 2.44 ×
10
18
GeV. In the limit ξ → 0
+
the non-minimal gravitational cou-
pling
term ξ ϕ
2
R vanishes and we approach minimal λϕ
4
chaotic
inflation. In the Einstein frame with a canonical gravity sector, we
can describe the action with a new inflaton field (σ ) which has a
canonical kinetic term. The relation between σ and ϕ is given by
http://dx.doi.org/10.1016/j.physletb.2016.12.038
0370-2693/
© 2016 Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.