186 research outputs found

### Decoupling of Heavy Kaluza-Klein Modes In Models With Five-Dimensional Scalar Fields

We investigate the decoupling of heavy Kaluza-Klein modes in $\phi^{4}$
theory and scalar QED with space-time topology $\mathbb{R}^{3,1} \times S^{1}$.
We calculate the effective action due to integrating out heavy KK modes. We
construct generalized RGE's for the couplings with respect to the
compactification scale $M$. With the solutions to the RGE's we find the
$M$-scale dependence of the effective theory due to higher dimensional quantum
effects. We find that the heavy modes decouple in $\phi^{4}$ theory, but do not
decouple in scalar QED. This is due to the zero mode of the 5-th component
$A_{5}$ of the 5-d gauge field. Because $A_{5}$ is a scalar under 4-d Lorentz
transformations, there is no gauge symmetry protecting it from getting mass and
$A_{5}^{4}$ interaction terms after loop corrections. In light of these
unpleasant features, we explore $S^{1}/\mathbb{Z}_{2}$ compactifications, which
eliminate $A_{5}$, allowing for the heavy modes to decouple at low energies. We
also explore the possibility of decoupling by including higher dimensional
operators. It is found that this is possible, but a high degree of fine tuning
is required.Comment: 9 pages, no figures; sign error on equations 20, 36, 37; Added
additional reference

### Higher dimensional operators and their effects in (non)supersymmetric models

It is shown that a 4D N=1 softly broken supersymmetric theory with higher
derivative operators in the Kahler or the superpotential part of the Lagrangian
and with an otherwise arbitrary superpotential, can be re-formulated as a
theory without higher derivatives but with additional (ghost) superfields and
modified interactions. The importance of the analytical continuation
Minkowski-Euclidean space-time for the UV behaviour of such theories is
discussed in detail. In particular it is shown that power counting for
divergences in Minkowski space-time does not always work in models with higher
derivative operators.Comment: Based on talk presented at "Supersymmetry 2007"; 11 pages, LaTe

### Fixing the EW scale in supersymmetric models after the Higgs discovery

TeV-scale supersymmetry was originally introduced to solve the hierarchy
problem and therefore fix the electroweak (EW) scale in the presence of quantum
corrections. Numerical methods testing the SUSY models often report a good
likelihood L (or chi^2=-2ln L) to fit the data {\it including} the EW scale
itself (m_Z^0) with a {\it simultaneously} large fine-tuning i.e. a large
variation of this scale under a small variation of the SUSY parameters. We
argue that this is inconsistent and we identify the origin of this problem. Our
claim is that the likelihood (or chi^2) to fit the data that is usually
reported in such models does not account for the chi^2 cost of fixing the EW
scale. When this constraint is implemented, the likelihood (or chi^2) receives
a significant correction (delta_chi^2) that worsens the current data fits of
SUSY models. We estimate this correction for the models: constrained MSSM
(CMSSM), models with non-universal gaugino masses (NUGM) or higgs soft masses
(NUHM1, NUHM2), the NMSSM and the general NMSSM (GNMSSM). For a higgs mass
m_h\approx 126 GeV, one finds that in these models (delta_chi^2)/ndf> 1.5
(approx 1 for GNMSSM), which violates the usual condition of a good fit (total
chi^2/ndf approx 1) already before fitting observables other than the EW scale
itself (ndf=number of degrees of freedom). This has (negative) implications for
SUSY models and it is suggested that future data fits properly account for this
effect, if one remains true to the original goal of SUSY. Since the expression
of delta_chi^2 that emerges from our calculation depends on a familiar measure
of fine-tuning, one concludes that EW fine-tuning is an intrinsic part of the
likelihood to fit the data that includes the EW scale (m_Z^0).Comment: 18 pages; (v4: added text in Conclusions

### One-loop potential with scale invariance and effective operators

We study quantum corrections to the scalar potential in classically scale
invariant theories, using a manifestly scale invariant regularization. To this
purpose, the subtraction scale $\mu$ of the dimensional regularization is
generated after spontaneous scale symmetry breaking, from a subtraction
function of the fields, $\mu(\phi,\sigma)$. This function is then uniquely
determined from general principles showing that it depends on the dilaton only,
with $\mu(\sigma)\sim \sigma$. The result is a scale invariant one-loop
potential $U$ for a higgs field $\phi$ and dilaton $\sigma$ that contains an
additional {\it finite} quantum correction $\Delta U(\phi,\sigma)$, beyond the
Coleman Weinberg term. $\Delta U$ contains new, non-polynomial effective
operators like $\phi^6/\sigma^2$ whose quantum origin is explained. A flat
direction is maintained at the quantum level, the model has vanishing vacuum
energy and the one-loop correction to the mass of $\phi$ remains small without
tuning (of its self-coupling, etc) beyond the initial, classical tuning (of the
dilaton coupling) that enforces a hierarchy $\langle\sigma\rangle\gg
\langle\phi\rangle$. The approach is useful to models that investigate scale
symmetry at the quantum level.Comment: 10 pages; Contribution to the Proceedings of the Corfu Summer
Institute 2015, Sep 2015, Corfu, Greec

### SUSY naturalness without prejudice

Unlike the Standard Model (SM), supersymmetric models stabilize the
electroweak (EW) scale $v$ at the quantum level and {\it predict} that $v$ is a
function of the TeV-valued SUSY parameters ($\gamma_\alpha$) of the UV
Lagrangian. We show that the (inverse of the) covariance matrix of the model in
the basis of these parameters and the usual deviation $\delta\chi^2$ (from
$\chi^2_{min}$ of a model) automatically encode information about the
"traditional" EW fine-tuning measuring this stability, {\it provided that} the
EW scale $v\sim m_Z$ is indeed regarded as a function $v=v(\gamma)$. It is
known that large EW fine-tuning may signal an incomplete theory of soft terms
and can be reduced when relations among $\gamma_\alpha$ exist (due to GUT
symmetries, etc). The global correlation coefficient of this matrix can help
one investigate if such relations are present. An upper bound on the usual EW
fine-tuning measure ("in quadrature") emerges from the analysis of the
$\delta\chi^2$ and the s-standard deviation confidence interval by using
$v=v(\gamma)$ and the theoretical approximation (loop order) considered for the
calculation of the observables. This upper bound avoids subjective criteria for
the "acceptable" level of EW fine-tuning for which the model is still
"natural".Comment: 13 pages. LaTeX, (v4: minor corrections

### Palatini quadratic gravity: spontaneous breaking of gauged scale symmetry and inflation

We study quadratic gravity $R^2+R_{[\mu\nu]}^2$ in the Palatini formalism
where the connection and the metric are independent. This action has a {\it
gauged} scale symmetry (also known as Weyl gauge symmetry) of Weyl gauge field
$v_\mu= (\tilde\Gamma_\mu-\Gamma_\mu)/2$, with $\tilde\Gamma_\mu$
($\Gamma_\mu$) the trace of the Palatini (Levi-Civita) connection,
respectively. The underlying geometry is non-metric due to the $R_{[\mu\nu]}^2$
term acting as a gauge kinetic term for $v_\mu$. We show that this theory has
an elegant spontaneous breaking of gauged scale symmetry and mass generation in
the absence of matter, where the necessary scalar field ($\phi$) is not added
ad-hoc to this purpose but is "extracted" from the $R^2$ term. The gauge field
becomes massive by absorbing the derivative term $\partial_\mu\ln\phi$ of the
Stueckelberg field ("dilaton"). In the broken phase one finds the
Einstein-Proca action of $v_\mu$ of mass proportional to the Planck scale
$M\sim \langle\phi\rangle$, and a positive cosmological constant. Below this
scale $v_\mu$ decouples, the connection becomes Levi-Civita and metricity and
Einstein gravity are recovered. These results remain valid in the presence of
non-minimally coupled scalar field (Higgs-like) with Palatini connection and
the potential is computed. In this case the theory gives successful inflation
and a specific prediction for the tensor-to-scalar ratio $0.007\leq r \leq
0.01$ for current spectral index $n_s$ (at $95\%$CL) and N=60 efolds. This
value of $r$ is mildly larger than in inflation in Weyl quadratic gravity of
similar symmetry, due to different non-metricity. This establishes a connection
between non-metricity and inflation predictions and enables us to test such
theories by future CMB experiments.Comment: 22 pages, 2 figures, LaTe

### Manifestly scale-invariant regularization and quantum effective operators

Scale invariant theories are often used to address the hierarchy problem,
however the regularization of their quantum corrections introduces a
dimensionful coupling (dimensional regularization) or scale (Pauli-Villars,
etc) which break this symmetry explicitly. We show how to avoid this problem
and study the implications of a manifestly scale invariant regularization in
(classical) scale invariant theories. We use a dilaton-dependent subtraction
function $\mu(\sigma)$ which after spontaneous breaking of scale symmetry
generates the usual DR subtraction scale $\mu(\langle\sigma\rangle)$. One
consequence is that "evanescent" interactions generated by scale invariance of
the action in $d=4-2\epsilon$ (but vanishing in $d=4$), give rise to new,
finite quantum corrections. We find a (finite) correction $\Delta
U(\phi,\sigma)$ to the one-loop scalar potential for $\phi$ and $\sigma$,
beyond the Coleman-Weinberg term. $\Delta U$ is due to an evanescent correction
($\propto\epsilon$) to the field-dependent masses (of the states in the loop)
which multiplies the pole ($\propto 1/\epsilon$) of the momentum integral, to
give a finite quantum result. $\Delta U$ contains a non-polynomial operator
$\sim \phi^6/\sigma^2$ of known coefficient and is independent of the
subtraction dimensionless parameter. A more general $\mu(\phi,\sigma)$ is ruled
out since, in their classical decoupling limit, the visible sector (of the
higgs $\phi$) and hidden sector (dilaton $\sigma$) still interact at the
quantum level, thus the subtraction function must depend on the dilaton only.
The method is useful in models where preserving scale symmetry at quantum level
is important.Comment: 16 pages (added references; published version

### Compact Dimensions and their Radiative Mixing

For one and two dimensional field theory orbifolds we compute in the DR
scheme the full dependence on the momentum scale (q) of the one-loop radiative
corrections to the 4D gauge coupling. Imposing a discrete "shift" symmetry of
summing the infinite towers of associated Kaluza-Klein (KK) modes, it is shown
that higher dimension operators are radiatively generated as one-loop
counterterms for the case of two (but not for one) compact dimension(s). They
emerge as a ``radiative mixing'' of effects (Kaluza-Klein infinite sums)
associated with both compact dimensions. Particular attention is paid to the
link of the one-loop corrections with their counterparts computed in infrared
regularised 4D N=1 heterotic string orbifolds with N=2 sectors. The correction
from these sectors usually ignores higher order terms in the IR string
regulator (lambda_s->0) of type lambda_s ln(alpha'), but these become relevant
in the field theory limit alpha'->0. Such terms ultimately re-emerge in pure
field theory calculations of $\Pi(q^2)$ as higher dimension one-loop
counterterms. We stress the importance of such terms for the unification of
gauge couplings and for the predicted value of the string scale.Comment: 14 pages, LaTeX; additional comment

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