24 research outputs found
Continuum-Mediated Dark Matter-Baryon Scattering
Many models of dark matter scattering with baryons may be treated either as a
simple contact interaction or as the exchange of a light mediator particle. We
study an alternative, in which a continuum of light mediator states may be
exchanged. This could arise, for instance, from coupling to a sector which is
approximately conformal at the relevant momentum transfer scale. In the
non-relativistic effective theory of dark matter-baryon scattering, which is
useful for parametrizing direct detection signals, the effect of such continuum
mediators is to multiply the amplitude by a function of the momentum transfer
q, which in the simplest case is just a power law. We develop the basic
framework and study two examples: the case where the mediator is a scalar
operator coupling to the Higgs portal (which turns out to be highly
constrained) and the case of an antisymmetric tensor operator that mixes with the hypercharge field strength and couples to dark matter
tensor currents, which has an interesting viable parameter space. We describe
the effect of such mediators on the cross sections and recoil energy spectra
that could be observed in direct detection.Comment: 30 pages, 6 figures. v2: minor changes, references adde
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An effective theory on the light shell
We describe work on the construction of an effective field theory on a spherical light shell. The motivation arises from classical electromagnetism: If a collision produces charged particles with zero net charge emerging simultaneously from a point and instantaneously accelerating to the speed of light, then the electromagnetic fields due to these charges lie entirely on a spherical shell expanding at the speed of light. We show that this also applies to classical color radiation from high-energy collisions that produce colored particles. Specifically, the color fields produced in such a process are associated with a non-linear σ-model on the 2D light shell with specific symmetry-breaking terms. The quantum version of such a picture exhibits asymptotic freedom and should therefore be a useful starting point for a light-shell effective theory for QCD.
We start in the simplified context of zero-flavor scalar quantum electrodynamics. Our effective theory has 3 major ingredients: breaking down the fields into soft and hard sectors with the large energy of the hard fields in the radial direction scaled out, a special gauge called light-shell gauge in which the picture simplifies, and a gauge-invariant source defined on a spherical light shell having infinitesimal radius.
We match the fields between the effective theory and the full theory, meaning zero-flavor scalar QED. This allows us to compute the amplitude for the production of any number of scalars from the gauge-invariant source. We then find the tree-level amplitude for the emission of a photon using our effective theory and show that our result agrees with the full theory.
To calculate loop effects in our effective theory, we need the photon propagator in light-shell gauge. We derive this propagator and use it to calculate the 1-loop correction to the amplitude for the production of a scalar and anti-scalar pair arising from virtual photon effects. This reduces to a pair of purely angular integrals in the effective theory and reproduces the familiar double logs of the full theory subject to an appropriate interpretation of an angular cutoff.Physic
Naturalness, b to s gamma, and SUSY Heavy Higgses
We explore naturalness constraints on the masses of the heavy Higgs bosons
H^0, H^+/-, and A^0 in supersymmetric theories. We show that, in any extension
of MSSM which accommodates the 125 GeV Higgs at the tree level, one can derive
an upper bound on the SUSY Higgs masses from naturalness considerations. As is
well-known for the MSSM, these bounds become weak at large tan beta. However,
we show that measurements of b to s gamma together with naturalness arguments
lead to an upper bound on tan beta, strengthening the naturalness case for
heavy Higgs states near the TeV scale. The precise bound depends somewhat on
the SUSY mediation scale: allowing a factor of 10 tuning in the stop sector,
the measured rate of b to s gamma implies tan beta < 30 for running down from
10 TeV but tan beta < 4 for mediation at or above 100 TeV, placing m_A near the
TeV scale for natural EWSB. Because the signatures of heavy Higgs bosons at
colliders are less susceptible to being "hidden" than standard superpartner
signatures, there is a strong motivation to make heavy Higgs searches a key
part of the LHC's search for naturalness. In an appendix we comment on how the
Goldstone boson equivalence theorem links the rates for H to hh and H to ZZ
signatures.Comment: 29 pages, 10 figures. V2: minor changes, accepted by JHE
Attaining quantum limited precision of localizing an object in passive imaging
We investigate our ability to determine the mean position, or centroid, of a
linear array of equally-bright incoherent point sources of light, whose
continuum limit is the problem of estimating the center of a
uniformly-radiating object. We consider two receivers: an image-plane ideal
direct-detection imager and a receiver that employs Hermite-Gaussian (HG)
Spatial-mode Demultiplexing (SPADE) in the image plane, prior to
shot-noise-limited photon detection. We compare the Fisher Information (FI) for
estimating the centroid achieved by these two receivers, which quantifies the
information-accrual rate per photon, and compare those with the Quantum Fisher
Information (QFI): the maximum attainable FI by any choice of measurement on
the collected light allowed by physics. We find that focal-plane direct imaging
is strictly sub-optimal, although not by a large margin. We also find that the
HG mode sorter, which is the optimal measurement for estimating the separation
between point sources (or the length of a line object) is not only suboptimal,
but it performs worse than direct imaging. We study the scaling behavior of the
QFI and direct imaging's FI for a continuous, uniformly-bright object in terms
of its length, and find that both are inversely proportional to the object's
length when it is sufficiently larger than the Rayleigh length. Finally, we
propose a two-stage adaptive modal receiver design that attains the QFI for
centroid estimation.Comment: 19 pages, 4 figure
Color Fields on the Light-Shell
We study the classical color radiation from very high energy collisions that
produce colored particles. In the extreme high energy limit, the classical
color fields are confined to a light-shell expanding at and are associated
with a non-linear -model on the 2D light-shell with specific symmetry
breaking terms. We argue that the quantum version of this picture exhibits
asymptotic freedom and may be a useful starting point for an effective
light-shell theory of the structure between the jets at a very high energy
collider.Comment: 11 pages, no figure
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Naturalness, b to sγ, and SUSY heavy Higgses
We explore naturalness constraints on the masses of the heavy Higgs bosons , , and in supersymmetric theories. We show that, in any extension of MSSM which accommodates the 125 GeV Higgs at the tree level, one can derive an upper bound on the SUSY Higgs masses from naturalness considerations. As is well-known for the MSSM, these bounds become weak at large tan β. However, we show that measurements of b → sγ together with naturalness arguments lead to an upper bound on tan β, strengthening the naturalness case for heavy Higgs states near the TeV scale. The precise bound depends somewhat on the SUSY mediation scale: allowing a factor of 10 tuning in the stop sector, the measured rate of b → sγ implies tan β ≲ 30 for running down from 10 TeV but tan β ≲ 4 for mediation at or above 100 TeV, placing m A near the TeV scale for natural EWSB. Because the signatures of heavy Higgs bosons at colliders are less susceptible to being “hidden” than standard superpartner signatures, there is a strong motivation to make heavy Higgs searches a key part of the LHC’s search for naturalness. In an appendix we comment on how the Goldstone boson equivalence theorem links the rates for H → hh and H → ZZ signatures.Physic
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Photon propagator in light-shell gauge
We derive the photon propagator in light-shell gauge (LSG), introduced in [1] in the context of light-shell effective theory.Physic
Towards an effective field theory on the light-shell
We discuss our work toward the construction of a light-shell effective theory (LSET), an effective field theory for describing the matter emerging from high-energy collisions and the accompanying radiation. We work in the highly simplified venue of 0-flavor scalar quantum electrodynamics, with a gauge invariant product of scalar fields at the origin of space-time as the source of high-energy charged particles. Working in this simple gauge theory allows us to focus on the essential features of LSET. We describe how the effective theory is constructed and argue that it can reproduce the full theory tree-level amplitude. We study the 1-loop radiative corrections in the LSET and suggest how the leading double-logs in the full theory at 1-loop order can be reproduced by a purely angular integral in the LSET.Physic