# Thomas HilgerTechnische Universität Dresden | TUD

Thomas Hilger

Dr.rer.nat.

## About

59

Publications

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1,327

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Introduction

Additional affiliations

March 2017 - present

October 2015 - February 2016

March 2014 - present

Education

October 2002 - April 2008

## Publications

Publications (59)

The third Gaia data release provides photometric time series covering 34 months for about 10 million stars. For many of those stars, a characterisation in Fourier space and their variability classification are also provided. This paper focuses on intermediate- to high-mass (IHM) main sequence pulsators M >= 1.3 Msun) of spectral types O, B, A, or F...

Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic so...

Context. Gaia Early Data Release 3 (Gaia EDR3) provides accurate astrometry for about 1.6 million compact (QSO-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions. Aims. The proper motions of QSO-like sources are used to reveal a systematic pattern due to the acceleration of the solar systemb...

Context. Gaia Early Data Release 3 (Gaia EDR3) provides accurate astrometry for about 1.6 million compact (QSO-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions. Aims. The proper motions of QSO-like sources are used to reveal a systematic pattern due to the acceleration of the solar systemb...

Context. Gaia Early Data Release 3 ( Gaia EDR3) gives trigonometric parallaxes for nearly 1.5 billion sources. Inspection of the EDR3 data for sources identified as quasars reveals that their parallaxes are biased, that is, they are systematically offset from the expected distribution around zero, by a few tens of microarcseconds.
Aims. We attempt...

Gaia Early Data Release 3 (Gaia EDR3) contains results for 1.812 billion sources in the magnitude range G = 3 to 21 based on observations collected by the European Space Agency Gaia satellite during the first 34 months of its operational phase. We describe the input data, the models, and the processing used for the astrometric content of Gaia EDR3,...

Context. Gaia Early Data Release 3 (Gaia EDR3) provides accurate astrometry for about 1.6 million compact (QSO-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions. Aims. The proper motions of QSO-like sources are used to reveal a systematic pattern due to the acceleration of the solar system...

Gaia Early Data Release 3 (Gaia EDR3) gives trigonometric parallaxes for nearly 1.5 billion sources. Inspection of the EDR3 data for sources identified as quasars reveals that their parallaxes are biased, that is systematically offset from the expected distribution around zero, by a few tens of microarcsec. We attempt to map the main dependencies o...

Context. Gaia Early Data Release 3 ( Gaia EDR3) contains results for 1.812 billion sources in the magnitude range G = 3–21 based on observations collected by the European Space Agency Gaia satellite during the first 34 months of its operational phase.
Aims. We describe the input data, the models, and the processing used for the astrometric content...

Recently, we completed a comprehensive investigation of a huge part of the entire meson spectrum by considering both quarkonia and open-flavour mesons by means of a single common framework which unites the homogeneous Bethe-Salpeter equation that describes mesons as quark-antiquark bound states and the Dyson-Schwinger equation that governs the full...

Gaia Data Release 2 (Gaia DR2) contains results for 1693 million sources in the magnitude range 3 to 21 based on observations collected by the European Space Agency Gaia satellite during the first 22 months of its operational phase. We describe the input data, models, and processing used for the astrometric content of Gaia DR2, and the validation o...

CONTEXT: The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Cele...

Exploiting an interplay of the Bethe-Salpeter equation enabling us to regard mesons as bound states of quark and antiquark and the Dyson-Schwinger equation controlling the dressed quark propagator, we amend existing studies of quarkonia by a comprehensive description of open-flavour mesons composed of all conceivable combinations of quark flavour....

We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several ill...

Gaia Data Release 2 (Gaia DR2) contains results for 1693 million sources in the magnitude range 3 to 21 based on observations collected by the European Space Agency Gaia satellite during the first 22 months of its operational phase. We describe the input data, models, and processing used for the astrometric content of Gaia DR2, and the validation o...

Utilizing QCD sum rules, we extract the temperature dependences of the spectral properties of the pseudo-scalar and scalar D mesons regarded as chiral partners. Besides the masses also decay constants are analyzed as the D meson yields in heavy-ion collisions may be sensitive to their altered decay properties in an ambient strongly interacting medi...

Exploiting an interplay of the Bethe-Salpeter equation enabling us to regard mesons as bound states of quark and antiquark and the Dyson-Schwinger equation controlling the dressed quark propagator, we amend existing studies of quarkonia by a comprehensive description of open-flavour mesons composed of all conceivable combinations of quark flavour....

We revisit earlier calculations of leptonic decay constants of vector charmonia and present and illustrate our decomposition of the corresponding covariant Bethe-Salpeter amplitudes in terms of orbital angular momentum as interpreted in the meson's rest frame. Our results confirm our previous conclusions drawn from the magnitudes of vector-meson le...

We investigate the light-quarkonium spectrum using a covariant Dyson–Schwinger–Bethe–Salpeter-equation approach to QCD. We discuss splittings among as well as orbital angular momentum properties of various states in detail and analyze common features of mass splittings with regard to properties of the effective interaction. In particular, we predic...

Open-flavour meson studies are the necessary completion to any comprehensive investigation of quarkonia. We extend recent studies of quarkonia in the Dyson-Schwinger-Bethe-Salpeter equation approach to explore their results for all possible flavour combinations. Within the inherent limitations of the setup, we present the most comprehensive results...

We discuss charmed mesons in the covariant Dyson-Schwinger-Bethe-Salpeter-equation approach. In particular we computed masses, leptonic decay constants, and an orbital-angular-momentum decomposition for a basic set of states. We also report an efficient way to treat the two coupled quark propagator dressing functions via a single
function.

Meson states with exotic quantum numbers arise naturally in a covariant bound-state framework in QCD. We investigate the consequences of shifting quark masses such that the states are no longer restricted to certain C-parities, but only by J^P. Then, a priori, one can no longer distinguish exotic or conventional states. In order to identify signatu...

We extend earlier investigations of heavy-light pseudoscalar mesons to the vector case, using a simple model in the context of the Dyson-Schwinger-Bethe-Salpeter approach. We investigate the effects of a dressed quark-gluon vertex in a systematic fashion and illustrate and attempt to quantify corrections beyond the phenomenologically very useful an...

We give a short and basic introduction to our covariant Dyson-Schwinger-Bethe-Salpeter-equation approach using a rainbow-ladder truncated model of QCD, in which we investigate the leptonic decay properties of heavy quarkonium states in the pseudoscalar and vector channels. Comparing the magnitudes of decay constants, we identify radial 1-- excitati...

Utilizing the in-medium Lorentz decomposition of operators generating QCD
condensates we derive general constraints among the latter ones by the
requirement of a smooth transition from medium to vacuum. In this way we relate
the vacuum limits of heretofore unrelated condensates and provide consistency
checks for the vacuum saturation hypothesis and...

The coupled quark Dyson-Schwinger and meson Bethe-Salpeter equations in
rainbow-ladder truncation for spin-0 mesons are solved in Wigner-Weyl phase in
the chiral limit and beyond, retaining only the ultraviolet finite terms of the
phenomenologically most successful Maris-Tandy interaction. This allows to
reveal and discuss the scalar and pseudoscal...

QCD sum rules serve as tools to investigate changing hadronic properties in a
hot and/or dense nuclear medium. The role of chiral symmetry breaking and
restoration effects in a medium can be addressed also in the heavy-light meson
sector. Thus, we consider Weinberg sum rules which refer to chiral partner
mesons composed of a light and a heavy quark...

We investigate the light quarkonium spectrum using a covariant
Dyson-Schwinger-Bethe-Salpeter-equation approach with a rainbow-ladder
truncated model of quantum chromodynamics. We attempt to tie properties of the
effective interaction in this setup to features in the spectrum and draw
conclusions about the applicability of the rainbow-ladder trunca...

Using a simple model in the context of the Dyson-Schwinger-Bethe-Salpeter
approach, we investigate the effects of a dressed-quark-gluon vertex on
pseudoscalar meson masses. In particular, we focus on the unequal-mass case and
investigate heavy-light meson masses; in addition, we study the premise of the
effective treatment of heavy quarks in our ap...

We investigate the properties of mesons with the exotic J^PC = 1^-+ quantum
numbers. Starting out from the light-quark domain, where the \pi_1 states are
used as references, we predict the masses of analogous quarkonia for c\bar{c}
and b\bar{b} configurations. We employ a covariant
Dyson-Schwinger-Bethe-Salpeter-equation approach with a rainbow-lad...

Wilson coefficients of light four-quark condensates in QCD sum rules are
evaluated for pseudo-scalar $D$ mesons, thus, pushing the sum rules toward mass
dimension six. Contrary to the situation for $\bar{q}q$ mesons the impact of
the four-quark condensates for vacuum as well as in-medium situations is found
to be rather small within the Borel windo...

The planned experiments at FAIR enable the study of medium modifications of
$D$ and $B$ mesons in (dense) nuclear matter. Evaluating QCD sum rules as a
theoretical prerequisite for such investigations encounters heavy-light
four-quark condensates. We utilize an extended heavy-quark expansion to cope
with the condensation of heavy quarks.

QCD sum rules for $D$ and $B$ mesons in a strongly interacting environment
require the decomposition of Gibbs averaged operators related to tensor
structures. We present a procedure to decompose these operators into vacuum and
medium-specific parts, thus defining plain medium-specific condensates with
coefficients vanishing in vacuum. Our decomposi...

In a covariant Bethe-Salpeter-equation approach and with a rainbow-ladder truncated model of quantum chromodynamics (QCD), we investigate the use of an effective interaction with the goal of reproducing QCD phenomenology. We extend previous studies and present results for ground and excited meson states in the bottomonium and charmonium systems, wh...

Following up on earlier work, we investigate possible effects of a dressed
quark-gluon vertex in heavy-light mesons. In particular, we study corrections
to the popular rainbow-ladder truncation of the Dyson-Schwinger-Bethe-Salpeter
equation system. We adopt a simple interaction kernel which reduces the
resulting set of coupled integral equations to...

We investigate capabilities of the effective interaction in a rainbow-ladder
truncated meson model of QCD within a covariant Landau-gauge
Bethe-Salpeter-equation approach. Based upon past success for the light- as
well as heavy-quark domains, we discuss the range of applicability and features
of an effort with comprehensive phenomenological claim a...

D mesons serve as excellent probes of hot and/or dense strongly interacting
matter. They can provide insight into the restoration of chiral symmetry. The
chiral condensate as well as other chirally odd condensates, such as certain
four-quark condensates, are linked to order parameters of spontaneous chiral
symmetry breaking. Thus, the evaluation of...

In view of the mass spectrum of heavy mesons in vacuum the analytical
properties of the solutions of the truncated Dyson-Schwinger equatio for the
quark propagator within the rainbow approximation are analysed in some detail.
In Euclidean space, the quark propagator is not an analytical function
possessing, in general, an infinite number of singula...

Based on QCD sum rules we explore the consequences of a scenario for the rho meson, where the chiral symmetry breaking condensates are set to zero whereas the chirally symmetric condensates remain at their vacuum values. This clean-cut scenario causes a lowering of the rho spectral moment by about 120 MeV. The complementarity of mass shift and broa...

Recently, in Hilger et al. (2011) [1] QCD sum rules for chiral partners in
the open-charm meson sector have been presented at nonzero baryon net density
or temperature up to and including mass dimension 5. Referring to this, details
concerning the cancelation of infrared divergences are presented and important
technical and conceptional ingredients...

The operator product expansion (OPE) for heavy-light-quark pseudoscalar
mesons (D-mesons and B-mesons) in medium is determined, both for a moving meson
with respect to the surrounding medium as well as for a meson at rest. First of
all, the OPE is given in terms of normal-ordered operators up to mass dimension
5, and the mass of the heavy-quark and...

QCD sum rules for chiral partners in the open-charm meson sector are presented at nonzero baryon net density or temperature. We focus on the differences between pseudo-scalar and scalar as well as vector and axial-vector D mesons and derive the corresponding Weinberg-type sum rules. This allows for the identification of such QCD condensates which d...

The mass spectrum of heavy pseudoscalar mesons, described as quark-antiquark bound systems, is considered within the Bethe-Salpeter formalism with momentum dependent masses of the constituents. This dependence is found by solving the Schwinger-Dyson equation for quark propagators in rainbow-ladder approximation. Such an approximation is known to pr...

Employing QCD sum rules the in-medium modifications of scalar charm mesons in
a cold nuclear matter environment are estimated. The mass splitting of
D*-D*-bar is quantified.

The mass spectrum of heavy pseudoscalar mesons, as quark–antiquark bound systems, is considered within the Bethe-Salpeter formalism with momentum-dependent masses of the constituents. This dependence is prior found by solving the Schwinger-Dyson equation for quark propagators in rainbow-ladder approximation. Such approximation is known to provide f...

We survey some prospects of identifying further in-medium modifications of hadrons in a strongly interacting medium with respect to ongoing experiment series of the HADES Collaboration and planned experiments of the CBM Collaboration at FAIR. Di-electrons, strange and charm mesons are considered and their potential for signaling imprints of chiral...

Open charm mesons (pseudo-scalar and scalar as well as axial-vector and vector) propagating or resting in nuclear matter display an enhanced sensitivity to the chiral condensate. This offers new prospects to seek for signals of chiral restoration, in particular in p-A and p-bar-A reactions as envisaged in first-round experiments by the CBM and PAND...

Pseudo-scalar and scalar $D$ mesons are considered within the QCD sum rule approach. We present an analysis of the mass splitting of the pseudo-scalar D - D-bar mesons and the relation to QCD condensates. Weinberg type sum rules are derived for chiral partners which highlight the role of the chiral condensate. Comment: 4 pages, 2 figures, conferenc...

QCD sum rules for D and B mesons embedded in cold nuclear matter are evaluated. We quantify the mass splitting of D - D-bar and B - B-bar mesons as a function of the nuclear matter density; extrapolated to saturation density it is in the order of 60 and 130 MeV driven essentially by the condensates , and . The genuine chiral condensate , amplified...

The QCD sum rule approach to the in-medium behavior of hadrons is discussed for omega meson, nucleon and D meson. Emphasis is devoted to the impact of four-quark condensates and to order parameters of spontaneous symmetry breaking.

The in-medium behavior of the nucleon spectral density including self-energies is revisited within the framework of QCD sum rules. Special emphasis is given to the density dependence of four-quark condensates. A complete catalog of four-quark condensates is presented and relations among them are derived. Generic differences of such four-quark conde...

Spectral properties of hadrons in nuclear matter are treated in the framework of QCD
sum rules. The influence of the ambient strongly interacting medium is encoded in various condensates. Especially, the structure of different four‐quark condensates and their density dependencies in light quark systems are exemplified for the ω meson and the nucle...

With QCD sum rule evaluations, spectral changes of hadrons inside nuclear matter are considered, which shed light on QCD condensates and thus on the non-perturbative structure of the QCD ground state. For some light quark configurations, omega meson and nucleon, the relevance of four-quark condensates is compared; the D meson as a representative of...

## Projects

Project (1)