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Introduction, Notations and Definitions
We begin by recalling some standard notations and terminology. Let a, q be complex numbers with 0 < |q| < 1. Then the q − shifted factorial is defined by
\matrix{{{{(a;q)}_n} = (1 - a)(1 - aq)...(1 - a{q^{n - 1}}) {\kern 1pt} {\rm if}{\kern 1pt} n > 0,} \cr {{{(a;q)}_0} = 1}}
and
{(a;q)_\infty} = \prod\limits_{r = 0}^\infty (1 - a{q^r}).
For the sake of brevity, we often write
{({a_1};q)_n}{({a_2};q)_n}...({a_r};q{)_n} = ({a_1},{a_2},{a_3},...,{a_r};q{)_n}.
The basic hypergeometric series is defined by
{\,_r}{\Phi_s} = \left[ {\matrix{{{a_1},{a_2},...,{a_r};q;z} \hfill \cr {{b_1},{b_2},...,{b_s}} \hfill \cr}} \right] = \sum\limits_{n = 0}^\infty {{{{({a_1},{a_2},...,{a_r};q)}_n}{z^n}} \over {{{(q,{b_1},{b_2},...,{b_s};q)}_n}}}{\left\{{{{(- 1)}^n}{q^{n(n - 1)/2}}} \right\}^{1 + s - r}}.
In an attempt to clarify Rogers second proof [3] of the Rogers-Ramanujan identities, Bailey [1] made the following simple but very useful observation,
The proof is straightforword and merely requires an interchange of sums. Of course, in the above transform, suitable convergence conditions need to be imposed to make the definition of γn and interchange of sums meaningful.
In application of the transform, Bailey chose
{u_r} = {1 \over {{{(q;q)}_r}}}
,
{v_r} = {1 \over {{{(aq;q)}_r}}}
and with this choice equations (1.1) and (1.2) became
{\beta_n} = \sum\limits_{r = 0}^n {{{\alpha_r}} \over {{{(q;q)}_{n - r}}{{(aq;q)}_{n + r}}}}
and
{\gamma_n} = \sum\limits_{r = 0}^\infty {{{\delta_{r + n}}} \over {{{(q;q)}_r}{{(aq;q)}_{r + 2n}}}}
respectively.
A pair of sequence 〈αn, βn〉 that satisfies (1.4) is called a Bailey pair relative to the parameter a. Similarly, the pair of sequence 〈γn, δn〉 which satisfies (1.5) is called conjugate Bailey pair relative to a. For these Bailey and conjugate Bailey pairs we have
\sum\limits_{n = 0}^\infty {\alpha_n}{\gamma_n} = \sum\limits_{n = 0}^\infty {\beta_n}{\delta_n},
provided series involved are convergent.
Theorems Involving Bailey Pairs
(i) Choosing
{\delta_r} = ({\rho_1},{\rho_2};q{)_r}{\left({{{aq} \over {{\rho_1}{\rho_2}}}} \right)^r}
in (1.5) and using the summation formula [2, App. II(II.8) p. 236] we have,
{\gamma_n} = {{{{\left({{{aq} \over {{\rho_1}}},{{aq} \over {{\rho_2}}};q} \right)}_\infty}{{({\rho_1},{\rho_2};q)}_n}{{\left({{{aq} \over {{\rho_1}{\rho_2}}}} \right)}^n}} \over {{{\left({aq,{{aq} \over {{\rho_1}{\rho_2}}};q} \right)}_\infty}{{\left({{{aq} \over {{\rho_1}}},{{aq} \over {{\rho_2}}};q} \right)}_n}}}.
Putting these values of γn and δn in (1.6) we obtain the following theorem.
If 〈αn(a,k), βn(a,k)〉 is a WP-Bailey pair and 〈γn(a,k), δn(a,k)〉 is a WP-Conjugate Bailey pair then Bailey lemma gives,
\sum\limits_{n = 0}^\infty {\alpha_n}(a,k){\gamma_n}(a,k) = \sum\limits_{n = 0}^\infty {\beta_n}(a,k){\delta_n}(a,k),
provided series involved in (3.2) and (3.3) are convergent.
(i) Choosing
{\delta_r}(a,k) = {\left({{{{a^2}q} \over {{k^2}}}} \right)^r}
in (3.2) and using the summation formula [2, App. II(II.8), p. 236] we find,
{\gamma_n}(a,k) = {{{{\left({{{{a^2}q} \over k},{{aq} \over k};q} \right)}_\infty}} \over {{{\left({aq,{{{a^2}q} \over {{k^2}}};q} \right)}_\infty}}}{{{{(k;q)}_{2n}}} \over {{{\left({{{{a^2}q} \over k};q} \right)}_{2n}}}}{\left({{{{a^2}q} \over {{k^2}}}} \right)^n}.
Putting these values of 〈γn(a,k), δn(a,k)〉 in (3.3) we have following theorem.
In this section we give numerous Bailey pairs deducible from certain summation formulas.
(i) Choosing
{\alpha_r} = {{{q^{r(r + 1)/2}}{{(a,q\sqrt a, - q\sqrt a;q)}_r}{q^{- {3 \over 2}r}}} \over {{{(q,\sqrt a, - \sqrt a;q)}_r}}}
in (1.4) and using the summation formula [5, (4.1), p.76] we get,
{\beta_n} = {1 \over 2}\left[ {{{{{(- {q^{- {1 \over 2}}};q)}_n}(1 + \sqrt a)} \over {{{(q,\sqrt {aq}, - \sqrt a;q)}_n}}} + {{{{(- {q^{- {1 \over 2}}};q)}_n}(1 - \sqrt a)} \over {{{(q, - \sqrt {aq},\sqrt a;q)}_n}}}} \right].αn and βn given in (4.1) form a Bailey pair.
(ii) Taking
{\alpha_r} = {{{q^{r(r + 1)/2}}{{(a,q\sqrt a;q)}_r}{q^{- r}}} \over {{{(q,\sqrt a;q)}_r}}}
in (1.4) and using the summation formula [5, (4.2), p.76] we get,
{\beta_n} = {{1 + \sqrt a} \over 2}{{{{(- 1;q)}_n}} \over {{{(q,\sqrt {aq}, - \sqrt {aq};q)}_n}}} + {{1 - \sqrt a} \over 2}{{{{(- 1;q)}_n}} \over {{{(q,\sqrt a, - q\sqrt a;q)}_n}}}.αn and βn given in (4.2) form a Bailey pair.
(iii) Taking
{\alpha_r} = {{{q^{r(r + 1)/2}}{{(a;q)}_r}{q^{- {1 \over 2}r}}} \over {{{(q;q)}_r}}}
in (1.4) and making use of the summation formula [5, (4.3), p.76] we find,
{\beta_n} = {{1 + \sqrt a} \over 2}{{{{(- {q^{{1 \over 2}}};q)}_n}} \over {{{(q, - \sqrt {aq},q\sqrt a;q)}_n}}} + {{1 - \sqrt a} \over 2}{{{{(- {q^{{1 \over 2}}};q)}_n}} \over {{{(q,\sqrt {aq}, - q\sqrt a;q)}_n}}}.αn and βn given in (4.3) form a Bailey pair.
(iv) Choosing
{\alpha_r} = {{{q^{{1 \over 2}{r^2}}}{{(a;q)}_r}(1 - a{q^{2r}})} \over {{{(q;q)}_r}(1 - a)}}
in (1.4) and using the summation formula [5, (4.5), p.77] we find,
{\beta_n} = {{1 + \sqrt a} \over {2\sqrt a}}{{{{(- {q^{- {1 \over 2}}};q)}_n}} \over {{{(q,\sqrt {aq}, - q\sqrt a;q)}_n}}} - {{1 - \sqrt a} \over {2\sqrt a}}{{{{(- {q^{- {1 \over 2}}};q)}_n}} \over {{{(q, - \sqrt {aq},q\sqrt a;q)}_n}}}.αn and βn given in (4.4) form a Bailey pair.
(v) Taking
{\alpha_r} = {{{q^{r(r + 1)/2}}{{(a,q\sqrt a;q)}_r}} \over {{{(q,\sqrt a;q)}_r}}}
in (1.4) and using the summation formula [5, (4.6), p.77] we find,
{\beta_n} = {{1 + \sqrt a} \over {2\sqrt a}}{{{{(- 1;q)}_n}} \over {{{(q,\sqrt {aq}, - \sqrt {aq};q)}_n}}} - {{1 - \sqrt a} \over {2\sqrt a}}{{{{(- 1;q)}_n}} \over {{{(q,\sqrt a, - q\sqrt a;q)}_n}}}.αn and βn given in (4.5) form a Bailey pair.
(vi) Choosing
{\alpha_r} = {{{q^{r(r + 1)/2}}{{(a;q)}_r}{q^{{1 \over 2}r}}} \over {{{(q;q)}_r}}}
in (1.4) and making use of the summation formula [5, (4.7), p.77] we find,
{\beta_n} = {{1 + \sqrt a} \over {2\sqrt a}}{{{{(- {q^{{1 \over 2}}};q)}_n}} \over {{{(q, - \sqrt {aq},q\sqrt a;q)}_n}}} - {{1 - \sqrt a} \over {2\sqrt a}}{{{{(- {q^{{1 \over 2}}};q)}_n}} \over {{{(q,\sqrt {aq}, - q\sqrt a;q)}_n}}}.αn and βn given in (4.6) form a Bailey pair.
(vii) Taking
{\alpha_r} = {{{q^{r(r + 1)/2}}{{(a, - q\sqrt a,b;q)}_r}{{\left({- {{\sqrt a} \over b}} \right)}^r}} \over {{{\left({q, - \sqrt a,{{aq} \over b};q} \right)}_r}}}
in (1.4) and using the summation formula [2, App. II (II.14), p. 237] we get
{\beta_n} = {{{{\left({{{q\sqrt a} \over b};q} \right)}_n}} \over {{{\left({q,q\sqrt a,{{aq} \over b};q} \right)}_n}}}.
〈αn, βn〉 given in (4.7) form a Bailey pair.
(viii) Taking
{\alpha_r} = {{{q^{r(r + 1)/2}}{{(a,b,c;q)}_r}(1 - a{q^{2r}}){{\left({- {a \over {bc}}} \right)}^r}} \over {{{\left({q,{{aq} \over b},{{aq} \over c};q} \right)}_r}(1 - a)}}
in (1.4) and using the summation formula [2, App. II (II.21), p. 238] we get
{\beta_n} = {{{{\left({{{aq} \over {bc}};q} \right)}_n}} \over {{{\left({q,{{aq} \over b},{{aq} \over c};q} \right)}_n}}}.
〈αn, βn〉 given in (4.8) form a Bailey pair.
WP-Bailey Pairs
In this section we give certain WP-Bailey pairs out of which some are known and some are new.
(i) Taking
{\alpha_r}(a,k) = {{{{(a,b;q)}_r}(1 - a{q^{2r}})} \over {{{\left({q,{{aq} \over b};q} \right)}_r}(1 - a)}}{\left({{1 \over b}} \right)^r}
in (3.1) and summing the series by making use of [2, App. II (II.21), p. 238] we get,
{\beta_n}(a,k) = {{{{\left({k,{{kb} \over a};q} \right)}_n}} \over {{{\left({q,{{aq} \over b};q} \right)}_n}{b^n}}}.
〈αn(a,k), βn(a,k)〉 given in (5.1) form a WP-Bailey pair.
(ii) Choosing
{\alpha_r}(a,k) = {{{{\left({a,b,c,{{{a^2}q} \over {bck}};q} \right)}_r}(1 - a{q^{2r}})} \over {{{\left({q,{{aq} \over b},{{aq} \over c},{{bck} \over a};q} \right)}_r}(1 - a)}}{\left({{k \over a}} \right)^r}
in (3.1) and using the summation formula [2, App. II (II.22), p. 238] we get,
{\beta_n}(a,k) = {{{{\left({k,{{aq} \over {bc}},{{kb} \over a},{{kc} \over a};q} \right)}_n}} \over {{{\left({q,{{aq} \over b},{{aq} \over c},{{kbc} \over a};q} \right)}_n}}}.
〈αn(a,k), βn(a,k)〉 given in (5.2) form a WP-Bailey pair.
(iii) Again, choosing
{\alpha_n}(a,k) = {{{{\left({a,{a \over k};q} \right)}_n}(1 - a{q^{2n}})} \over {{{\left({q,kq;q} \right)}_n}(1 - a)}}{\left({{k \over a}} \right)^n}
in (3.1) and summing the series by making use of [2, App. II (II.21), p. 238] we get,
{\beta_n}(a,k) = \left\{{\matrix{{1, n = 0} \hfill \cr {0, n \ge 1.} \hfill \cr}} \right.
So, 〈αn(a,k), βn(a,k)〉 given in (5.3) form a WP-Bailey pair.
(iv) If we take αr(a,k) = δr,0 in (3.1) we find,
{\beta_n}(a,k) = {{{{\left({k,{k \over a};q} \right)}_n}} \over {{{\left({q,aq;q} \right)}_n}}}.
〈αn(a,k), βn(a,k)〉 given in (5.4) also form a WP-Bailey pair.
Now, choosing
{\alpha_n}(a,k) = {{{{\left({a,{{a{q^{{1 \over 2}}}} \over k};q} \right)}_n}} \over {{{\left({q,k{q^{{1 \over 2}}};q} \right)}_n}}}{\left({{{kq} \over a}} \right)^n}
in (3.1) and using (5.7) we get
\matrix{{{\beta_n}(a,k)} \hfill & {= {{1 + \sqrt a} \over {2\sqrt a}}{{{{\left({k,{q^{{1 \over 2}}},{k \over {\sqrt a}},k\sqrt {{q \over a}};q} \right)}_n}} \over {{{\left({q,k{q^{{1 \over 2}}},q\sqrt a,\sqrt {aq};q} \right)}_n}}}} \hfill \cr {} \hfill & {- {{1 - \sqrt a} \over {2\sqrt a}}{{{{\left({k,{q^{{1 \over 2}}}, - {k \over {\sqrt a}}, - k\sqrt {{q \over a}};q} \right)}_n}} \over {{{\left({q,k{q^{{1 \over 2}}}, - q\sqrt a, - \sqrt {aq};q} \right)}_n}}}.} \hfill}
〈αn(a,k), βn(a,k)〉 given in (5.8) form a WP-Bailey pair. Bailey pairs given in (5.6) and (5.8) are believed to be new.
Bailey Chain
If 〈αn, βn〉 is a Bailey pair i.e.
{\beta_n} = \sum\nolimits_{r = 0}^n {{{\alpha_r}} \over {{{(q;q)}_r}{{(aq;q)}_r}}}
, then so 〈
\alpha_n^{'}
,
\beta_n^{'}
〉 is also a Bailey pair, where
{\alpha_{n'}} = {{{{({\rho_1},{\rho_2};q)}_n}{{\left({{{aq} \over {{\rho_1}{\rho_2}}}} \right)}^n}} \over {{{\left({{{aq} \over {{\rho_1}}},{{aq} \over {{\rho_2}}};q} \right)}_n}}}{\alpha_n}.
and
\matrix{{{\beta_{n'}}} \hfill & {= \sum\limits_{r = 0}^\infty {{{{({\rho_1},{\rho_2};q)}_r}{{\left({{{aq} \over {{\rho_1}{\rho_2}}};q} \right)}_{n - r}}{{\left({{{aq} \over {{\rho_1}{\rho_2}}}} \right)}^r}{\beta_r}} \over {{{(q;q)}_{n - r}}{{\left({{{aq} \over {{\rho_1}}},{{aq} \over {{\rho_2}}};q} \right)}_n}}}} \hfill \cr {} \hfill & {= {{{{\left({{{aq} \over {{\rho_1}{\rho_2}}};q} \right)}_n}} \over {{{\left({q,{{aq} \over {{\rho_1}}},{{aq} \over {{\rho_2}}};q} \right)}_n}}}\sum\limits_{r = 0}^\infty {{{{({\rho_1},{\rho_2};q)}_r}{{\left({{q^{- n}};q} \right)}_r}{q^r}} \over {{{\left({{{{\rho_1}{\rho_2}} \over a}{q^{- n}};q} \right)}_r}}}{\beta_r}.} \hfill}
Thus, we find that if one Bailey pair 〈αn, βn〉 is known then a new Bailey pair 〈
\alpha_n^{'}
,
\beta_n^{'}
〉 can be constructed as shown above in (6.2). Repeating this process we can have infinite number of Bailey pairs if one initial pair is known. These Bailey pairs so constructed from an initial Bailey pair form a chain called Bailey chain.
WP-Bailey Tree
Andrews proved following two theorems for constructing WP-Bailey pairs from a initial known Bailey pair.
Theorem 13
If 〈αn(a,k), βn(a,k)〉 is a WP-Bailey pair, then so is the pair 〈
\alpha_n^{'}(a,k)
,
\beta_n^{'}(a,k)
〉 given by,
\matrix{{{\alpha_n^{'}}(a,k) = {{{{(b,c;q)}_n}} \over {{{\left({{{aq} \over b},{{aq} \over c};q} \right)}_n}}}{{\left({{k \over m}} \right)}^n}{\alpha_n}(a,m),} \cr {{\beta_n^{'}}(a,k) = {{{{\left({{{mq} \over b},{{mq} \over c};q} \right)}_n}} \over {{{\left({{{aq} \over b},{{aq} \over c};q} \right)}_n}}}\sum\limits_{r = 0}^n {{1 - m{q^{2r}}} \over {1 - m}}{{{{(b,c;q)}_r}{{\left({{k \over m};q} \right)}_{n - r}}{{(k;q)}_{n + r}}} \over {{{\left({{{mq} \over b},{{mq} \over c};q} \right)}_r}{{(q;q)}_{n - r}}{{(mq;q)}_{m + r}}}}{{\left({{k \over m}} \right)}^r}{\beta_r}(a,m),}}
From these two theorems, each WP-Bailey pair gives rise to a binary tree of WP-Bailey pairs. Andrews coined this the WP-Bailey tree. The following four theorems due to Warnaar give additional branches to the Bailey tree.
The freedom in the choice of σ simply reflects that the above expressions are invariant under the simultaneous negation of
{k^{{1 \over 2}}}
,
{m^{{1 \over 2}}}
and σ.
Theorem 16
If 〈αn(a,k), βn(a,k)〉 is a WP-Bailey pair, then so is the pair 〈
\alpha_n^{'}(a,k)
,
\beta_n^{'}(a,k)
〉 given by,
\matrix{{\alpha_n^{'}({a^2},k;{q^2}) = {\alpha_n}(a,m;q),} \cr {\beta_n^{'}({a^2},k;{q^2}) = {{{{(- mq;q)}_{2n}}} \over {{{(- aq;q)}_{2n}}}}\sum\limits_{r = 0}^n {{(1 - m{q^{2r}})} \over {(1 - m)}}{{{{\left({{k \over {{m^2}}};{q^2}} \right)}_{n - r}}{{(k;{q^2})}_{n + r}}{{\left({{m \over a}} \right)}^{n - r}}} \over {{{({q^2};{q^2})}_{n - r}}{{({m^2}{q^2};{q^2})}_{n + r}}}}{\beta_r}(a,m;q),}}
In this paper, certain transformation formulas involving q-hypergeometric series have been obtained by making use of theorems, Bailey Pairs and WP-Bailey Pairs established herein. From these transformation formulas q-series identities can be deduced which may have partition theoretic interpretations. Results of this paper are quite useful and we hope that these results will form the base of further research in the subject.